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  • Http Requests POST vs GET

    - by behrk2
    Hi everyone, I am using a lot of HTTP Requests in an application that I am writing which uses OAuth. Currently, I am sending my GET and POST requests the same way: HttpConnection connection = (HttpConnection) Connector.open(url + connectionParameters); connection.setRequestMethod(method); connection.setRequestProperty("WWW-Authenticate", "OAuth realm=api.netflix.com"); int responseCode = connection.getResponseCode(); And this is working fine. I am successfully POSTing and GETing. However, I am worried that I am not doing POST the right way. Do I need to include in the above code the following if-statement? if (method.equals("POST") && postData != null) { connection.setRequestProperty("Content-type", "application/x-www-form-urlencoded"); connection.setRequestProperty("Content-Length", Integer .toString(postData.length)); OutputStream requestOutput = connection.openOutputStream(); requestOutput.write(postData); requestOutput.close(); } If so, why? What's the difference? I would appreciate any feedback. Thanks!

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  • Java HTTP Requests Buffer size

    - by behrk2
    Hello, I have an HTTP Request Dispatcher class that works most of the time, but I had noticed that it "stalls" when receiving larger requests. After looking into the problem, I thought that perhaps I wasn't allocating enough bytes to the buffer. Before, I was doing: byte[] buffer = new byte[10000]; After changing it to 20000, it seems to have stopped stalling: String contentType = connection.getHeaderField("Content-type"); ByteArrayOutputStream baos = new ByteArrayOutputStream(); InputStream responseData = connection.openInputStream(); byte[] buffer = new byte[20000]; int bytesRead = responseData.read(buffer); while (bytesRead > 0) { baos.write(buffer, 0, bytesRead); bytesRead = responseData.read(buffer); } baos.close(); connection.close(); Am I doing this right? Is there anyway that I can dynamically set the number of bytes for the buffer based on the size of the request? Thanks...

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  • Sharing session variables from http and https versio

    - by tangurena
    I am trying to fix an ASP.NET site that a friend had botched converting from older technologies. To the user, the site appears to have public and secured sections. Behind the scenes, the public and private sites are separate web applications with separate app pools. The difficulty arises because it appears that the applications share the same session IDs (when going from the public to the secured pages, the session ID remains the same), yet none of the (InProc) session variables are getting passed from the public site to the private one. Basically, the workflow consists of the user checking a checkbox ("I agree" type of stuff) on the public site (let's call that page http://www.boring.gov/iAgree.aspx), then logging in on the secured site (let's call that page https://www.boring.gov/login.aspx). The commandments from the parent agency in DC are that the user may not bookmark the login page, the user has to click "I agree" every time they log in, and that the "I agree" stuff has to be on a separate page. What am I missing? How would you do it? Notes: 1 - This is getting hosted on a single Windows 2003 server. 2 - Yes, it is a government agency. 3 - I would have done things very differently if I was doing the conversion, but I wasn't brought in until the poop hit the fan, and it is too late to redo things. 4 - Two previous SO threads that appear to be related, yet don't apply are this and that

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  • Passing array values in an HTTP request in .NET

    - by Zarjay
    What's the standard way of passing and processing an array in an HTTP request in .NET? I have a solution, but I don't know if it's the best approach. Here's my solution: <form action="myhandler.ashx" method="post"> <input type="checkbox" name="user" value="Aaron" /> <input type="checkbox" name="user" value="Bobby" /> <input type="checkbox" name="user" value="Jimmy" /> <input type="checkbox" name="user" value="Kelly" /> <input type="checkbox" name="user" value="Simon" /> <input type="checkbox" name="user" value="TJ" /> <input type="submit" value="Submit" /> </form> The ASHX handler receives the "user" parameter as a comma-delimited string. You can get the values easily by splitting the string: public void ProcessRequest(HttpContext context) { string[] users = context.Request.Form["user"].Split(','); } So, I already have an answer to my problem: assign multiple values to the same parameter name, assume the ASHX handler receives it as a comma-delimited string, and split the string. My question is whether or not this is how it's typically done in .NET. What's the standard practice for this? Is there a simpler way to grab the multiple values than assuming that the value is comma-delimited and calling Split() on it? Is this how arrays are typically passed in .NET, or is XML used instead? Does anyone have any insight on whether or not this is the best approach?

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  • ASP.NET Response Filter to Reformat the rendered output of ASPX pages?

    - by PropellerHead
    I've created a simple HttpModule and response stream to reformat the rendered output of web pages (see code snippets below). In the HttpModule I set the Response.Filter to my PageStream: m_Application.Context.Response.Filter = new PageStream(m_Application.Context); In the PageStream I overwrite the Write method in order to do my reformatting of the rendered output: public override void Write(byte[] buffer, int offset, int count) { string html = System.Text.Encoding.UTF8.GetString(buffer); //Do some string resplace operations here... byte[] input = System.Text.Encoding.UTF8.GetBytes(html); m_DefaultStream.Write(input, 0, input.Length); } And this work fine when using it on simple HTML pages (.html), but when I use this method on ASPX pages (.aspx), the Write method is called several times, splitting up the reformatting into different steps, and potentially destroying the string replacement operations. How do I solve this? Is there a way to let the ASPX page NOT call Write several times, e.g. by changing its buffer size, or have I chosen the wrong approach entirely, by using this Response.Filter method to manipulate the rendered output?

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  • Why Response.Write behavior varies in the given scenario?

    - by Sri Kumar
    Hello All, When i POST the page using the following code, the Response.write("Hey") doesn't write the content ("Hello") to the parent page <form method="post" name="upload" enctype="multipart/form-data" action="http://localhost:2518/Web/CrossPage.aspx?cmd=getvalue" > <input type="file" name="filename" /> <input type="submit" value="Upload Data File" name="cmdSubmit" /> </form> But When i use following code , and POST the data, the Response.write("Hey") can be obtained in the parent page HttpWebRequest requestToSender = (HttpWebRequest)WebRequest.Create("http://localhost:2518/Web/CrossPage.aspx?cmd=getvalue"); requestToSender.Method = "POST"; requestToSender.ContentType = "multipart/form-data"; HttpWebResponse responseFromSender = (HttpWebResponse)requestToSender.GetResponse(); string fromSender = string.Empty; using (StreamReader responseReader = new StreamReader(responseFromSender.GetResponseStream())) { fromSender = responseReader.ReadToEnd(); } In the CrossPage.aspx i have the following code if (!Page.IsPostBack) { NameValueCollection postPageCollection = Request.Form; foreach (string name in postPageCollection.AllKeys) { Response.Write(name + " " + postPageCollection[name]); } HttpFileCollection postCollection = Request.Files; foreach (string name in postCollection.AllKeys) { HttpPostedFile aFile = postCollection[name]; aFile.SaveAs(Server.MapPath(".") + "/" + Path.GetFileName(aFile.FileName)); } Response.Write("Hey"); } I don't have any code in the Page_Load event of parent page.? What could be the cause? I need to write the "hey" to the Parent page using the first scenario. Both the application are of different domain. Edit: "Hey" would be from the CrossPage.aspx. I need to write this back to the Parent Page

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  • How to handle building and parsing HTTP URL's / URI's / paths in Perl

    - by Robert S. Barnes
    I have a wget like script which downloads a page and then retrieves all the files linked in img tags on that page. Given the URL of the original page and the the link extracted from the img tag in that page I need to build the URL for the image file I want to retrieve. Currently I use a function I wrote: sub build_url { my ( $base, $path ) = @_; # if the path is absolute just prepend the domain to it if ($path =~ /^\//) { ($base) = $base =~ /^(?:http:\/\/)?(\w+(?:\.\w+)+)/; return "$base$path"; } my @base = split '/', $base; my @path = split '/', $path; # remove a trailing filename pop @base if $base =~ /[[:alnum:]]+\/[\w\d]+\.[\w]+$/; # check for relative paths my $relcount = $path =~ /(\.\.\/)/g; while ( $relcount-- ) { pop @base; shift @path; } return join '/', @base, @path; } The thing is, I'm surely not the first person solving this problem, and in fact it's such a general problem that I assume there must be some better, more standard way of dealing with it, using either a core module or something from CPAN - although via a core module is preferable. I was thinking about File::Spec but wasn't sure if it has all the functionality I would need.

