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• question about missing element in array

  - by davit-datuashvili

  i have following problem from book introduction algorithm second edition by MIT university problem is following An array A[1 . . n] contains all the integers from 0 to n except one. It would be easy to determine the missing integer in O(n) time by using an auxiliary array B[0 . . n] to record which numbers appear in A. In this problem, however, we cannot access an entire integer in A with a single operation. The elements of A are represented in binary, and the only operation we can use to access them is “fetch the j th bit of A[i],” which takes constant time. Show that if we use only this operation, we can still determine the missing inte- ger in O(n) time please help

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• Can a variable like 'int' be considered a primitive/fundamental data structure?

  - by Ravi Gupta

  A rough definition of a data structure is that it allows you to store data and apply a set of operations on that data while preserving consistency of data before and after the operation. However some people insist that a primitive variable like 'int' can also be considered as a data structure. I get that part where it allows you to store data but I guess the operation part is missing. Primitive variables don't have operations attached to them. So I feel that unless you have a set of operations defined and attached to it you cannot call it a data structure. 'int' doesn't have any operation attached to it, it can be operated upon with a set of generic operators. Please advise if I got something wrong here.

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• Optimality of Binary Search

  - by templatetypedef

  Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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• Want to avoid the particular rows from select join query... See description

  - by OM The Eternity

  I have a Select Left Join Query whis displays me the rows for the latest changedone(its a time) column name ("field" should not be equal) column name ("trackid" should not be equal), and column name "Operation should be "UPDATE" ", below is the query I am talking about... SELECT j1. * FROM jos_audittrail j1 LEFT OUTER JOIN jos_audittrail j2 ON ( j1.trackid != j2.trackid AND j1.field != j2.field AND j1.changedone < j2.changedone ) WHERE j1.operation = 'UPDATE' AND j2.id IS NULL Now here I don't want a row to be displayed with a two particular column's value i.e. "field's value" the value is "LastvisitDate" and "hits" Now if if append the condition in the above query that " AND j1.field != 'lastvistDate' AND j1.field != 'hits' " theni do not get any result... The table structure is jos_audittrail: id trackid operation oldvalue newvalue table_name live changedone(its a time) I hope i have given the details properly If u still find something missing I will try to provide it more better way... Pls help me to avoid those two rows with those to mentioned value of "field"

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• Is the syntax written in descrition is correct for MySQL Triggers? will it work?

  - by Parth

  Is the syntax written in descrition is correct for MySQL Triggers? will it work? CREATE OR REPLACE TRIGGER myTableAuditTrigger 2 AFTER INSERT OR DELETE OR UPDATE ON myTable 3 FOR EACH ROW 4 BEGIN 5 IF INSERTING THEN 6 INSERT INTO myTableAudit (id, Operation, NewName, NewPhone) 7 VALUES (1, 'Insert ', :NEW.Name, :NEW.PhoneNo); 8 ELSIF DELETING THEN 9 INSERT INTO myTableAudit (id, Operation, OldName, OldPhone) 10 VALUES (1, 'Delete ', :OLD.Name, :OLD.PhoneNo); 11 ELSIF UPDATING THEN 12 INSERT INTO myTableAudit (id, Operation, 13 OldName, OldPhone, NewName, NewPhone) 14 VALUES (1, 'Update ', 15 :OLD.Name, :OLD.PhoneNo, :NEW.Name, :NEW.PhoneNo); 16 END IF; 17 END; 18 /

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• Best neural network for certain type of pattern analysis?

  - by fred basset

  Hi All, I'm working on a system that will send telemetry data on machine operation back to a central server for analysis. One of the machine parameters we're measuring is motor current drawn vs time. After an operation is finished we plan to send back an array of currents vs time to the server. A successful operation would have a pattern like a trapezoid, problematic operations would have a pattern completely different, more like a large spike in values. Can anyone recommend a type of neural network that would be good at classifying these 1D vectors of current values into a pass/fail type output? Thanks, Fred

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• What response should be made to a continued web-app crack attempt?

  - by Tchalvak

  I've issues with a continuous, concerted cracking attempt on a website (coded in php). The main problem is sql-injection attempts, running on a Debian server. A secondary effect of the problem is being spidered or repeatedly spammed with urls that, though a security hole has been closed, are still obviously related attempts to crack the site, and continue to add load to the site, and thus should be blocked. So what measures can I take to: A: Block known intruders/known attack machines (notably making themselves anonymous via botnet or relaying servers) to prevent their repeated, continuous, timed access from affecting the load of the site, and B: report & respond to the attack (I'm aware that the reporting to law enforcement is almost certainly futile, as may be reporting to the ip/machine where the attacks are originating, but other responses to take would be welcome).

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• Replicate a big, dense Windows volume over a WAN -- too big for DFS-R

  - by Jesse

  I've got a server with a LOT of small files -- many millions files, and over 1.5 TB of data. I need a decent backup strategy. Any filesystem-based backup takes too long -- just enumerating which files need to be copied takes a day. Acronis can do a disk image in 24 hours, but fails when it tries to do a differential backup the next day. DFS-R won't replicate a volume with this many files. I'm starting to look at Double Take, which seems to be able to do continuous replication. Are there other solutions that can do continuous replication at a block or sector level -- not file-by-file over a WAN?

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• Database version control resources

  - by Wes McClure

  In the process of creating my own DB VCS tool tsqlmigrations.codeplex.com I ran into several good resources to help guide me along the way in reviewing existing offerings and in concepts that would be needed in a good DB VCS.  This is my list of helpful links that others can use to understand some of the concepts and some of the tools in existence.  In the next few posts I will try to explain how I used these to create TSqlMigrations.   Blogs entries Three rules for database work - K. Scott Allen http://odetocode.com/blogs/scott/archive/2008/01/30/three-rules-for-database-work.aspx Versioning databases - the baseline http://odetocode.com/blogs/scott/archive/2008/01/31/versioning-databases-the-baseline.aspx Versioning databases - change scripts http://odetocode.com/blogs/scott/archive/2008/02/02/versioning-databases-change-scripts.aspx Versioning databases - views, stored procedures and the like http://odetocode.com/blogs/scott/archive/2008/02/02/versioning-databases-views-stored-procedures-and-the-like.aspx Versioning databases - branching and merging http://odetocode.com/blogs/scott/archive/2008/02/03/versioning-databases-branching-and-merging.aspx Evolutionary Database Design - Martin Fowler http://martinfowler.com/articles/evodb.html Are database migration frameworks worth the effort? - Good challenges http://www.ridgway.co.za/archive/2009/01/03/are-database-migration-frameworks-worth-the-effort.aspx Continuous Integration (in general) http://martinfowler.com/articles/continuousIntegration.html http://martinfowler.com/articles/originalContinuousIntegration.html Is Your Database Under Version Control? http://www.codinghorror.com/blog/archives/000743.html 11 Tools for Database Versioning http://secretgeek.net/dbcontrol.asp How to do database source control and builds http://mikehadlow.blogspot.com/2006/09/how-to-do-database-source-control-and.html .Net Database Migration Tool Roundup http://flux88.com/blog/net-database-migration-tool-roundup/ Books Book Description Refactoring Databases: Evolutionary Database Design Martin Fowler signature series on refactoring databases. Book site: http://databaserefactoring.com/ Recipes for Continuous Database Integration: Evolutionary Database Development (Digital Short Cut) A good question/answer layout of common problems and solutions with database version control. http://www.informit.com/store/product.aspx?isbn=032150206X

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• Silverlight Cream for May 19, 2010 -- #865

  - by Dave Campbell

  In this Issue: Michael Washington, Mike Snow(-2-), Justin Angel(-2-), Jeremy Likness, and David Kelley. Shoutout: Erik Mork and crew have their latest up: Silverlight Week – Silverlight Android? From SilverlightCream.com: Simple Silverlight 4 Example Using oData and RX Extensions Michael Washington has a follow-on tutorial up on ViewModel, Rx, and lashed up to OData... good detailed tutorial with external links for more information. Silverlight Tip of the Day #21 – Animation Easing Mike Snow has a couple new tips up -- this first one is about easing... great diagrams to help visualize and a cool demo application to boot. Silverlight Tip of the Day #22 – Data Validation Mike Snow's second tip (#22) is about validation and again he has a great demo app on the post. Windows Phone 7 - Emulator Automation Justin Angel has a WP7 post up about Automating the emulator... and in the process, loading the emulator from something other than VS2010... lots of good information. TFS2010 WP7 Continuous Integration Justin Angel hinted at continuous integration for WP7 in the last post, and he pays off with this one... even without all the bits installed on the build server. Making the ScrollViewer Talk in Silverlight 4 Jeremy Likness tried to respond to a user query about knowing when a user scrolled to the bottom of a ScrollViewer... Jeremy resolved it by listening to the right property. MEF (Microsoft Extensibility Framework) made simple (ish) David Kelley is discussing MEF and using a real-world example while doing so. Good discussion and code available in his code browser app... check thecomments. Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight    Silverlight 3    Silverlight 4    Windows Phone MIX10

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• Third year in a row- Microsoft MVP again!!

  - by Jalpesh P. Vadgama

  Today is Sunday and I was not expecting this as today is holiday although I know it was Microsoft Mvp renewal day. At evening I got the congratulation email from the Microsoft. Yeah!! I am Microsoft Most Valuable Professional again. I got the same message as a part of Mvp. Thanks Microsoft again. Dear Jalpesh Vadgama, Congratulations! We are pleased to present you with the 2012 Microsoft® MVP Award! This award is given to exceptional technical community leaders who actively share their high quality, real world expertise with others. We appreciate your outstanding contributions in Visual C# technical communities during the past year. Feeling is again same as first time. I am going to dedicated this award to my family. My parents who always inspired me to do new things. My wife who scarifies her time to write blogs. My brother who support me in every possible way.  On this occasion, I would also like to thanks my reader without their support it was no possible to achieve this. Thanks for reading my blog!!. Please do keep reading this. I will try to write as much as possible. I would also like to thanks ‘Tanmay Kapoor’ My Mvp lead for continuous support.     Once again thank you all for your continuous support and love. There are lots of new technologies in Microsoft Stack and I am going to write lots of blog post about all the new stuff. So stay tuned for the same.

