Mitigate spoofing attempt using Latin letters.

net/base/lookup_string_in_fixed_set.h

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef NET_BASE_LOOKUP_STRING_IN_FIXED_SET_H_
-#define NET_BASE_LOOKUP_STRING_IN_FIXED_SET_H_
-
-#include <stddef.h>
-
-#include "net/base/net_export.h"
-
-namespace net {
-
-enum {
-  kDafsaNotFound = -1,  // key is not in set
-  kDafsaFound = 0,      // key is in set
-  // The following return values are used by the implementation of
-  // GetDomainAndRegistry() and are probably not generally useful.
-  kDafsaExceptionRule = 1,  // key excluded from set via exception
-  kDafsaWildcardRule = 2,   // key matched a wildcard rule
-  kDafsaPrivateRule = 4,    // key matched a private rule
-};
-
-// Looks up the string |key| with length |key_length| in a fixed set of
-// strings. The set of strings must be known at compile time. It is converted to
-// a graph structure named a DAFSA (Deterministic Acyclic Finite State
-// Automaton) by the script make_dafsa.py during compilation. This permits
-// efficient (in time and space) lookup. The graph generated by make_dafsa.py
-// takes the form of a constant byte array which should be supplied via the
-// |graph| and |length| parameters.  The return value is kDafsaNotFound,
-// kDafsaFound, or a bitmap consisting of one or more of kDafsaExceptionRule,
-// kDafsaWildcardRule and kDafsaPrivateRule ORed together.
-//
-// TODO(nick): Replace this with FixedSetIncrementalLookup everywhere.
-NET_EXPORT int LookupStringInFixedSet(const unsigned char* graph,
-                                      size_t length,
-                                      const char* key,
-                                      size_t key_length);
-
-// FixedSetIncrementalLookup provides efficient membership and prefix queries
-// against a fixed set of strings. The set of strings must be known at compile
-// time. The set is converted to a graph structure named a DAFSA (Deterministic
-// Acyclic Finite State Automaton) by the script //net/tools/dafsa/make_dafsa.py
-// during compilation. The conversion generates a C++ header file defining the
-// encoded graph as a constant byte array. This class provides a fast, constant-
-// space lookup operation against such byte arrays.
-//
-// The lookup proceeds incrementally, with input characters provided one at a
-// time. This approach allow queries of the form: "given an input string, which
-// prefixes of that string that appear in the fixed set?" As the matching
-// prefixes (and their result codes) are enumerated, the most suitable match
-// among them can be selected in a single pass.
-//
-// This class can also be used to perform suffix queries (instead of prefix
-// queries) against a fixed set, so long as the DAFSA is constructed on reversed
-// values, and the input is provided in reverse order.
-//
-// Example usage for simple membership query; |input| is a std::string:
-//
-//    FixedSetIncrementalLookup lookup(kDafsa, sizeof(kDafsa));
-//    for (char c : input) {
-//      if (!lookup.Advance(c))
-//         return false;
-//    }
-//    return lookup.GetResultForCurrentSequence() != kDafsaNotFound;
-//
-// Example usage for 'find longest prefix in set with result code == 3' query:
-//
-//    FixedSetIncrementalLookup prefix_lookup(kDafsa, sizeof(kDafsa));
-//    size_t longest_match_end = 0;
-//    for (size_t i = 0; i < input.length(); ++i) {
-//      if (!prefix_lookup.Advance(input[i]))
-//         break;
-//      if (prefix_lookup.GetResultForCurrentSequence() == 3)
-//        longest_match_end = (i + 1);
-//    }
-//    return input.substr(0, longest_match_end);
-//
-class NET_EXPORT FixedSetIncrementalLookup {
- public:
-  // Begin a lookup against the provided fixed set. |graph| and |length|
-  // describe a byte buffer generated by the make_dafsa.py script, as described
-  // in the class comment.
-  //
-  // FixedSetIncrementalLookup is initialized to a state corresponding to the
-  // empty input sequence. Calling GetResultForCurrentSequence() in the initial
-  // state would indicate whether the empty string appears in the fixed set.
-  // Characters can be added to the sequence by calling Advance(), and the
-  // lookup result can be checked after each addition by calling
-  // GetResultForCurrentSequence().
-  FixedSetIncrementalLookup(const unsigned char* graph, size_t length);
-
-  // FixedSetIncrementalLookup is copyable so that callers can save/restore
-  // their position in the search. This is for cases where branching or
-  // backtracking might be required (e.g. to probe for the presence of a
-  // designated wildcard character).
-  FixedSetIncrementalLookup(const FixedSetIncrementalLookup&);
-  FixedSetIncrementalLookup& operator=(const FixedSetIncrementalLookup&);
-
-  ~FixedSetIncrementalLookup();
-
-  // Advance the query by adding a character to the input sequence. |input| can
-  // be any char value, but only ASCII characters will ever result in matches,
-  // since the fixed set itself is limited to ASCII strings.
-  //
-  // Returns true if the resulting input sequence either appears in the fixed
-  // set itself, or is a prefix of some longer string in the fixed set. Returns
-  // false otherwise, implying that the graph is exhausted and
-  // GetResultForCurrentSequence() will return kDafsaNotFound.
-  //
-  // Once Advance() has returned false, the caller can safely stop feeding more
-  // characters, as subsequent calls to Advance() will return false and have no
-  // effect.
-  bool Advance(char input);
-
-  // Returns the result code corresponding to the input sequence provided thus
-  // far to Advance().
-  //
-  // If the sequence does not appear in the fixed set, the return value is
-  // kDafsaNotFound. Otherwise, the value is a non-negative integer (currently
-  // limited to 0-7) corresponding to the result code for that string, as listed
-  // in the .gperf file from which the DAFSA was generated. For
-  // GetDomainAndRegistry DAFSAs, these values should be interpreted as a
-  // bitmask of kDafsaExceptionRule, kDafsaWildcardRule, and kDafsaPrivateRule.
-  //
-  // It is okay to call this function, and then extend the sequence further by
-  // calling Advance().
-  int GetResultForCurrentSequence() const;
-
- private:
-  // Pointer to the current position in the graph indicating the current state
-  // of the automaton, or nullptr if the graph is exhausted.
-  const unsigned char* pos_;
-
-  // Pointer just past the end of the graph. |pos_| should never get here. This
-  // is used only in DCHECKs.
-  const unsigned char* end_;
-
-  // Contains the current decoder state. If true, |pos_| points to a label
-  // character or a return code. If false, |pos_| points to a sequence of
-  // offsets that indicate the child nodes of the current state.
-  bool pos_is_label_character_;
-};
-
-}  // namespace net
-
-#endif  // NET_BASE_LOOKUP_STRING_IN_FIXED_SET_H_