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  • Forwarding HTTP Request with Direct Server Return

    - by Daniel Crabtree
    I have servers spread across several data centers, each storing different files. I want users to be able to access the files on all servers through a single domain and have the individual servers return the files directly to the users. The following shows a simple example: 1) The user's browser requests http://www.example.com/files/file1.zip 2) Request goes to server A, based on the DNS A record for example.com. 3) Server A analyzes the request and works out that /files/file1.zip is stored on server B. 4) Server A forwards the request to server B. 5) Server B returns file1.zip directly to the user without going through server A. Note: steps 4 and 5 must be transparent to the user and cannot involve sending a redirect to the user as that would violate the requirement of a single domain. From my research, what I want to achieve is called "Direct Server Return" and it is a common setup for load balancing. It is also sometimes called a half reverse proxy. For step 4, it sounds like I need to do MAC Address Translation and then pass the request back onto the network and for servers outside the network of server A tunneling will be required. For step 5, I simply need to configure server B, as per the real servers in a load balancing setup. Namely, server B should have server A's IP address on the loopback interface and it should not answer any ARP requests for that IP address. My problem is how to actually achieve step 4? I have found plenty of hardware and software that can do this for simple load balancing at layer 4, but these solutions fall short and cannot handle the kind of custom routing I require. It seems like I will need to roll my own solution. Ideally, I would like to do the routing / forwarding at the web server level, i.e. in PHP or C# / ASP.net. However, I am open to doing it at a lower level such as Apache or IIS, or at an even lower level, i.e. a custom proxy service in front of everything.

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  • Sending an HTTP POST request through the android emulator doesn't work

    - by Sotirios Delimanolis
    I'm running a tomcat servlet on my local machine and an Android emulator with an app that makes a post request to the servlet. The code for the POST is below (without exceptions and the like): String strUrl = "http://10.0.2.2:8080/DeviceDiscoveryServer/server/devices/"; Device device = Device.getUniqueInstance(); urlParameters += URLEncoder.encode("user", "UTF-8") + "=" + URLEncoder.encode(device.getUser(), "UTF-8"); urlParameters += "&" + URLEncoder.encode("port", "UTF-8") + "=" + URLEncoder.encode(new Integer(Device.PORT).toString(), "UTF-8"); urlParameters += "&" + URLEncoder.encode("address", "UTF-8") + "=" + URLEncoder.encode(device.getAddress().getHostAddress(), "UTF-8"); URL url = new URL(strUrl); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setDoOutput(true); connection.setRequestMethod("POST"); OutputStreamWriter wr = new OutputStreamWriter(connection.getOutputStream()); wr.write(urlParameters); wr.flush(); wr.close(); Whenever this code is executed, the servlet isn't called. However if I change the type of the request to 'GET' and don't write anything to the outputstream, the servlet gets called and everything works fine. Am I just not making the POST correctly or is there some other error?

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  • Write transparent HTTP Proxy script in PHP

    - by Leo Izen
    Is there an easy forwarding/transparent php proxy script that I can host on my web server? These are my conditions: I'm using free web hosting, so I have pretty much no control over my machine. Otherwise I could use Perl's HTTP::Proxy module. This means no root password. It does run php though. I already have a server running on port 80. What I mean is I would like to put a php script as index.php on my server that will forward all requests. I don't want a script like PHProxy or Glype where I go to the site, then enter a URL. I want a server so I can enter proxy.example.com:80 in Firefox's or IE's or whatever's proxy settings and it will forward all requests to the server. Preferably (though not fatal if not possible) I would like for it to pass on the USER_AGENT environmental variable (That's the browser) instead of setting itself to be the USER_AGENT I can't start a new Daemon. My server won't allow it. Is there a script that will do this? If so, which?

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  • Configuring Oracle HTTP Server 12c for WebLogic Server Domain

    - by Emin Askerov
    Oracle HTTP Server (OHS) 12c 12.1.2 which was released in July 2013 as a part of Oracle Web Tier 12c is the web server component of Oracle Fusion Middleware. In essence this is Apache HTTP Server 2.2.22 (with critical bug fixes from higher versions) which includes modules developed specifically by Oracle. It provides a listener functionality for Oracle WebLogic Server and the framework for hosting static pages, dynamic pages, and applications over the Web. OHS can be easily managed by Weblogic Management Framework, a set of tools which provides administrative capabilities (start, stop, lifecycle operations, etc.) for Oracle Fusion Middleware products. In other words all tools which are familiar to us (Node Manager, WLST, Administration Console, Fusion Middleware Control etc.) presented as a part of Weblogic Management Framework and using for managing Java and System Components both for Weblogic Server and Standalone Domain types. You can familiarize yourself with these terms using related documentation: 1. Introduction to Oracle HTTP Server: http://docs.oracle.com/middleware/1212/webtier/index.html 2. Weblogic Management Framework: http://docs.oracle.com/middleware/1212/core/ASCON/terminology.htm#ASCON11260 In the given post I would like to cover rather simple use case how to configure OHS as web proxy in Weblogic Cluster environment. For example, we have existing Weblogic Domain where some managed servers have been joined to cluster and host business applications. We need to configure web proxy component which will act as entry point, load balancer for our cluster for user requests. Of course, we could install old good Apache HTTP Server and configure mod_wl plugin. However this solution not optimal from manageability perspective: we need to install Apache, install additional plugin then configure it by editing configuration file which is not really convenient for FMW Administrators and often increase time of performing of simple administrative task. Alternatively, we could use OHS as System Component within Weblogic Domain and use full power of Weblogic Management Framework in order to configure, manage and monitor it! I like this idea! What about you? I hope after reading this post you will agree with me. First of all it is necessary to download OHS binaries. You can use this link for downloading: http://www.oracle.com/technetwork/java/webtier/downloads/index2-303202.html As we will use Fusion Middleware Control for managing OHS instances it is necessary to extend your domain with Enterprise Manager and Oracle ADF and JRF templates. This is not topic for focusing in this post, but you could get more information from documentation or one of my previous posts: http://docs.oracle.com/middleware/1212/wls/WLDTR/fmw_templates.htm#sthref64 https://blogs.oracle.com/imc/entry/the_specifics_of_adf_12c Note: you should have properly configured Node Manager utility for managing OHS instances Let’s consider configuration process step by step: 1. Shut down all Weblogic instances of existing domain including Admin Server; 2. Install Oracle HTTP Server. You should use your Fusion Middleware Home Path (e.g. /u01/Oracle/FMW12) for Installation Location and select Colocated HTTP Server option as Installation Type. I will not focus on this topic in this post. All information related to OHS installation you could find here: http://docs.oracle.com/middleware/1212/webtier/WTINS/install_gui.htm#i1082009 3. Next we need to extend our existing domain with OHS component. In order to do this you should do the following: a. Run Fusion Middleware Configuration Wizard (ORACLE_HOME/oracle_common/common/bin/config.sh); b. On the step 1 select Update an existing domain option and point your Fusion Middleware Home Path; c. On the step 2 check Oracle HTTP Server, Oracle Enterprise Manager Plugin for WEBTIER templates; d. Go through other steps without any changes and finish configuration process. 4. Start Admin Server and all managed servers related to your cluster 5. Log in to Enterprise Manager FMW Control using http://<hostname>:<port>/em URL 6. Now we will create OHS instance within our Weblogic Domain Infrastructure. Navigate to Weblogic Domain -> Administration -> Create/Delete OHS menu item; 7. Enter to edit mode, clicking Changes -> Lock&Edit menu item; 8. Create new OHS instance clicking Create button; 9. Define Instance Name (e.g. DevOSH) and Machine parameters; 10. Now we need to define listen port. By default OHS will use 7777 port number for income HTTP requests. We could change it to any free port number we would like to use. In order to do it, right click on our created OHS instance (left hand panel) and navigate to Administration -> Port Configuration; 11. Click on record with port number 7777 and then click Edit button; 12. Change port number value (in our case this will be 8080) and then click OK button; 13. Now we need to edit mod_wl_ohs configuration in order to enable OHS to act as proxy for WebLogic Server Instances/Cluster; 14. In order to do it right click on our created OHS instance (left panel) and navigate to Administration -> mod_wl_ohs Configuration; a. In Weblogic Cluster you should enter cluster address (define <host:port> for all managed servers which participated in cluster), e.g: 192.168.56.2:7004,192.168.56.2:7005 b. Define Weblogic Port parameter at which the Oracle WebLogic Server host is listening for connection requests from the module (or from other servers); c. Check Dynamic Server List option. This will dynamically update cluster list for every request; d. In the Location table define list of endpoint locations which you would like to process. In order to do this click Add Row button and define Location, Weblogic Cluster, Path Trim and Path Prefix parameters (if required); e. Click Apply button in order to save changes. 15. Activate changes clicking Changes ? Activate Changes menu item; 16. Finally we will start configured OHS instance. Right click on OHS instance tree item under Web Tier folder, select Control -> Start Up menu item; 17. Ensure that OHS instance up and running and then test your environment. Run deployed application to your Weblogic Cluster accessing via OHS web proxy; Normal 0 false false false RU X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}

