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  • Java XMLRPC request-String

    - by Philip
    Hi, I'm using Apache XML-RPC 3.1.2 to talk to an online-service. They have something special, they need a hash over the whole XML with a secret key for some kind of security, like this: String hash = md5(xmlRequest + secretKey); String requestURL = "http://foo.bar/?authHash=" + hash; So I need the XML-request like this: <?xml version="1.0"?> <methodCall> <methodName>foo.bar</methodName> <params> <param> <value><struct> <member><name>bla</name> <value><int>1</int></value> </member> <member><name>blubb</name> <value><int>2</int></value> </member> </struct></value> </param> </params> </methodCall> But how do I get this String-representation of the XMLRPC-Request with the lib Apache XML-RPC?

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  • If attacker has original data and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require storage in the database. I'm leaning towards the the one-way-hash-stored-in-the-db, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • Encryption puzzle / How to create a ProxyStub for a Remote Assistance ticket

    - by Jon Clegg
    I am trying to create a ticket for Remote Assistance. Part of that requires creating a PassStub parameter. As of the documenation: http://msdn.microsoft.com/en-us/library/cc240115(PROT.10).aspx PassStub: The encrypted novice computer's password string. When the Remote Assistance Connection String is sent as a file over e-mail, to provide additional security, a password is used.<16 In part 16 they detail how to create as PassStub. In Windows XP and Windows Server 2003, when a password is used, it is encrypted using PROV_RSA_FULL predefined Cryptographic provider with MD5 hashing and CALG_RC4, the RC4 stream encryption algorithm. As PassStub looks like this in the file: PassStub="LK#6Lh*gCmNDpj" If you want to generate one yourself run msra.exe in Vista or run the Remote Assistance tool in WinXP. The documentation says this stub is the result of the function CryptEncrypt with the key derived from the password and encrypted with the session id (Those are also in the ticket file). The problem is that CryptEncrypt produces a binary output way larger then the 15 byte PassStub. Also the PassStub isn't encoding in any way I've seen before. Some interesting things about the PassStub encoding. After doing statistical analysis the 3rd char is always a one of: !#$&()+-=@^. Only symbols seen everywhere are: *_ . Otherwise the valid characters are 0-9 a-z A-Z. There are a total of 75 valid characters and they are always 15 bytes. Running msra.exe with the same password always generates a different PassStub, indicating that it is not a direct hash but includes the rasessionid as they say. Some other ideas I've had is that it is not the direct result of CryptEncrypt, but a result of the rasessionid in the MD5 hash. In MS-RA (http://msdn.microsoft.com/en-us/library/cc240013(PROT.10).aspx). The "PassStub Novice" is simply hex encoded, and looks to be the right length. The problem is I have no idea how to go from any hash to way the ProxyStub looks like.

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  • How to make a small engine like Wolfram|Alpha?

    - by Koning WWWWWWWWWWWWWWWWWWWWWWW
    Lets say I have three models/tables: operating_systems, words, and programming_languages: # operating_systems name:string created_by:string family:string Windows Microsoft MS-DOS Mac OS X Apple UNIX Linux Linus Torvalds UNIX UNIX AT&T UNIX # words word:string defenitions:string window (serialized hash of defenitions) hello (serialized hash of defenitions) UNIX (serialized hash of defenitions) # programming_languages name:string created_by:string example_code:text C++ Bjarne Stroustrup #include <iostream> etc... HelloWorld Jeff Skeet h AnotherOne Jon Atwood imports 'SORULEZ.cs' etc... When a user searches hello, the system shows the defenitions of 'hello'. This is relatively easy to implement. However, when a user searches UNIX, the engine must choose: word or operating_system. Also, when a user searches windows (small letter 'w'), the engine chooses word, but should also show Assuming 'windows' is a word. Use as an <a href="etc..">operating system</a> instead. Can anyone point me in the right direction with parsing and choosing the topic of the search query? Thanks. Note: it doesn't need to be able to perform calculations as WA can do.

