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• Ignoring extra keys in a hash passed in to create

  - by denniss

  Does rails provide a way to ignore extra keys that are passed in to create. Supposed User has two attributes, first_name and last_name. When I do User.create({ :first_name => "first", :last_name => "last", :age => 10}) that line gives me an UknonwnAttributeError. Well, that makes sense, it happens cause age is not one of the attributes. But is there a way to just ignore key-value pair that is not one of the attributes for User?

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• Glib segfault g_free hash table

  - by Mike

  I'm not quite sure why if I try to free the data I get segfault. Any help will be appreciate it. static GHashTable *hashtable; static void add_inv(char *q) { gpointer old_key, old_value; if(!g_hash_table_lookup_extended(hashtable, q, &old_key, &old_value)){ g_hash_table_insert(hashtable, g_strdup(q), GINT_TO_POINTER(10)); }else{ (old_value)++; g_hash_table_insert(hashtable, g_strdup(q), old_value); g_hash_table_remove (hashtable, q); // segfault g_free(old_key); // segfault g_free(old_value); // segfault } } ... int main(int argc, char *argv[]){ hashtable = g_hash_table_new(g_str_hash, g_str_equal); ... g_hash_table_destroy(hashtable); }

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• accessing a value of a nested hash

  - by st

  Hello! I am new to perl and I have a problem that's very simple but I cannot find the answer when consulting my perl book. When printing the result of Dumper($request); I get the following result: $VAR1 = bless( { '_protocol' => 'HTTP/1.1', '_content' => '', '_uri' => bless( do{\(my $o = 'http://myawesomeserver.org:8081/counter/')}, 'URI::http' ), '_headers' => bless( { 'user-agent' => 'Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.4) Gecko/20080528 Epiphany/2.22 Firefox/3.0', 'connection' => 'keep-alive', 'cache-control' => 'max-age=0', 'keep-alive' => '300', 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'accept-language' => 'en-us,en;q=0.5', 'accept-encoding' => 'gzip,deflate', 'host' => 'localhost:8081', 'accept-charset' => 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' }, 'HTTP::Headers' ), '_method' => 'GET', '_handle' => bless( \*Symbol::GEN0, 'FileHandle' ) }, 'HTTP::Server::Simple::Dispatched::Request' ); How can I access the values of '_method' ('GET') or of 'host' ('localhost:8081'). I know that's an easy question, but perl is somewhat cryptic at the beginning. Thank you, St.

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• Will a SHA256 hash always have 64 characters?

  - by Sergio Tapia

  I'm setting up my database to receive hashed passwords and not accept plain text. Would I go something like this? create table User( username varchar(20) not null, password varchar(64) not null, );

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• Hash Digest / Array Comparison in C#

  - by Erik Karulf

  Hi All, I'm writing an application that needs to verify HMAC-SHA256 checksums. The code I currently have looks something like this: static bool VerifyIntegrity(string secret, string checksum, string data) { // Verify HMAC-SHA256 Checksum byte[] key = System.Text.Encoding.UTF8.GetBytes(secret); byte[] value = System.Text.Encoding.UTF8.GetBytes(data); byte[] checksum_bytes = System.Text.Encoding.UTF8.GetBytes(checksum); using (var hmac = new HMACSHA256(key)) { byte[] expected_bytes = hmac.ComputeHash(value); return checksum_bytes.SequenceEqual(expected_bytes); } } I know that this is susceptible to timing attacks. Is there a message digest comparison function in the standard library? I realize I could write my own time hardened comparison method, but I have to believe that this is already implemented elsewhere.

