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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
// Copyright (c) 2012 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.
#include "Dafsa.h"
#include "mozilla/Assertions.h"
#include "nsAString.h"
const int mozilla::Dafsa::kKeyNotFound = -1;
// Note the DAFSA implementation was lifted from eTLD code in Chromium that was
// originally lifted from Firefox.
// Read next offset from pos.
// Returns true if an offset could be read, false otherwise.
static bool GetNextOffset(const unsigned char** pos, const unsigned char* end,
const unsigned char** offset) {
if (*pos == end) return false;
// When reading an offset the byte array must always contain at least
// three more bytes to consume. First the offset to read, then a node
// to skip over and finally a destination node. No object can be smaller
// than one byte.
MOZ_ASSERT(*pos + 2 < end);
size_t bytes_consumed;
switch (**pos & 0x60) {
case 0x60: // Read three byte offset
*offset += (((*pos)[0] & 0x1F) << 16) | ((*pos)[1] << 8) | (*pos)[2];
bytes_consumed = 3;
break;
case 0x40: // Read two byte offset
*offset += (((*pos)[0] & 0x1F) << 8) | (*pos)[1];
bytes_consumed = 2;
break;
default:
*offset += (*pos)[0] & 0x3F;
bytes_consumed = 1;
}
if ((**pos & 0x80) != 0) {
*pos = end;
} else {
*pos += bytes_consumed;
}
return true;
}
// Check if byte at offset is last in label.
static bool IsEOL(const unsigned char* offset, const unsigned char* end) {
MOZ_ASSERT(offset < end);
return (*offset & 0x80) != 0;
}
// Check if byte at offset matches first character in key.
// This version matches characters not last in label.
static bool IsMatch(const unsigned char* offset, const unsigned char* end,
const char* key) {
MOZ_ASSERT(offset < end);
return *offset == *key;
}
// Check if byte at offset matches first character in key.
// This version matches characters last in label.
static bool IsEndCharMatch(const unsigned char* offset,
const unsigned char* end, const char* key) {
MOZ_ASSERT(offset < end);
return *offset == (*key | 0x80);
}
// Read return value at offset.
// Returns true if a return value could be read, false otherwise.
static bool GetReturnValue(const unsigned char* offset,
const unsigned char* end, int* return_value) {
MOZ_ASSERT(offset < end);
if ((*offset & 0xE0) == 0x80) {
*return_value = *offset & 0x0F;
return true;
}
return false;
}
// Lookup a domain key in a byte array generated by make_dafsa.py.
// The rule type is returned if key is found, otherwise kKeyNotFound is
// returned.
static int LookupString(const unsigned char* graph, size_t length,
const char* key, size_t key_length) {
const unsigned char* pos = graph;
const unsigned char* end = graph + length;
const unsigned char* offset = pos;
const char* key_end = key + key_length;
while (GetNextOffset(&pos, end, &offset)) {
// char <char>+ end_char offsets
// char <char>+ return value
// char end_char offsets
// char return value
// end_char offsets
// return_value
bool did_consume = false;
if (key != key_end && !IsEOL(offset, end)) {
// Leading <char> is not a match. Don't dive into this child
if (!IsMatch(offset, end, key)) continue;
did_consume = true;
++offset;
++key;
// Possible matches at this point:
// <char>+ end_char offsets
// <char>+ return value
// end_char offsets
// return value
// Remove all remaining <char> nodes possible
while (!IsEOL(offset, end) && key != key_end) {
if (!IsMatch(offset, end, key)) return mozilla::Dafsa::kKeyNotFound;
++key;
++offset;
}
}
// Possible matches at this point:
// end_char offsets
// return_value
// If one or more <char> elements were consumed, a failure
// to match is terminal. Otherwise, try the next node.
if (key == key_end) {
int return_value;
if (GetReturnValue(offset, end, &return_value)) return return_value;
// The DAFSA guarantees that if the first char is a match, all
// remaining char elements MUST match if the key is truly present.
if (did_consume) return mozilla::Dafsa::kKeyNotFound;
continue;
}
if (!IsEndCharMatch(offset, end, key)) {
if (did_consume) return mozilla::Dafsa::kKeyNotFound; // Unexpected
continue;
}
++key;
pos = ++offset; // Dive into child
}
return mozilla::Dafsa::kKeyNotFound; // No match
}
namespace mozilla {
int Dafsa::Lookup(const nsACString& aKey) const {
return LookupString(mData.Elements(), mData.Length(), aKey.BeginReading(),
aKey.Length());
}
} // namespace mozilla