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• Why use hashing to create pathnames for large collections of files?

  - by Stephen

  Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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• PHP Captcha without session

  - by Anton N

  Ok, here is an issue: in the project i'm working on, we can't rely on server-side sessions for any functionality. The problem is that common captcha solutions from preventing robotic submits require session to store the string to match captcha against. The question is - is there any way to solve the problem without using sessions? What comes to my mind - is serving hidden form field, containing some hash, along with captcha input field, so that server then can match these two values together. But how can we make this method secure, so that it couldn't be used to break captcha easily.

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• relating data stored in NoSQL DB to data stored in SQL DB

  - by seanbrant

  Whats the best way to use a SQL DB along side a NoSQL DB? I want to keep my users and other data in postgres but have some data that would be better suited for a NoSQL DB like redis. I see a lot of talk about switching to NoSQL but little talk on integrating it with existing systems. I think it would be foolish to throw the baby out with the bath water and ditch SQL all together, unless it makes things easier to maintain and develop. I'm wondering what the best approach is for relating data stored in SQL to my data in redis. I was thinking of something along the line of this. User object stored in SQL Book object in redis, key sh1 hash of value, value is a JSON string Relations stored in redis, key User.pk:books, value redis set of sha1's Anyone have experience, tips, better ways?

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• Serial numbers generation without user data

  - by Sphynx

  This is a followup to this question. The accepted answer is generally sufficient, but requires user to supply personal information (e.g. name) for generating the key. I'm wondering if it's possible to generate different keys based on a common seed, in a way that program would be able to validate if those keys belong to particular product, but without making this process obvious to the end user. I mean it could be a hash of product ID plus some random sequence of characters, but that would allow user to guess potential new keys. There should be some sort of algorithm difficult to guess.

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• What's the fastest way to compare two objects in PHP?

  - by johnnietheblack

  Let's say I have an object - a User object in this case - and I'd like to be able to track changes to with a separate class. The User object should not have to change it's behavior in any way for this to happen. Therefore, my separate class creates a "clean" copy of it, stores it somewhere locally, and then later can compare the User object to the original version to see if anything changed during its lifespan. Is there a function, a pattern, or anything that can quickly compare the two versions of the User object? Option 1 Maybe I could serialize each version, and directly compare, or hash them and compare? Option 2 Maybe I should simply create a ReflectionClass, run through each of the properties of the class and see if the two versions have the same property values? Option 3 Maybe there is a simple native function like objects_are_equal($object1,$object2);? What's the fastest way to do this?

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• Get current session /process id from inside a mysql query

  - by Indra Ginanjar

  I'm trying to create a table for pseudo array variable. That looks like CREATE TABLE IF NOT EXISTS `MyArray`.`ArrayTable` ( `ID` INT UNSIGNED NOT NULL COMMENT 'Hash value of SessionID + ArrayName' , `SessionID` INT UNSIGNED NOT NULL , `ArrayName` CHAR(26) NOT NULL COMMENT '32 digit char - 6 digit longest process id (assumtion)' , `Index` INT UNSIGNED NOT NULL , `Value` TEXT NOT NULL , PRIMARY KEY (`ID`, `SessionID`) ) ENGINE = MyISAM; The table is not normalized yet, 'hope this will make it a little simpler to understand :) To avoid collission between client, there should be a differentiator between client session. For that reason i think need to know current session/process id (just like "SHOW PROCESSLIST") but really need to know IN WHICH process the query are?

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• Twisted Spread: How to authenticate each RPC with digital signature

  - by kronat

  I have remote objects which talk each others with RPCs, using Twisted Spread. I want that objects authenticate messages, before using them, with digital signatures, but I don't know where to start to implement this. In my head, the Root object must have a public/private key pair, and the Client too. When a message is sent, a digital signature of the hash is added, and when it is received, the signature is checked. Is the Protocol part where I need to add these adds and checks? Thank you

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• Separating an Array into a comma seperated string with quotes

  - by user548744

  I'm manually building an SQL query where I'm using an Array in the params hash for an SQL IN statement, like: ("WHERE my_field IN('blue','green','red')"). So I need to take the contents of the array and output them into a string where each element is single quoted and comma seperated (and with no ending comma). So if the array was: my_array = ['blue','green','red'] I'd need a string that looked like: "'blue','green','red'" I'm pretty new to Ruby/Rails but came up with something that worked: if !params[:colors].nil? @categories_array = params[:colors][:categories] @categories_string ="" for x in @categories_array @categories_string += "'" + x + "'," end @categories_string.chop! #remove the last comma end So, I'm good but curious as to what a proper and more consise way of doing this would look like? Thanks

