1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
// Copyright 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "chrome/common/visitedlink_common.h"
#include "base/logging.h"
#include "base/md5.h"
const VisitedLinkCommon::Fingerprint VisitedLinkCommon::null_fingerprint_ = 0;
const VisitedLinkCommon::Hash VisitedLinkCommon::null_hash_ = -1;
VisitedLinkCommon::VisitedLinkCommon() :
hash_table_(NULL),
table_length_(0) {
}
VisitedLinkCommon::~VisitedLinkCommon() {
}
// FIXME: this uses linear probing, it should be replaced with quadratic
// probing or something better. See VisitedLinkMaster::AddFingerprint
bool VisitedLinkCommon::IsVisited(const char* canonical_url,
size_t url_len) const {
if (url_len == 0)
return false;
if (!hash_table_ || table_length_ == 0) {
// Init() will always create a table, this means somebody forgot
NOTREACHED();
return false;
}
return IsVisited(ComputeURLFingerprint(canonical_url, url_len, salt_));
}
bool VisitedLinkCommon::IsVisited(Fingerprint fingerprint) const {
// Go through the table until we find the item or an empty spot (meaning it
// wasn't found). This loop will terminate as long as the table isn't full,
// which should be enforced by AddFingerprint.
Hash first_hash = HashFingerprint(fingerprint);
Hash cur_hash = first_hash;
while (true) {
Fingerprint cur_fingerprint = FingerprintAt(cur_hash);
if (cur_fingerprint == null_fingerprint_)
return false; // End of probe sequence found.
if (cur_fingerprint == fingerprint)
return true; // Found a match.
// This spot was taken, but not by the item we're looking for, search in
// the next position.
cur_hash++;
if (cur_hash == table_length_)
cur_hash = 0;
if (cur_hash == first_hash) {
// Wrapped around and didn't find an empty space, this means we're in an
// infinite loop because AddFingerprint didn't do its job resizing.
NOTREACHED();
return false;
}
}
}
// Uses the top 64 bits of the MD5 sum of the canonical URL as the fingerprint,
// this is as random as any other subset of the MD5SUM.
//
// FIXME: this uses the MD5SUM of the 16-bit character version. For systems where
// wchar_t is not 16 bits (Linux uses 32 bits, I think), this will not be
// compatable. We should define explicitly what should happen here across
// platforms, and convert if necessary (probably to UTF-16).
// static
VisitedLinkCommon::Fingerprint VisitedLinkCommon::ComputeURLFingerprint(
const char* canonical_url,
size_t url_len,
const uint8 salt[LINK_SALT_LENGTH]) {
DCHECK(url_len > 0) << "Canonical URLs should not be empty";
MD5Context ctx;
MD5Init(&ctx);
MD5Update(&ctx, salt, sizeof(salt));
MD5Update(&ctx, canonical_url, url_len * sizeof(char));
MD5Digest digest;
MD5Final(&digest, &ctx);
// This is the same as "return *(Fingerprint*)&digest.a;" but if we do that
// direct cast the alignment could be wrong, and we can't access a 64-bit int
// on arbitrary alignment on some processors. This reinterpret_casts it
// down to a char array of the same size as fingerprint, and then does the
// bit cast, which amounts to a memcpy. This does not handle endian issues.
return bit_cast<Fingerprint, uint8[8]>(
*reinterpret_cast<uint8(*)[8]>(&digest.a));
}
|