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  • Encryption puzzle / How to create a PassStub for a Remote Assistance ticket

    - by Jon Clegg
    I am trying to create a ticket for Remote Assistance. Part of that requires creating a PassStub parameter. As of the documentation: http://msdn.microsoft.com/en-us/library/cc240115(PROT.10).aspx PassStub: The encrypted novice computer's password string. When the Remote Assistance Connection String is sent as a file over e-mail, to provide additional security, a password is used.<16 In part 16 they detail how to create as PassStub. In Windows XP and Windows Server 2003, when a password is used, it is encrypted using PROV_RSA_FULL predefined Cryptographic provider with MD5 hashing and CALG_RC4, the RC4 stream encryption algorithm. As PassStub looks like this in the file: PassStub="LK#6Lh*gCmNDpj" If you want to generate one yourself run msra.exe in Vista or run the Remote Assistance tool in WinXP. The documentation says this stub is the result of the function CryptEncrypt with the key derived from the password and encrypted with the session id (Those are also in the ticket file). The problem is that CryptEncrypt produces a binary output way larger then the 15 byte PassStub. Also the PassStub isn't encoding in any way I've seen before. Some interesting things about the PassStub encoding. After doing statistical analysis the 3rd char is always a one of: !#$&()+-=@^. Only symbols seen everywhere are: *_ . Otherwise the valid characters are 0-9 a-z A-Z. There are a total of 75 valid characters and they are always 15 bytes. Running msra.exe with the same password always generates a different PassStub, indicating that it is not a direct hash but includes the rasessionid as they say. Some other ideas I've had is that it is not the direct result of CryptEncrypt, but a result of the rasessionid in the MD5 hash. In MS-RA (http://msdn.microsoft.com/en-us/library/cc240013(PROT.10).aspx). The "PassStub Novice" is simply hex encoded, and looks to be the right length. The problem is I have no idea how to go from any hash to way the PassStub looks like.

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  • Http Digest Authentication, Handle different browser char-sets...

    - by user160561
    Hi all, I tried to use the Http Authentication Digest Scheme with my php (apache module) based website. In general it works fine, but when it comes to verification of the username / hash against my user database i run into a problem. Of course i do not want to store the user´s password in my database, so i tend to store the A1 hashvalue (which is md5($username . ':' . $realm . ':' . $password)) in my db. This is just how the browser does it too to create the hashes to send back. The Problem: I am not able to detect if the browser does this in ISO-8859-1 fallback (like firefox, IE) or UTF-8 (Opera) or whatever. I have chosen to do the calculation in UTF-8 and store this md5 hash. Which leads to non-authentication in Firefox and IE browsers. How do you solve this problem? Just do not use this auth-scheme? Or Store a md5 Hash for each charset? Force users to Opera? (Terms of A1 refer to the http://php.net/manual/en/features.http-auth.php example.) (for digest access authentication read the according wikipedia entry)

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  • Password Cracking in 2010 and Beyond

    - by mttr
    I have looked a bit into cryptography and related matters during the last couple of days and am pretty confused by now. I have a question about password strength and am hoping that someone can clear up my confusion by sharing how they think through the following questions. I am becoming obsessed about these things, but need to spend my time otherwise :-) Let's assume we have an eight-digit password that consists of upper and lower-case alphabetic characters, numbers and common symbols. This means we have 8^96 ~= 7.2 quadrillion different possible passwords. As I understand there are at least two approaches to breaking this password. One is to try a brute-force attack where we try to guess each possible combination of characters. How many passwords can modern processors (in 2010, Core i7 Extreme for eg) guess per second (how many instructions does a single password guess take and why)? My guess would be that it takes a modern processor in the order of years to break such a password. Another approach would consist of obtaining a hash of my password as stored by operating systems and then search for collisions. Depending on the type of hash used, we might get the password a lot quicker than by the bruteforce attack. A number of questions about this: Is the assertion in the above sentence correct? How do I think about the time it takes to find collisions for MD4, MD5, etc. hashes? Where does my Snow Leopard store my password hash and what hashing algorithm does it use? And finally, regardless of the strength of file encryption using AES-128/256, the weak link is still my en/decryption password used. Even if breaking the ciphered text would take longer than the lifetime of the universe, a brute-force attack on my de/encryption password (guess password, then try to decrypt file, try next password...), might succeed a lot earlier than the end of the universe. Is that correct? I would be very grateful, if people could have mercy on me and help me think through these probably simple questions, so that I can get back to work.

