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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#include "components/visitedlink/browser/visitedlink_writer.h"
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <array>
#include <memory>
#include <string_view>
#include <utility>
#include "base/files/file_util.h"
#include "base/files/scoped_file.h"
#include "base/functional/bind.h"
#include "base/functional/callback_helpers.h"
#include "base/logging.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/histogram_macros.h"
#include "base/rand_util.h"
#include "base/strings/string_util.h"
#include "base/threading/thread_restrictions.h"
#include "base/trace_event/trace_event.h"
#include "build/build_config.h"
#include "components/visitedlink/browser/visitedlink_delegate.h"
#include "components/visitedlink/browser/visitedlink_event_listener.h"
#include "content/public/browser/browser_context.h"
#include "content/public/browser/browser_task_traits.h"
#include "content/public/browser/browser_thread.h"
#include "third_party/abseil-cpp/absl/container/inlined_vector.h"
#include "url/gurl.h"
#include "url/origin.h"
#if BUILDFLAG(IS_WIN)
#include <windows.h>
#include <io.h>
#include <shlobj.h>
#endif // BUILDFLAG(IS_WIN)
using content::BrowserThread;
namespace visitedlink {
const int32_t VisitedLinkWriter::kFileHeaderSignatureOffset = 0;
const int32_t VisitedLinkWriter::kFileHeaderVersionOffset = 4;
const int32_t VisitedLinkWriter::kFileHeaderLengthOffset = 8;
const int32_t VisitedLinkWriter::kFileHeaderUsedOffset = 12;
const int32_t VisitedLinkWriter::kFileHeaderSaltOffset = 16;
const int32_t VisitedLinkWriter::kFileCurrentVersion = 3;
// the signature at the beginning of the URL table = "VLnk" (visited links)
const int32_t VisitedLinkWriter::kFileSignature = 0x6b6e4c56;
const size_t VisitedLinkWriter::kFileHeaderSize =
kFileHeaderSaltOffset + LINK_SALT_LENGTH;
// This value should also be the same as the smallest size in the lookup
// table in NewTableSizeForCount (prime number).
const unsigned VisitedLinkWriter::kDefaultTableSize = 16381;
bool VisitedLinkWriter::fail_table_creation_for_testing_ = false;
namespace {
// Fills the given salt structure with some quasi-random values
// It is not necessary to generate a cryptographically strong random string,
// only that it be reasonably different for different users.
void GenerateSalt(uint8_t (&salt)[LINK_SALT_LENGTH]) {
uint64_t randval = base::RandUint64();
static_assert(sizeof(salt) == sizeof(randval), "Salt size mismatch");
memcpy(salt, &randval, sizeof(salt));
}
// Opens file on a background thread to not block UI thread.
void AsyncOpen(base::ScopedFILE* file, const base::FilePath& filename) {
DCHECK(file);
DCHECK(!*file);
file->reset(base::OpenFile(filename, "wb+"));
DLOG_IF(ERROR, !*file) << "Failed to open file " << filename.value();
}
// Returns true if the write was complete.
static bool WriteToFile(FILE* file,
off_t offset,
const void* data,
size_t data_len) {
if (fseek(file, offset, SEEK_SET) != 0)
return false; // Don't write to an invalid part of the file.
size_t num_written = fwrite(data, 1, data_len, file);
// The write may not make it to the kernel (stdlib may buffer the write)
// until the next fseek/fclose call. If we crash, it's easy for our used
// item count to be out of sync with the number of hashes we write.
// Protect against this by calling fflush.
int ret = fflush(file);
DCHECK_EQ(0, ret);
return num_written == data_len;
}
// This task executes on a background thread and executes a write. This
// prevents us from blocking the UI thread doing I/O. This is ignored if the
// previous call to AsyncOpen() failed to open the file.
void AsyncWrite(base::ScopedFILE* file,
int32_t offset,
const std::string& data) {
DCHECK(file);
if (*file) {
WriteToFile(file->get(), offset, data.data(), data.size());
}
}
// Truncates the file to the current position asynchronously on a background
// thread. This is ignored if the previous call to AsyncOpen() failed to open
// the file.
void AsyncTruncate(base::ScopedFILE* file) {
DCHECK(file);
if (*file) {
base::IgnoreResult(base::TruncateFile(file->get()));
}
}
// These values are logged to UMA. Entries should not be renumbered and
// numeric values should never be reused. NOTE: Please also keep in line with
// components/visitedlink/browser/partitioned_visitedlink_writer.cc:
// AddFingerprint.