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• Creating a unique key based on file content in python

  - by Cawas

  I got many, many files to be uploaded to the server, and I just want a way to avoid duplicates. Thus, generating a unique and small key value from a big string seemed something that a checksum was intended to do, and hashing seemed like the evolution of that. So I was going to use hash md5 to do this. But then I read somewhere that "MD5 are not meant to be unique keys" and I thought that's really weird. What's the right way of doing this? edit: by the way, I took two sources to get to the following, which is how I'm currently doing it and it's working just fine, with Python 2.5: import hashlib def md5_from_file (fileName, block_size=2**14): md5 = hashlib.md5() f = open(fileName) while True: data = f.read(block_size) if not data: break md5.update(data) f.close() return md5.hexdigest()

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• Question about the mathematical properties of hashes

  - by levand

  Take a commonly used binary hash function - for example, SHA-256. As the name implies, it outputs a 256 bit value. Let A be the set of all possible 256 bit binary values. A is extremely large, but finite. Let B be the set of all possible binary values. B is infinite. Let C be the set of values obtained by running SHA-256 on every member of B. Obviously this can't be done in practice, but I'm guessing we can still do mathematical analysis of it. My Question: By necessity, C ? A. But does C = A?

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• Ruby: rules for implicit hashes

  - by flyer

  Why second output shows me only one element of Array? Is it still Array or Hash already? def printArray(arr) arr.each { | j | k, v = j.first printf("%s %s %s \n", k, v, j) } end print "Array 1\n" printArray( [ {kk: { 'k1' => 'v1' }}, {kk: { 'k2' => 'v2' }}, {kk: { 'k3' => 'v3' }}, ]) print "Array 2\n" printArray( [ kk: { 'k1' => 'v1' }, kk: { 'k2' => 'v2' }, kk: { 'k3' => 'v3' }, ]) exit # Output: # # Array 1 # kk {"k1"=>"v1"} {:kk=>{"k1"=>"v1"}} # kk {"k2"=>"v2"} {:kk=>{"k2"=>"v2"}} # kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}} # Array 2 # kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}}

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• Perl: Get the length of an array within a hash

  - by Magicked

  I have the following: $data{host} -> [$i] -> {someotherstuff} How can I get the length of the array where [$i] is? Thanks!

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• Accessing a nested hash in a controller

  - by Magicked

  I have the following (snipped) parameters passed into my controller. Parameters: {"commit"=>"OK", "action"=>"set_incident_incident_status_id", "id"=>"1", "controller"=>"incidents", "incident"=>{"incident_status_id"=>"1"}} I know that if I want to select the incident, I can do: @incident = Incident.find(params[:id]) How do I access the "incident"={"incident_status_id"="1"}? I thought to try something like: @incident_status = IncidentStatus.find(params[:incident => :incident_status_id]) But that didn't work. I'm assuming it's just a syntax problem at this point, and I haven't found a solution yet. Any help would be much appreciated!

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• password/login system in php

  - by Jonathan

  For a login system in php would this be a suitable outline of how it would work: users types in username and password, clicks login button. Checks if user exists in database, if it does, then retrieve the salt for that user hash the password and salt (would this be done on the client or server side? I think client side would be better, but php is server side so how would you do this?) check value against value in database, if the values match then user has typed in correct password and they are logged in.

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• Do encryption algorithms provide really unique results?

  - by Mikulas Dite

  I was wondering whether md5, sha1 and anothers return unique values. For example, sha1() for test returns a94a8fe5ccb19ba61c4c0873d391e987982fbbd3, which is 40 characters long. So, sha1 for strings larger than 40 chars must be the same (of course it's scrambled, because the given input may contain whitespaces and special chars etc.). Due to this, when we are storing users' passwords, they can enter either their original password or some super-long one, which nobody knows. Is this right, or do these hash algorithms provide really unique results - I'm quite sure it's hardly possible.

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• Population count of rightmost n integers

  - by Jason Baker

  I'm implementing Bagwell's Ideal Hash Trie in Haskell. To find an element in a sub-trie, he says to do the following: Finding the arc for a symbol s, requires ?nding its corresponding bit in the bit map and then counting the one bits below it in the map to compute an index into the ordered sub-trie. What is the best way to do this? It sounds like the most straightforward way of doing this is to select the bits below that bit and do a population count on the resulting number. Is there a faster or better way to do this?