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  • Multiplication of 2 positive numbers giving a negative result

    - by krandiash
    My program is an implementation of a bloom filter. However, when I'm storing my hash function results in the bit array, the function (of the form f(i) = (a*i + b) % m where a,b,i,m are all positive integers) is giving me a negative result. The problem seems to be in the calculation of a*i which is coming out to be negative. Ignore the print statements in the code; those were for debugging. Basically, the value of temp in this block of code is coming out to be negative and so I'm getting an ArrayOutOfBoundsException. m is the bit array length, z is the number of hash functions being used, S is the set of values which are members of this bloom filter and H stores the values of a and b for the hash functions f1, f2, ..., fz. public static int[] makeBitArray(int m, int z, ArrayList<Integer> S, int[] H) { int[] C = new int[m]; for (int i = 0; i < z; i++) { for (int q = 0; q < S.size() ; q++) { System.out.println(H[2*i]); int temp = S.get(q)*(H[2*i]); System.out.println(temp); System.out.println(S.get(q)); System.out.println(H[2*i + 1]); System.out.println(m); int t = ((H[2*i]*S.get(q)) + H[2*i + 1])%m; System.out.println(t); C[t] = 1; } } return C; } Any help is appreciated.

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  • Drupal Views api, add simple argument handler

    - by LanguaFlash
    Background: I have a complex search form that stores the query and it's hash in a cache. Once the cache is set, I redirect to something like /searchresults/e6c86fadc7e4b7a2d068932efc9cc358 where that big long string on the end is the md5 hash of my query. I need to make a new argument for views to know what the hash is good for. The reason for all this hastle is because my original search form is way to complex and has way to many arguments to consider putting them all into the path and expecting to do the filtering with the normal views arguments. Now for my question. I have been reading views 2 documentation but not figuring out how to accomplish this custom argument. It doesn't seem to me like this should be as hard as it seems to me like it must be. Leaving aside any knowledge of the veiws api, it would seem that all I need is a callback function that will take the argument from the path as it's only argument and return a list of node id's to filter to. Can anyone point me to a solution or give me some example code? Thanks for your help! You guys are great. PS. I am pretty sure that my design is the best I can come up with, lets don't get off my question and into cross checking my design logic if we can help it.

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  • Hashtable is that fast

    - by Costa
    Hi s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]. Is the hash function of the java string, I assume the rest of languages is similar or close to this implementation. If we have hash-Table and a list of 50 elements. each element is 7 chars ABCDEF1, ABCDEF2, ABCDEF3..... ABCDEFn If each bucket of hashtable contains 5 strings (I think this function will make it one string per bucket, but let us assume it is 5). If we call col.Contains("ABCDEFn"); // will do 6 comparisons and discover the difference on the 7th. The hash-table will take around 70 operations (multiplication and additions) to get the hashcode and to compare with 5 strings in bucket. and BANG it found. For list it will take around 300 comparisons to find it. for the case that there is only 10 elements, the list will take around 70 operations but the Hashtable will take around 50 operations. and note that hashtable operations are more time consuming (it is multiplications). I conclude that HybirdDictionary in .Net probably is the best choice for that most cases that require Hashtable with unknown size, because it will let me use a list till the list becomes more than 10 elements. still need something like HashSet rather than a Dictionary of keys and values, I wonder why there is no HybirdSet!! So what do u think? Thanks

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  • What's the recommended implementation for hashing OLE Variants?

    - by Barry Kelly
    OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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  • autologin component doesn't work on remote server