//
// LINT.IfChange(AddFingerprint)
enum class AddFingerprint {
kNewVisit = 0,
kAlreadyVisited = 1,
kTableError = 2,
kMaxValue = kTableError,
};
// LINT.ThenChange(//tools/metrics/histograms/metadata/history/enums.xml:AddFingerprint)
} // namespace
struct VisitedLinkWriter::LoadFromFileResult
: public base::RefCountedThreadSafe<LoadFromFileResult> {
LoadFromFileResult(base::ScopedFILE file,
base::MappedReadOnlyRegion hash_table_memory,
int32_t num_entries,
int32_t used_count,
uint8_t salt[LINK_SALT_LENGTH]);
LoadFromFileResult(const LoadFromFileResult&) = delete;
LoadFromFileResult& operator=(const LoadFromFileResult&) = delete;
base::ScopedFILE file;
base::MappedReadOnlyRegion hash_table_memory;
int32_t num_entries;
int32_t used_count;
uint8_t salt[LINK_SALT_LENGTH];
private:
friend class base::RefCountedThreadSafe<LoadFromFileResult>;
virtual ~LoadFromFileResult();
};
VisitedLinkWriter::LoadFromFileResult::LoadFromFileResult(
base::ScopedFILE file,
base::MappedReadOnlyRegion hash_table_memory,
int32_t num_entries,
int32_t used_count,
uint8_t salt[LINK_SALT_LENGTH])
: file(std::move(file)),
hash_table_memory(std::move(hash_table_memory)),
num_entries(num_entries),
used_count(used_count) {
memcpy(this->salt, salt, LINK_SALT_LENGTH);
}
VisitedLinkWriter::LoadFromFileResult::~LoadFromFileResult() = default;
// TableBuilder ---------------------------------------------------------------
// How rebuilding from history works
// ---------------------------------
//
// We mark that we're rebuilding from history by setting the table_builder_
// member in VisitedLinkWriter to the TableBuilder we create. This builder
// will be called on the history thread by the history system for every URL
// in the database.
//
// The builder will store the fingerprints for those URLs, and then marshalls
// back to the main thread where the VisitedLinkWriter will be notified. The
// writer then replaces its table with a new table containing the computed
// fingerprints.
//
// The builder must remain active while the history system is using it.
// Sometimes, the writer will be deleted before the rebuild is complete, in
// which case it notifies the builder via DisownWriter(). The builder will
// delete itself once rebuilding is complete, and not execute any callback.
class VisitedLinkWriter::TableBuilder
: public VisitedLinkDelegate::URLEnumerator {
public:
TableBuilder(VisitedLinkWriter* writer, const uint8_t salt[LINK_SALT_LENGTH]);
TableBuilder(const TableBuilder&) = delete;
TableBuilder& operator=(const TableBuilder&) = delete;
// Called on the main thread when the writer is being destroyed. This will
// prevent a crash when the query completes and the writer is no longer
// around. We can not actually do anything but mark this fact, since the
// table will be being rebuilt simultaneously on the other thread.
void DisownWriter();
// VisitedLinkDelegate::URLEnumerator
void OnURL(const GURL& url) override;
void OnComplete(bool succeed) override;
private:
~TableBuilder() override = default;
// OnComplete mashals to this function on the main thread to do the
// notification.
void OnCompleteMainThread();
// Owner of this object. MAY ONLY BE ACCESSED ON THE MAIN THREAD!
raw_ptr<VisitedLinkWriter, FlakyDanglingUntriaged> writer_;
// Indicates whether the operation has failed or not.
bool success_;
// Salt for this new table.
uint8_t salt_[LINK_SALT_LENGTH];
// Stores the fingerprints we computed on the background thread.
VisitedLinkCommon::Fingerprints fingerprints_;
};
// VisitedLinkWriter ----------------------------------------------------------
VisitedLinkWriter::VisitedLinkWriter(content::BrowserContext* browser_context,
VisitedLinkDelegate* delegate,
bool persist_to_disk)
: browser_context_(browser_context),
delegate_(delegate),
listener_(std::make_unique<VisitedLinkEventListener>(browser_context)),
persist_to_disk_(persist_to_disk) {}
VisitedLinkWriter::VisitedLinkWriter(Listener* listener,
VisitedLinkDelegate* delegate,
bool persist_to_disk,
bool suppress_rebuild,
const base::FilePath& filename,
int32_t default_table_size)
: delegate_(delegate),
listener_(listener),
persist_to_disk_(persist_to_disk),
database_name_override_(filename),
table_size_override_(default_table_size),
suppress_rebuild_(suppress_rebuild) {
DCHECK(listener_);
}
VisitedLinkWriter::~VisitedLinkWriter() {
if (table_builder_) {
// Prevent the table builder from calling us back now that we're being
// destroyed. Note that we DON'T delete the object, since the history
// system is still writing into it. When that is complete, the table
// builder will destroy itself when it finds we are gone.
table_builder_->DisownWriter();
}
FreeURLTable();
// FreeURLTable() will schedule closing of the file and deletion of
// |scoped_file_holder_|. So nothing should be done here.
if (table_is_loading_from_file_ &&
(!added_since_load_.empty() || !deleted_since_load_.empty())) {
// Delete the database file if it exists because we don't have enough time
// to load the table from the database file and now we have inconsistent
// state. On the next start table will be rebuilt.
base::FilePath filename;
GetDatabaseFileName(&filename);
PostIOTask(FROM_HERE, base::GetDeleteFileCallback(filename));
}
DCHECK(!scoped_file_holder_); // Must have been moved to the IO thread for
// releasing the file in the correct sequence.
}
bool VisitedLinkWriter::Init() {
TRACE_EVENT0("browser", "VisitedLinkWriter::Init");
// Create the temporary table. If the table is rebuilt that temporary table
// will be became the main table.
// The salt must be generated before the table so that it can be copied to
// the shared memory.