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• Creating a simple java hash server

  - by Blankman

  Is it possible to create a simple server in Java that returns a response based on a given key? So it would be a simple program, that stores a hashmap and returns the result based on a key provided by the client. What would be the fasted implementation, to have it over HTTP or a socket? The client will be a web based application.

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• How can I map URLs to filenames with perl?

  - by eugene y

  In a simple webapp I need to map URLs to filenames or filepaths. This app has a requirement that it can depend only on modules in the core Perl ditribution (5.6.0 and later). The problem is that filename length on most filesystems is limited to 255. Another limit is about 32k subdirectories in a single folder. My solution: my $filename = $url; if (length($filename) > $MAXPATHLEN) { # if filename longer than 255 my $part1 = substr($filename, 0, $MAXPATHLEN - 13); # first 242 chars my $part2 = crypt(0, substr($filename, $MAXPATHLEN - 13)); # 13 chars hash $filename = $part1.$part2; } $filename =~ s!/!_!g; # escape directory separator Is it reliable ? How can it be improved ?

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• Hashing and salting values

  - by Avanst

  I am developing a small web app that internally authenticates users. Once the user is authenticated my web app then passes some information such as userID and Person's name to a third party web application. The third party developer is suggesting that we hash and salt the values. Forgive my ignorance, but what exactly does that mean? I am writing the app in Java. So what I am planning on doing is hashing the userID, Person's name, and some Math.random() value as the salt with Apache Commons Digest Utils SHA512 and passing that hashed string along with the userID and person's name. Is that the standard practice? I should be passing the third party the salt as well correct?

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• Ruby hash value truthiness and symbols

  - by John Topley

  Could somebody please explain why the variable named foo remains true in the code below, even though it's set to false when the method is called? And why the symbol version behaves as expected? def test(options = {}) foo = options[:foo] || true bar = options[:bar] || :true puts "foo is #{foo}, bar is #{bar}" end >> test(:foo => false, :bar => :false) foo is true, bar is false I've only tried this using Ruby 1.8.7.

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• Merging hashes into one hash in perl

  - by Nick

  how do I get this: $VAR1 = { '999' => { '998' => [ '908', '906', '0', '998', '907' ] } }; $VAR1 = { '999' => { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } }; $VAR1 = { '999' => { '996' => [] } }; $VAR1 = { '999' => { '995' => [] } }; $VAR1 = { '999' => { '994' => [] } }; $VAR1 = { '999' => { '993' => [] } }; $VAR1 = { '999' => { '997' => [ '986', '987', '990', '984', '989', '988' ] } }; $VAR1 = { '995' => { '101' => [] } }; $VAR1 = { '995' => { '102' => [] } }; $VAR1 = { '995' => { '103' => [] } }; $VAR1 = { '995' => { '104' => [] } }; $VAR1 = { '995' => { '105' => [] } }; $VAR1 = { '995' => { '106' => [] } }; $VAR1 = { '995' => { '107' => [] } }; $VAR1 = { '994' => { '910' => [] } }; $VAR1 = { '993' => { '909' => [] } }; $VAR1 = { '993' => { '904' => [] } }; $VAR1 = { '994' => { '985' => [] } }; $VAR1 = { '994' => { '983' => [] } }; $VAR1 = { '993' => { '902' => [] } }; $VAR1 = { '999' => { '992' => [ '905' ] } }; to this: $VAR1 = { '999:' => [ { '992' => [ '905' ] }, { '993' => [ { '909' => [] }, { '904' => [] }, { '902' => [] } ] }, { '994' => [ { '910' => [] }, { '985' => [] }, { '983' => [] } ] }, { '995' => [ { '101' => [] }, { '102' => [] }, { '103' => [] }, { '104' => [] }, { '105' => [] }, { '106' => [] }, { '107' => [] } ] }, { '996' => [] }, { '997' => [ '986', '987', '990', '984', '989', '988' ] }, { '998' => [ '908', '906', '0', '998', '907' ] }, { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } ]}; in Perl?

