blob: 06bb6a101b4a4ecf1118dc14f431aecbad344500 [file] [log] [blame]
// Copyright 2020 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 "chromeos/printing/printer_config_cache.h"
#include <memory>
#include <utility>
#include <vector>
#include "base/location.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "base/strings/strcat.h"
#include "base/strings/string_piece.h"
#include "base/task/post_task.h"
#include "base/time/clock.h"
#include "base/time/time.h"
#include "net/base/load_flags.h"
#include "net/base/net_errors.h"
#include "url/gurl.h"
namespace chromeos {
namespace {
// Defines the serving root in which all PPDs and PPD metadata reside.
const char kServingRoot[] =
// Prepends the serving root to |name|, returning the result.
std::string PrependServingRoot(const std::string& name) {
return base::StrCat({base::StringPiece(kServingRoot), name});
// Accepts a relative |path| to a value in the Chrome OS Printing
// serving root) and returns a resource request to satisfy the same.
std::unique_ptr<network::ResourceRequest> FormRequest(const std::string& path) {
GURL full_url(PrependServingRoot(path));
if (!full_url.is_valid()) {
return nullptr;
auto request = std::make_unique<network::ResourceRequest>();
request->url = full_url;
request->load_flags = net::LOAD_BYPASS_CACHE | net::LOAD_DISABLE_CACHE;
request->credentials_mode = network::mojom::CredentialsMode::kOmit;
return request;
} // namespace
// In case of fetch failure, only the key is meaningful feedback.
// static
PrinterConfigCache::FetchResult PrinterConfigCache::FetchResult::Failure(
const std::string& key) {
return PrinterConfigCache::FetchResult{false, key, std::string(),
// static
PrinterConfigCache::FetchResult PrinterConfigCache::FetchResult::Success(
const std::string& key,
const std::string& contents,
base::Time time_of_fetch) {
return PrinterConfigCache::FetchResult{true, key, contents, time_of_fetch};
class PrinterConfigCacheImpl : public PrinterConfigCache {
explicit PrinterConfigCacheImpl(
const base::Clock* clock,
network::mojom::URLLoaderFactory* loader_factory)
: clock_(clock), loader_factory_(loader_factory), weak_factory_(this) {}
~PrinterConfigCacheImpl() override {
void Fetch(const std::string& key,
base::TimeDelta expiration,
FetchCallback cb) override {
// Try to answer this fetch request locally.
const auto& finding = cache_.find(key);
if (finding != cache_.end()) {
const Entry& entry = finding->second;
if (entry.time_of_fetch + expiration > clock_->Now()) {
FetchResult::Success(key, entry.contents, entry.time_of_fetch));
// We couldn't answer this request locally. Issue a networked fetch
// and defer the answer to when we hear back.
auto context = std::make_unique<FetchContext>(key, std::move(cb));
void Drop(const std::string& key) override {
// A FetchContext saves off the key and the FetchCallback that a
// caller passes to PrinterConfigCacheImpl::Fetch().
struct FetchContext {
const std::string key;
PrinterConfigCache::FetchCallback cb;
FetchContext(const std::string& arg_key,
PrinterConfigCache::FetchCallback arg_cb)
: key(arg_key), cb(std::move(arg_cb)) {}
~FetchContext() = default;
// If a PrinterConfigCache maps keys to values, then Entry structs
// represent values.
struct Entry {
std::string contents;
base::Time time_of_fetch;
Entry(const std::string& arg_contents, base::Time time)
: contents(arg_contents), time_of_fetch(time) {}
~Entry() = default;
void TryToStartNetworkedFetch() {
// Either
// 1. a networked fetch is already in flight or
// 2. there are no more pending networked fetches to act upon.
// In either case, we can't do anything at the moment; back off
// and let a future call to Fetch() or FinishNetworkedFetch()
// return here to try again.
if (fetcher_ || fetch_queue_.empty()) {
std::unique_ptr<FetchContext> context = std::move(fetch_queue_.front());
auto request = FormRequest(context->key);
// TODO( add traffic annotation.
fetcher_ = network::SimpleURLLoader::Create(std::move(request),
weak_factory_.GetWeakPtr(), std::move(context)),
// Called by |fetcher_| once DownloadToString() completes.
void FinishNetworkedFetch(std::unique_ptr<FetchContext> context,
std::unique_ptr<std::string> contents) {
// Wherever |fetcher_| works its sorcery, it had better have posted
// back onto _our_ sequence.
if (fetcher_->NetError() == net::Error::OK) {
// We only want to update our local cache if the |fetcher_|
// succeeded; otherwise, prefer to either retain the stale entry
// (if extant) or retain no entry at all (if not).
const Entry newly_inserted = Entry(*contents, clock_->Now());
cache_.insert_or_assign(context->key, newly_inserted);
.Run(FetchResult::Success(context->key, newly_inserted.contents,
} else {
// The heart of an PrinterConfigCache: the local cache itself.
base::flat_map<std::string, Entry> cache_;
// Enqueues networked requests.
base::queue<std::unique_ptr<FetchContext>> fetch_queue_;
// Dispenses Time objects to mark time of fetch on Entry instances.
const base::Clock* clock_;
// Mutably borrowed from caller at construct-time.
network::mojom::URLLoaderFactory* loader_factory_;
// Talks to the networked service to fetch resources.
// Because this class is sequenced, a non-nullptr value here (observed
// on-sequence) denotes an ongoing fetch. See the
// TryToStartNetworkedFetch() and FinishNetworkedFetch() methods.
std::unique_ptr<network::SimpleURLLoader> fetcher_;
// Dispenses weak pointers to our |fetcher_|. This is necessary
// because |this| could be deleted while the loader is in flight
// off-sequence.
base::WeakPtrFactory<PrinterConfigCacheImpl> weak_factory_;
// static
std::unique_ptr<PrinterConfigCache> PrinterConfigCache::Create(
const base::Clock* clock,
network::mojom::URLLoaderFactory* loader_factory) {
return std::make_unique<PrinterConfigCacheImpl>(clock, loader_factory);
} // namespace chromeos