GenerateSalt(salt_);
if (!CreateURLTable(DefaultTableSize()))
return false;
if (mapped_table_memory_.region.IsValid())
listener_->NewTable(&mapped_table_memory_.region);
#ifndef NDEBUG
DebugValidate();
#endif
if (persist_to_disk_) {
if (InitFromFile())
return true;
}
return InitFromScratch(suppress_rebuild_);
}
void VisitedLinkWriter::AddURL(const GURL& url, bool update_file) {
TRACE_EVENT0("browser", "VisitedLinkWriter::AddURL");
UMA_HISTOGRAM_COUNTS_10M("History.VisitedLinks.HashTableUsageOnLinkAdded",
used_items_);
Hash index = TryToAddURL(url);
if (!table_builder_ && !table_is_loading_from_file_ && index != null_hash_) {
// Not rebuilding, so we want to keep the file on disk up to date.
if (update_file && persist_to_disk_) {
WriteUsedItemCountToFile();
WriteHashRangeToFile(index, index);
}
ResizeTableIfNecessary();
}
}
VisitedLinkWriter::Hash VisitedLinkWriter::TryToAddURL(const GURL& url) {
// Extra check that we are not incognito. This should not happen.
// TODO(boliu): Move this check to HistoryService when IsOffTheRecord is
// removed from BrowserContext.
if (browser_context_ && browser_context_->IsOffTheRecord()) {
NOTREACHED();
}
if (!url.is_valid())
return null_hash_; // Don't add invalid URLs.
Fingerprint fingerprint = ComputeURLFingerprint(url.spec(), salt_);
// If the table isn't loaded the table will be rebuilt and after
// that accumulated fingerprints will be applied to the table.
if (table_builder_.get() || table_is_loading_from_file_) {
// If we have a pending delete for this fingerprint, cancel it.
deleted_since_rebuild_.erase(fingerprint);
// A rebuild or load is in progress, save this addition in the temporary
// list so it can be added once rebuild is complete.
added_since_rebuild_.insert(fingerprint);
}
if (table_is_loading_from_file_) {
// If we have a pending delete for this url, cancel it.
deleted_since_load_.erase(url);
// The loading is in progress, save this addition in the temporary
// list so it can be added once the loading is complete.
added_since_load_.insert(url);
}
// If the table is "full", we don't add URLs and just drop them on the floor.
// This can happen if we get thousands of new URLs and something causes
// the table resizing to fail. This check prevents a hang in that case. Note
// that this is *not* the resize limit, this is just a sanity check.
if (used_items_ / 8 > table_length_ / 10)
return null_hash_; // Table is more than 80% full.
return AddFingerprint(fingerprint, true);
}
void VisitedLinkWriter::PostIOTask(const base::Location& from_here,
base::OnceClosure task) {
DCHECK(persist_to_disk_);
file_task_runner_->PostTask(from_here, std::move(task));
}
void VisitedLinkWriter::AddURL(const GURL& url) {
AddURL(url, /*update_file=*/true);
}
void VisitedLinkWriter::AddURLs(const std::vector<GURL>& urls) {
TRACE_EVENT0("browser", "VisitedLinkWriter::AddURLs");
bool bulk_write = (urls.size() > kBulkOperationThreshold);
for (const GURL& url : urls)
AddURL(url, !bulk_write);
// Write the full table if in bulk mode.
if (bulk_write && persist_to_disk_ && !table_builder_ &&
!table_is_loading_from_file_) {
WriteFullTable();
}
}
void VisitedLinkWriter::DeleteAllURLs() {
// Any pending modifications are invalid.
added_since_rebuild_.clear();
deleted_since_rebuild_.clear();
added_since_load_.clear();
deleted_since_load_.clear();
table_is_loading_from_file_ = false;
// Clear the hash table.
used_items_ = 0;
memset(hash_table_, 0, this->table_length_ * sizeof(Fingerprint));
// Resize it if it is now too empty. Resize may write the new table out for
// us, otherwise, schedule writing the new table to disk ourselves.
if (!ResizeTableIfNecessary() && persist_to_disk_)
WriteFullTable();
listener_->Reset(false);
}
VisitedLinkDelegate* VisitedLinkWriter::GetDelegate() {
return delegate_;
}
std::optional<uint64_t> VisitedLinkWriter::GetOrAddOriginSalt(
const url::Origin& origin) {
// To avoid race conditions, we should not get from or add to the salt map
// while the hashtable is building.
if (table_builder_ || table_is_loading_from_file_) {
return std::nullopt;
}
// Obtain the salt for this origin if it already exists.
auto it = salts_.find(origin);
if (it != salts_.end()) {
return it->second;
}
// Otherwise, generate a new salt for this origin.
const uint64_t generated_salt = base::RandUint64();
salts_.insert({origin, generated_salt});
return generated_salt;
}
void VisitedLinkWriter::DeleteURLs(URLIterator* urls) {
if (!urls->HasNextURL())
return;
listener_->Reset(false);
if (table_builder_.get() || table_is_loading_from_file_) {
// A rebuild or load is in progress, save this deletion in the temporary
// list so it can be added once rebuild is complete.
while (urls->HasNextURL()) {
const GURL& url(urls->NextURL());
if (!url.is_valid())
continue;
Fingerprint fingerprint = ComputeURLFingerprint(url.spec(), salt_);
deleted_since_rebuild_.insert(fingerprint);
// If the URL was just added and now we're deleting it, it may be in the
// list of things added since the last rebuild. Delete it from that list.
added_since_rebuild_.erase(fingerprint);
if (table_is_loading_from_file_) {
deleted_since_load_.insert(url);
added_since_load_.erase(url);
}
// Delete the URLs from the in-memory table, but don't bother writing
// to disk since it will be replaced soon.