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  • Custom webserver caching

    - by Mark Kinsella
    I'm working with a custom webserver on an embedded system and having some problems correctly setting my HTTP Headers for caching. Our webserver is generating all dynamic content as XML and we're using semi-static XSL files to display it with some dynamic JSON requests thrown in for good measure along with semi-static images. I say "semi-static" because the problems occur when we need to do a firmware update which might change the XSL and image files. Here's what needs to be done: cache the XSL and image files and do not cache the XML and JSON responses. I have full control over the HTTP response and am currently: Using ETags with the XSL and image files, using the modified time and size to generate the ETag Setting Cache-Control: no-cache on the XML and JSON responses As I said, everything works dandy until a firmware update when the XSL and image files are sometimes cached. I've seen it work fine with the latest versions of Firefox and Safari but have had some problems with IE. I know one solution to this problem would be simply rename the XSL and image files after each version (eg. logo-v1.1.png, logo-v1.2.png) and set the Expires header to a date in the future but this would be difficult with the XSL files and I'd like to avoid this. Note: There is a clock on the unit but requires the user to set it and might not be 100% reliable which is what might be causing my caching issues when using ETags. What's the best practice that I should employ? I'd like to avoid as many webserver requests as possible but invalidating old XSL and image files after a software update is the #1 priority.

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  • Email Tracking - GMail

    - by Abs
    Hello all, I am creating my own email tracking system for email marketing tracking. I have been able to determine each persons email client they are using by using the http referrer but for some reason GMAIL does not send a HTTP_REFERRER at all! So I am trying to find another way of identifying when gmail requests a transparent image from my server. I get the following headers print_r($_SERVER);: DOCUMENT_ROOT = /usr/local/apache/htdocs GATEWAY_INTERFACE = CGI/1.1 HTTP_ACCEPT = */* HTTP_ACCEPT_CHARSET = ISO-8859-1,utf-8;q=0.7,*;q=0.3 HTTP_ACCEPT_ENCODING = gzip,deflate,sdch HTTP_ACCEPT_LANGUAGE = en-GB,en-US;q=0.8,en;q=0.6 HTTP_CONNECTION = keep-alive HTTP_COOKIE = __utmz=156230011.1290976484.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=156230011.422791272.1290976484.1293034866.1293050468.7 HTTP_HOST = xx.xxx.xx.xxx HTTP_USER_AGENT = Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10 PATH = /bin:/usr/bin QUERY_STRING = i=MTA= REDIRECT_STATUS = 200 REMOTE_ADDR = xx.xxx.xx.xxx REMOTE_PORT = 61296 REQUEST_METHOD = GET Is there anything of use in that list? Or is there something else I can do to actually get the http referrer, if not how are other ESPs managing to find whether gmail was used to view an email? Btw, I appreciate it if we can hold back on whether this is ethical or not as many ESPs do this already, I just don't want to pay for their service and I want to do it internally. Thanks all for any implementation advice. Update Just thought I would update this question and make it clearer in light of the bounty. I would like to find out when a user opens my email when sent to a GMail inbox. Assume, I have the usual transparent image tracking and the user does not block images. I would like to do this with the single request and the header details I get when the transparent image is requested.

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  • Creating ASP.NET MVC Negotiated Content Results