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• Facebook like iframe ignores my specified href

  - by Zhami

  I have Javascript that imputes (computes and injects) HTML into my DOM for the Facebook "Like" function. I need to specify a "canonical" URL because the actual URL doesn't reflect all the DOM manipulations that have been made (driven by user activity on the Web "page"). Alas, Facebook's code doesn't use the url I supply but the window.location value (which has #hash aspects that influence the page's presentation, but that aren't accessible to the server). Anyway... why is FB's code ignoring the url I give to it? I generate the HTML thus: var html = '<iframe src="http://www.facebook.com/plugins/like.php?href=' + encodeURI(url) + '&layout=standard&show_faces=false&width=100&action=recommend&font=arial&colorscheme=light" style="border:none; overflow:hidden; width:270px; height:26px;" allowTransparency="true" frameborder="0" scrolling="no"</iframe'

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• find a duplicate entry in an array in constant space and O(n) time [closed]

  - by Anubhav Agarwal

  Possible Duplicate: Algorithm to find a duplicate entry in constant space and O(n) time Given an array of N integer such that only one integer is repeated. Find the repeated integer in O(n) time and constant space. There is no range for the value of integers or the value of N For example given an array of 6 integers as 23 45 67 87 23 47. The answer is 23 (I hope this covers ambiguous and vague part) I searched on the net but was unable to find any such question in which range of integers was not fixed. Also here is an example that answers a similar question to mine but here he created a hash table with the highest integer value in C++.But the cpp does not allow such to create an array with 2^64 element(on a 64-bit computer).

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• Should I make sure arguments aren't null before using them in a function.

  - by Nathan W

  The title may not really explain what I'm really trying to get at, couldn't really think of a way to describe what I mean. I was wondering if it is good practice to check the arguments that a function accepts for nulls or empty before using them. I have this function which just wraps some hash creation like so. Public Shared Function GenerateHash(ByVal FilePath As IO.FileInfo) As String If (FilePath Is Nothing) Then Throw New ArgumentNullException("FilePath") End If Dim _sha As New Security.Cryptography.MD5CryptoServiceProvider Dim _Hash = Convert.ToBase64String(_sha.ComputeHash(New IO.FileStream(FilePath.FullName, IO.FileMode.Open, IO.FileAccess.Read))) Return _Hash End Function As you can see I just takes a IO.Fileinfo as an argument, at the start of the function I am checking to make sure that it is not nothing. I'm wondering is this good practice or should I just let it get to the actual hasher and then throw the exception because it is null.? Thanks.

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• rails rollback updates when task fails

  - by ash34

  Hi, I have the following "generate_report" method being called from a rake task, which gets a hash as an input, that contains the reported hours spent by each user on a task and outputs the data as a .csv report. desc "Task reporting" task :report, [:inp_dt] => [:environment] do |t, args| h = select_data(args.inp_dt) /* not shown here */ generate_report(h) end def generate_report(h) out_dir = File.dirname(__FILE__) + '/../../output' myfile = "#{out_dir}" + "/monthly_#{Date.today.strftime("%m%d%Y")}.csv" writer = CSV.open(myfile, 'w') h.each do |h,v| v.each do |key,val| writer << val end end writer.close end where h = {:BILL=>{:PROJA=>["CYR", "00876", "2", 24], :PROJB=>["EPR", "00876", "2", 16]}, :JANE=>{:PROJA=>["TRB", "049576", "2", 16]}} I would like to set/update a 'processed' flag for each reported transaction and only commit the update when the file is written correctly or rollback the updates when the task fails. How can I accomplish this. thanks, ash

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• Rails application and multilingual content, Model dilemma

  - by dakull

  I'm writing in Rails a website that will be multilingual, for the application translation part i will use the simple I18n gem, for messages and everything related. Yet, all the content must be translated, and we're talking about lots of pages, that will be stored into the database ( like articles, news, etc. ) For now, I'm thinking of two approaches: Lets say i have a Pages table, the content in diff. languages, i will be storing it in a different table called PagesContent that will belong_to Pages and also to a Languages table. The problem here, is that I'll essentially duplicate the no. of tables needed. Pros: flexibility, in the box validation To skip that duplication i can serialize a hash into the content column of Pages, containing the translation. The problem here, is validation, arguably more code to write, and less flexibility when adding a new language. Pros: Less tables. Any other idea ?