DeleteFingerprint(fingerprint, false);
}
return;
}
// Compute the deleted URLs' fingerprints and delete them
std::set<Fingerprint> deleted_fingerprints;
while (urls->HasNextURL()) {
const GURL& url(urls->NextURL());
if (!url.is_valid())
continue;
deleted_fingerprints.insert(ComputeURLFingerprint(url.spec(), salt_));
}
DeleteFingerprintsFromCurrentTable(deleted_fingerprints);
}
// See VisitedLinkCommon::IsVisited which should be in sync with this algorithm
VisitedLinkWriter::Hash VisitedLinkWriter::AddFingerprint(
Fingerprint fingerprint,
bool send_notifications) {
if (!hash_table_ || table_length_ == 0) {
UMA_HISTOGRAM_ENUMERATION("History.VisitedLinks.TryToAddFingerprint",
AddFingerprint::kTableError);
NOTREACHED(); // Not initialized.
}
Hash cur_hash = HashFingerprint(fingerprint);
Hash first_hash = cur_hash;
while (true) {
Fingerprint cur_fingerprint = FingerprintAt(cur_hash);
if (cur_fingerprint == fingerprint) {
UMA_HISTOGRAM_ENUMERATION("History.VisitedLinks.TryToAddFingerprint",
AddFingerprint::kAlreadyVisited);
return null_hash_; // This fingerprint is already in there, do nothing.
}
if (cur_fingerprint == null_fingerprint_) {
// End of probe sequence found, insert here.
hash_table_[cur_hash] = fingerprint;
used_items_++;
// If allowed, notify listener that a new visited link was added.
if (send_notifications)
listener_->Add(fingerprint);
UMA_HISTOGRAM_ENUMERATION("History.VisitedLinks.TryToAddFingerprint",
AddFingerprint::kNewVisit);
return cur_hash;
}
// Advance in the probe sequence.
cur_hash = IncrementHash(cur_hash);
if (cur_hash == first_hash) {
// This means that we've wrapped around and are about to go into an
// infinite loop. Something was wrong with the hashtable resizing
// logic, so stop here.
UMA_HISTOGRAM_ENUMERATION("History.VisitedLinks.TryToAddFingerprint",
AddFingerprint::kTableError);
NOTREACHED();
}
}
}
void VisitedLinkWriter::DeleteFingerprintsFromCurrentTable(
const std::set<Fingerprint>& fingerprints) {
bool bulk_write = (fingerprints.size() > kBulkOperationThreshold);
// Delete the URLs from the table.
for (auto i = fingerprints.begin(); i != fingerprints.end(); ++i)
DeleteFingerprint(*i, !bulk_write);
// These deleted fingerprints may make us shrink the table.
if (ResizeTableIfNecessary())
return; // The resize function wrote the new table to disk for us.
// Nobody wrote this out for us, write the full file to disk.
if (bulk_write && persist_to_disk_)
WriteFullTable();
}
bool VisitedLinkWriter::DeleteFingerprint(Fingerprint fingerprint,
bool update_file) {
if (!hash_table_ || table_length_ == 0) {
NOTREACHED(); // Not initialized.
}
if (!IsVisited(fingerprint))
return false; // Not in the database to delete.
// First update the header used count.
used_items_--;
if (update_file && persist_to_disk_)
WriteUsedItemCountToFile();
Hash deleted_hash = HashFingerprint(fingerprint);
// Find the range of "stuff" in the hash table that is adjacent to this
// fingerprint. These are things that could be affected by the change in
// the hash table. Since we use linear probing, anything after the deleted
// item up until an empty item could be affected.
Hash end_range = deleted_hash;
while (true) {
Hash next_hash = IncrementHash(end_range);
if (next_hash == deleted_hash)
break; // We wrapped around and the whole table is full.
if (!hash_table_[next_hash])
break; // Found the last spot.
end_range = next_hash;
}
// We could get all fancy and move the affected fingerprints around, but
// instead we just remove them all and re-add them (minus our deleted one).
// This will mean there's a small window of time where the affected links
// won't be marked visited.
absl::InlinedVector<Fingerprint, 32> shuffled_fingerprints;
Hash stop_loop = IncrementHash(end_range); // The end range is inclusive.
for (Hash i = deleted_hash; i != stop_loop; i = IncrementHash(i)) {
if (hash_table_[i] != fingerprint) {
// Don't save the one we're deleting!
shuffled_fingerprints.push_back(hash_table_[i]);
// This will balance the increment of this value in AddFingerprint below
// so there is no net change.
used_items_--;
}
hash_table_[i] = null_fingerprint_;
}
if (!shuffled_fingerprints.empty()) {
// Need to add the new items back.
for (size_t i = 0; i < shuffled_fingerprints.size(); i++) {
AddFingerprint(shuffled_fingerprints[i], false);
}
}
// Write the affected range to disk [deleted_hash, end_range].
if (update_file && persist_to_disk_)
WriteHashRangeToFile(deleted_hash, end_range);
return true;
}
void VisitedLinkWriter::WriteFullTable() {
// This function can get called when the file is open, for example, when we
// resize the table. We must handle this case and not try to reopen the file,
// since there may be write operations pending on the file I/O thread.