    - by Rick Strahl
    In a recent ASP.NET MVC application I’m involved with, we had a late in the process request to handle Content Negotiation: Returning output based on the HTTP Accept header of the incoming HTTP request. This is standard behavior in ASP.NET Web API but ASP.NET MVC doesn’t support this functionality directly out of the box. Another reason this came up in discussion is last week’s announcements of ASP.NET vNext, which seems to indicate that ASP.NET Web API is not going to be ported to the cloud version of vNext, but rather be replaced by a combined version of MVC and Web API. While it’s not clear what new API features will show up in this new framework, it’s pretty clear that the ASP.NET MVC style syntax will be the new standard for all the new combined HTTP processing framework. Why negotiated Content? Content negotiation is one of the key features of Web API even though it’s such a relatively simple thing. But it’s also something that’s missing in MVC and once you get used to automatically having your content returned based on Accept headers it’s hard to go back to manually having to create separate methods for different output types as you’ve had to with Microsoft server technologies all along (yes, yes I know other frameworks – including my own – have done this for years but for in the box features this is relatively new from Web API). As a quick review,  Accept Header content negotiation works off the request’s HTTP Accept header:POST http://localhost/mydailydosha/Editable/NegotiateContent HTTP/1.1 Content-Type: application/json Accept: application/json Host: localhost Content-Length: 76 Pragma: no-cache { ElementId: "header", PageName: "TestPage", Text: "This is a nice header" } If I make this request I would expect to get back a JSON result based on my application/json Accept header. To request XML  I‘d just change the accept header:Accept: text/xml and now I’d expect the response to come back as XML. Now this only works with media types that the server can process. In my case here I need to handle JSON, XML, HTML (using Views) and Plain Text. HTML results might need more than just a data return – you also probably need to specify a View to render the data into either by specifying the view explicitly or by using some sort of convention that can automatically locate a view to match. Today ASP.NET MVC doesn’t support this sort of automatic content switching out of the box. Unfortunately, in my application scenario we have an application that started out primarily with an AJAX backend that was implemented with JSON only. So there are lots of JSON results like this:[Route("Customers")] public ActionResult GetCustomers() { return Json(repo.GetCustomers(),JsonRequestBehavior.AllowGet); } These work fine, but they are of course JSON specific. Then a couple of weeks ago, a requirement came in that an old desktop application needs to also consume this API and it has to use XML to do it because there’s no JSON parser available for it. Ooops – stuck with JSON in this case. While it would have been easy to add XML specific methods I figured it’s easier to add basic content negotiation. And that’s what I show in this post. Missteps – IResultFilter, IActionFilter My first attempt at this was to use IResultFilter or IActionFilter which look like they would be ideal to modify result content after it’s been generated using OnResultExecuted() or OnActionExecuted(). Filters are great because they can look globally at all controller methods or individual methods that are marked up with the Filter’s attribute. But it turns out these filters don’t work for raw POCO result values from Action methods. What we wanted to do for API calls is get back to using plain .NET types as results rather than result actions. That is  you write a method that doesn’t return an ActionResult, but a standard .NET type like this:public Customer UpdateCustomer(Customer cust) { … do stuff to customer :-) return cust; } Unfortunately both OnResultExecuted and OnActionExecuted receive an MVC ContentResult instance from the POCO object. MVC basically takes any non-ActionResult return value and turns it into a ContentResult by converting the value using .ToString(). Ugh. The ContentResult itself doesn’t contain the original value, which is lost AFAIK with no way to retrieve it. So there’s no way to access the raw customer object in the example above. Bummer. Creating a NegotiatedResult This leaves mucking around with custom ActionResults. ActionResults are MVC’s standard way to return action method results – you basically specify that you would like to render your result in a specific format. Common ActionResults are ViewResults (ie. View(vn,model)), JsonResult, RedirectResult etc. They work and are fairly effective and work fairly well for testing as well as it’s the ‘standard’ interface to return results from actions. The problem with the this is mainly that you’re explicitly saying that you want a specific result output type. This works well for many things, but sometimes you do want your result to be negotiated. My first crack at this solution here is to create a simple ActionResult subclass that looks at the Accept header and based on that writes the output. I need to support JSON and XML content and HTML as well as text – so effectively 4 media types: application/json, text/xml, text/html and text/plain. Everything else is passed through as ContentResult – which effecively returns whatever .ToString() returns. Here’s what the NegotiatedResult usage looks like:public ActionResult GetCustomers() { return new NegotiatedResult(repo.GetCustomers()); } public ActionResult GetCustomer(int id) { return new NegotiatedResult("Show", repo.GetCustomer(id)); } There are two overloads of this method – one that returns just the raw result value and a second version that accepts an optional view name. The second version returns the Razor view specified only if text/html is requested – otherwise the raw data is returned. This is useful in applications where you have an HTML front end that can also double as an API interface endpoint that’s using the same model data you send to the View. For the application I mentioned above this was another actual use-case we needed to address so this was a welcome side effect of creating a custom ActionResult. There’s also an extension method that directly attaches a Negotiated() method to the controller using the same syntax:public ActionResult GetCustomers() { return this.Negotiated(repo.GetCustomers()); } public ActionResult GetCustomer(int id) { return this.Negotiated("Show",repo.GetCustomer(id)); } Using either of these mechanisms now allows you to return JSON, XML, HTML or plain text results depending on the Accept header sent. Send application/json you get just the Customer JSON data. Ditto for text/xml and XML data. Pass text/html for the Accept header and the "Show.cshtml" Razor view is rendered passing the result model data producing final HTML output. While this isn’t as clean as passing just POCO objects back as I had intended originally, this approach fits better with how MVC action methods are intended to be used and we get the bonus of being able to specify a View to render (optionally) for HTML. How does it work An ActionResult implementation is pretty straightforward. You inherit from ActionResult and implement the ExecuteResult method to send your output to the ASP.NET output stream. ActionFilters are an easy way to effectively do post processing on ASP.NET MVC controller actions just before the content is sent to the output stream, assuming your specific action result was used. Here’s the full code to the NegotiatedResult class (you can also check it out on GitHub):/// <summary> /// Returns a content negotiated result based on the Accept header. /// Minimal implementation that works with JSON and XML content, /// can also optionally return a view with HTML. /// </summary> /// <example> /// // model data only /// public ActionResult GetCustomers() /// { /// return new NegotiatedResult(repo.Customers.OrderBy( c=> c.Company) ) /// } /// // optional view for HTML /// public ActionResult GetCustomers() /// { /// return new NegotiatedResult("List", repo.Customers.OrderBy( c=> c.Company) ) /// } /// </example> public class NegotiatedResult : ActionResult { /// <summary> /// Data stored to be 'serialized'. Public /// so it's potentially accessible in filters. /// </summary> public object Data { get; set; } /// <summary> /// Optional name of the HTML view to be rendered /// for HTML responses /// </summary> public string ViewName { get; set; } public static bool FormatOutput { get; set; } static NegotiatedResult() { FormatOutput = HttpContext.Current.IsDebuggingEnabled; } /// <summary> /// Pass in data to serialize /// </summary> /// <param name="data">Data to serialize</param> public NegotiatedResult(object data) { Data = data; } /// <summary> /// Pass in data and an optional view for HTML views /// </summary> /// <param name="data"></param> /// <param name="viewName"></param> public NegotiatedResult(string viewName, object data) { Data = data; ViewName = viewName; } public override void ExecuteResult(ControllerContext context) { if (context == null) throw new ArgumentNullException("context"); HttpResponseBase response = context.HttpContext.Response; HttpRequestBase request = context.HttpContext.Request; // Look for specific content types if (request.AcceptTypes.Contains("text/html")) { response.ContentType = "text/html"; if (!string.IsNullOrEmpty(ViewName)) { var viewData = context.Controller.ViewData; viewData.Model = Data; var viewResult = new ViewResult { ViewName = ViewName, MasterName = null, ViewData = viewData, TempData = context.Controller.TempData, ViewEngineCollection = ((Controller)context.Controller).ViewEngineCollection }; viewResult.ExecuteResult(context.Controller.ControllerContext); } else response.Write(Data); } else if (request.AcceptTypes.Contains("text/plain")) { response.ContentType = "text/plain"; response.Write(Data); } else if (request.AcceptTypes.Contains("application/json")) { using (JsonTextWriter writer = new JsonTextWriter(response.Output)) { var settings = new JsonSerializerSettings(); if (FormatOutput) settings.Formatting = Newtonsoft.Json.Formatting.Indented; JsonSerializer serializer = JsonSerializer.Create(settings); serializer.Serialize(writer, Data); writer.Flush(); } } else if (request.AcceptTypes.Contains("text/xml")) { response.ContentType = "text/xml"; if (Data != null) { using (var writer = new XmlTextWriter(response.OutputStream, new UTF8Encoding())) { if (FormatOutput) writer.Formatting = System.Xml.Formatting.Indented; XmlSerializer serializer = new XmlSerializer(Data.GetType()); serializer.Serialize(writer, Data); writer.Flush(); } } } else { // just write data as a plain string response.Write(Data); } } } /// <summary> /// Extends Controller with Negotiated() ActionResult that does /// basic content negotiation based on the Accept header. /// </summary> public static class NegotiatedResultExtensions { /// <summary> /// Return content-negotiated content of the data based on Accept header. /// Supports: /// application/json - using JSON.NET /// text/xml - Xml as XmlSerializer XML /// text/html - as text, or an optional View /// text/plain - as text /// </summary> /// <param name="controller"></param> /// <param name="data">Data to return</param> /// <returns>serialized data</returns> /// <example> /// public ActionResult GetCustomers() /// { /// return this.Negotiated( repo.Customers.OrderBy( c=> c.Company) ) /// } /// </example> public static NegotiatedResult Negotiated(this Controller controller, object data) { return new NegotiatedResult(data); } /// <summary> /// Return content-negotiated content of the data based on Accept header. /// Supports: /// application/json - using JSON.NET /// text/xml - Xml as XmlSerializer XML /// text/html - as text, or an optional View /// text/plain - as text /// </summary> /// <param name="controller"></param> /// <param name="viewName">Name of the View to when Accept is text/html</param> /// /// <param name="data">Data to return</param> /// <returns>serialized data</returns> /// <example> /// public ActionResult GetCustomers() /// { /// return this.Negotiated("List", repo.Customers.OrderBy( c=> c.Company) ) /// } /// </example> public static NegotiatedResult Negotiated(this Controller controller, string viewName, object data) { return new NegotiatedResult(viewName, data); } } Output Generation – JSON and XML Generating output for XML and JSON is simple – you use the desired serializer and off you go. Using XmlSerializer and JSON.NET it’s just a handful of lines each to generate serialized output directly into the HTTP output stream. Please note this implementation uses JSON.NET for its JSON generation rather than the default JavaScriptSerializer that MVC uses which I feel is an additional bonus to implementing this custom action. I’d already been using a custom JsonNetResult class previously, but now this is just rolled into this custom ActionResult. Just keep in mind that JSON.NET outputs slightly different JSON for certain things like collections for example, so behavior may change. One addition to this implementation might be a flag to allow switching the JSON serializer. Html View Generation Html View generation actually turned out to be easier than anticipated. Initially I used my generic ASP.NET ViewRenderer Class that can render MVC views from any ASP.NET application. However it turns out since we are executing inside of an active MVC request there’s an easier way: We can simply create a custom ViewResult and populate its members and then execute it. The code in text/html handling code that renders the view is simply this:response.ContentType = "text/html"; if (!string.IsNullOrEmpty(ViewName)) { var viewData = context.Controller.ViewData; viewData.Model = Data; var viewResult = new ViewResult { ViewName = ViewName, MasterName = null, ViewData = viewData, TempData = context.Controller.TempData, ViewEngineCollection = ((Controller)context.Controller).ViewEngineCollection }; viewResult.ExecuteResult(context.Controller.ControllerContext); } else response.Write(Data); which is a neat and easy way to render a Razor view assuming you have an active controller that’s ready for rendering. Sweet – dependency removed which makes this class self-contained without any external dependencies other than JSON.NET. Summary While this isn’t exactly a new topic, it’s the first time I’ve actually delved into this with MVC. I’ve been doing content negotiation with Web API and prior to that with my REST library. This is the first time it’s come up as an issue in MVC. But as I have worked through this I find that having a way to specify both HTML Views *and* JSON and XML results from a single controller certainly is appealing to me in many situations as we are in this particular application returning identical data models for each of these operations. Rendering content negotiated views is something that I hope ASP.NET vNext will provide natively in the combined MVC and WebAPI model, but we’ll see how this actually will be implemented. In the meantime having a custom ActionResult that provides this functionality is a workable and easily adaptable way of handling this going forward. Whatever ends up happening in ASP.NET vNext the abstraction can probably be changed to support the native features of the future. Anyway I hope some of you found this useful if not for direct integration then as insight into some of the rendering logic that MVC uses to get output into the HTTP stream… Related Resources Latest Version of NegotiatedResult.cs on GitHub Understanding Action Controllers Rendering ASP.NET Views To String© Rick Strahl, West Wind Technologies, 2005-2014Posted in MVC  ASP.NET  HTTP   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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  • Copying a list in Microsoft word