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• Set a session hash outside of RoR program?

  - by Sindri Guðmundsson

  Hi, I have had my new rails program up for a few days now. I'm running it on Ubuntu 10.4 with apache2 in another location than the website it's made for (it's a standalone database application for physiotherapists). The people I made it for now want me to deploy it to the public part of their website, only with one change. Those who open it via the link in the public-part should not be able to click one button! I was thinking of doing something like this in my view: <% if session[:inside]%> <%=button_to 'Sækja mælitæki', @link_to_mt%> <%end%> How could I set session[:inside] only to true if the program was started from within the private part of the webpage? I thought of creating two new actions, the other would set session[:inside] to true and the other to false, but that seems to me like a security risk, is it not? BR, Sindri

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• How do I quiet image_submit_tag from params hash?

  - by Alan S

  Does anyone know how to eliminate the x and y params when you use image_submit_tag with a get method? I have a simple search form, and using get to pass the value in the url. When I use image_submit_tag, it also appends the x and y coords, so I get urls like http://example.com?q=somesearchterm&x=15&y=12 When I have used submit_tag, I can use the :name = nil attribute (was in one of Ryan Bates' Railscasts), but it doesn't seem to work for image_submit_tag. Granted it doesn't affect functionality, but I don't need them and would like them quieted.

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• What hash/map based programming language exist?

  - by Davorak

  Much like lisp is often considered a list based programming language what languages are considered map based? I remember reading about one a few years back, but can not longer find a reference to it. It looked something like: [if:test then:<code> else:<more code>] edit: and more where quoted code blocks which would be conditional evaluated. In this fashion if/cond and others would not be special form as they are in lisp/scheme.

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• Birthday effect - clarification needed plz.

  - by Mark

  Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: 1) Pick any message m and compute h(m). 2) Update list L. Check if h(m) is in the list L. 3) if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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• Can someone please clarify the Birthday Effect for me?

  - by Mark

  Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: Pick any message m and compute h(m). Update list L. Check if h(m) is in the list L. if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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• When should I define an hash code function for my types?

  - by devoured elysium

  Is there any other reason for implementing an hash code function for my types other than allowing for good use of hash tables? Let's say I am designing some types that I intend to use internally. I know that types are "internal" to the system, and I also know I will never use those types in hash tables. In spite of this, I decide I will have to redefine the equals() method. Theory says I should also redefine the hash code method, but I can't see any reason why, in this case, I should do it. Can anyone point me out any other reason? This question can be rephrased to : in which situations should we implement a hash code method in our types. PS : I am not asking how to implement one. I am asking when.

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• Union of two or more (hash)maps

  - by javierfp

  I have two Maps that contain the same type of Objects: Map<String, TaskJSO> a = new HashMap<String, TaskJSO>(); Map<String, TaskJSO> b = new HashMap<String, TaskJSO>(); public class TaskJSO { String id; } The map keys are the "id" properties. a.put(taskJSO.getId(), taskJSO); I want to obtain a list with: all values in "Map b" + all values in "Map a" that are not in "Map b". What is the fastest way of doing this operation? Thanks EDIT: The comparaison is done by id. So, two TaskJSOs are considered as equal if they have the same id (equals method is overrided). My intention is to know which is the fastest way of doing this operation from a performance point of view. For instance, is there any difference if I do the "comparaison" in a map (as suggested by Peter): Map<String, TaskJSO> ab = new HashMap<String, TaskJSO>(a); ab.putAll(b); ab.values() or if instead I use a set (as suggested by Nishant): Set s = new Hashset(); s.addAll(a.values()); s.addAll(b.values());

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