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• VSDB to SSDT part 3 : command-line deployment with SqlPackage.exe, replacement for Vsdbcmd.exe

  - by Etienne Giust

  For our continuous integration needs, we use a powershell script to handle deployment. A simpler approach would be to have a deployment task embedded within the build process. See the solution provided here by Jakob Ehn (a most interesting read which also dives into the '”deploying from Visual Studio” specifics) : http://geekswithblogs.net/jakob/archive/2012/04/25/deploying-ssdt-projects-with-tfs-build.aspx   For our needs, though, clearly separating our build phase from our deployment phase is important. It allows us to instantly deploy old versions. Also it is more convenient for continuous integration. So we stick with the powershell script approach. With VSDB projects, that script used to call the following command (the vsdbcmd executable was locally available, along with needed libraries): vsdbcmd.exe /a:Deploy /dd /cs:<CONNECTIONSTRING TO TARGET DB> /dsp:SQL /manifest:< PATH TO .deploymanifest FILE>   To be able to do the approximately same thing with a SSDT produced file (dacpac), you would call this command on a machine which has VS2012 installed (or the SSDT installed, see here : http://msdn.microsoft.com/en-us/library/hh500335%28v=vs.103%29):   C:\Program Files (x86)\Microsoft SQL Server\110\DAC\bin\SqlPackage.exe /Action:Publish /SourceFile:<PATH TO Database.dacpac FILE> /Profile:<PATH TO .publish.xml FILE>   And from within a powershell script :   & "C:\Program Files (x86)\Microsoft SQL Server\110\DAC\bin\SqlPackage.exe" /Action:Publish /SourceFile:<PATH TO Database.dacpac FILE> /Profile:<PATH TO .publish.xml FILE>   The command will consume a publish.xml file where the connection string and the deployment options are specified. You must be familiar with it if you have done some deployments from visual studio. If not, please refer to the above mentioned article by Jakob Ehn.   It is also possible to pass those parameters in the command line. The complete SqlPackage.exe syntax is detailed here : http://msdn.microsoft.com/en-us/library/hh550080%28v=vs.103%29.aspx

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• Adopting Technologies for the Sake of Technologies

  - by shiju

  Unlike other engineering industries, the software engineering industry is really lacking maturity. The lack of maturity can see in different aspects of entire software development life cycle. I think other engineering industries are well organised and structured with common, proven engineering practices. The software engineering industry is greatly a diverse industry with different operating systems, and variety of development platforms, programming languages, frameworks and tools. Now these days, people are going behind the hypes and intellectual thoughts without understanding their core business problems and adopting technologies and practices for the sake of technologies and practices and simply becoming a “poster child” of technologies and practices. Understanding the core business problem and providing best, solid solution with a platform neutral approach, will give you more business values and ROI, instead of blindly adopting technologies and tailor-made your applications for the sake of technologies and practices. People have been simply migrating their solutions in favour of new technologies and different versions of frameworks without any business need. The “Pepsi Challenge” in the Software Development  Pepsi Challenge marketing campaign of the 1980s was a popular and very interesting marketing promotion in which people taste one cup of Pepsi and another cup with Coca Cola. In the taste test, more than 50% of people were preferred Pepsi  over Coca Cola. The success story behind the Pepsi was more sweetness contains in the Pepsi cola. They have simply added more sugar and more people preferred more sweet flavour. You can’t simply identify the better one after sipping one cup of cola based on the sweetness which contains. These things have been happening in the software industry for choosing development frameworks and technologies. People have been simply choosing frameworks based on the initial sugary feeling without understanding its core strengths and weakness. The sugary framework might be more harmful when you develop real-world systems. There is not any silver bullet for solving all kind of problems and frameworks and tools do have strengths and weakness. So it would be better to understand their strength and weakness. And please keep in mind that you have to develop real apps to understand the real capabilities and weakness of a framework. Evaluating a technology based on few blog posts will harm your projects and these bloggers might be lacking real-world experience with the framework. The Problem with Align a Development Practice with Tools Recently I have observed a discussion in a group where one guy asked suggestions for practicing Continuous Delivery (CD) as part of the agile based application engineering. Then the discussion quickly went to using and choosing a Continuous Integration (CI) tool and different people suggested different Continuous Integration (CI) tools for simply practicing Continuous Delivery. If you have worked with core agile engineering practices, you could clearly know that the real essence of agile is neither choosing a tool nor choosing a process. By simply choosing CI tool from a particular vendor will not ensure that you are delivering an evolving software based on customer feedback. You have to understand the real essence of a engineering practice and choose a right tool for practicing it instead of simply focus on a particular tool for a practicing an development practice. If you want to adopt a practice, you need a solid understanding on it with its real essence where tools are just helping us for better automation. Adopting New Technologies for the Sake of Technologies The another problem is that developers have been a tendency to adopt new technologies and simply migrating their existing apps to new technologies. It is okay if your existing system is having problem  with a technology stack or or maintainability challenge with existing solution, and moving to new technology for solving the current problems. We have been adopting new technologies for solving new challenges like solving the scalability challenges when the application or user bases is growing unpredictably. Please keep in mind that all new technologies will become old after working with it for few years. The below Facebook status update of Janakiraman, expresses the attitude of a typical customer. For an example, Node.js is becoming a hottest buzzword in the software industry and many developers are trying to adopt Node.js for their apps. The important thing is that Node.js is a minimalist framework that does some great things for some problems, but it’s not a silver bullet. I have been also working with Node.js which is good for some problems, but really bad for choosing it for all kind of problems. By adopting new technologies for new projects is good if we could get real business values from it because newer framework would solve some existing well known problems and provide better solutions where it can incorporate good solutions for the latest challenges . But adopting a new technology for the sake of new technology is really bad idea. Another example is JavaScript is getting lot of attention so that lot of developers are developing heavy JavaScript centric web apps. First, they will adopt a client-side JavaScript MV* framework from AngularJS, Ember, Backbone etc, and develop a Single Page App(SPA) where they are repeating the mistakes we did in the past with server-side. The mistakes we did in the server-side is transforming to client-side. The problem is that people are just adopting new technologies, but not improving their solutions. I predict that many Single Page App will suck in the future. We need a hybrid approach where we should be able to leverage both server-side and client-side for developing next-generation web apps. The another problem is that if you like a particular framework, use it for all kind of apps. In the past, I know some Silverlight passionate guys were tried to use that framework for all kind of apps including larger line of business apps. And these days developers are migrating their existing Silverlight apps in favour of HTML5 buzzword. So the real question is, what is the business values we are getting from these apps when we are developing it for the sake of a particular technology instead of business need. The another problem is that our solutions consultants are trying to provide unnecessary solutions for the sake of a particular technology or for a hype. For an example, Big Data solutions are great for solving the problem of three Vs : volume, velocity and variety. But trying to put this for every application will make problems. Let’s say, there is a small web site running with limited budget and saying that we need a recommendation engine for the web site with a Hadoop based solution with a 16 node cluster, would be really horrible. If we really need a Hadoop based solution, got for it, but trying to put this for all application would be a big disaster. It would be great if could understand the core business problems first, and later choose a right framework for providing solutions for the actual business problem, instead of trying to provide so many solutions. The Problem with Tied Up to a Platform Vendor Some organizations and teams are tied up with a particular platform vendor where they don’t want to use any product other than their preferred or existing platform vendor. They will accept any product provided by the vendor regardless of its capability. This will lets you some benefits regards with integration and collaboration of different products provided by the same vendor, but it will loose your opportunity to provide better solution for your business problems. For a real world sample scenario, lot of companies have been using SAP for their ERP solutions. When they are thinking about mobility or thinking about developing hybrid mobile apps, they can easily find out a framework from SAP. SAP provides a framework for HTML 5 based UI development named SAPUI5. If you are simply adopting that framework only based for the preference of existing platform vendor, you might be loose different opportunities for providing better solution. Initially you might enjoy the sugary feeling provided by the platform vendor, but you have to think about developing apps which should be capable for solving future challenges. I am not saying that any framework is not good and I believe that all frameworks are good over another one for solving at least one problem. My point is that we should not tied up with any specific platform vendor unless your organization is having resource availability problems. Being Polyglot for Providing Right Solutions The modern software engineering industry is greatly diverse with different tools and platforms. Lot of open source frameworks and new programming languages have been releasing to the developer community, where choosing the right platform without any biased opinion, is really a difficult task. But it would really great if we could develop an attitude with platform neutral mindset and being a polyglot developer for providing better solutions based on the actual business problems. IMHO, we should learn a new programming language and a new framework every year. This will improve the quality of our developer capabilities and also improve the quality of our primary programming language skills. Being polyglot for individual developers and organizational teams will give you greater opportunity to your developer experience and also for your applications. Organizations can analyse their business problem without tied with any technology and later they can provide solutions by choosing different platform and tools. Summary    In this blog post, what I was trying to say that we should not tied up or biased with any development platform, technology, vendor or programming language and we should not adopt technologies and practices for the sake of technologies. If we are adopting a technology or a practice for the sake of it, we are simply becoming a “poster child” of the technology and practice. We should not become a poster child of other people’s intellectual thoughts and theories, instead of it we should become solutions developers and solutions consultants where we should be able to provide better solutions for the business problems. Being a polyglot developer is a good idea for improving your developer skills which lets you provide better solutions for the business problems. The most important thing is that we should become platform neutral developers where our passion should be for providing brilliant solutions. It would be great if we could provide minimalist, pragmatic business solutions. You can follow me on Twitter @shijucv

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• Agile Testing Days 2012 – Day 2 – Learn through disagreement