    - by TaoistWA
    I have a list that looks like this ( notice the list is of the pattern A, B, C etc..) 1. [Insert question 1] A. [Insert response A] B. [Insert response B] C. [Insert response C] D. [Insert response D] 2. [Insert question 2] A. [Insert response A] B. [Insert response B] C. [Insert response C] D. [Insert response D] When I copy and paste it I want it to look exactly the same. However this does not happen. What I get instead is ( the A,B,C, pattern continues on with the rest of the alphabet) 1. [Insert question 1] A. [Insert response A] B. [Insert response B] C. [Insert response C] D. [Insert response D] 2. [Insert question 2] A. [Insert response A] B. [Insert response B] C. [Insert response C] D. [Insert response D] 3. [Insert question 1] E. [Insert response A] F. [Insert response B] G. [Insert response C] H. [Insert response D] 4. [Insert question 2] I. [Insert response A] J. [Insert response B] K. [Insert response C] How do I fix this? Thank you!

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  • When is it safe to do a Response.Redirect() without throwing an exception?

    - by DDechant
    I have an intermediary class extending System.Web.UI.Page for all of my pages that require authentication. The class mostly does custom authentication handling. When a user with insufficient access attempts to visit a page, I try to redirect the user back to the login page while preventing any further page events from being executed (ie. Page_load). The first solution that came to mind was the default implementation of Response.Redirect. Of course the downside to this is the possibility of ThreadAbortExceptions being thrown. So my question is this: When (if at all) during the page life cycle is it actually safe to execute Response.Redirect() without ThreadAbortException ever being thrown? public class CustomPage : System.Web.UI.Page { protected override void OnInit(EventArgs e) { base.OnInit(e); if (!IsValid()) Response.Redirect("login.aspx", true); } }

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  • Should filters write to the response during or after filtering?

    - by Mark
    I have a filter which processes generated HTML and rewrites certain elements. For example, it adds class attributes to some anchors. Finally, it writes the processed HTML to the response (a subclass of HttpServletResponseWrapper). Naturally, this means that the processed HTML is a different length after it has passed through the filter. I can see two ways of approaching this. One is to iterate over the HTML, using a StringBuilder to build up the processed HTML, and write the processed HTML to the response once all filtering is complete. The other is to iterate over the HTML but to write it to the response as soon as each element has been processed. Which is the better way for this operation, or is there another option which would be preferable? I am looking to minimise temporary memory usage primarily.

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  • A Taxonomy of Numerical Methods v1