//
// Note that once we start writing, we do not delete on error. This means
// there can be a partial file, but the short file will be detected next time
// we start, and will be replaced.
//
// This might possibly get corrupted if we crash in the middle of writing.
// We should pick up the most common types of these failures when we notice
// that the file size is different when we load it back in, and then we will
// regenerate the table.
DCHECK(persist_to_disk_);
if (!scoped_file_holder_) {
scoped_file_holder_ = std::make_unique<base::ScopedFILE>();
base::FilePath filename;
GetDatabaseFileName(&filename);
PostIOTask(FROM_HERE,
base::BindOnce(&AsyncOpen, scoped_file_holder_.get(), filename));
}
// Write the new header.
int32_t header[4];
header[0] = kFileSignature;
header[1] = kFileCurrentVersion;
header[2] = table_length_;
header[3] = used_items_;
WriteToFile(scoped_file_holder_.get(), 0, header, sizeof(header));
WriteToFile(scoped_file_holder_.get(), sizeof(header), salt_,
LINK_SALT_LENGTH);
// Write the hash data.
WriteToFile(scoped_file_holder_.get(), kFileHeaderSize, hash_table_,
table_length_ * sizeof(Fingerprint));
// The hash table may have shrunk, so make sure this is the end.
PostIOTask(FROM_HERE,
base::BindOnce(&AsyncTruncate, scoped_file_holder_.get()));
}
bool VisitedLinkWriter::InitFromFile() {
DCHECK_CURRENTLY_ON(BrowserThread::UI);
DCHECK(!scoped_file_holder_);
DCHECK(persist_to_disk_);
base::FilePath filename;
if (!GetDatabaseFileName(&filename))
return false;
table_is_loading_from_file_ = true;
TableLoadCompleteCallback callback = base::BindOnce(
&VisitedLinkWriter::OnTableLoadComplete, weak_ptr_factory_.GetWeakPtr());
PostIOTask(FROM_HERE, base::BindOnce(&VisitedLinkWriter::LoadFromFile,
filename, std::move(callback)));
return true;
}
// static
void VisitedLinkWriter::LoadFromFile(const base::FilePath& filename,
TableLoadCompleteCallback callback) {
scoped_refptr<LoadFromFileResult> load_from_file_result;
bool success = LoadApartFromFile(filename, &load_from_file_result);
content::GetUIThreadTaskRunner({})->PostTask(
FROM_HERE,
base::BindOnce(std::move(callback), success, load_from_file_result));
}
// static
bool VisitedLinkWriter::LoadApartFromFile(
const base::FilePath& filename,
scoped_refptr<LoadFromFileResult>* load_from_file_result) {
DCHECK(load_from_file_result);
base::ScopedFILE file_closer(base::OpenFile(filename, "rb+"));
if (!file_closer.get())
return false;
int32_t num_entries, used_count;
uint8_t salt[LINK_SALT_LENGTH];
if (!ReadFileHeader(file_closer.get(), &num_entries, &used_count, salt))
return false; // Header isn't valid.
// Allocate and read the table.
base::MappedReadOnlyRegion hash_table_memory;
if (!CreateApartURLTable(num_entries, salt, &hash_table_memory))
return false;
if (!ReadFromFile(file_closer.get(), kFileHeaderSize,
GetHashTableFromMapping(hash_table_memory.mapping),
num_entries * sizeof(Fingerprint))) {
return false;
}
*load_from_file_result = new LoadFromFileResult(
std::move(file_closer), std::move(hash_table_memory), num_entries,
used_count, salt);
return true;
}
void VisitedLinkWriter::OnTableLoadComplete(
bool success,
scoped_refptr<LoadFromFileResult> load_from_file_result) {
DCHECK_CURRENTLY_ON(BrowserThread::UI);
DCHECK(persist_to_disk_);
DCHECK(!table_builder_);
// When the apart table was loading from the database file the current table
// have been cleared.
if (!table_is_loading_from_file_)
return;
table_is_loading_from_file_ = false;
if (!success) {
// This temporary sets are used only when table was loaded.
added_since_load_.clear();
deleted_since_load_.clear();
// If the table isn't loaded the table will be rebuilt.
if (!suppress_rebuild_) {
RebuildTableFromDelegate();
} else {
// When we disallow rebuilds (normally just unit tests), just use the
// current empty table.
WriteFullTable();
}
return;
}
// This temporary sets are needed only to rebuild table.
added_since_rebuild_.clear();
deleted_since_rebuild_.clear();
DCHECK(load_from_file_result);
// Delete the previous table.
DCHECK(mapped_table_memory_.region.IsValid());
mapped_table_memory_ = base::MappedReadOnlyRegion();
// Assign the open file.