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• Semicolon in object variable name

  - by milkfilk

  There's a common LDAP attribute called userCertificate;binary. It actually has a semi-colon in the attribute name. In ruby, I turn an LDAP entry into a OpenStruct object called 'struct'. struct.class = OpenStruct But of course ruby thinks it's an end-of-line character. ? struct.userCertificate;binary NameError: undefined local variable or method `binary' for main:Object from (irb):52 from :0 IRB knows that the local variable is there, because it gives me struct.userCertificate;binary from the tab auto-completion. I can also see the class variable when calling struct.methods on it. struct.methods = ... "send", "methods", "userCertificate;binary=", "hash", ... It's definitely there, I can see the contents if I print the whole variable to_s(). But how can I access the local variable when it has a semicolon in it? I have workarounds for this but I thought it was an interesting problem to post.

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• How to I count key collisions when using boost::unordered_map?

  - by Nikhil

  I have a data structure with 15 unsigned longs, I have defined a hash function using hash_combine as follows: friend std::size_t hash_value(const TUPLE15& given) { std::size_t seed = 0; boost::hash_combine(seed, val1); boost::hash_combine(seed, val2); ... return seed; } I insert a large number of values into a boost::unordered_map but the performance is not good enough. Probably, I could do better with an alternative hashing function. To confirm this, I need to check how many collisions I am getting. How do I do this?

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• How to validate Windows VC++ DLL on Unix systems

  - by Guildencrantz

  I have a solution, mostly C#, but with a few VC++ projects, that is pushed through our standard release process (perl and bash scripts on Unix boxes). Currently the initiative is to validate DLL and EXE versions as they pass through the process. All the versioning is set so that File Version is of the format $Id: $ (between the colon and the second dollar should be a git commit hash), and the Product Version is of the format $Hudson Build: $ (between the colon and the second dollar should be a string representing the hudson build details). Currently this system works extremely well for the C# projects because this version information is stored as plain strings within the compiled code (you can literally use the unix strings command and see the version information); the problem is that the VC++ projects do not expose this information as strings (I have used a windows system to verify that the version information is correctly being set), so I'm not sure how to extract the version on a unix system. Any suggestions for either A) Getting a string representation of the version embedded in the compiled code, or B) A utility/script which can extract this information?

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• Secure password transmission over unencrypted tcp/ip

  - by academicRobot

  I'm in the designing stages of a custom tcp/ip protocol for mobile client-server communication. When not required (data is not sensitive), I'd like to avoid using SSL for overhead reasons (both in handshake latency and conserving cycles). My question is, what is the best practices way of transmitting authentication information over an unencrypted connection? Currently, I'm liking SRP or J-PAKE (they generate secure session tokens, are hash/salt friendly, and allow kicking into TLS when necessary), which I believe are both implemented in OpenSSL. However, I am a bit wary since I don't see many people using these algorithms for this purpose. Would also appreciate pointers to any materials discussing this topic in general, since I had trouble finding any.

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• MVC Forms Authentication with custom database

  - by AndrewVos

  I'm trying to get forms authentication working for an mvc site. I have a custom database with a users table, and I would like to do my own password validation. I am logging in my user like this: if (PasswordHasher.Hash(password) == dataUser.Password) { FormsAuthentication.SetAuthCookie(email, true); return true; } The problem is, when the session expires obviously the user has to login again. I am thinking I should be storing this Auth cookie in my users table? Update: I'm obviously in desperate need of more education in this area. I just noticed that the user stays authenticated even after an iisreset. I guess what I'm asking is how can I get persistent and non persistent authentication working properly. I want a user to not have to login again if they click "remember", and if they don't then their authentication should expire when the forms authentication is set to expire.