  - by Chris George

  I think I was in the right place! During Day 1 I kept on reading tweets about Lean Coffee that has happened earlier that morning. It intrigued me and I figured in for a penny in for a pound, and set my alarm for 6:45am. Following the award night the night before, it was _really_ hard getting up when it went off, but I did and after a very early breakfast, set off for the 10 min walk to the Dorint. With Lean Coffee due to start at 07:30, I arrived at the hotel and made my way to one of the hotel bars. I soon realised I was in the right place as although the bar was empty, there was a table with post-it’s and pens! This MUST be the place! The premise of Lean Coffee is to have several small timeboxed discussions. Everyone writes down what they would like to discuss on post-its that are then briefly explained and submitted to the pile. Once everyone is done, the group dot-votes on the topics. The topics are then sorted by the dot vote counts and the discussions begin. Each discussion had 8 mins to start with, which meant it prevented the discussions getting off topic too much. After the time elapsed, the group had a vote whether to extend the discussion by a further 4 mins or move on. Several discussion were had around training, soft skills etc. The conversations were really interesting and there were quite a few good ideas. Overall it was a very enjoyable experience, certainly worth the early start! Make Melly Happy Following Lean Coffee was real coffee, and much needed that was! The first keynote of the day was “Let’s help Melly (Changing Work into Life)”by Jurgen Appelo. Draw lines to track happiness This was a very interesting presentation, and set the day nicely. The theme to the keynote was projects are about the people, more-so than the actual tasks. So he started by showing a photo of an employee ‘Melly’ who looked happy enough. He then stated that she looked happy but actually hated her job. In fact 50% of Americans hate their jobs. He went on to say that the world over 50% of people hate Americans their jobs. Jurgen talked about many ways to reduce the feedback cycle, not only of the project, but of the people management. Ideas such as Happiness doors, happiness tracking (drawing lines on a wall indicating your happiness for that day), kudo boxes (to compliment a colleague for good work). All of these (and more) ideas stimulate conversation amongst the team, lead to early detection of issues and investigation of solutions. I’ve massively simplified Jurgen’s keynote and have certainly not done it justice, so I will post a link to the video once it’s available. Following more coffee, the next talk was “How releasing faster changes testing” by Alexander Schwartz. This is a topic very close to our hearts at the moment, so I was eager to find out any juicy morsels that could help us achieve more frequent releases, and Alex did not disappoint. He started off by confirming something that I have been a firm believer in for a number of years now; adding more people can do more harm than good when trying to release. This is for a number of reasons, but just adding new people to a team at such a critical time can be more of a drain on resources than they add. The alternative is to have the whole team have shared responsibility for faster delivery. So the whole team is responsible for quality and testing. Obviously you will have the test engineers on the project who have the specialist skills, but there is no reason that the entire team cannot do exploratory testing on the product. This links nicely with the Developer Exploratory testing presented by Sigge on Day 1, and certainly something that my team are really striving towards. Focus on cycle time, so what can be done to reduce the time between dev cycles, release cycles. What’s stops a release, what delays a release? all good solid questions that can be answered. Alex suggested that perhaps the product doesn’t need to be fully tested. Doing less testing will reduce the cycle time therefore get the release out faster. He suggested a risk-based approach to planning what testing needs to happen. Reducing testing could have an impact on revenue if it causes harm to customers, so test the ‘right stuff’! Determine a set of tests that are ‘face saving’ or ‘smoke’ tests. These tests cover the core functionality of the product and aim to prevent major embarrassment if these areas were to fail! Amongst many other very good points, Alex suggested that a good approach would be to release after every new feature is added. So do a bit of work -> release, do some more work -> release. By releasing small increments of work, the impact on the customer of bugs being introduced is reduced. Red Pill, Blue Pill The second keynote of the day was “Adaptation and improvisation – but your weakness is not your technique” by Markus Gartner and proved to be another very good presentation. It started off quoting lines from the Matrix which relate to adapting, improvising, realisation and mastery. It has alot of nerds in the room smiling! Markus went on to explain how through deliberate practice ( and a lot of it!) you can achieve mastery, but then you never stop learning. Through methods such as code retreats, testing dojos, workshops you can continually improve and learn. The code retreat idea was one that interested me. It involved pairing to write an automated test for, say, 45 mins, they deleting all the code, finding a different partner and writing the same test again! This is another keynote where the video will speak louder than anything I can write here! Markus did elaborate on something that Lisa and Janet had touched on yesterday whilst busting the myth that “Testers Must Code”. Whilst it is true that to be a tester, you don’t need to code, it is becoming more common that there is this crossover happening where more testers are coding and more programmers are testing. Markus made a special distinction between programmers and developers as testers develop tests code so this helped to make that clear. “Extending Continuous Integration and TDD with Continuous Testing” by Jason Ayers was my next talk after lunch. We already do CI and a bit of TDD on my project team so I was interested to see what this continuous testing thing was all about and whether it would actually work for us. At the start of the presentation I was of the opinion that it just would not work for us because our tests are too slow, and that would be the case for many people. Jason started off by setting the scene and saying that those doing TDD spend between 10-15% of their time waiting for tests to run. This can be reduced by testing less often, reducing the test time but this then increases the risk of introduced bugs not being spotted quickly. Therefore, in comes Continuous Testing (CT). CT systems run your unit tests whenever you save some code and runs them in the background so you can continue working. This is a really nice idea, but to do this, your tests must be fast, independent and reliable. The latter two should be the case anyway, and the first is ideal, but hard! Jason makes several suggestions to make tests fast. Firstly keep the scope of the test small, secondly spin off any expensive tests into a suite which is run, perhaps, overnight or outside of the CT system at any rate. So this started to change my mind, perhaps we could re-engineer our tests, and continuously run the quick ones to give an element of coverage. This talk was very interesting and I’ve already tried a couple of the tools mentioned on our product (Mighty Moose and NCrunch). Sadly due to the way our solution is built, it currently doesn’t work, but we will look at whether we can make this work because this has the potential to be a mini-game-changer for us. Using the wrong data Gojko’s Hierarchy of Quality The final keynote of the day was “Reinventing software quality” by Gojko Adzic. He opened the talk with the statement “We’ve got quality wrong because we are using the wrong data”! Gojko then went on to explain that we should judge a bug by whether the customer cares about it, not by whether we think it’s important. Why spend time fixing issues that the customer just wouldn’t care about and releasing months later because of this? Surely it’s better to release now and get customer feedback? This was another reference to the idea of how it’s better to build the right thing wrong than the wrong thing right. Get feedback early to make sure you’re making the right thing. Gojko then showed something which was very analogous to Maslow’s heirachy of needs. Successful – does it contribute to the business? Useful – does it do what the user wants Usable – does it do what it’s supposed to without breaking Performant/Secure – is it secure/is the performance acceptable Deployable Functionally ok – can it be deployed without breaking? He then explained that User Stories should focus on change. In other words they should focus on the users needs, not the users process. Describe what the change will be, how that change will happen then measure it! Networking and Beer Following the day’s closing keynote, there were drinks and nibble for the ‘Networking’ evening. This was a great opportunity to talk to people. I find approaching strangers very uncomfortable but once again, when in Rome! Pete Walen and I had a long conversation about only fixing issues that the customer cares about versus fixing issues that make you proud of your software! Without saying much, and asking the right questions, Pete made me re-evaluate my thoughts on the matter. Clever, very clever!  Oh and he ‘bought’ me a beer! My Takeaway Triple from Day 2: release small and release often to minimize issues creeping in and get faster feedback from ‘the real world’ Focus on issues that the customers care about, not what we think is important It’s okay to disagree with someone, even if they are well respected agile testing gurus, that’s how discussion and learning happens!  

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• In search of database delivery practitioners and enthusiasts

  - by Claire Brooking

  We know from speaking with many of you at tradeshows and user groups that database delivery is not a factory production line. During planning, evaluation, quality control, and disaster mitigation, the people having their say at each step means that successful database deployment is a carefully managed course of action. With so many factors involved at every stage, we would love to find a way for our software to help out, by simplifying processes, speeding them up or joining together the people and the steps that make it all happen. We’re hoping our new research group for database delivery (SQL Server and Oracle) will help us understand the views and experiences of those of you out there in the trenches managing database changes. As part of our new group, we’ll be running a variety of research sessions, including surveys and phone interviews, over coming months. If you have opinions to share on Continuous Integration or Continuous Delivery for databases, we’d love to hear from you. Your feedback really will count as the product teams at Red Gate build plans. For some of our more in-depth sessions, we’ll also be offering participants an Amazon voucher as a thank-you for your time. If you’re not yet practising automated database deployment processes, but are contemplating or planning it, please do consider joining our research group too. If you’d like to sign up to the group and find out more, please fill in a quick form online, and we’ll be in touch to let you know about new research opportunities you might be interested in. We look forward to hearing your stories!

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• ArchBeat Link-o-Rama for October 18, 2013

  - by OTN ArchBeat

  Enriching XMLType data using relational data – XQuery and fn:collection in action | Lucas Jellema Another detailed technical post from the always prolific Lucas Jellema. Evil Behind ChangeEventPolicy PPR in CRUD ADF 12c and WebLogic Stuck Threads | Andrejus Baranovskis The latest post from Oracle ACE Director Andrejus Baranovskis is a bit of a preview of his presentation at the upcoming UKOUG 2013 event. Podcast: Interview with authors of "Hudson Continuous Integration in Practice" For your listening pleasure... Here's an Oracle Author Podcast Interview with "Hudson Continuous Integration in Practice" authors Ed Burns and Winston Prakash. Manual Recovery Mechanisms in SOA Suite and AIA | Shreenidhi Raghuram Solution architect Shreenidhi Raghuram's post combines information from several sources to provide "a quick reference for Manual Recovery of Faults within the SOA and AIA contexts." Event: Harnessing Oracle Weblogic and Oracle Coherence This OTN Virtual Developer Day event features eight sessions in two tracks, with presentations and hands-on labs for developers and architects delivered by experts in Weblogic, Coherence, and ADF. Registration is free. November 5th, 2013. 9am-1pm PT / 12pm-4pm ET / 1pm-5pm BRT Podcast: IoT Challenges and Opportunities - Part 2 Part 2 of the OTN ArchBeat Internet of Things podcast features a roundtable discussion of IoT challenges: massive data streams, security and privacy issues, evolving standards and protocols. Listen! Video: Design - ADF Architectural Patterns - Two for One Deal | Chris Muir Chris Muir explores the reuse of BTF workspaces across multiple applications and the advantages and disadvantages of reuse at the application level. Thought for the Day "Can't nothing make your life work if you ain't the architect." — Terry McMillan, American author (Born October 18, 1951) Source: brainyquote.com

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• LOD in modern games

  - by Firas Assaad

  I'm currently working on my master's thesis about LOD and mesh simplification, and I've been reading many academic papers and articles about the subject. However, I can't find enough information about how LOD is being used in modern games. I know many games use some sort of dynamic LOD for terrain, but what about elsewhere? Level of Detail for 3D Graphics for example points out that discrete LOD (where artists prepare several models in advance) is widely used because of the performance overhead of continuous LOD. That book was published in 2002 however, and I'm wondering if things are different now. There has been some research in performing dynamic LOD using the geometry shader (this paper for example, with its implementation in ShaderX6), would that be used in a modern game? To summarize, my question is about the state of LOD in modern video games, what algorithms are used and why? In particular, is view dependent continuous simplification used or does the runtime overhead make using discrete models with proper blending and impostors a more attractive solution? If discrete models are used, is an algorithm used (e.g. vertex clustering) to generate them offline, do artists manually create the models, or perhaps a combination of both methods is used?