    - by JoshReuben
    Numerical Analysis – When, What, (but not how) Once you understand the Math & know C++, Numerical Methods are basically blocks of iterative & conditional math code. I found the real trick was seeing the forest for the trees – knowing which method to use for which situation. Its pretty easy to get lost in the details – so I’ve tried to organize these methods in a way that I can quickly look this up. I’ve included links to detailed explanations and to C++ code examples. I’ve tried to classify Numerical methods in the following broad categories: Solving Systems of Linear Equations Solving Non-Linear Equations Iteratively Interpolation Curve Fitting Optimization Numerical Differentiation & Integration Solving ODEs Boundary Problems Solving EigenValue problems Enjoy – I did ! Solving Systems of Linear Equations Overview Solve sets of algebraic equations with x unknowns The set is commonly in matrix form Gauss-Jordan Elimination http://en.wikipedia.org/wiki/Gauss%E2%80%93Jordan_elimination C++: http://www.codekeep.net/snippets/623f1923-e03c-4636-8c92-c9dc7aa0d3c0.aspx Produces solution of the equations & the coefficient matrix Efficient, stable 2 steps: · Forward Elimination – matrix decomposition: reduce set to triangular form (0s below the diagonal) or row echelon form. If degenerate, then there is no solution · Backward Elimination –write the original matrix as the product of ints inverse matrix & its reduced row-echelon matrix à reduce set to row canonical form & use back-substitution to find the solution to the set Elementary ops for matrix decomposition: · Row multiplication · Row switching · Add multiples of rows to other rows Use pivoting to ensure rows are ordered for achieving triangular form LU Decomposition http://en.wikipedia.org/wiki/LU_decomposition C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-lu-decomposition-for-solving.html Represent the matrix as a product of lower & upper triangular matrices A modified version of GJ Elimination Advantage – can easily apply forward & backward elimination to solve triangular matrices Techniques: · Doolittle Method – sets the L matrix diagonal to unity · Crout Method - sets the U matrix diagonal to unity Note: both the L & U matrices share the same unity diagonal & can be stored compactly in the same matrix Gauss-Seidel Iteration http://en.wikipedia.org/wiki/Gauss%E2%80%93Seidel_method C++: http://www.nr.com/forum/showthread.php?t=722 Transform the linear set of equations into a single equation & then use numerical integration (as integration formulas have Sums, it is implemented iteratively). an optimization of Gauss-Jacobi: 1.5 times faster, requires 0.25 iterations to achieve the same tolerance Solving Non-Linear Equations Iteratively find roots of polynomials – there may be 0, 1 or n solutions for an n order polynomial use iterative techniques Iterative methods · used when there are no known analytical techniques · Requires set functions to be continuous & differentiable · Requires an initial seed value – choice is critical to convergence à conduct multiple runs with different starting points & then select best result · Systematic - iterate until diminishing returns, tolerance or max iteration conditions are met · bracketing techniques will always yield convergent solutions, non-bracketing methods may fail to converge Incremental method if a nonlinear function has opposite signs at 2 ends of a small interval x1 & x2, then there is likely to be a solution in their interval – solutions are detected by evaluating a function over interval steps, for a change in sign, adjusting the step size dynamically. Limitations – can miss closely spaced solutions in large intervals, cannot detect degenerate (coinciding) solutions, limited to functions that cross the x-axis, gives false positives for singularities Fixed point method http://en.wikipedia.org/wiki/Fixed-point_iteration C++: http://books.google.co.il/books?id=weYj75E_t6MC&pg=PA79&lpg=PA79&dq=fixed+point+method++c%2B%2B&source=bl&ots=LQ-5P_taoC&sig=lENUUIYBK53tZtTwNfHLy5PEWDk&hl=en&sa=X&ei=wezDUPW1J5DptQaMsIHQCw&redir_esc=y#v=onepage&q=fixed%20point%20method%20%20c%2B%2B&f=false Algebraically rearrange a solution to isolate a variable then apply incremental method Bisection method http://en.wikipedia.org/wiki/Bisection_method C++: http://numericalcomputing.wordpress.com/category/algorithms/ Bracketed - Select an initial interval, keep bisecting it ad midpoint into sub-intervals and then apply incremental method on smaller & smaller intervals – zoom in Adv: unaffected by function gradient à reliable Disadv: slow convergence False Position Method http://en.wikipedia.org/wiki/False_position_method C++: http://www.dreamincode.net/forums/topic/126100-bisection-and-false-position-methods/ Bracketed - Select an initial interval , & use the relative value of function at interval end points to select next sub-intervals (estimate how far between the end points the solution might be & subdivide based on this) Newton-Raphson method http://en.wikipedia.org/wiki/Newton's_method C++: http://www-users.cselabs.umn.edu/classes/Summer-2012/csci1113/index.php?page=./newt3 Also known as Newton's method Convenient, efficient Not bracketed – only a single initial guess is required to start iteration – requires an analytical expression for the first derivative of the function as input. Evaluates the function & its derivative at each step. Can be extended to the Newton MutiRoot method for solving multiple roots Can be easily applied to an of n-coupled set of non-linear equations – conduct a Taylor Series expansion of a function, dropping terms of order n, rewrite as a Jacobian matrix of PDs & convert to simultaneous linear equations !!! Secant Method http://en.wikipedia.org/wiki/Secant_method C++: http://forum.vcoderz.com/showthread.php?p=205230 Unlike N-R, can estimate first derivative from an initial interval (does not require root to be bracketed) instead of inputting it Since derivative is approximated, may converge slower. Is fast in practice as it does not have to evaluate the derivative at each step. Similar implementation to False Positive method Birge-Vieta Method http://mat.iitm.ac.in/home/sryedida/public_html/caimna/transcendental/polynomial%20methods/bv%20method.html C++: http://books.google.co.il/books?id=cL1boM2uyQwC&pg=SA3-PA51&lpg=SA3-PA51&dq=Birge-Vieta+Method+c%2B%2B&source=bl&ots=QZmnDTK3rC&sig=BPNcHHbpR_DKVoZXrLi4nVXD-gg&hl=en&sa=X&ei=R-_DUK2iNIjzsgbE5ID4Dg&redir_esc=y#v=onepage&q=Birge-Vieta%20Method%20c%2B%2B&f=false combines Horner's method of polynomial evaluation (transforming into lesser degree polynomials that are more computationally efficient to process) with Newton-Raphson to provide a computational speed-up Interpolation Overview Construct new data points for as close as possible fit within range of a discrete set of known points (that were obtained via sampling, experimentation) Use Taylor Series Expansion of a function f(x) around a specific value for x Linear Interpolation http://en.wikipedia.org/wiki/Linear_interpolation C++: http://www.hamaluik.com/?p=289 Straight line between 2 points à concatenate interpolants between each pair of data points Bilinear Interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation C++: http://supercomputingblog.com/graphics/coding-bilinear-interpolation/2/ Extension of the linear function for interpolating functions of 2 variables – perform linear interpolation first in 1 direction, then in another. Used in image processing – e.g. texture mapping filter. Uses 4 vertices to interpolate a value within a unit cell. Lagrange Interpolation http://en.wikipedia.org/wiki/Lagrange_polynomial C++: http://www.codecogs.com/code/maths/approximation/interpolation/lagrange.php For polynomials Requires recomputation for all terms for each distinct x value – can only be applied for small number of nodes Numerically unstable Barycentric Interpolation http://epubs.siam.org/doi/pdf/10.1137/S0036144502417715 C++: http://www.gamedev.net/topic/621445-barycentric-coordinates-c-code-check/ Rearrange the terms in the equation of the Legrange interpolation by defining weight functions that are independent of the interpolated value of x Newton Divided Difference Interpolation http://en.wikipedia.org/wiki/Newton_polynomial C++: http://jee-appy.blogspot.co.il/2011/12/newton-divided-difference-interpolation.html Hermite Divided Differences: Interpolation polynomial approximation for a given set of data points in the NR form - divided differences are used to approximately calculate the various differences. For a given set of 3 data points , fit a quadratic interpolant through the data Bracketed functions allow Newton divided differences to be calculated recursively Difference table Cubic Spline Interpolation http://en.wikipedia.org/wiki/Spline_interpolation C++: https://www.marcusbannerman.co.uk/index.php/home/latestarticles/42-articles/96-cubic-spline-class.html Spline is a piecewise polynomial Provides smoothness – for interpolations with significantly varying data Use weighted coefficients to bend the function to be smooth & its 1st & 2nd derivatives are continuous through the edge points in the interval Curve Fitting A generalization of interpolating whereby given data points may contain noise à the curve does not necessarily pass through all the points Least Squares Fit http://en.wikipedia.org/wiki/Least_squares C++: http://www.ccas.ru/mmes/educat/lab04k/02/least-squares.c Residual – difference between observed value & expected value Model function is often chosen as a linear combination of the specified functions Determines: A) The model instance in which the sum of squared residuals has the least value B) param values for which model best fits data Straight Line Fit Linear correlation between independent variable and dependent variable Linear Regression http://en.wikipedia.org/wiki/Linear_regression C++: http://www.oocities.org/david_swaim/cpp/linregc.htm Special case of statistically exact extrapolation Leverage least squares Given a basis function, the sum of the residuals is determined and the corresponding gradient equation is expressed as a set of normal linear equations in matrix form that can be solved (e.g. using LU Decomposition) Can be weighted - Drop the assumption that all errors have the same significance –-> confidence of accuracy is different for each data point. Fit the function closer to points with higher weights Polynomial Fit - use a polynomial basis function Moving Average http://en.wikipedia.org/wiki/Moving_average C++: http://www.codeproject.com/Articles/17860/A-Simple-Moving-Average-Algorithm Used for smoothing (cancel fluctuations to highlight longer-term trends & cycles), time series data analysis, signal processing filters Replace each data point with average of neighbors. Can be simple (SMA), weighted (WMA), exponential (EMA). Lags behind latest data points – extra weight can be given to more recent data points. Weights can decrease arithmetically or exponentially according to distance from point. Parameters: smoothing factor, period, weight basis Optimization Overview Given function with multiple variables, find Min (or max by minimizing –f(x)) Iterative approach Efficient, but not necessarily reliable Conditions: noisy data, constraints, non-linear models Detection via sign of first derivative - Derivative