components/previews/content/hint_cache.cc

// Copyright 2018 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/previews/content/hint_cache.h"

#include <algorithm>

#include "base/bind.h"
#include "url/gurl.h"

namespace previews {

namespace {

// Realistic minimum length of a host suffix.
const int kMinHostSuffix = 6;  // eg., abc.tv

// The default number of hints retained within the memory cache. When the limit
// is exceeded, the least recently used hint is purged from the cache.
const size_t kDefaultMaxMemoryCacheHints = 20;

}  // namespace

HintCache::HintCache(
    std::unique_ptr<HintCacheStore> hint_store,
    base::Optional<int> max_memory_cache_hints /*= base::Optional<int>()*/)
    : hint_store_(std::move(hint_store)),
      memory_cache_(
          std::max(max_memory_cache_hints.value_or(kDefaultMaxMemoryCacheHints),
                   1)) {
  DCHECK(hint_store_);
}

HintCache::~HintCache() = default;

void HintCache::Initialize(bool purge_existing_data,
                           base::OnceClosure callback) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  hint_store_->Initialize(
      purge_existing_data,
      base::BindOnce(&HintCache::OnStoreInitialized, base::Unretained(this),
                     std::move(callback)));
}

std::unique_ptr<HintCacheStore::ComponentUpdateData>
HintCache::MaybeCreateComponentUpdateData(const base::Version& version) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return hint_store_->MaybeCreateComponentUpdateData(version);
}

void HintCache::UpdateComponentData(
    std::unique_ptr<HintCacheStore::ComponentUpdateData> component_data,
    base::OnceClosure callback) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(component_data);

  // Clear the memory cache prior to updating the store with the new component
  // data.
  memory_cache_.Clear();

  hint_store_->UpdateComponentData(std::move(component_data),
                                   std::move(callback));
}

bool HintCache::HasHint(const std::string& host) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  HintCacheStore::EntryKey hint_entry_key;
  return FindHintEntryKey(host, &hint_entry_key);
}

void HintCache::LoadHint(const std::string& host, HintLoadedCallback callback) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  HintCacheStore::EntryKey hint_entry_key;
  if (!FindHintEntryKey(host, &hint_entry_key)) {
    std::move(callback).Run(nullptr);
    return;
  }

  // Search for the entry key in the memory cache; if it is not already there,
  // then asynchronously load it from the store and return.
  auto hint_it = memory_cache_.Get(hint_entry_key);
  if (hint_it == memory_cache_.end()) {
    hint_store_->LoadHint(
        hint_entry_key,
        base::BindOnce(&HintCache::OnLoadStoreHint, base::Unretained(this),
                       std::move(callback)));
    return;
  }

  // Run the callback with the hint from the memory cache.
  std::move(callback).Run(hint_it->second.get());
}

const optimization_guide::proto::Hint* HintCache::GetHintIfLoaded(
    const std::string& host) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  // Try to retrieve the hint entry key for the host. If no hint exists for the
  // host, then simply return.
  HintCacheStore::EntryKey hint_entry_key;
  if (!FindHintEntryKey(host, &hint_entry_key)) {
    return nullptr;
  }

  // Find the hint within the memory cache. It will only be available here if
  // it has been loaded recently enough to be retained within the MRU cache.
  auto hint_it = memory_cache_.Get(hint_entry_key);
  if (hint_it != memory_cache_.end()) {
    return hint_it->second.get();
  }

  return nullptr;
}

void HintCache::OnStoreInitialized(base::OnceClosure callback) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  std::move(callback).Run();
}

void HintCache::OnLoadStoreHint(
    HintLoadedCallback callback,
    const HintCacheStore::EntryKey& hint_entry_key,
    std::unique_ptr<optimization_guide::proto::Hint> hint) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (!hint) {
    std::move(callback).Run(nullptr);
    return;
  }

  // Check if the hint was cached in memory after the load was requested from
  // the store. This can occur if multiple loads for the same entry key occur
  // consecutively prior to any returning.
  auto hint_it = memory_cache_.Get(hint_entry_key);
  if (hint_it == memory_cache_.end()) {
    hint_it = memory_cache_.Put(hint_entry_key, std::move(hint));
  }

  std::move(callback).Run(hint_it->second.get());
}

bool HintCache::FindHintEntryKey(
    const std::string& host,
    HintCacheStore::EntryKey* out_hint_entry_key) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(out_hint_entry_key);

  // Look for longest host name suffix that has a hint. No need to continue
  // lookups and substring work once get to a root domain like ".com" or
  // ".co.in" (MinHostSuffix length check is a heuristic for that).
  std::string host_suffix(host);
  while (host_suffix.length() >= kMinHostSuffix) {
    // Attempt to find a hint entry key associated with the current host suffix
    // within the store.
    if (hint_store_->FindHintEntryKey(host_suffix, out_hint_entry_key)) {
      return true;
    }

    size_t pos = host_suffix.find_first_of('.');
    if (pos == std::string::npos) {
      break;
    }
    host_suffix = host_suffix.substr(pos + 1);
  }
  return false;
}

}  // namespace previews