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• I'm a SubVersion geek, why I should consider or not consider Mercurial or Git or any other DRCS?

  - by Pierre 303

  I tried to understand the benefits of DRCS. I must recognize I still doesn't get it. Here are my current beliefs. I'm ready to destroy them thanks to your expertise. I know I'm probably resisting to change. I just want to evaluate how much that change will cost me. Merging hell can be solved by just applying good practices such as continuous integration. There is no such good practice than having a private branch for a few days when you are in a self managing team with real collaboration. I use branching for that for very rare cases, and I keep a branch for every major version, in which I fix bugs merged from the trunk. I see the value of committing offline then pushing online. But continuous integration can help on this too. I work on very large projects, and I never noticed SubVersion to be slow even when the server is 5000km away on the internet and my small connection (less than 1024D/128U). Harddisk space is cheap, so having a copy of source code locally doesn't look like a problem to me. I already have a full copy of the last version on my disk. I don't understand the distributed thing there (maybe THIS IS the key to my understanding?) I not new in the industry, and judging by my difficulty to understand, I don't think DRCS are easier to understand than SubVersion like. If fact, I don't understand... Doctor, give me your diagnostic.

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• Is there a (family of) monotonically non-decreasing noise function(s)?

  - by Joe Wreschnig

  I'd like a function to animate an object moving from point A to point B over time, such that it reaches B at some fixed time, but its position at any time is randomly perturbed in a continuous fashion, but never goes backwards. The objects move along straight lines, so I only need one dimension. Mathematically, that means I'm looking for some continuous f(x), x ? [0,1], such that: f(0) = 0 f(1) = 1 x < y ? f(x) = f(y) At "most" points f(x + d) - f(x) bears no obvious relation to d. (The function is not uniformly increasing or otherwise predictable; I think that's also equivalent to saying no degree of derivative is a constant.) Ideally, I would actually like some way to have a family of these functions, providing some seed state. I'd need at least 4 bits of seed (16 possible functions), for my current use, but since that's not much feel free to provide even more. To avoid various issues with accumulation errors, I'd prefer the function not require any kind of internal state. That is, I want it to be a real function, not a programming "function".

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• A better alternative to incompatible implementations for the same interface?

  - by glenatron

  I am working on a piece of code which performs a set task in several parallel environments where the behaviour of the different components in the task are similar but quite different. This means that my implementations are quite different but they are all based on the relationships between the same interfaces, something like this: IDataReader -> ContinuousDataReader -> ChunkedDataReader IDataProcessor -> ContinuousDataProcessor -> ChunkedDataProcessor IDataWriter -> ContinuousDataWriter -> ChunkedDataWriter So that in either environment we have an IDataReader, IDataProcessor and IDataWriter and then we can use Dependency Injection to ensure that we have the correct one of each for the current environment, so if we are working with data in chunks we use the ChunkedDataReader, ChunkedDataProcessor and ChunkedDataWriter and if we have continuous data we have the continuous versions. However the behaviour of these classes is quite different internally and one could certainly not go from a ContinuousDataReader to the ChunkedDataReader even though they are both IDataProcessors. This feels to me as though it is incorrect ( possibly an LSP violation? ) and certainly not a theoretically correct way of working. It is almost as though the "real" interface here is the combination of all three classes. Unfortunately in the project I am working on with the deadlines we are working to, we're pretty much stuck with this design, but if we had a little more elbow room, what would be a better design approach in this kind of scenario?

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• Toolset agnostic build server and Silverlight projects

  - by Marko Apfel

  Problem Normally I try to have my continuous integration as most a possible toolset free to ensure that no local stuff could have an impact to my build. My Silverlight app references a special compile target in a folder outside my developer tree: <Import Project="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v10.0\WebApplications\Microsoft.WebApplication.targets" /> So I copied the stuff from this folder to a local one and changed the call to this target in my csproj: <Import Project="..\..\..\tools\WebApplications\Microsoft.WebApplication.targets" /> And now Visual Studio Conversion Wizard welcomes my with this: Solution Regardless of which line I write – this conversion comes back again and again, if the line has another form than <Import Project="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v10.0\WebApplications\Microsoft.WebApplication.targets" /> So it seems that there is no simple way to change this behaviour. Workaraound I must accept, that this line must be in the csproj and to run the build the toolset must be copied to the build server at the correct location. So go to your development machine where Visual Studio is installed and copy the folder “C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v10.0\WebApplications” to your build server at the equivalent location.   Xmas wishes to Microsoft: Please provide technologies to let us developers bundle all needed stuff for a project in one developer tree. It should be possible that one checkout starts us up! No additional installations regardless whether it is a developing machine or dedicated build or continuous integration server. Silverlight is only one example, code analysis configurations could also be terrible and much more …

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• Space Invaders-type game: Keeping the enemies aligned with each other as they turn around?

  - by CorundumGames

  OK, so here's the lowdown of the problem I'm trying to solve. I'm developing a game in PyGame that's a cross between Space Invaders and Columns. I'm trying to make the motion of the enemies similar to that of the aliens in Space Invaders; that is, they're all clustered in a grid, and if even one hits the side of the screen, the entire formation moves down and turns around. However, the motion of these aliens is continuous (as continuous as a monitor can be, anyway), not on a discrete grid like in the original. The enemies are instances of an Enemy class, and in turn they're held by a 2D array in a enemysquadron module (which, if you don't use Python, is in this case essentially a singleton due to the way Python modules work). Inside the Enemy class I have a class-scope velocity vector that is reversed every time an Enemy object touches the edge of the screen. This won't do, though, because as time goes on the enemies just become disorganized and jumbled (i.e. not in a grid as planned). I haven't implemented the Enemies going downward yet, so let's not worry about that right now. Any tips?

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• At the Java DEMOgrounds - ZeroTurnaround and its LiveRebel 2.5

  - by Janice J. Heiss

  At the ZeroTurnaround demo, I spoke with Krishnan Badrinarayanan, their Product Marketing Manager. ZeroTurnaround, the creator of JRebel and LiveRebel, describes itself on their site as a company “dedicated to changing the way the world develops, tests and runs Java applications."“We just launched LiveRebel 2.5 today,” stated Badrinarayanan, “which enables companies to embrace the concept and practice of continuous delivery, which means having a pipeline that takes products right from the developers to an end-user, faster, more frequently -- all the while ensuring that it’s a quality product that does not break in production. So customers don’t feel the discontinuity that something has changed under them and that they can’t deal with the change. And all this happens while there is zero down time.”He pointed out that Salesforce.com is not useable from 3 a.m. to 5 a.m. on Saturday because they are engaged in maintenance. “With LiveRebel 2.5, you can unify the whole delivery chain without having any downtime at all,” he said. “There are many products that tell customers to take their tools and change how they work as an organization so that you they have to conform to the way the tool prescribes them to work as an application team. We take a more pragmatic approach. A lot of companies might use Jenkins or Bamboo to do continuous integration. We extend that. We say, take our product, take LiveRebel okay, and integrate it with Jenkins – you can do that quickly, so that, in half a day, you will be up and running. And let LiveRebel automate your deployment processes and all the automated tasks that go with it. Right from tests to the staging environment to production -- all with zero downtime and with no impact on users currently using the system.” “So if you were to make the update right now and you had 100 users on your system, they would not even know this was happening. It would maintain their sessions and transfer them over to the new version, all in the background.”

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• Is it possible to run dhcpd3 as non-root user in a chroot jail?