    - by user606521
    I am using autologin component from http://milesj.me/code/cakephp/auto-login (v 3.5.1). It works on my localhost WAMP server but fails on remote server. I am using this settings in beforeFilter() callback: $this->AutoLogin->settings = array( // Model settings 'model' => 'User', 'username' => 'username', 'password' => 'password', // Controller settings 'plugin' => '', 'controller' => 'users', // Cookie settings 'cookieName' => 'rememberMe', 'expires' => '+1 month', // Process logic 'active' => true, 'redirect' => true, 'requirePrompt' => true ); On remote server it simply doesn't autolog users after the browser was closed. I can't figure out what may cause the problem. -------------------- edit I figured out what is causing the problem but I don't know how to fix this. First of all cookie is set like this: $this->Cookie->write('key',array('username' => 'someusername', 'hash' => 'somehash', ...) ); Then it's readed like this: $cookie = $this->Cookie->read('key'); On my WAMP server $cookie is array('username' => 'someusername', 'hash' => 'somehash', ...) and on remote server returned $cookie is string(159) "{\"username\":\"YWxlay5iYXJzsdsdZXdza2ldssd21haWwuY29t\",\"password\":\"YWxlazc3ODEy\",\"hash\":\"aa15bffff9ca12cdcgfgb351d8bfg2f370bf458\",\"time\":1339923926}" and it should be: array( 'username' => "YWxlay5iYXJzsdsdZXdza2ldssd21haWwuY29t", 'password' => "YWxlazc3ODEy", ...) Why the retuned cookie is string not array?

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  • LINQ Joins - Performance

    - by Meiscooldude
    I am curious on how exactly LINQ (not LINQ to SQL) is performing is joins behind the scenes in relation to how Sql Server performs joins. Sql Server before executing a query, generates an Execution Plan. The Execution Plan is basically an Expression Tree on what it believes is the best way to execute the query. Each node provides information on whether to do a Sort, Scan, Select, Join, ect. On a 'Join' node in our execution plan, we can see three possible algorithms; Hash Join, Merge Join, and Nested Loops Join. Sql Server will choose which algorithm to for each Join operation based on expected number of rows in Inner and Outer tables, what type of join we are doing (some algorithms don't support all types of joins), whether we need data ordered, and probably many other factors. Join Algorithms: Nested Loop Join: Best for small inputs, can be optimized with ordered inner table. Merge Join: Best for medium to large inputs sorted inputs, or an output that needs to be ordered. Hash Join: Best for medium to large inputs, can be parallelized to scale linearly. LINQ Query: DataTable firstTable, secondTable; ... var rows = from firstRow in firstTable.AsEnumerable () join secondRow in secondTable.AsEnumerable () on firstRow.Field<object> (randomObject.Property) equals secondRow.Field<object> (randomObject.Property) select new {firstRow, secondRow}; SQL Query: SELECT * FROM firstTable fT INNER JOIN secondTable sT ON fT.Property = sT.Property Sql Server might use a Nested Loop Join if it knows there are a small number of rows from each table, a merge join if it knows one of the tables has an index, and Hash join if it knows there are a lot of rows on either table and neither has an index. Does Linq choose its algorithm for joins? or does it always use one?

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  • PHP does not store all variables in session

    - by Flurin Juvalta
    Dear all I'm assigning session variables by filling the $_SESSION - Array throughout my script. My problem is, that for some reason not all variables are available in the session. here is a shortened version of my code for explaining this issue: session_start(); print_r($_SESSION); $_SESSION['lang'] = 'de'; $_SESSION['location_id'] = 11; $_SESSION['region_id'] = 1; $_SESSION['userid'] = 'eccbc87e4b5ce2fe28308fd9f2a7baf3'; $_SESSION['hash'] = 'dce57f1e3bc6fba32afab93b0c38b662'; print_r($_SESSION); first call prints something like this: Array ( ) Array ( [lang] => de [location_id] => 11 [region_id] => 1 [userid] => eccbc87e4b5ce2fe28308fd9f2a7baf3 [hash] => dce57f1e3bc6fba32afab93b0c38b662 ) the second call prints: Array ( [lang] => de [location_id] => 11 [region_id] => 1 ) Array ( [lang] => de [location_id] => 11 [region_id] => 1 [userid] => eccbc87e4b5ce2fe28308fd9f2a7baf3 [hash] => dce57f1e3bc6fba32afab93b0c38b662 ) As you can see, the important login information is not stored in the session. Does anybody has an idea what could be wrong with my session? Thanks for your answers!

