123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105 |
- // Copyright (c) 2011 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 "components/visitedlink/common/visitedlink_common.h"
- #include <string.h> // for memset()
- #include <ostream>
- #include "base/bit_cast.h"
- #include "base/check.h"
- #include "base/hash/md5.h"
- #include "base/notreached.h"
- #include "url/gurl.h"
- namespace visitedlink {
- const VisitedLinkCommon::Fingerprint VisitedLinkCommon::null_fingerprint_ = 0;
- const VisitedLinkCommon::Hash VisitedLinkCommon::null_hash_ = -1;
- VisitedLinkCommon::VisitedLinkCommon()
- : hash_table_(nullptr), table_length_(0) {
- memset(salt_, 0, sizeof(salt_));
- }
- VisitedLinkCommon::~VisitedLinkCommon() {
- }
- // FIXME: this uses linear probing, it should be replaced with quadratic
- // probing or something better. See VisitedLinkWriter::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)
- return false;
- return IsVisited(ComputeURLFingerprint(canonical_url, url_len));
- }
- bool VisitedLinkCommon::IsVisited(const GURL& url) const {
- return IsVisited(url.spec().data(), url.spec().size());
- }
- 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_t salt[LINK_SALT_LENGTH]) {
- DCHECK(url_len > 0) << "Canonical URLs should not be empty";
- base::MD5Context ctx;
- base::MD5Init(&ctx);
- base::MD5Update(&ctx, base::StringPiece(reinterpret_cast<const char*>(salt),
- LINK_SALT_LENGTH));
- base::MD5Update(&ctx, base::StringPiece(canonical_url, url_len));
- base::MD5Digest digest;
- base::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 base::bit_cast<Fingerprint, uint8_t[8]>(
- *reinterpret_cast<uint8_t(*)[8]>(&digest.a));
- }
- } // namespace visitedlink
|