  - by Lenain

  Hi everyone. I would like to run dhcpd3 from a chroot jail on Debian Lenny. At the moment, I can run it as root from my jail. Now I want to do this as non-root user (as "-u blah -t /path/to/jail" Bind option). If I start my process like this : start-stop-daemon --chroot /home/jails/dhcp --chuid dhcp \ --start --pidfile /home/jails/dhcp/var/run/dhcp.pid --exec /usr/sbin/dhcpd3 I get stuck with these errors : Internet Systems Consortium DHCP Server V3.1.1 Copyright 2004-2008 Internet Systems Consortium. All rights reserved. For info, please visit http://www.isc.org/sw/dhcp/ unable to create icmp socket: Operation not permitted Wrote 0 deleted host decls to leases file. Wrote 0 new dynamic host decls to leases file. Wrote 0 leases to leases file. Open a socket for LPF: Operation not permitted strace : brk(0) = 0x911b000 fcntl64(0, F_GETFD) = 0 fcntl64(1, F_GETFD) = 0 fcntl64(2, F_GETFD) = 0 access("/etc/suid-debug", F_OK) = -1 ENOENT (No such file or directory) access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb775d000 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = -1 ENOENT (No such file or directory) open("/lib/tls/i686/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/i686/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/i686", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/i686/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i686/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i686", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/libc.so.6", O_RDONLY) = 3 read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260e\1\0004\0\0\0t"..., 512) = 512 fstat64(3, {st_mode=S_IFREG|0755, st_size=1294572, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb775c000 mmap2(NULL, 1300080, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb761e000 mmap2(0xb7756000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x138) = 0xb7756000 mmap2(0xb7759000, 9840, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7759000 close(3) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761d000 set_thread_area({entry_number:-1 - 6, base_addr:0xb761d6b0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 mprotect(0xb7756000, 4096, PROT_READ) = 0 open("/dev/null", O_RDWR) = 3 close(3) = 0 brk(0) = 0x911b000 brk(0x913c000) = 0x913c000 socket(PF_FILE, SOCK_DGRAM, 0) = 3 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0 connect(3, {sa_family=AF_FILE, path="/dev/log"...}, 110) = 0 time(NULL) = 1284760816 open("/etc/localtime", O_RDONLY) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 fstat64(4, {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761c000 read(4, "TZif2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\f\0\0\0\f\0\0\0\0\0"..., 4096) = 2945 _llseek(4, -28, [2917], SEEK_CUR) = 0 read(4, "\nCET-1CEST,M3.5.0,M10.5.0/3\n"..., 4096) = 28 close(4) = 0 munmap(0xb761c000, 4096) = 0 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Intern"..., 73, MSG_NOSIGNAL) = 73 write(2, "Internet Systems Consortium DHCP "..., 46Internet Systems Consortium DHCP Server V3.1.1) = 46 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Copyri"..., 75, MSG_NOSIGNAL) = 75 write(2, "Copyright 2004-2008 Internet Syst"..., 48Copyright 2004-2008 Internet Systems Consortium.) = 48 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: All ri"..., 47, MSG_NOSIGNAL) = 47 write(2, "All rights reserved."..., 20All rights reserved.) = 20 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: For in"..., 77, MSG_NOSIGNAL) = 77 write(2, "For info, please visit http://www"..., 50For info, please visit http://www.isc.org/sw/dhcp/) = 50 write(2, "\n"..., 1 ) = 1 socket(PF_FILE, SOCK_STREAM, 0) = 4 fcntl64(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"...}, 110) = -1 ENOENT (No such file or directory) close(4) = 0 socket(PF_FILE, SOCK_STREAM, 0) = 4 fcntl64(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"...}, 110) = -1 ENOENT (No such file or directory) close(4) = 0 open("/etc/nsswitch.conf", O_RDONLY) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=475, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761c000 read(4, "# /etc/nsswitch.conf\n#\n# Example "..., 4096) = 475 read(4, ""..., 4096) = 0 close(4) = 0 munmap(0xb761c000, 4096) = 0 open("/lib/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/libnss_files.so.2", O_RDONLY) = 4 read(4, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\320\30\0\0004\0\0\0\250"..., 512) = 512 fstat64(4, {st_mode=S_IFREG|0644, st_size=38408, ...}) = 0 mmap2(NULL, 41624, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 4, 0) = 0xb7612000 mmap2(0xb761b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4, 0x8) = 0xb761b000 close(4) = 0 open("/etc/services", O_RDONLY|O_CLOEXEC) = 4 fcntl64(4, F_GETFD) = 0x1 (flags FD_CLOEXEC) fstat64(4, {st_mode=S_IFREG|0644, st_size=18480, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7611000 read(4, "# Network services, Internet styl"..., 4096) = 4096 read(4, "9/tcp\t\t\t\t# Quick Mail Transfer Pr"..., 4096) = 4096 read(4, "note\t1352/tcp\tlotusnotes\t# Lotus "..., 4096) = 4096 read(4, "tion\nafs3-kaserver\t7004/udp\nafs3-"..., 4096) = 4096 read(4, "backup\t2989/tcp\t\t\t# Afmbackup sys"..., 4096) = 2096 read(4, ""..., 4096) = 0 close(4) = 0 munmap(0xb7611000, 4096) = 0 time(NULL) = 1284760816 open("/etc/protocols", O_RDONLY|O_CLOEXEC) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=2626, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7611000 read(4, "# Internet (IP) protocols\n#\n# Upd"..., 4096) = 2626 close(4) = 0 munmap(0xb7611000, 4096) = 0 socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = -1 EPERM (Operation not permitted) time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: unable"..., 80, MSG_NOSIGNAL) = 80 write(2, "unable to create icmp socket: Ope"..., 53unable to create icmp socket: Operation not permitted) = 53 write(2, "\n"..., 1 ) = 1 open("/etc/dhcp3/dhcpd.conf", O_RDONLY) = 4 lseek(4, 0, SEEK_END) = 1426 lseek(4, 0, SEEK_SET) = 0 read(4, "#----------------------------\n# G"..., 1426) = 1426 close(4) = 0 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75b0000 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb754e000 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74ec000 brk(0x916f000) = 0x916f000 close(3) = 0 socket(PF_FILE, SOCK_DGRAM, 0) = 3 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0 connect(3, {sa_family=AF_FILE, path="/dev/log"...}, 110) = 0 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Inter"..., 74, MSG_NOSIGNAL) = 74 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Copyr"..., 76, MSG_NOSIGNAL) = 76 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: All r"..., 48, MSG_NOSIGNAL) = 48 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: For i"..., 78, MSG_NOSIGNAL) = 78 open("/var/lib/dhcp3/dhcpd.leases", O_RDONLY) = 4 lseek(4, 0, SEEK_END) = 126 lseek(4, 0, SEEK_SET) = 0 read(4, "# The format of this file is docu"..., 126) = 126 close(4) = 0 open("/var/lib/dhcp3/dhcpd.leases", O_WRONLY|O_CREAT|O_APPEND, 0666) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=126, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74eb000 fstat64(4, {st_mode=S_IFREG|0644, st_size=126, ...}) = 0 _llseek(4, 126, [126], SEEK_SET) = 0 time(NULL) = 1284760816 time(NULL) = 1284760816 open("/var/lib/dhcp3/dhcpd.leases.1284760816", O_WRONLY|O_CREAT|O_TRUNC, 0664) = 5 fcntl64(5, F_GETFL) = 0x1 (flags O_WRONLY) fstat64(5, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74ea000 _llseek(5, 0, [0], SEEK_CUR) = 0 close(4) = 0 munmap(0xb74eb000, 4096) = 0 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 70, MSG_NOSIGNAL) = 70 write(2, "Wrote 0 deleted host decls to lea"..., 42Wrote 0 deleted host decls to leases file.) = 42 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 74, MSG_NOSIGNAL) = 74 write(2, "Wrote 0 new dynamic host decls to"..., 46Wrote 0 new dynamic host decls to leases file.) = 46 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 58, MSG_NOSIGNAL) = 58 write(2, "Wrote 0 leases to leases file."..., 30Wrote 0 leases to leases file.) = 30 write(2, "\n"..., 1 ) = 1 write(5, "# The format of this file is docu"..., 126) = 126 fsync(5) = 0 unlink("/var/lib/dhcp3/dhcpd.leases~") = 0 link("/var/lib/dhcp3/dhcpd.leases", "/var/lib/dhcp3/dhcpd.leases~") = 0 rename("/var/lib/dhcp3/dhcpd.leases.1284760816", "/var/lib/dhcp3/dhcpd.leases") = 0 socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 4 ioctl(4, SIOCGIFCONF, {0 - 64, NULL}) = 0 ioctl(4, SIOCGIFCONF, {64, {{"lo", {AF_INET, inet_addr("127.0.0.1")}}, {"eth0", {AF_INET, inet_addr("192.168.0.10")}}}}) = 0 ioctl(4, SIOCGIFFLAGS, {ifr_name="lo", ifr_flags=IFF_UP|IFF_LOOPBACK|IFF_RUNNING}) = 0 ioctl(4, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST}) = 0 ioctl(4, SIOCGIFHWADDR, {ifr_name="eth0", ifr_hwaddr=00:c0:26:87:55:c0}) = 0 socket(PF_PACKET, SOCK_PACKET, 768) = -1 EPERM (Operation not permitted) time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Open "..., 74, MSG_NOSIGNAL) = 74 write(2, "Open a socket for LPF: Operation "..., 46Open a socket for LPF: Operation not permitted) = 46 write(2, "\n"..., 1 ) = 1 exit_group(1) = ? I understand that dhcpd wants to create sockets on port 67... but I don't know how to authorize that through the chroot. Any idea?

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• An Introduction to ASP.NET Web API

