SS14-17313 Chatfactor: Chat Censorship Systems (#25908)
* SS14-17313 Chat Censorship Systems Adds some systems to manage chat censorship: 1. No-op: does nothing 2. SimpleCensor: a regex-free censor with a variety of rules to use 3. RegexCensor: a censor that uses regex. This exposes a singleton backed by a builder pattern (ChatCensor) that is set up, probably during the code init phase, and then globally available for your censorship needs. * Migrate to Shared * Add a reset function to the builder. * Resolve PJB's feedback; add unit tests
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Hannah Giovanna Dawson
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340
Content.Shared/Chat/V2/Moderation/SimpleCensor.cs
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340
Content.Shared/Chat/V2/Moderation/SimpleCensor.cs
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using System.Collections.Frozen;
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using System.Linq;
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using System.Text;
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using System.Text.Unicode;
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namespace Content.Shared.Chat.V2.Moderation;
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/// <summary>
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/// A basic censor. Not bullet-proof.
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/// </summary>
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public sealed class SimpleCensor : IChatCensor
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{
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// Common substitution symbols are replaced with one of the characters they commonly substitute.
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private bool _shouldSanitizeLeetspeak;
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private FrozenDictionary<char, char> _leetspeakReplacements = FrozenDictionary<char, char>.Empty;
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// Special characters are replaced with spaces.
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private bool _shouldSanitizeSpecialCharacters;
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private HashSet<char> _specialCharacterReplacements = [];
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// Censored words are removed unless they're a false positive (e.g. Scunthorpe)
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private string[] _censoredWords = Array.Empty<string>();
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private string[] _falsePositives = Array.Empty<string>();
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// False negatives are censored words that contain a false positives.
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private string[] _falseNegatives = Array.Empty<string>();
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// What unicode ranges are allowed? If this array is empty, don't filter by range.
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private UnicodeRange[] _allowedUnicodeRanges= Array.Empty<UnicodeRange>();
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/// <summary>
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/// Censors the input string.
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/// </summary>
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/// <param name="input">The input string</param>
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/// <param name="output">The output string</param>
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/// <param name="replaceWith">The character to replace with</param>
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/// <returns>If output is valid</returns>
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public bool Censor(string input, out string output, char replaceWith = '*')
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{
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output = Censor(input, replaceWith);
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return !string.Equals(input, output);
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}
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public string Censor(string input, char replaceWith = '*')
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{
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// We flat-out ban anything not in the allowed unicode ranges, stripping them
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input = SanitizeOutBlockedUnicode(input);
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var originalInput = input.ToCharArray();
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input = SanitizeInput(input);
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var censored = input.ToList();
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// Remove false negatives
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input = CheckProfanity(input, censored, _falseNegatives, replaceWith);
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// Get false positives
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var falsePositives = FindFalsePositives(censored, replaceWith);
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// Remove censored words
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CheckProfanity(input, censored, _censoredWords, replaceWith);
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// Reconstruct
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// Reconstruct false positives
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for (var i = 0; i < falsePositives.Length; i++)
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{
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if (falsePositives[i] != replaceWith)
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{
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censored[i] = falsePositives[i];
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}
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}
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for (var i = 0; i < originalInput.Length; i++)
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{
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if (originalInput[i] == ' ')
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{
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censored.Insert(i, ' ');
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continue;
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}
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if (_shouldSanitizeSpecialCharacters && _specialCharacterReplacements.Contains(originalInput[i]))
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{
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censored.Insert(i, originalInput[i]);
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continue;
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}
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if (_shouldSanitizeLeetspeak || _shouldSanitizeSpecialCharacters)
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{
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// detect "()"
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if (originalInput[i] == '(' && i != originalInput.Length - 1 && originalInput[i+1] == ')')
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{
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// censored has now had "o" replaced with "o) so both strings line up again..."
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censored.Insert(i+1, censored[i] != replaceWith ? ')' : replaceWith);
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}
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}
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if (censored[i] != replaceWith)
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{
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censored[i] = originalInput[i];
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}
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}
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// SO says this is fast...