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  • SQL Server compare table entries for update

    - by Dave
    I have a trade table with several million rows. Each row represents the version of a trade. If I'm given a possibly new trade I compare it to the latest version in the trade table. If it has changed I add a new version, otherwise I do nothing. In order to compare the 2 trades I read the version from the trade table into my application. This doesn't work well when I'm given 10s of thousands of possibly new trades. Even batching reads to read in a 1000 trades at once and compare them the whole process can take several minutes. All the time is spent in the DB. I'm trying to find a way to compare the possibly new trades to the ones in the trade table without so much I/O. What I've come up with so far is adding a hash column to each row in the trade table. The hash is of all the trade fields. Then when I'm given possibly new trades I compute their hash, put the values into a temporary table, then find ones that are different. This feels very hacky. Is there a better way of doing it? Thanks

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  • Digitally sign MS Office (Word, Excel, etc..) and PDF files on the server

    - by Sébastien Nussbaumer
    I need to digitally sign MS Office and PDF files that are stored on a server. I really mean a digital signature that is integrated in the document, according to each specific file formats. This is the process I had in mind : Create a hash of the file's content Send the hash to a custom written java applet in the browser The user encrypts the hash with his/her private key (on an usb token via PKCS#11 for example), thus effectively signing the file. The applet then sends the signature to the server On the server I would then incorporate the signature in the file's (MS Office and PDF files can do that without changing the file's content, probably by just setting some metadata field) What is cool is that you never have to download and upload the complete file to the server again. What is even cooler, the customer doesn't need Office or PDF Writer to sign the files. Parts 2, 3 and 4 are OK for me, my company bought all the JAVA technology I need for that for a previous project I worked on. Problem : I can't seem to find any documentation/examples to do parts 1 and 5 for Office files . Are my google skills failing me this time ? Do you have any pointers to documentation or examples for doing that for MS Office files ? The underlying technology isn't that important to me : I can use Java, .Net, COM, any working technology is OK ! Note : I'm 95% sure I can nail points 1 and 5 for PDF files using iText Thanks ** Edit : If I can't do that with hashes and must download the complete file to the client, it's also possible. But then I still need the documentation to be able to sign Office file... in java this time (from an applet)

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  • If attacker has original data, and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require this extra table. I'm leaning towards the the one-way hash + extra table solution, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • jQuery / Loading content into div and changing url's (working but buggy)

    - by Bruno
    This is working, but I'm not being able to set an index.html file on my server root where i can specify the first page to go. It also get very buggy in some situations. Basically it's a common site (menu content) but the idea is to load the content without refreshing the page, defining the div to load the content, and make each page accessible by the url. One of the biggest problems here it's dealing with all url situations that may occur. The ideal would be to have a rel="divToLoadOn" and then pass it on my loadContent() function... so I would like or ideas/solutions for this please. Thanks in advance! //if page comes from URL if(window.location.hash != ''){ var url = window.location.hash; url = '..'+url.substr(1, url.length); loadContent(url); } //if page comes from an internal link $("a:not([target])").click(function(e){ e.preventDefault(); var url = $(this).attr("href"); if(url != '#'){ loadContent($(this).attr("href")); } }); //LOAD CONTENT function loadContent(url){ var contentContainer = $("#content"); //set load animation $(contentContainer).ajaxStart(function() { $(this).html('loading...'); }); $.ajax({ url: url, dataType: "html", success: function(data){ //store data globally so it can be used on complete window.data = data; }, complete: function(){ var content = $(data).find("#content").html(); var contentTitle = $(data).find("title").text(); //change url var parsedUrl = url.substr(2,url.length) window.location.hash = parsedUrl; //change title var titleRegex = /(.*)<\/title/.exec(data); contentTitle = titleRegex[1]; document.title = contentTitle; //renew content $(contentContainer).fadeOut(function(){ $(this).html(content).fadeIn(); }); }); }

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  • how to run href="#var=something" before onclick function fires in javascript?

    - by korben
    i'm using the below javascript to change an image on an aspx in asp.net c# <script language="JavaScript" type="text/javascript"> var updateImageWhenHashChanges = function() { theImage = document.getElementById("ctl00_ContentPlaceHolder1_Image1a"); if(window.location.hash == "#size=2") { theImage.src = "<%# Eval("realfilename", "/files/l{0}") %>"; } else if(window.location.hash == "#size=3") { theImage.src = "<%# Eval("realfilename", "/files/{0}") %>"; } else if(window.location.hash == "#size=1") { theImage.src = "<%# Eval("fullthumbname", "/thumbnails/{0}") %>"; } else { } } </script> here's how i call it with a link <a href="#size=3" onclick="updateImageWhenHashChanges();">test</a> the problem is that it only does what i'm expecting on the SECOND click of the link, because it seems onclick fires before the href, so the first time i'm just placing the var and the 2nd time i'm actually getting what i want. does anyone know how i can fix this? i'm trying to get the image to change on each click