  - by Rick Strahl

  Microsoft recently released ASP.NET MVC 4.0 and .NET 4.5 and along with it, the brand spanking new ASP.NET Web API. Web API is an exciting new addition to the ASP.NET stack that provides a new, well-designed HTTP framework for creating REST and AJAX APIs (API is Microsoft’s new jargon for a service, in case you’re wondering). Although Web API ships and installs with ASP.NET MVC 4, you can use Web API functionality in any ASP.NET project, including WebForms, WebPages and MVC or just a Web API by itself. And you can also self-host Web API in your own applications from Console, Desktop or Service applications. If you're interested in a high level overview on what ASP.NET Web API is and how it fits into the ASP.NET stack you can check out my previous post: Where does ASP.NET Web API fit? In the following article, I'll focus on a practical, by example introduction to ASP.NET Web API. All the code discussed in this article is available in GitHub: https://github.com/RickStrahl/AspNetWebApiArticle [republished from my Code Magazine Article and updated for RTM release of ASP.NET Web API] Getting Started To start I’ll create a new empty ASP.NET application to demonstrate that Web API can work with any kind of ASP.NET project. Although you can create a new project based on the ASP.NET MVC/Web API template to quickly get up and running, I’ll take you through the manual setup process, because one common use case is to add Web API functionality to an existing ASP.NET application. This process describes the steps needed to hook up Web API to any ASP.NET 4.0 application. Start by creating an ASP.NET Empty Project. Then create a new folder in the project called Controllers. Add a Web API Controller Class Once you have any kind of ASP.NET project open, you can add a Web API Controller class to it. Web API Controllers are very similar to MVC Controller classes, but they work in any kind of project. Add a new item to this folder by using the Add New Item option in Visual Studio and choose Web API Controller Class, as shown in Figure 1. Figure 1: This is how you create a new Controller Class in Visual Studio   Make sure that the name of the controller class includes Controller at the end of it, which is required in order for Web API routing to find it. Here, the name for the class is AlbumApiController. For this example, I’ll use a Music Album model to demonstrate basic behavior of Web API. The model consists of albums and related songs where an album has properties like Name, Artist and YearReleased and a list of songs with a SongName and SongLength as well as an AlbumId that links it to the album. You can find the code for the model (and the rest of these samples) on Github. To add the file manually, create a new folder called Model, and add a new class Album.cs and copy the code into it. There’s a static AlbumData class with a static CreateSampleAlbumData() method that creates a short list of albums on a static .Current that I’ll use for the examples. Before we look at what goes into the controller class though, let’s hook up routing so we can access this new controller. Hooking up Routing in Global.asax To start, I need to perform the one required configuration task in order for Web API to work: I need to configure routing to the controller. Like MVC, Web API uses routing to provide clean, extension-less URLs to controller methods. Using an extension method to ASP.NET’s static RouteTable class, you can use the MapHttpRoute() (in the System.Web.Http namespace) method to hook-up the routing during Application_Start in global.asax.cs shown in Listing 1.using System; using System.Web.Routing; using System.Web.Http; namespace AspNetWebApi { public class Global : System.Web.HttpApplication { protected void Application_Start(object sender, EventArgs e) { RouteTable.Routes.MapHttpRoute( name: "AlbumVerbs", routeTemplate: "albums/{title}", defaults: new { symbol = RouteParameter.Optional, controller="AlbumApi" } ); } } } This route configures Web API to direct URLs that start with an albums folder to the AlbumApiController class. Routing in ASP.NET is used to create extensionless URLs and allows you to map segments of the URL to specific Route Value parameters. A route parameter, with a name inside curly brackets like {name}, is mapped to parameters on the controller methods. Route parameters can be optional, and there are two special route parameters – controller and action – that determine the controller to call and the method to activate respectively. HTTP Verb Routing Routing in Web API can route requests by HTTP Verb in addition to standard {controller},{action} routing. For the first examples, I use HTTP Verb routing, as shown Listing 1. Notice that the route I’ve defined does not include an {action} route value or action value in the defaults. Rather, Web API can use the HTTP Verb in this route to determine the method to call the controller, and a GET request maps to any method that starts with Get. So methods called Get() or GetAlbums() are matched by a GET request and a POST request maps to a Post() or PostAlbum(). Web API matches a method by name and parameter signature to match a route, query string or POST values. In lieu of the method name, the [HttpGet,HttpPost,HttpPut,HttpDelete, etc] attributes can also be used to designate the accepted verbs explicitly if you don’t want to follow the verb naming conventions. Although HTTP Verb routing is a good practice for REST style resource APIs, it’s not required and you can still use more traditional routes with an explicit {action} route parameter. When {action} is supplied, the HTTP verb routing is ignored. I’ll talk more about alternate routes later. When you’re finished with initial creation of files, your project should look like Figure 2.   Figure 2: The initial project has the new API Controller Album model   Creating a small Album Model Now it’s time to create some controller methods to serve data. For these examples, I’ll use a very simple Album and Songs model to play with, as shown in Listing 2. public class Song { public string AlbumId { get; set; } [Required, StringLength(80)] public string SongName { get; set; } [StringLength(5)] public string SongLength { get; set; } } public class Album { public string Id { get; set; } [Required, StringLength(80)] public string AlbumName { get; set; } [StringLength(80)] public string Artist { get; set; } public int YearReleased { get; set; } public DateTime Entered { get; set; } [StringLength(150)] public string AlbumImageUrl { get; set; } [StringLength(200)] public string AmazonUrl { get; set; } public virtual List<Song> Songs { get; set; } public Album() { Songs = new List<Song>(); Entered = DateTime.Now; // Poor man's unique Id off GUID hash Id = Guid.NewGuid().GetHashCode().ToString("x"); } public void AddSong(string songName, string songLength = null) { this.Songs.Add(new Song() { AlbumId = this.Id, SongName = songName, SongLength = songLength }); } } Once the model has been created, I also added an AlbumData class that generates some static data in memory that is loaded onto a static .Current member. The signature of this class looks like this and that's what I'll access to retrieve the base data:public static class AlbumData { // sample data - static list public static List<Album> Current = CreateSampleAlbumData(); /// <summary> /// Create some sample data /// </summary> /// <returns></returns> public static List<Album> CreateSampleAlbumData() { … }} You can check out the full code for the data generation online. Creating an AlbumApiController Web API shares many concepts of ASP.NET MVC, and the implementation of your API logic is done by implementing a subclass of the System.Web.Http.ApiController class. Each public method in the implemented controller is a potential endpoint for the HTTP API, as long as a matching route can be found to invoke it. The class name you create should end in Controller, which is how Web API matches the controller route value to figure out which class to invoke. Inside the controller you can implement methods that take standard .NET input parameters and return .NET values as results. Web API’s binding tries to match POST data, route values, form values or query string values to your parameters. Because the controller is configured for HTTP Verb based routing (no {action} parameter in the route), any methods that start with Getxxxx() are called by an HTTP GET operation. You can have multiple methods that match each HTTP Verb as long as the parameter signatures are different and can be matched by Web API. In Listing 3, I create an AlbumApiController with two methods to retrieve a list of albums and a single album by its title .public class AlbumApiController : ApiController { public IEnumerable<Album> GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); return albums; } public Album GetAlbum(string title) { var album = AlbumData.Current .SingleOrDefault(alb => alb.AlbumName.Contains(title)); return album; }} To access the first two requests, you can use the following URLs in your browser: http://localhost/aspnetWebApi/albumshttp://localhost/aspnetWebApi/albums/Dirty%20Deeds Note that you’re not specifying the actions of GetAlbum or GetAlbums in these URLs. Instead Web API’s routing uses HTTP GET verb to route to these methods that start with Getxxx() with the first mapping to the parameterless GetAlbums() method and the latter to the GetAlbum(title) method that receives the title parameter mapped as optional in the route. Content Negotiation When you access any of the URLs above from a browser, you get either an XML or JSON result returned back. The album list result for Chrome 17 and Internet Explorer 9 is shown Figure 3. Figure 3: Web API responses can vary depending on the browser used, demonstrating Content Negotiation in action as these two browsers send different HTTP Accept headers.   Notice that the results are not the same: Chrome returns an XML response and IE9 returns a JSON response. Whoa, what’s going on here? Shouldn’t we see the same result in both browsers? Actually, no. Web API determines what type of content to return based on Accept headers. HTTP clients, like browsers, use Accept headers to specify what kind of content they’d like to see returned. Browsers generally ask for HTML first, followed by a few additional content types. Chrome (and most other major browsers) ask for: Accept: text/html, application/xhtml+xml,application/xml; q=0.9,*/*;q=0.8 IE9 asks for: Accept: text/html, application/xhtml+xml, */* Note that Chrome’s Accept header includes application/xml, which Web API finds in its list of supported media types and returns an XML response. IE9 does not include an Accept header type that works on Web API by default, and so it returns the default format, which is JSON. This is an important and very useful feature that was missing from any previous Microsoft REST tools: Web API automatically switches output formats based on HTTP Accept headers. Nowhere in the server code above do you have to explicitly specify the output format. Rather, Web API determines what format the client is requesting based on the Accept headers and automatically returns the result based on the available formatters. This means that a single method can handle both XML and JSON results.. Using this simple approach makes it very easy to create a single controller method that can return JSON, XML, ATOM or even OData feeds by providing the appropriate Accept header from the client. By default you don’t have to worry about the output format in your code. Note that you can still specify an explicit output format if you choose, either globally by overriding the installed formatters, or individually by returning a lower level HttpResponseMessage instance and setting the formatter explicitly. More on that in a minute. Along the same lines, any content sent to the server via POST/PUT is parsed by Web API based on the HTTP Content-type of the data sent. The same formats allowed for output are also allowed on input. Again, you don’t have to do anything in your code – Web API automatically performs the deserialization from the content. Accessing Web API JSON Data with jQuery A very common scenario for Web API endpoints is to retrieve data for AJAX calls from the Web browser. Because JSON is the default format for Web API, it’s easy to access data from the server using jQuery and its getJSON() method. This example receives the albums array from GetAlbums() and databinds it into the page using knockout.js.$.getJSON("albums/", function (albums) { // make knockout template visible $(".album").show(); // create view object and attach array var view = { albums: albums }; ko.applyBindings(view); }); Figure 4 shows this and the next example’s HTML output. You can check out the complete HTML and script code at http://goo.gl/Ix33C (.html) and http://goo.gl/tETlg (.js). Figu Figure 4: The Album Display sample uses JSON data loaded from Web API.   