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• Amazon EC2 multiple servers share session state

  - by Theofanis Pantelides

  Hi everyone, I have a bunch of EC2 servers that are load balanced. Some of the servers are not sharing session, and users keep getting logged in and out. How can I make all the server share the one session, possibly even using a partitionresolver solution public class PartitionResolver : System.Web.IPartitionResolver { private String[] partitions; public void Initialize() { // create the partition connection string table // web1, web2 partitions = new String[] { "192.168.1.1" }; } public String ResolvePartition(Object key) { String oHost = System.Web.HttpContext.Current.Request.Url.Host.ToLower().Trim(); if (oHost.StartsWith("10.0.0") || oHost.Equals("localhost")) return "tcpip=127.0.0.1:42424"; String sid = (String)key; // hash the incoming session ID into // one of the available partitions Int32 partitionID = Math.Abs(sid.GetHashCode()) % partitions.Length; return ("tcpip=" + partitions[partitionID] + ":42424"); } } -theo

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• changing window.location without triggering refresh

  - by jdwyah

  I have an AJAX form that submits GET requests. Because these are all GET requests these should be easily bookmark-able. Preferably I'd make my Ajax request, update the screen and then update window.location.href to be the URL for the new page. Unfortunately this reloads the page. Is there any way I can get around this? Basically I'd like the URL bar to be a permalink bar, but it needs to be able to change to keep up with the state of the page. window.location.hash is no good because that doesn't get sent to the server.

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• Ruby string encoding problem

  - by John Prideaux

  I've looked at the other ruby/encoding related posts but haven't been able to figure out why the following is not working. Likely just because I'm dense, but here's the situation. Using Ruby 1.9 on windows. I have a set of CSV files that need some data appended to the end of each line. Whenever I run my script, the appended characters are gibberish. The input text appears to be IBM437 encoding, whereas my string I'm appending starts as US-ASCII. Nothing I've tried with respect to forcing encoding on the input strings or the append string seems to change the resultant output. I'm stumped. The current encoding version is simply the last that I tried. def append_salesperson(txt, salesperson) if txt.length > 2 return txt.chomp.force_encoding('US-ASCII') + %(, "", "", "#{salesperson}") end end salespeople = Hash[ "fname", "Record Manager"] outfile = File.open("ActData.csv", "w:US-ASCII") salespeople.each do | filename, recordManager | infile = File.open("#{filename}.txt") infile.each do |line| outfile.puts append_salesperson(line, recordManager) end infile.close end outfile.close

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• Best Practice for CouchDB Document Versioning

  - by Groundwater

  Following my question here I am exmploring ideas for a generic approach to document versioning in CouchDB. While I imagine there may be no canonical approach, I had the following idea and am looking for feedback. I would like to maintain readable document ids as much as possible, so a document existing at /document1 would contain a pointer document to all existing versions on the system. The actual revision documents would be at something like /document1/308ef032a3801a where 308ef032a3801a is some random number or hash. Example The pointer document { "_id" : "document1", "versions" : [ "document1/308ef032a3801a" ] } The version document { "_id" : "document1/308ef032a3801a", ... actual content }

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• Obtain patterns in one file from another using ack or awk or better way than grep?

  - by Rock

  Is there a way to obtain patterns in one file (a list of patterns) from another file using ack as the -f option in grep? I see there is an -f option in ack but it's different with the -f in grep. Perhaps an example will give you a better idea. Suppose I have file1: file1: a c e And file2: file2: a 1 b 2 c 3 d 4 e 5 And I want to obtain all the patterns in file1 from file2 to give: a 1 c 3 e 5 Can ack do this? Otherwise, is there a better way to handle the job (such like awk or using hash) because I have millions of records in both files and really need an efficient way to complete? Thanks!

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• How can I speed up line by line reading of an ASCII file? (C++)

  - by Jon

  Here's a bit of code that is a considerable bottleneck after doing some measuring: //----------------------------------------------------------------------------- // Construct dictionary hash set from dictionary file //----------------------------------------------------------------------------- void constructDictionary(unordered_set<string> &dict) { ifstream wordListFile; wordListFile.open("dictionary.txt"); string word; while( wordListFile >> word ) { if( !word.empty() ) { dict.insert(word); } } wordListFile.close(); } I'm reading in ~200,000 words and this takes about 240 ms on my machine. Is the use of ifstream here efficient? Can I do better? I'm reading about mmap() implementations but I'm not understanding them 100%. The input file is simply text strings with *nix line terminations.

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