DCHECK(!scoped_file_holder_);
DCHECK(load_from_file_result->file.get());
scoped_file_holder_ = std::make_unique<base::ScopedFILE>();
*scoped_file_holder_ = std::move(load_from_file_result->file);
// Assign the loaded table.
DCHECK(load_from_file_result->hash_table_memory.region.IsValid() &&
load_from_file_result->hash_table_memory.mapping.IsValid());
memcpy(salt_, load_from_file_result->salt, LINK_SALT_LENGTH);
mapped_table_memory_ = std::move(load_from_file_result->hash_table_memory);
hash_table_ = GetHashTableFromMapping(mapped_table_memory_.mapping);
table_length_ = load_from_file_result->num_entries;
used_items_ = load_from_file_result->used_count;
#ifndef NDEBUG
DebugValidate();
#endif
// Send an update notification to all child processes.
listener_->NewTable(&mapped_table_memory_.region);
if (!added_since_load_.empty() || !deleted_since_load_.empty()) {
// Resize the table if the table doesn't have enough capacity.
int new_used_items =
used_items_ + static_cast<int>(added_since_load_.size());
if (new_used_items >= table_length_)
ResizeTable(NewTableSizeForCount(new_used_items));
// Also add anything that was added while we were asynchronously
// loading the table.
for (const GURL& url : added_since_load_) {
Fingerprint fingerprint = ComputeURLFingerprint(url.spec(), salt_);
AddFingerprint(fingerprint, false);
}
added_since_load_.clear();
// Now handle deletions.
for (const GURL& url : deleted_since_load_) {
Fingerprint fingerprint = ComputeURLFingerprint(url.spec(), salt_);
DeleteFingerprint(fingerprint, false);
}
deleted_since_load_.clear();
if (persist_to_disk_)
WriteFullTable();
}
// All tabs which was loaded when table was being loaded drop their cached
// visited link hashes and invalidate their links again.
listener_->Reset(true);
}
bool VisitedLinkWriter::InitFromScratch(bool suppress_rebuild) {
if (suppress_rebuild && persist_to_disk_) {
// When we disallow rebuilds (normally just unit tests), just use the
// current empty table.
WriteFullTable();
return true;
}
// This will build the table from history. On the first run, history will
// be empty, so this will be correct. This will also write the new table
// to disk. We don't want to save explicitly here, since the rebuild may
// not complete, leaving us with an empty but valid visited link database.
// In the future, we won't know we need to try rebuilding again.
return RebuildTableFromDelegate();
}
// static
bool VisitedLinkWriter::ReadFileHeader(FILE* file,
int32_t* num_entries,
int32_t* used_count,
uint8_t salt[LINK_SALT_LENGTH]) {
// Get file size.
// Note that there is no need to seek back to the original location in the
// file since ReadFromFile() [which is the next call accessing the file]
// seeks before reading.
if (fseek(file, 0, SEEK_END) == -1)
return false;
size_t file_size = ftell(file);
if (file_size <= kFileHeaderSize)
return false;
uint8_t header[kFileHeaderSize];
if (!ReadFromFile(file, 0, &header, kFileHeaderSize))
return false;
// Verify the signature.
int32_t signature;
memcpy(&signature, &header[kFileHeaderSignatureOffset], sizeof(signature));
if (signature != kFileSignature)
return false;
// Verify the version is up to date. As with other read errors, a version
// mistmatch will trigger a rebuild of the database from history, which will
// have the effect of migrating the database.
int32_t version;
memcpy(&version, &header[kFileHeaderVersionOffset], sizeof(version));
if (version != kFileCurrentVersion)
return false; // Bad version.
// Read the table size and make sure it matches the file size.
memcpy(num_entries, &header[kFileHeaderLengthOffset], sizeof(*num_entries));
if (*num_entries * sizeof(Fingerprint) + kFileHeaderSize != file_size)
return false; // Bad size.
// Read the used item count.
memcpy(used_count, &header[kFileHeaderUsedOffset], sizeof(*used_count));
if (*used_count > *num_entries)
return false; // Bad used item count;
// Read the salt.
memcpy(salt, &header[kFileHeaderSaltOffset], LINK_SALT_LENGTH);
// This file looks OK from the header's perspective.
return true;
}
bool VisitedLinkWriter::GetDatabaseFileName(base::FilePath* filename) {
if (!database_name_override_.empty()) {
// use this filename, the directory must exist
*filename = database_name_override_;
return true;
}
if (!browser_context_ || browser_context_->GetPath().empty())
return false;
base::FilePath profile_dir = browser_context_->GetPath();
*filename = profile_dir.Append(FILE_PATH_LITERAL("Visited Links"));
return true;
}
// Initializes the shared memory structure. The salt should already be filled
// in so that it can be written to the shared memory
bool VisitedLinkWriter::CreateURLTable(int32_t num_entries) {
base::MappedReadOnlyRegion table_memory;
if (!VisitedLinkWriter::fail_table_creation_for_testing_ &&
CreateApartURLTable(num_entries, salt_, &table_memory)) {
mapped_table_memory_ = std::move(table_memory);
hash_table_ = GetHashTableFromMapping(mapped_table_memory_.mapping);
table_length_ = num_entries;
used_items_ = 0;
return true;
}
return false;
}
// static
bool VisitedLinkWriter::CreateApartURLTable(
int32_t num_entries,
const uint8_t salt[LINK_SALT_LENGTH],
base::MappedReadOnlyRegion* memory) {
DCHECK(salt);
DCHECK(memory);
// The table is the size of the table followed by the entries.
uint32_t alloc_size =
num_entries * sizeof(Fingerprint) + sizeof(SharedHeader);
UMA_HISTOGRAM_CUSTOM_COUNTS("History.VisitedLinks.HashTableSizeOnTableCreate",
alloc_size / 1024 / 1024, 1, 10000, 100);
// Create the shared memory object.
