libpsl/src/lookup_string_in_fixed_set.c

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/* 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.chromium file.
*
* Converted to C89 2015 by Tim Rühsen
*/
#include <stddef.h>
#if defined(__GNUC__) && defined(__GNUC_MINOR__)
# define _GCC_VERSION_AT_LEAST(major, minor) ((__GNUC__ > (major)) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
#else
# define _GCC_VERSION_AT_LEAST(major, minor) 0
#endif
#if _GCC_VERSION_AT_LEAST(4,0)
# define _HIDDEN __attribute__ ((visibility ("hidden")))
#else
# define _HIDDEN
#endif
#define CHECK_LT(a, b) if ((a) >= b) return 0
/*
* Read next offset from pos.
* Returns true if an offset could be read, false otherwise.
*/
static int GetNextOffset(const unsigned char** pos,
const unsigned char* end,
const unsigned char** offset)
{
size_t bytes_consumed;
if (*pos == end)
return 0;
/* 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. */
CHECK_LT(*pos + 2, end);
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 1;
}
/*
* Check if byte at offset is last in label.
*/
static int IsEOL(const unsigned char* offset, const unsigned char* end)
{
CHECK_LT(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 int IsMatch(const unsigned char* offset,
const unsigned char* end,
const char* key)
{
CHECK_LT(offset, end);
return *offset == *key;
}
/*
* Check if byte at offset matches first character in key.
* This version matches characters last in label.
*/
static int IsEndCharMatch(const unsigned char* offset,
const unsigned char* end,
const char* key)
{
CHECK_LT(offset, end);
return *offset == (*key | 0x80);
}
/*
* Read return value at offset.
* Returns true if a return value could be read, false otherwise.
*/
static int GetReturnValue(const unsigned char* offset,
const unsigned char* end,
int* return_value)
{
CHECK_LT(offset, end);
if ((*offset & 0xE0) == 0x80) {
*return_value = *offset & 0x0F;
return 1;
}
return 0;
}
/*
* 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.
*
* Lookup a domain key in a byte array generated by make_dafsa.py.
*/
/* prototype to skip warning with -Wmissing-prototypes */
int _HIDDEN LookupStringInFixedSet(const unsigned char*, size_t,const char*, size_t);
int _HIDDEN LookupStringInFixedSet(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
*/
int did_consume = 0;
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 = 1;
++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 -1;
++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 -1;
continue;
}
if (!IsEndCharMatch(offset, end, key)) {
if (did_consume)
return -1; /* Unexpected */
continue;
}
++key;
pos = ++offset; /* Dive into child */
}
return -1; /* No match */
}