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  • Datastructure choices for highspeed and memory efficient detection of duplicate of strings

    - by Jonathan Holland
    I have a interesting problem that could be solved in a number of ways: I have a function that takes in a string. If this function has never seen this string before, it needs to perform some processing. If the function has seen the string before, it needs to skip processing. After a specified amount of time, the function should accept duplicate strings. This function may be called thousands of time per second, and the string data may be very large. This is a highly abstracted explanation of the real application, just trying to get down to the core concept for the purpose of the question. The function will need to store state in order to detect duplicates. It also will need to store an associated timestamp in order to expire duplicates. It does NOT need to store the strings, a unique hash of the string would be fine, providing there is no false positives due to collisions (Use a perfect hash?), and the hash function was performant enough. The naive implementation would be simply (in C#): Dictionary<String,DateTime> though in the interest of lowering memory footprint and potentially increasing performance I'm evaluating a custom data structures to handle this instead of a basic hashtable. So, given these constraints, what would you use? EDIT, some additional information that might change proposed implementations: 99% of the strings will not be duplicates. Almost all of the duplicates will arrive back to back, or nearly sequentially. In the real world, the function will be called from multiple worker threads, so state management will need to be synchronized.

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  • Why doesn't String's hashCode() cache 0?

    - by polygenelubricants
    I noticed in the Java 6 source code for String that hashCode only caches values other than 0. The difference in performance is exhibited by the following snippet: public class Main{ static void test(String s) { long start = System.currentTimeMillis(); for (int i = 0; i < 10000000; i++) { s.hashCode(); } System.out.format("Took %d ms.%n", System.currentTimeMillis() - start); } public static void main(String[] args) { String z = "Allocator redistricts; strict allocator redistricts strictly."; test(z); test(z.toUpperCase()); } } Running this in ideone.com gives the following output: Took 1470 ms. Took 58 ms. So my questions are: Why doesn't String's hashCode() cache 0? What is the probability that a Java string hashes to 0? What's the best way to avoid the performance penalty of recomputing the hash value every time for strings that hash to 0? Is this the best-practice way of caching values? (i.e. cache all except one?) For your amusement, each line here is a string that hash to 0: pollinating sandboxes amusement & hemophilias schoolworks = perversive electrolysissweeteners.net constitutionalunstableness.net grinnerslaphappier.org BLEACHINGFEMININELY.NET WWW.BUMRACEGOERS.ORG WWW.RACCOONPRUDENTIALS.NET Microcomputers: the unredeemed lollipop... Incentively, my dear, I don't tessellate a derangement. A person who never yodelled an apology, never preened vocalizing transsexuals.

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  • Been asked a dozen times, but no luck from what I've read. Prevent Anchor Jumping on page load

    - by jasenmp
    I'm currently working with WP theme that can be found here: sanjay.dmediastudios.com I'm currently using 'smooth scroll' on my page, I'm attempting to have the page smoothly scroll to the requested section when coming from an external link (for instance coming from the blog page takes you to sanjay.dmediastudios.com/#portfolio) from there I want the page to start at the top and THEN scroll to the portfolio section. What's happening is it briefly displays the 'portfolio section' (anchor jump) and THEN resets to the top and scrolls down. It's driving me nuts :(. Here is the code I'm using: Click function for smooth scroll: $(function() { $('.menu li a').click(function() { if (location.pathname.replace(/^\//, '') == this.pathname.replace(/^\//, '') && location.hostname == this.hostname) { var target = $(this.hash); target = target.length ? target : $('[name=' + this.hash.slice(1) + ']'); if (target.length) { $root.animate({ scrollTop: target.offset().top - 75 }, 800, 'swing'); return false; } } }); //end of click function }); The page load function: $(window).on("load", function() { if (location.hash) { // do the test straight away window.scrollTo(0, 0); // execute it straight away setTimeout(function() { window.scrollTo(0, 0); // run it a bit later also for browser compatibility }, 1); } var urlHash = window.location.href.split("#")[1]; if (urlHash && $('#' + urlHash).length) $('html,body').animate({ scrollTop: $('#' + urlHash).offset().top - 75 }, 800, 'swing'); }); Any help would be MUCH appreciated.