of saddle points will be 0 Local minima Bisection method Similar method for finding a root for a non-linear equation Start with an interval that contains a minimum Golden Search method http://en.wikipedia.org/wiki/Golden_section_search C++: http://www.codecogs.com/code/maths/optimization/golden.php Bisect intervals according to golden ratio 0.618.. Achieves reduction by evaluating a single function instead of 2 Newton-Raphson Method Brent method http://en.wikipedia.org/wiki/Brent's_method C++: http://people.sc.fsu.edu/~jburkardt/cpp_src/brent/brent.cpp Based on quadratic or parabolic interpolation – if the function is smooth & parabolic near to the minimum, then a parabola fitted through any 3 points should approximate the minima – fails when the 3 points are collinear , in which case the denominator is 0 Simplex Method http://en.wikipedia.org/wiki/Simplex_algorithm C++: http://www.codeguru.com/cpp/article.php/c17505/Simplex-Optimization-Algorithm-and-Implemetation-in-C-Programming.htm Find the global minima of any multi-variable function Direct search – no derivatives required At each step it maintains a non-degenerative simplex – a convex hull of n+1 vertices. Obtains the minimum for a function with n variables by evaluating the function at n-1 points, iteratively replacing the point of worst result with the point of best result, shrinking the multidimensional simplex around the best point. Point replacement involves expanding & contracting the simplex near the worst value point to determine a better replacement point Oscillation can be avoided by choosing the 2nd worst result Restart if it gets stuck Parameters: contraction & expansion factors Simulated Annealing http://en.wikipedia.org/wiki/Simulated_annealing C++: http://code.google.com/p/cppsimulatedannealing/ Analogy to heating & cooling metal to strengthen its structure Stochastic method – apply random permutation search for global minima - Avoid entrapment in local minima via hill climbing Heating schedule - Annealing schedule params: temperature, iterations at each temp, temperature delta Cooling schedule – can be linear, step-wise or exponential Differential Evolution http://en.wikipedia.org/wiki/Differential_evolution C++: http://www.amichel.com/de/doc/html/ More advanced stochastic methods analogous to biological processes: Genetic algorithms, evolution strategies Parallel direct search method against multiple discrete or continuous variables Initial population of variable vectors chosen randomly – if weighted difference vector of 2 vectors yields a lower objective function value then it replaces the comparison vector Many params: #parents, #variables, step size, crossover constant etc Convergence is slow – many more function evaluations than simulated annealing Numerical Differentiation Overview 2 approaches to finite difference methods: · A) approximate function via polynomial interpolation then differentiate · B) Taylor series approximation – additionally provides error estimate Finite Difference methods http://en.wikipedia.org/wiki/Finite_difference_method C++: http://www.wpi.edu/Pubs/ETD/Available/etd-051807-164436/unrestricted/EAMPADU.pdf Find differences between high order derivative values - Approximate differential equations by finite differences at evenly spaced data points Based on forward & backward Taylor series expansion of f(x) about x plus or minus multiples of delta h. Forward / backward difference - the sums of the series contains even derivatives and the difference of the series contains odd derivatives – coupled equations that can be solved. Provide an approximation of the derivative within a O(h^2) accuracy There is also central difference & extended central difference which has a O(h^4) accuracy Richardson Extrapolation http://en.wikipedia.org/wiki/Richardson_extrapolation C++: http://mathscoding.blogspot.co.il/2012/02/introduction-richardson-extrapolation.html A sequence acceleration method applied to finite differences Fast convergence, high accuracy O(h^4) Derivatives via Interpolation Cannot apply Finite Difference method to discrete data points at uneven intervals – so need to approximate the derivative of f(x) using the derivative of the interpolant via 3 point Lagrange Interpolation Note: the higher the order of the derivative, the lower the approximation precision Numerical Integration Estimate finite & infinite integrals of functions More accurate procedure than numerical differentiation Use when it is not possible to obtain an integral of a function analytically or when the function is not given, only the data points are Newton Cotes Methods http://en.wikipedia.org/wiki/Newton%E2%80%93Cotes_formulas C++: http://www.siafoo.net/snippet/324 For equally spaced data points Computationally easy – based on local interpolation of n rectangular strip areas that is piecewise fitted to a polynomial to get the sum total area Evaluate the integrand at n+1 evenly spaced points – approximate definite integral by Sum Weights are derived from Lagrange Basis polynomials Leverage Trapezoidal Rule for default 2nd formulas, Simpson 1/3 Rule for substituting 3 point formulas, Simpson 3/8 Rule for 4 point formulas. For 4 point formulas use Bodes Rule. Higher orders obtain more accurate results Trapezoidal Rule uses simple area, Simpsons Rule replaces the integrand f(x) with a quadratic polynomial p(x) that uses the same values as f(x) for its end points, but adds a midpoint Romberg Integration http://en.wikipedia.org/wiki/Romberg's_method C++: http://code.google.com/p/romberg-integration/downloads/detail?name=romberg.cpp&can=2&q= Combines trapezoidal rule with Richardson Extrapolation Evaluates the integrand at equally spaced points The integrand must have continuous derivatives Each R(n,m) extrapolation uses a higher order integrand polynomial replacement rule (zeroth starts with trapezoidal) à a lower triangular matrix set of equation coefficients where the bottom right term has the most accurate approximation. The process continues until the difference between 2 successive diagonal terms becomes sufficiently small. Gaussian Quadrature http://en.wikipedia.org/wiki/Gaussian_quadrature C++: http://www.alglib.net/integration/gaussianquadratures.php Data points are chosen to yield best possible accuracy – requires fewer evaluations Ability to handle singularities, functions that are difficult to evaluate The integrand can include a weighting function determined by a set of orthogonal polynomials. Points & weights are selected so that the integrand yields the exact integral if f(x) is a polynomial of degree <= 2n+1 Techniques (basically different weighting functions): · Gauss-Legendre Integration w(x)=1 · Gauss-Laguerre Integration w(x)=e^-x · Gauss-Hermite Integration w(x)=e^-x^2 · Gauss-Chebyshev Integration w(x)= 1 / Sqrt(1-x^2) Solving ODEs Use when high order differential equations cannot be solved analytically Evaluated under boundary conditions RK for systems – a high order differential equation can always be transformed into a coupled first order system of equations Euler method http://en.wikipedia.org/wiki/Euler_method C++: http://rosettacode.org/wiki/Euler_method First order Runge–Kutta method. Simple recursive method – given an initial value, calculate derivative deltas. Unstable & not very accurate (O(h) error) – not used in practice A first-order method - the local error (truncation error per step) is proportional to the square of the step size, and the global error (error at a given time) is proportional to the step size In evolving solution between data points xn & xn+1, only evaluates derivatives at beginning of interval xn à asymmetric at boundaries Higher order Runge Kutta http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods C++: http://www.dreamincode.net/code/snippet1441.htm 2nd & 4th order RK - Introduces parameterized midpoints for more symmetric solutions à accuracy at higher computational cost Adaptive RK – RK-Fehlberg – estimate the truncation at each integration step & automatically adjust the step size to keep error within prescribed limits. At each step 2 approximations are compared – if in disagreement to a specific accuracy, the step size is reduced Boundary Value Problems Where solution of differential equations are located at 2 different values of the independent variable x à more difficult, because cannot just start at point of initial value – there may not be enough starting conditions available at the end points to produce a unique solution An n-order equation will require n boundary conditions – need to determine the missing n-1 conditions which cause the given conditions at the other boundary to be satisfied Shooting Method http://en.wikipedia.org/wiki/Shooting_method C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-shooting-method-for-solving.html Iteratively guess the missing values for one end & integrate, then inspect the discrepancy with the boundary values of the other end to adjust the estimate Given the starting boundary values u1 & u2 which contain the root u, solve u given the false position method (solving the differential equation as an initial value problem via 4th order RK), then use u to solve the differential equations. Finite Difference Method For linear & non-linear systems Higher order derivatives require more computational steps – some combinations for boundary conditions may not work though Improve the accuracy by increasing the number of mesh points Solving EigenValue Problems An eigenvalue can substitute a matrix when doing matrix multiplication à convert matrix multiplication into a polynomial EigenValue For a given set of equations in matrix form, determine what are the solution eigenvalue & eigenvectors Similar Matrices - have same eigenvalues. Use orthogonal similarity transforms to reduce a matrix to diagonal form from which eigenvalue(s) & eigenvectors can be computed iteratively Jacobi method http://en.wikipedia.org/wiki/Jacobi_method C++: http://people.sc.fsu.edu/~jburkardt/classes/acs2_2008/openmp/jacobi/jacobi.html Robust but Computationally intense – use for small matrices < 10x10 Power Iteration http://en.wikipedia.org/wiki/Power_iteration For any given real symmetric matrix, generate the largest single eigenvalue & its eigenvectors Simplest method – does not compute matrix decomposition à suitable for large, sparse matrices Inverse Iteration Variation of power iteration method – generates the smallest eigenvalue from the inverse matrix Rayleigh Method http://en.wikipedia.org/wiki/Rayleigh's_method_of_dimensional_analysis Variation of power iteration method Rayleigh Quotient Method Variation of inverse iteration method Matrix Tri-diagonalization Method Use householder algorithm to reduce an NxN symmetric matrix to a tridiagonal real symmetric matrix vua N-2 orthogonal transforms     Whats Next Outside of Numerical Methods there are lots of different types of algorithms that I’ve learned over the decades: Data Mining – (I covered this briefly in a previous post: http://geekswithblogs.net/JoshReuben/archive/2007/12/31/ssas-dm-algorithms.aspx ) Search & Sort Routing Problem Solving Logical Theorem Proving Planning Probabilistic Reasoning Machine Learning Solvers (eg MIP) Bioinformatics (Sequence Alignment, Protein Folding) Quant Finance (I read Wilmott’s books – interesting) Sooner or later, I’ll cover the above topics as well.