The result from the getJSON() call is a JavaScript object of the server result, which comes back as a JavaScript array. In the code, I use knockout.js to bind this array into the UI, which as you can see, requires very little code, instead using knockout’s data-bind attributes to bind server data to the UI. Of course, this is just one way to use the data – it’s entirely up to you to decide what to do with the data in your client code. Along the same lines, I can retrieve a single album to display when the user clicks on an album. The response returns the album information and a child array with all the songs. The code to do this is very similar to the last example where we pulled the albums array:$(".albumlink").live("click", function () { var id = $(this).data("id"); // title $.getJSON("albums/" + id, function (album) { ko.applyBindings(album, $("#divAlbumDialog")[0]); $("#divAlbumDialog").show(); }); }); Here the URL looks like this: /albums/Dirty%20Deeds, where the title is the ID captured from the clicked element’s data ID attribute. Explicitly Overriding Output Format When Web API automatically converts output using content negotiation, it does so by matching Accept header media types to the GlobalConfiguration.Configuration.Formatters and the SupportedMediaTypes of each individual formatter. You can add and remove formatters to globally affect what formats are available and it’s easy to create and plug in custom formatters.The example project includes a JSONP formatter that can be plugged in to provide JSONP support for requests that have a callback= querystring parameter. Adding, removing or replacing formatters is a global option you can use to manipulate content. It’s beyond the scope of this introduction to show how it works, but you can review the sample code or check out my blog entry on the subject (http://goo.gl/UAzaR). If automatic processing is not desirable in a particular Controller method, you can override the response output explicitly by returning an HttpResponseMessage instance. HttpResponseMessage is similar to ActionResult in ASP.NET MVC in that it’s a common way to return an abstract result message that contains content. HttpResponseMessage s parsed by the Web API framework using standard interfaces to retrieve the response data, status code, headers and so on[MS2] . Web API turns every response – including those Controller methods that return static results – into HttpResponseMessage instances. Explicitly returning an HttpResponseMessage instance gives you full control over the output and lets you mostly bypass WebAPI’s post-processing of the HTTP response on your behalf. HttpResponseMessage allows you to customize the response in great detail. Web API’s attention to detail in the HTTP spec really shows; many HTTP options are exposed as properties and enumerations with detailed IntelliSense comments. Even if you’re new to building REST-based interfaces, the API guides you in the right direction for returning valid responses and response codes. For example, assume that I always want to return JSON from the GetAlbums() controller method and ignore the default media type content negotiation. To do this, I can adjust the output format and headers as shown in Listing 4.public HttpResponseMessage GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); // Create a new HttpResponse with Json Formatter explicitly var resp = new HttpResponseMessage(HttpStatusCode.OK); resp.Content = new ObjectContent<IEnumerable<Album>>( albums, new JsonMediaTypeFormatter()); // Get Default Formatter based on Content Negotiation //var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); resp.Headers.ConnectionClose = true; resp.Headers.CacheControl = new CacheControlHeaderValue(); resp.Headers.CacheControl.Public = true; return resp; } This example returns the same IEnumerable<Album> value, but it wraps the response into an HttpResponseMessage so you can control the entire HTTP message result including the headers, formatter and status code. In Listing 4, I explicitly specify the formatter using the JsonMediaTypeFormatter to always force the content to JSON.  If you prefer to use the default content negotiation with HttpResponseMessage results, you can create the Response instance using the Request.CreateResponse method:var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); This provides you an HttpResponse object that's pre-configured with the default formatter based on Content Negotiation. Once you have an HttpResponse object you can easily control most HTTP aspects on this object. What's sweet here is that there are many more detailed properties on HttpResponse than the core ASP.NET Response object, with most options being explicitly configurable with enumerations that make it easy to pick the right headers and response codes from a list of valid codes. It makes HTTP features available much more discoverable even for non-hardcore REST/HTTP geeks. Non-Serialized Results The output returned doesn’t have to be a serialized value but can also be raw data, like strings, binary data or streams. You can use the HttpResponseMessage.Content object to set a number of common Content classes. Listing 5 shows how to return a binary image using the ByteArrayContent class from a Controller method. [HttpGet] public HttpResponseMessage AlbumArt(string title) { var album = AlbumData.Current.FirstOrDefault(abl => abl.AlbumName.StartsWith(title)); if (album == null) { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found")); return resp; } // kinda silly - we would normally serve this directly // but hey - it's a demo. var http = new WebClient(); var imageData = http.DownloadData(album.AlbumImageUrl); // create response and return var result = new HttpResponseMessage(HttpStatusCode.OK); result.Content = new ByteArrayContent(imageData); result.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg"); return result; } The image retrieval from Amazon is contrived, but it shows how to return binary data using ByteArrayContent. It also demonstrates that you can easily return multiple types of content from a single controller method, which is actually quite common. If an error occurs - such as a resource can’t be found or a validation error – you can return an error response to the client that’s very specific to the error. In GetAlbumArt(), if the album can’t be found, we want to return a 404 Not Found status (and realistically no error, as it’s an image). Note that if you are not using HTTP Verb-based routing or not accessing a method that starts with Get/Post etc., you have to specify one or more HTTP Verb attributes on the method explicitly. Here, I used the [HttpGet] attribute to serve the image. Another option to handle the error could be to return a fixed placeholder image if no album could be matched or the album doesn’t have an image. When returning an error code, you can also return a strongly typed response to the client. For example, you can set the 404 status code and also return a custom error object (ApiMessageError is a class I defined) like this:return Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found") );   If the album can be found, the image will be returned. The image is downloaded into a byte[] array, and then assigned to the result’s Content property. I created a new ByteArrayContent instance and assigned the image’s bytes and the content type so that it displays properly in the browser. There are other content classes available: StringContent, StreamContent, ByteArrayContent, MultipartContent, and ObjectContent are at your disposal to return just about any kind of content. You can create your own Content classes if you frequently return custom types and handle the default formatter assignments that should be used to send the data out . Although HttpResponseMessage results require more code than returning a plain .NET value from a method, it allows much more control over the actual HTTP processing than automatic processing. It also makes it much easier to test your controller methods as you get a response object that you can check for specific status codes and output messages rather than just a result value. Routing Again Ok, let’s get back to the image example. Using the original routing we have setup using HTTP Verb routing there's no good way to serve the image. In order to return my album art image I’d like to use a URL like this: http://localhost/aspnetWebApi/albums/Dirty%20Deeds/image In order to create a URL like this, I have to create a new Controller because my earlier routes pointed to the AlbumApiController using HTTP Verb routing. HTTP Verb based routing is great for representing a single set of resources such as albums. You can map operations like add, delete, update and read easily using HTTP Verbs. But you cannot mix action based routing into a an HTTP Verb routing controller - you can only map HTTP Verbs and each method has to be unique based on parameter signature. You can't have multiple GET operations to methods with the same signature. So GetImage(string id) and GetAlbum(string title) are in conflict in an HTTP GET routing scenario. In fact, I was unable to make the above Image URL work with any combination of HTTP Verb plus Custom routing using the single Albums controller. There are number of ways around this, but all involve additional controllers.  Personally, I think it’s easier to use explicit Action routing and then add custom routes if you need to simplify your URLs further. So in order to accommodate some of the other examples, I created another controller – AlbumRpcApiController – to handle all requests that are explicitly routed via actions (/albums/rpc/AlbumArt) or are custom routed with explicit routes defined in the HttpConfiguration. I added the AlbumArt() method to this new AlbumRpcApiController class. For the image URL to work with the new AlbumRpcApiController, you need a custom route placed before the default route from Listing 1.RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); Now I can use either of the following URLs to access the image: Custom route: (/albums/rpc/{title}/image)http://localhost/aspnetWebApi/albums/PowerAge/image Action route: (/albums/rpc/action/{title})http://localhost/aspnetWebAPI/albums/rpc/albumart/PowerAge Sending Data to the Server To send data to the server and add a new album, you can use an HTTP POST operation. Since I’m using HTTP Verb-based routing in the original AlbumApiController, I can implement a method called PostAlbum()to accept a new album from the client. Listing 6 shows the Web API code to add a new album.public HttpResponseMessage PostAlbum(Album album) { if (!this.ModelState.IsValid) { // my custom error class var error = new ApiMessageError() { message = "Model is invalid" }; // add errors into our client error model for client foreach (var prop in ModelState.Values) { var modelError = prop.Errors.FirstOrDefault(); if (!string.IsNullOrEmpty(modelError.ErrorMessage)) error.errors.Add(modelError.ErrorMessage); else error.errors.Add(modelError.Exception.Message); } return Request.CreateResponse<ApiMessageError>(HttpStatusCode.Conflict, error); } // update song id which isn't provided foreach (var song in album.Songs) song.AlbumId = album.Id; // see if album exists already var matchedAlbum = AlbumData.Current .SingleOrDefault(alb => alb.Id == album.Id || alb.AlbumName == album.AlbumName); if (matchedAlbum == null) AlbumData.Current.Add(album); else matchedAlbum = album; // return a string to show that the value got here var resp = Request.CreateResponse(HttpStatusCode.OK, string.Empty); resp.Content = new StringContent(album.AlbumName + " " + album.Entered.ToString(), Encoding.UTF8, "text/plain"); return resp; } The PostAlbum() method receives an album parameter, which is automatically deserialized from the POST buffer the client sent. The data passed from the client can be either XML or JSON. Web API automatically figures out what format it needs to deserialize based on the content type and binds the content to the album object. Web API uses model binding to bind the request content to the parameter(s) of controller methods. Like MVC you can check the model by looking at ModelState.IsValid. If it’s not valid, you can run through the ModelState.Values collection and check each binding for errors. Here I collect the error messages into a string array that gets passed back to the client via the result ApiErrorMessage object. When a binding error occurs, you’ll want to return an HTTP error response and it’s best to do that with an HttpResponseMessage result. In Listing 6, I used a custom error class that holds a message and an array of detailed error messages for each binding error. I used this object as the content to return to the client along with my Conflict HTTP Status Code response. If binding succeeds, the example returns a string with the name and date entered to demonstrate that you captured the data. Normally, a method like this should return a Boolean or no response at all (HttpStatusCode.NoConent). The sample uses a simple static list to hold albums, so once you’ve added the album using the Post operation, you can hit the /albums/ URL to see that the new album was added. The client jQuery code to call the POST operation from the client with jQuery is shown in Listing 7. var id = new Date().getTime().toString(); var album = { "Id": id, "AlbumName": "Power Age", "Artist": "AC/DC", "YearReleased": 1977, "Entered": "2002-03-11T18:24:43.5580794-10:00", "AlbumImageUrl": http://ecx.images-amazon.com/images/…, "AmazonUrl": http://www.amazon.com/…, "Songs": [ { "SongName": "Rock 'n Roll Damnation", "SongLength": 3.12}, { "SongName": "Downpayment Blues", "SongLength": 4.22 }, { "SongName": "Riff Raff", "SongLength": 2.42 } ] } $.ajax( { url: "albums/", type: "POST", contentType: "application/json", data: JSON.stringify(album), processData: false, beforeSend: function (xhr) { // not required since JSON is default output xhr.setRequestHeader("Accept", "application/json"); }, success: function (result) { // reload list of albums page.loadAlbums(); }, error: function (xhr, status, p3, p4) { var err = "Error"; if (xhr.responseText && xhr.responseText[0] == "{") err = JSON.parse(xhr.responseText).message; alert(err); } }); The code in Listing 7 creates an album object in JavaScript to match the structure of the .NET Album class. This object is passed to the $.ajax() function to send to the server as POST. The data is turned into JSON and the content type set to application/json so that the server knows what to convert when deserializing in the Album instance. The jQuery code hooks up success and failure events. Success returns the result data, which is a string that’s echoed back with an alert box. If