*memory = base::ReadOnlySharedMemoryRegion::Create(alloc_size);
if (!memory->IsValid())
return false;
memset(memory->mapping.memory(), 0, alloc_size);
// Save the header for other processes to read.
SharedHeader* header = static_cast<SharedHeader*>(memory->mapping.memory());
header->length = num_entries;
memcpy(header->salt, salt, LINK_SALT_LENGTH);
return true;
}
void VisitedLinkWriter::FreeURLTable() {
mapped_table_memory_ = base::MappedReadOnlyRegion();
if (scoped_file_holder_) {
DCHECK(persist_to_disk_);
// Release the file on the IO thread:
PostIOTask(FROM_HERE,
base::DoNothingWithBoundArgs(std::move(scoped_file_holder_)));
}
}
bool VisitedLinkWriter::ResizeTableIfNecessary() {
DCHECK(table_length_ > 0) << "Must have a table";
// Load limits for good performance/space. We are pretty conservative about
// keeping the table not very full. This is because we use linear probing
// which increases the likelihood of clumps of entries which will reduce
// performance.
const float max_table_load = 0.5f; // Grow when we're > this full.
const float min_table_load = 0.2f; // Shrink when we're < this full.
float load = ComputeTableLoad();
if (load < max_table_load &&
(table_length_ <= static_cast<float>(kDefaultTableSize) ||
load > min_table_load))
return false;
// Table needs to grow or shrink.
int new_size = NewTableSizeForCount(used_items_);
DCHECK(new_size > used_items_);
DCHECK(load <= min_table_load || new_size > table_length_);
ResizeTable(new_size);
return true;
}
void VisitedLinkWriter::ResizeTable(int32_t new_size) {
DCHECK(mapped_table_memory_.region.IsValid() &&
mapped_table_memory_.mapping.IsValid());
#ifndef NDEBUG
DebugValidate();
#endif
auto old_hash_table_mapping = std::move(mapped_table_memory_.mapping);
int32_t old_table_length = table_length_;
if (!CreateURLTable(new_size)) {
// Restore modified members.
mapped_table_memory_.mapping = std::move(old_hash_table_mapping);
return;
}
shared_memory_serial_++;
{
Fingerprint* old_hash_table =
GetHashTableFromMapping(old_hash_table_mapping);
// Now we have two tables, our local copy which is the old one, and the new
// one loaded into this object where we need to copy the data.
for (int32_t i = 0; i < old_table_length; i++) {
Fingerprint cur = old_hash_table[i];
if (cur)
AddFingerprint(cur, false);
}
}
// Send an update notification to all child processes so they read the new
// table.
listener_->NewTable(&mapped_table_memory_.region);
#ifndef NDEBUG
DebugValidate();
#endif
// The new table needs to be written to disk.
if (persist_to_disk_)
WriteFullTable();
}
uint32_t VisitedLinkWriter::DefaultTableSize() const {
if (table_size_override_)
return table_size_override_;
return kDefaultTableSize;
}
uint32_t VisitedLinkWriter::NewTableSizeForCount(int32_t item_count) const {
// These table sizes are selected to be the maximum prime number less than
// a "convenient" multiple of 1K.
static const auto table_sizes = std::to_array<int>({
16381, // 16K = 16384 <- don't shrink below this table size
// (should be == default_table_size)
32767, // 32K = 32768
65521, // 64K = 65536
130051, // 128K = 131072
262127, // 256K = 262144
524269, // 512K = 524288
1048549, // 1M = 1048576
2097143, // 2M = 2097152
4194301, // 4M = 4194304
8388571, // 8M = 8388608
16777199, // 16M = 16777216
33554347,
}); // 32M = 33554432
// Try to leave the table 33% full.
int desired = item_count * 3;
// Find the closest prime.
for (size_t i = 0; i < std::size(table_sizes); i++) {
if (table_sizes[i] > desired)
return table_sizes[i];
}
// Growing very big, just approximate a "good" number, not growing as much
// as normal.
return item_count * 2 - 1;
}
// See the TableBuilder definition in the header file for how this works.
bool VisitedLinkWriter::RebuildTableFromDelegate() {
DCHECK(!table_builder_);
// TODO(brettw) make sure we have reasonable salt!
table_builder_ = new TableBuilder(this, salt_);
delegate_->RebuildTable(table_builder_);
return true;
}
// See the TableBuilder declaration above for how this works.
void VisitedLinkWriter::OnTableRebuildComplete(
bool success,
const std::vector<Fingerprint>& fingerprints) {
if (success) {
// Replace the old table with a new blank one.