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  • Simple aggregating query very slow in PostgreSql, any way to improve?

    - by Ash
    HI I have a table which holds files and their types such as CREATE TABLE files ( id SERIAL PRIMARY KEY, name VARCHAR(255), filetype VARCHAR(255), ... ); and another table for holding file properties such as CREATE TABLE properties ( id SERIAL PRIMARY KEY, file_id INTEGER CONSTRAINT fk_files REFERENCES files(id), size INTEGER, ... // other property fields ); The file_id field has an index. The file table has around 800k lines, and the properties table around 200k (not all files necessarily have/need a properties). I want to do aggregating queries, for example find the average size and standard deviation for all file types. But it's very slow - around 70 seconds for the latter query. I understand it needs a sequential scan, but still it seems too much. Here's the query SELECT f.filetype, avg(size), stddev(size) FROM files as f, properties as pr WHERE f.id = pr.file_id GROUP BY f.filetype; and the explain HashAggregate (cost=140292.20..140293.94 rows=116 width=13) (actual time=74013.621..74013.954 rows=110 loops=1) -> Hash Join (cost=6780.19..138945.47 rows=179564 width=13) (actual time=1520.104..73156.531 rows=179499 loops=1) Hash Cond: (f.id = pr.file_id) -> Seq Scan on files f (cost=0.00..108365.41 rows=1140941 width=9) (actual time=0.998..62569.628 rows=805270 loops=1) -> Hash (cost=3658.64..3658.64 rows=179564 width=12) (actual time=1131.053..1131.053 rows=179499 loops=1) -> Seq Scan on properties pr (cost=0.00..3658.64 rows=179564 width=12) (actual time=0.753..557.171 rows=179574 loops=1) Total runtime: 74014.520 ms Any ideas why it is so slow/how to make it faster?

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  • In Rails 3, how does one render HTML within a JSON response?

    - by ylg
    I'm porting an application from Merb 1.1 / 1.8.7 to Rails 3 (beta) / 1.9.1 that uses JSON responses containing HTML fragments, e.g., a JSON container specifying an update, on a user record, and the updated user row looks like . In Merb, since whatever a controller method returns is given to the client, one can put together a Hash, assign a rendered partial to one of the keys and return hash.to_json (though that certainly may not be the best way.) In Rails, it seems that to get data back to the client one must use render and render can only be called once, so rendering the hash to json won't work because of the partial render. From reading around, it seems one could put that data into a JSON .erb view file, with <%= render partial % in and render that. Is there a Rails-way of solving this problem (return JSON containing one or more HTML fragments) other than that? In Merb: only_provides :json ... self.status = 204 # or appropriate if not async return { 'action' => 'update', 'type' => 'user', 'id' => @user.id, 'html' => partial('user_row', format: :html, user: @user) }.to_json In Rails?

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  • Python: Behavior of object in set operations

    - by Josh Arenberg
    I'm trying to create a custom object that behaves properly in set operations. I've generally got it working, but I want to make sure I fully understand the implications. In particular, I'm interested in the behavior when there is additional data in the object that is not included in the equal / hash methods. It seems that in the 'intersection' operation, it returns the set of objects that are being compared to, where the 'union' operations returns the set of objects that are being compared. To illustrate: class MyObject: def __init__(self,value,meta): self.value = value self.meta = meta def __eq__(self,other): if self.value == other.value: return True else: return False def __hash__(self): return hash(self.value) a = MyObject('1','left') b = MyObject('1','right') c = MyObject('2','left') d = MyObject('2','right') e = MyObject('3','left') print a == b # True print a == c # False for i in set([a,c,e]).intersection(set([b,d])): print "%s %s" % (i.value,i.meta) #returns: #1 right #2 right for i in set([a,c,e]).union(set([b,d])): print "%s %s" % (i.value,i.meta) #returns: #1 left #3 left #2 left Is this behavior documented somewhere and deterministic? If so, what is the governing principle?

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