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return string.Concat(censored);
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}
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/// <summary>
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/// Adds a l33tsp34k sanitization rule
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/// </summary>
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/// <returns>The censor for further configuration</returns>
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public SimpleCensor WithSanitizeLeetSpeak()
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{
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_shouldSanitizeLeetspeak = true;
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return BuildCharacterReplacements();
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}
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/// <summary>
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/// Adds a l33tsp34k sanitization rule
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/// </summary>
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/// <returns>The censor for further configuration</returns>
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public SimpleCensor WithSanitizeSpecialCharacters()
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{
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_shouldSanitizeSpecialCharacters = true;
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return BuildCharacterReplacements();
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}
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public SimpleCensor WithRanges(UnicodeRange[] ranges)
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{
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_allowedUnicodeRanges = ranges;
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return this;
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}
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public SimpleCensor WithCustomDictionary(string[] naughtyWords)
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{
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_censoredWords = naughtyWords;
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return this;
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}
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public SimpleCensor WithFalsePositives(string[] falsePositives)
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{
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_falsePositives = falsePositives;
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return this;
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}
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public SimpleCensor WithFalseNegatives(string[] falseNegatives)
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{
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_falseNegatives = falseNegatives;
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return this;
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}
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public SimpleCensor WithLeetspeakReplacements(Dictionary<char, char> replacements)
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{
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_leetspeakReplacements = replacements.ToFrozenDictionary();
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return this;
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}
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public SimpleCensor WithSpecialCharacterReplacements(Dictionary<char, char> replacements)
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{
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_leetspeakReplacements = replacements.ToFrozenDictionary();
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return this;
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}
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private string CheckProfanity(string input, List<char> censored, string[] words, char replaceWith = '*')
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{
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foreach (var word in words)
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{
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var wordLength = word.Length;
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var endOfFoundWord = 0;
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var foundIndex = input.IndexOf(word, endOfFoundWord, StringComparison.OrdinalIgnoreCase);
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while(foundIndex > -1)
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{
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endOfFoundWord = foundIndex + wordLength;
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for (var i = 0; i < wordLength; i++)
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{
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censored[foundIndex+i] = replaceWith;
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}
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foundIndex = input.IndexOf(word, endOfFoundWord, StringComparison.OrdinalIgnoreCase);
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}
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}
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return input;
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}
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private char[] FindFalsePositives(List<char> chars, char replaceWith = '*')
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{
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var input = string.Concat(chars);
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var output = Enumerable.Repeat(replaceWith, input.Length).ToArray();
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var inputAsARr = input.ToArray();
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foreach (var word in _falsePositives)
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{
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var wordLength = word.Length;
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var endOfFoundWord = 0;
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var foundIndex = input.IndexOf(word, endOfFoundWord, StringComparison.OrdinalIgnoreCase);
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while(foundIndex > -1)
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{
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endOfFoundWord = foundIndex + wordLength;
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for (var i = foundIndex; i < endOfFoundWord; i++)
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{
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output[i] = inputAsARr[i];
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}
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foundIndex = input.IndexOf(word, endOfFoundWord, StringComparison.OrdinalIgnoreCase);
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}
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}
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return output;
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}
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private string SanitizeInput(string input)
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{
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// "()" is a broad enough trick to beat censors that we we should check for it broadly.
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if (_shouldSanitizeLeetspeak || _shouldSanitizeSpecialCharacters)
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{
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input = input.Replace("()", "o");
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}
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var sb = new StringBuilder();
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// ReSharper disable once ForeachCanBePartlyConvertedToQueryUsingAnotherGetEnumerator
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foreach (var character in input)
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{
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if (character == ' ' || _shouldSanitizeSpecialCharacters && _specialCharacterReplacements.Contains(character))
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{
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continue;
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}
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if (_shouldSanitizeLeetspeak && _leetspeakReplacements.TryGetValue(character, out var leetRepl))
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{
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sb.Append(leetRepl);
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continue;
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}
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sb.Append(character);
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}
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return sb.ToString();
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}
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/// <summary>
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/// Returns a string with all characters not in ISO-8851-1 replaced with question marks
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/// </summary>
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private string SanitizeOutBlockedUnicode(string input)
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{
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if (_allowedUnicodeRanges.Length <= 0)
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{
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return input;
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}
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var sb = new StringBuilder();
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foreach (var symbol in input.EnumerateRunes())
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{
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// ReSharper disable once LoopCanBeConvertedToQuery
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foreach (var range in _allowedUnicodeRanges)
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{
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if (symbol.Value < range.FirstCodePoint || symbol.Value >= range.FirstCodePoint + range.Length)
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continue;
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sb.Append(symbol);
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break;
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}
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}
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return sb.ToString();
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}
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private SimpleCensor BuildCharacterReplacements()
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{
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if (_shouldSanitizeSpecialCharacters)
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{
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_specialCharacterReplacements =
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[
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'-',
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'_',
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'|',
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'.',
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',',
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'(',
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')',
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'<',
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'>',
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'"',
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'`',
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'~',
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'*',
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'&',
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'%',
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'$',
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'#',
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'@',
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'!',
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'?',
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'+'
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];
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}
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if (_shouldSanitizeLeetspeak)
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{
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_leetspeakReplacements = new Dictionary<char, char>
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{
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['4'] = 'a',
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['$'] = 's',
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['!'] = 'i',
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['+'] = 't',
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['#'] = 'h',
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['@'] = 'a',
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['0'] = 'o',
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['1'] = 'i', // also obviously can be l; gamer-words need i's more though.
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['7'] = 'l',
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['3'] = 'e',
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['5'] = 's',
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['9'] = 'g',
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['<'] = 'c'
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}.ToFrozenDictionary();
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}
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return this;
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}
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}
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