shared_memory_serial_++;
int new_table_size = NewTableSizeForCount(
static_cast<int>(fingerprints.size() + added_since_rebuild_.size()));
if (CreateURLTable(new_table_size)) {
// Add the stored fingerprints to the hash table.
for (const auto& fingerprint : fingerprints)
AddFingerprint(fingerprint, false);
// Also add anything that was added while we were asynchronously
// generating the new table.
for (const auto& fingerprint : added_since_rebuild_)
AddFingerprint(fingerprint, false);
added_since_rebuild_.clear();
// Now handle deletions. Do not shrink the table now, we'll shrink it when
// adding or deleting an url the next time.
for (const auto& fingerprint : deleted_since_rebuild_)
DeleteFingerprint(fingerprint, false);
deleted_since_rebuild_.clear();
// Send an update notification to all child processes.
listener_->NewTable(&mapped_table_memory_.region);
// All tabs which was loaded when table was being rebuilt
// invalidate their links again.
listener_->Reset(false);
if (persist_to_disk_)
WriteFullTable();
}
}
table_builder_ = nullptr; // Will release our reference to the builder.
// Notify the unit test that the rebuild is complete (will be NULL in prod.)
if (!rebuild_complete_task_.is_null())
std::move(rebuild_complete_task_).Run();
}
void VisitedLinkWriter::WriteToFile(base::ScopedFILE* file,
off_t offset,
void* data,
int32_t data_size) {
DCHECK(file);
DCHECK(persist_to_disk_);
DCHECK(!table_is_loading_from_file_);
PostIOTask(
FROM_HERE,
base::BindOnce(&AsyncWrite, file, offset,
std::string(static_cast<const char*>(data), data_size)));
}
void VisitedLinkWriter::WriteUsedItemCountToFile() {
DCHECK(persist_to_disk_);
if (!scoped_file_holder_) {
return; // See comment on the scoped_file_holder_ variable for why this
// might happen.
}
WriteToFile(scoped_file_holder_.get(), kFileHeaderUsedOffset, &used_items_,
sizeof(used_items_));
}
void VisitedLinkWriter::WriteHashRangeToFile(Hash first_hash, Hash last_hash) {
DCHECK(persist_to_disk_);
if (!scoped_file_holder_) {
return; // See comment on the scoped_file_holder_ variable for why this
// might happen.
}
if (last_hash < first_hash) {
// Handle wraparound at 0. This first write is first_hash->EOF
WriteToFile(scoped_file_holder_.get(),
first_hash * sizeof(Fingerprint) + kFileHeaderSize,
&hash_table_[first_hash],
(table_length_ - first_hash) * sizeof(Fingerprint));
// Now do 0->last_lash.
WriteToFile(scoped_file_holder_.get(), kFileHeaderSize, hash_table_,
(last_hash + 1) * sizeof(Fingerprint));
} else {
// Normal case, just write the range.
WriteToFile(scoped_file_holder_.get(),
first_hash * sizeof(Fingerprint) + kFileHeaderSize,
&hash_table_[first_hash],
(last_hash - first_hash + 1) * sizeof(Fingerprint));
}
}
// static
bool VisitedLinkWriter::ReadFromFile(FILE* file,
off_t offset,
void* data,
size_t data_size) {
if (fseek(file, offset, SEEK_SET) != 0)
return false;
size_t num_read = fread(data, 1, data_size, file);
return num_read == data_size;
}
// VisitedLinkTableBuilder ----------------------------------------------------
VisitedLinkWriter::TableBuilder::TableBuilder(
VisitedLinkWriter* writer,
const uint8_t salt[LINK_SALT_LENGTH])
: writer_(writer), success_(true) {
fingerprints_.reserve(4096);
memcpy(salt_, salt, LINK_SALT_LENGTH * sizeof(uint8_t));
}
// TODO(brettw): Do we want to try to cancel the request if this happens? It
// could delay shutdown if there are a lot of URLs.
void VisitedLinkWriter::TableBuilder::DisownWriter() {
writer_ = nullptr;
}
void VisitedLinkWriter::TableBuilder::OnURL(const GURL& url) {
if (!url.is_empty()) {
fingerprints_.push_back(
VisitedLinkWriter::ComputeURLFingerprint(url.spec(), salt_));
}
}
void VisitedLinkWriter::TableBuilder::OnComplete(bool success) {
success_ = success;
DLOG_IF(WARNING, !success) << "Unable to rebuild visited links";
// Marshal to the main thread to notify the VisitedLinkWriter that the
// rebuild is complete.
content::GetUIThreadTaskRunner({})->PostTask(
FROM_HERE, base::BindOnce(&TableBuilder::OnCompleteMainThread, this));
}
void VisitedLinkWriter::TableBuilder::OnCompleteMainThread() {
if (writer_)
writer_->OnTableRebuildComplete(success_, fingerprints_);
}
// static
VisitedLinkCommon::Fingerprint* VisitedLinkWriter::GetHashTableFromMapping(
base::WritableSharedMemoryMapping& hash_table_mapping) {
DCHECK(hash_table_mapping.IsValid());
// Our table pointer is just the data immediately following the header.
return reinterpret_cast<Fingerprint*>(
static_cast<char*>(hash_table_mapping.memory()) + sizeof(SharedHeader));
}
} // namespace visitedlink
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