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  • Authenticating clients in the new WCF Http stack

    - by cibrax
    About this time last year, I wrote a couple of posts about how to use the “Interceptors” from the REST starker kit for implementing several authentication mechanisms like “SAML”, “Basic Authentication” or “OAuth” in the WCF Web programming model. The things have changed a lot since then, and Glenn finally put on our hands a new version of the Web programming model that deserves some attention and I believe will help us a lot to build more Http oriented services in the .NET stack. What you can get today from wcf.codeplex.com is a preview with some cool features like Http Processors (which I already discussed here), a new and improved version of the HttpClient library, Dependency injection and better TDD support among others. However, the framework still does not support an standard way of doing client authentication on the services (This is something planned for the upcoming releases I believe). For that reason, moving the existing authentication interceptors to this new programming model was one of the things I did in the last few days. In order to make authentication simple and easy to extend,  I first came up with a model based on what I called “Authentication Interceptors”. An authentication interceptor maps to an existing Http authentication mechanism and implements the following interface, public interface IAuthenticationInterceptor{ string Scheme { get; } bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal);} An authentication interceptors basically needs to returns the http authentication schema that implements in the property “Scheme”, and implements the authentication mechanism in the method “DoAuthentication”. As you can see, this last method “DoAuthentication” only relies on the HttpRequestMessage and HttpResponseMessage classes, making the testing of this interceptor very simple (There is no need to do some black magic with the WCF context or messages). After this, I implemented a couple of interceptors for supporting basic authentication and brokered authentication with SAML (using WIF) in my services. The following code illustrates how the basic authentication interceptors looks like. public class BasicAuthenticationInterceptor : IAuthenticationInterceptor{ Func<UsernameAndPassword, bool> userValidation; string realm;  public BasicAuthenticationInterceptor(Func<UsernameAndPassword, bool> userValidation, string realm) { if (userValidation == null) throw new ArgumentNullException("userValidation");  if (string.IsNullOrEmpty(realm)) throw new ArgumentNullException("realm");  this.userValidation = userValidation; this.realm = realm; }  public string Scheme { get { return "Basic"; } }  public bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal) { string[] credentials = ExtractCredentials(request); if (credentials.Length == 0 || !AuthenticateUser(credentials[0], credentials[1])) { response.StatusCode = HttpStatusCode.Unauthorized; response.Content = new StringContent("Access denied"); response.Headers.WwwAuthenticate.Add(new AuthenticationHeaderValue("Basic", "realm=" + this.realm));  principal = null;  return false; } else { principal = new GenericPrincipal(new GenericIdentity(credentials[0]), new string[] {});  return true; } }  private string[] ExtractCredentials(HttpRequestMessage request) { if (request.Headers.Authorization != null && request.Headers.Authorization.Scheme.StartsWith("Basic")) { string encodedUserPass = request.Headers.Authorization.Parameter.Trim();  Encoding encoding = Encoding.GetEncoding("iso-8859-1"); string userPass = encoding.GetString(Convert.FromBase64String(encodedUserPass)); int separator = userPass.IndexOf(':');  string[] credentials = new string[2]; credentials[0] = userPass.Substring(0, separator); credentials[1] = userPass.Substring(separator + 1);  return credentials; }  return new string[] { }; }  private bool AuthenticateUser(string username, string password) { var usernameAndPassword = new UsernameAndPassword { Username = username, Password = password };  if (this.userValidation(usernameAndPassword)) { return true; }  return false; }} This interceptor receives in the constructor a callback in the form of a Func delegate for authenticating the user and the “realm”, which is required as part of the implementation. The rest is a general implementation of the basic authentication mechanism using standard http request and response messages. I also implemented another interceptor for authenticating a SAML token with WIF. public class SamlAuthenticationInterceptor : IAuthenticationInterceptor{ SecurityTokenHandlerCollection handlers = null;  public SamlAuthenticationInterceptor(SecurityTokenHandlerCollection handlers) { if (handlers == null) throw new ArgumentNullException("handlers");  this.handlers = handlers; }  public string Scheme { get { return "saml"; } }  public bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal) { SecurityToken token = ExtractCredentials(request);  if (token != null) { ClaimsIdentityCollection claims = handlers.ValidateToken(token);  principal = new ClaimsPrincipal(claims);  return true; } else { response.StatusCode = HttpStatusCode.Unauthorized; response.Content = new StringContent("Access denied");  principal = null;  return false; } }  private SecurityToken ExtractCredentials(HttpRequestMessage request) { if (request.Headers.Authorization != null && request.Headers.Authorization.Scheme == "saml") { XmlTextReader xmlReader = new XmlTextReader(new StringReader(request.Headers.Authorization.Parameter));  var col = SecurityTokenHandlerCollection.CreateDefaultSecurityTokenHandlerCollection(); SecurityToken token = col.ReadToken(xmlReader);  return token; }  return null; }}This implementation receives a “SecurityTokenHandlerCollection” instance as part of the constructor. This class is part of WIF, and basically represents a collection of token managers to know how to handle specific xml authentication tokens (SAML is one of them). I also created a set of extension methods for injecting these interceptors as part of a service route when the service is initialized. var basicAuthentication = new BasicAuthenticationInterceptor((u) => true, "ContactManager");var samlAuthentication = new SamlAuthenticationInterceptor(serviceConfiguration.SecurityTokenHandlers); // use MEF for providing instancesvar catalog = new AssemblyCatalog(typeof(Global).Assembly);var container = new CompositionContainer(catalog);var configuration = new ContactManagerConfiguration(container); RouteTable.Routes.AddServiceRoute<ContactResource>("contact", configuration, basicAuthentication, samlAuthentication);RouteTable.Routes.AddServiceRoute<ContactsResource>("contacts", configuration, basicAuthentication, samlAuthentication); In the code above, I am injecting the basic authentication and saml authentication interceptors in the “contact” and “contacts” resource implementations that come as samples in the code preview. I will use another post to discuss more in detail how the brokered authentication with SAML model works with this new WCF Http bits. The code is available to download in this location.

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  • How does Google maintain its codes?

    - by John Maxim
    Pagerank algorithm is not revealed to any of their associates programmers, but only accessible by Larry Page or maybe Sergey Brin. I wonder how do they go about managing their coding? There are times when you need to build something up and you may need more hands to help with coding, but you may also want to keep some secrets to yourself, I'm not saying I have secrets, but I wonder how do they manage their coding. I'm sure there are some ways to do it decently and professionally. The reason why friendster failed was because one of the factors they lost control over their coding part. I think this is an interesting question. But not easy to answer, maybe only a marginal knew.

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  • Meta tags with html special character codes?

    - by GEspinha
    This question is regarding best practices on SEO development meta tag filling. A name written in the Latin or the Cyrillic alphabet has certain special characters, such as the ccedil C, for example. When populating meta tags and other SEO assets in a page, what should be used, the HTML character code (for the given example: &ccedil;), the actual character or another character that looks close (using a C for the given example)?

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  • Speaking at UK DevConnections in www.DevConnections.com/uk and discount codes

    - by Testas
     HiI will be speaking at the UK DevConnections on Analysis Services at the ExCeL conference centre in London on 13th-15th June 2011. Join top SQL Server names such as Paul Randall, Kimberley Tripp, Simon Sabin and Allan Mitchell ( to name a few), at the IT & DevConnections powered by Microsoft UK  in London on 13th-15th June 2011. With UK DevConnections you can combine SQL Sessions with other Microsoft technology stacks. Microsoft and leading independent industry presenters will deliver in-depth presentations and cutting edge sessions on  SharePoint Windows Exchange and Unified Communications SQL Server Silverlight ASP.Net Virtualisation Cloud and Azure As a speaker I have a discount code that entitles give 20% off the cost to register for IT&DEvConnections in June.  The code is sql-bits, if people register before the 31st March when the Super Early Bird offer ends you will only pay £639.20 +vat (normal price £999)Furthermore, there are preferential hotel rates for this event at: https://logicalvenues.vbookings.co.uk/b/pentonlondon0611/  So if you want to attend a conference with a wide spectrum of technologies, then DevConnections may be up your street Thanks  Chris

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  • GA UA codes for testing site - set up

    - by Drew
    Anyone know the process for using a GA live UA code to test a site in development. I.e. I have a live site with a GA UA code attached, tracking live traffic data etc e.g. UA-123456. I've been told that there is a way to produce another code associated to the primary code to use on the testing version of my live site e.g. test code could be UA-123457. Can anyone shed some light on this? If not possible should I just set up a completely separate GA account for my testing site?

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  • Will using two different tracking codes affect my SERP

    - by Danny Hefer
    Hello everyone and thanks for your time! I am now facing a problem after a site migration. New site is basically an improved version of old site, with the same content and some extras. After pointing the domain name to the new site, the old site was still online for a while but didn't get any traffic. The new site has its own tracking code. So, old tracking code has age (something like 7 years) but no visitors for a month, but new tracking code is a month old with an acceptable traffic. How to you think google will react if I add old tracking code to new site? Thanks by advance!

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