an error occurs, jQuery returns the XHR instance and status code. You can check the XHR to see if a JSON object is embedded and if it is, you can extract it by de-serializing it and accessing the .message property. REST standards suggest that updates to existing resources should use PUT operations. REST standards aside, I’m not a big fan of separating out inserts and updates so I tend to have a single method that handles both. But if you want to follow REST suggestions, you can create a PUT method that handles updates by forwarding the PUT operation to the POST method:public HttpResponseMessage PutAlbum(Album album) { return PostAlbum(album); } To make the corresponding $.ajax() call, all you have to change from Listing 7 is the type: from POST to PUT. Model Binding with UrlEncoded POST Variables In the example in Listing 7 I used JSON objects to post a serialized object to a server method that accepted an strongly typed object with the same structure, which is a common way to send data to the server. However, Web API supports a number of different ways that data can be received by server methods. For example, another common way is to use plain UrlEncoded POST  values to send to the server. Web API supports Model Binding that works similar (but not the same) as MVC's model binding where POST variables are mapped to properties of object parameters of the target method. This is actually quite common for AJAX calls that want to avoid serialization and the potential requirement of a JSON parser on older browsers. For example, using jQUery you might use the $.post() method to send a new album to the server (albeit one without songs) using code like the following:$.post("albums/",{AlbumName: "Dirty Deeds", YearReleased: 1976 … },albumPostCallback); Although the code looks very similar to the client code we used before passing JSON, here the data passed is URL encoded values (AlbumName=Dirty+Deeds&YearReleased=1976 etc.). Web API then takes this POST data and maps each of the POST values to the properties of the Album object in the method's parameter. Although the client code is different the server can both handle the JSON object, or the UrlEncoded POST values. Dynamic Access to POST Data There are also a few options available to dynamically access POST data, if you know what type of data you're dealing with. If you have POST UrlEncoded values, you can dynamically using a FormsDataCollection:[HttpPost] public string PostAlbum(FormDataCollection form) { return string.Format("{0} - released {1}", form.Get("AlbumName"),form.Get("RearReleased")); } The FormDataCollection is a very simple object, that essentially provides the same functionality as Request.Form[] in ASP.NET. Request.Form[] still works if you're running hosted in an ASP.NET application. However as a general rule, while ASP.NET's functionality is always available when running Web API hosted inside of an  ASP.NET application, using the built in classes specific to Web API makes it possible to run Web API applications in a self hosted environment outside of ASP.NET. If your client is sending JSON to your server, and you don't want to map the JSON to a strongly typed object because you only want to retrieve a few simple values, you can also accept a JObject parameter in your API methods:[HttpPost] public string PostAlbum(JObject jsonData) { dynamic json = jsonData; JObject jalbum = json.Album; JObject juser = json.User; string token = json.UserToken; var album = jalbum.ToObject<Album>(); var user = juser.ToObject<User>(); return String.Format("{0} {1} {2}", album.AlbumName, user.Name, token); } There quite a few options available to you to receive data with Web API, which gives you more choices for the right tool for the job. Unfortunately one shortcoming of Web API is that POST data is always mapped to a single parameter. This means you can't pass multiple POST parameters to methods that receive POST data. It's possible to accept multiple parameters, but only one can map to the POST content - the others have to come from the query string or route values. I have a couple of Blog POSTs that explain what works and what doesn't here: Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API   Handling Delete Operations Finally, to round out the server API code of the album example we've been discussin, here’s the DELETE verb controller method that allows removal of an album by its title:public HttpResponseMessage DeleteAlbum(string title) { var matchedAlbum = AlbumData.Current.Where(alb => alb.AlbumName == title) .SingleOrDefault(); if (matchedAlbum == null) return new HttpResponseMessage(HttpStatusCode.NotFound); AlbumData.Current.Remove(matchedAlbum); return new HttpResponseMessage(HttpStatusCode.NoContent); } To call this action method using jQuery, you can use:$(".removeimage").live("click", function () { var $el = $(this).parent(".album"); var txt = $el.find("a").text(); $.ajax({ url: "albums/" + encodeURIComponent(txt), type: "Delete", success: function (result) { $el.fadeOut().remove(); }, error: jqError }); }   Note the use of the DELETE verb in the $.ajax() call, which routes to DeleteAlbum on the server. DELETE is a non-content operation, so you supply a resource ID (the title) via route value or the querystring. Routing Conflicts In all requests with the exception of the AlbumArt image example shown so far, I used HTTP Verb routing that I set up in Listing 1. HTTP Verb Routing is a recommendation that is in line with typical REST access to HTTP resources. However, it takes quite a bit of effort to create REST-compliant API implementations based only on HTTP Verb routing only. You saw one example that didn’t really fit – the return of an image where I created a custom route albums/{title}/image that required creation of a second controller and a custom route to work. HTTP Verb routing to a controller does not mix with custom or action routing to the same controller because of the limited mapping of HTTP verbs imposed by HTTP Verb routing. To understand some of the problems with verb routing, let’s look at another example. Let’s say you create a GetSortableAlbums() method like this and add it to the original AlbumApiController accessed via HTTP Verb routing:[HttpGet] public IQueryable<Album> SortableAlbums() { var albums = AlbumData.Current; // generally should be done only on actual queryable results (EF etc.) // Done here because we're running with a static list but otherwise might be slow return albums.AsQueryable(); } If you compile this code and try to now access the /albums/ link, you get an error: Multiple Actions were found that match the request. HTTP Verb routing only allows access to one GET operation per parameter/route value match. If more than one method exists with the same parameter signature, it doesn’t work. As I mentioned earlier for the image display, the only solution to get this method to work is to throw it into another controller. Because I already set up the AlbumRpcApiController I can add the method there. First, I should rename the method to SortableAlbums() so I’m not using a Get prefix for the method. This also makes the action parameter look cleaner in the URL - it looks less like a method and more like a noun. I can then create a new route that handles direct-action mapping:RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); As I am explicitly adding a route segment – rpc – into the route template, I can now reference explicit methods in the Web API controller using URLs like this: http://localhost/AspNetWebApi/rpc/SortableAlbums Error Handling I’ve already done some minimal error handling in the examples. For example in Listing 6, I detected some known-error scenarios like model validation failing or a resource not being found and returning an appropriate HttpResponseMessage result. But what happens if your code just blows up or causes an exception? If you have a controller method, like this:[HttpGet] public void ThrowException() { throw new UnauthorizedAccessException("Unauthorized Access Sucka"); } You can call it with this: http://localhost/AspNetWebApi/albums/rpc/ThrowException The default exception handling displays a 500-status response with the serialized exception on the local computer only. When you connect from a remote computer, Web API throws back a 500  HTTP Error with no data returned (IIS then adds its HTML error page). The behavior is configurable in the GlobalConfiguration:GlobalConfiguration .Configuration .IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Never; If you want more control over your error responses sent from code, you can throw explicit error responses yourself using HttpResponseException. When you throw an HttpResponseException the response parameter is used to generate the output for the Controller action. [HttpGet] public void ThrowError() { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.BadRequest, new ApiMessageError("Your code stinks!")); throw new HttpResponseException(resp); } Throwing an HttpResponseException stops the processing of the controller method and immediately returns the response you passed to the exception. Unlike other Exceptions fired inside of WebAPI, HttpResponseException bypasses the Exception Filters installed and instead just outputs the response you provide. In this case, the serialized ApiMessageError result string is returned in the default serialization format – XML or JSON. You can pass any content to HttpResponseMessage, which includes creating your own exception objects and consistently returning error messages to the client. Here’s a small helper method on the controller that you might use to send exception info back to the client consistently:private void ThrowSafeException(string message, HttpStatusCode statusCode = HttpStatusCode.BadRequest) { var errResponse = Request.CreateResponse<ApiMessageError>(statusCode, new ApiMessageError() { message = message }); throw new HttpResponseException(errResponse); } You can then use it to output any captured errors from code:[HttpGet] public void ThrowErrorSafe() { try { List<string> list = null; list.Add("Rick"); } catch (Exception ex) { ThrowSafeException(ex.Message); } }   Exception Filters Another more global solution is to create an Exception Filter. Filters in Web API provide the ability to pre- and post-process controller method operations. An exception filter looks at all exceptions fired and then optionally creates an HttpResponseMessage result. Listing 8 shows an example of a basic Exception filter implementation.public class UnhandledExceptionFilter : ExceptionFilterAttribute { public override void OnException(HttpActionExecutedContext context) { HttpStatusCode status = HttpStatusCode.InternalServerError; var exType = context.Exception.GetType(); if (exType == typeof(UnauthorizedAccessException)) status = HttpStatusCode.Unauthorized; else if (exType == typeof(ArgumentException)) status = HttpStatusCode.NotFound; var apiError = new ApiMessageError() { message = context.Exception.Message }; // create a new response and attach our ApiError object // which now gets returned on ANY exception result var errorResponse = context.Request.CreateResponse<ApiMessageError>(status, apiError); context.Response = errorResponse; base.OnException(context); } } Exception Filter Attributes can be assigned to an ApiController class like this:[UnhandledExceptionFilter] public class AlbumRpcApiController : ApiController or you can globally assign it to all controllers by adding it to the HTTP Configuration's Filters collection:GlobalConfiguration.Configuration.Filters.Add(new UnhandledExceptionFilter()); The latter is a great way to get global error trapping so that all errors (short of hard IIS errors and explicit HttpResponseException errors) return a valid error response that includes error information in the form of a known-error object. Using a filter like this allows you to throw an exception as you normally would and have your filter create a response in the appropriate output format that the client expects. For example, an AJAX application can on failure expect to see a JSON error result that corresponds to the real error that occurred rather than a 500 error along with HTML error page that IIS throws up. You can even create some custom exceptions so you can differentiate your own exceptions from unhandled system exceptions - you often don't want to display error information from 'unknown' exceptions as they may contain sensitive system information or info that's not generally useful to users of your application/site. This is just one example of how ASP.NET Web API is configurable and extensible. Exception filters are just one example of how you can plug-in into the Web API request flow to modify output. Many more hooks exist and I’ll take a closer look at extensibility in Part 2 of this article in the future. Summary Web API is a big improvement over previous Microsoft REST and AJAX toolkits. The key features to its usefulness are its ease of use with simple controller based logic, familiar MVC-style routing, low configuration impact, extensibility at all levels and tight attention to exposing and making HTTP semantics easily discoverable and easy to use. Although none of the concepts used in Web API are new or radical, Web API combines the best of previous platforms into a single framework that’s highly functional, easy to work with, and extensible to boot. I think that Microsoft has hit a home run with Web API. Related Resources Where does ASP.NET Web API fit? Sample Source Code on GitHub Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API Creating a JSONP Formatter for ASP.NET Web API Removing the XML Formatter from ASP.NET Web API Applications© Rick Strahl, West Wind Technologies, 2005-2012Posted in Web Api   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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