chromeos/printing/printer_config_cache.cc - chromium/src.git - Git at Google

 // Copyright 2020 The Chromium Authors
 // 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 <optional>
 #include <string_view>
 #include <utility>
 #include <vector>

 #include "base/containers/queue.h"
 #include "base/functional/callback.h"
 #include "base/location.h"
 #include "base/memory/raw_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/sequence_checker.h"
 #include "base/strings/strcat.h"
 #include "base/task/sequenced_task_runner.h"
 #include "base/time/clock.h"
 #include "base/time/time.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
 #include "services/network/public/cpp/resource_request.h"
 #include "services/network/public/cpp/simple_url_loader.h"
 #include "url/gurl.h"

 namespace chromeos {

 namespace {

 // Defines the serving root in which all PPDs and PPD metadata reside.
 constexpr char kServingRoot[] =
     "https://printerconfigurations.googleusercontent.com/"
     "chromeos_printing/";
 constexpr char kLocalhostRoot[] = "http://localhost:7002/";

 // Prepends the serving root to |name|, returning the result.
 std::string PrependServingRoot(const std::string& name,
                                bool use_localhost_as_root) {
   if (use_localhost_as_root) {
     return base::StrCat({kLocalhostRoot, name});
   }
   return base::StrCat({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,
     bool use_localhost_as_root) {
   GURL full_url(PrependServingRoot(path, use_localhost_as_root));
   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(),
                                          base::Time()};
 }

 // 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 {
  public:
   explicit PrinterConfigCacheImpl(
       const base::Clock* clock,
       base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
           loader_factory_dispenser,
       bool use_localhost_as_root)
       : clock_(clock),
         loader_factory_dispenser_(std::move(loader_factory_dispenser)),
         use_localhost_as_root_(use_localhost_as_root),
         weak_factory_(this) {}

   ~PrinterConfigCacheImpl() override {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   }

   void Fetch(const std::string& key,
              base::TimeDelta expiration,
              FetchCallback cb) override {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

     // 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()) {
         base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
             FROM_HERE, base::BindOnce(std::move(cb), FetchResult::Success(
                                                          key, entry.contents,
                                                          entry.time_of_fetch)));
         return;
       }
     }

     // 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));
     fetch_queue_.push(std::move(context));
     TryToStartNetworkedFetch();
   }

   void Drop(const std::string& key) override {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
     cache_.erase(key);
   }

  private:
   // 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()) {
       return;
     }

     std::unique_ptr<FetchContext> context = std::move(fetch_queue_.front());
     fetch_queue_.pop();
     auto request = FormRequest(context->key, use_localhost_as_root_);

     // Create traffic annotation tag.
     net::NetworkTrafficAnnotationTag traffic_annotation =
         net::DefineNetworkTrafficAnnotation("printer_config_fetch", R"(
           semantics {
             sender: "Printer Configuration"
             description:
               "This component sends requests to the Chrome OS Printing "
               "serving root during printer configuration. This can return "
               "two pieces of information, depending on the request: "
               "PostScript Printer Description (PPD) files for a specified "
               "printer, and PPD file metadata to help locate the desired PPD "
               "file."
             trigger: "On printer setup in ChromeOS."
             data: "Printer names (comprising of make and/or model)."
             user_data: {
               type: OTHER
             }
             destination: GOOGLE_OWNED_SERVICE
             internal: {
               contacts: {
                 email: "bmgordon@google.com"
               }
             }
             last_reviewed: "2023-01-18"
           }
           policy {
             cookies_allowed: NO
             setting:
               "Admins must disable access to both enterprise and "
               "non-enterprise printers. Enterprise printers should be left "
               "empty under 'Devices > Chrome > Printers'. Non-enterprise "
               "printers can be disabled under 'Devices > Chrome > Settings > "
               "Printer management' by setting to: 'Do not allow users to add "
               "new printers'."
             chrome_policy {
               UserPrintersAllowed {
                 UserPrintersAllowed: false
               }
               PrintersBulkConfiguration: {
                 PrintersBulkConfiguration: ""
               }
             }
             chrome_device_policy {
               # DevicePrinters
               device_printers: {
                 external_policy: ""
               }
             }
           })");
     fetcher_ = network::SimpleURLLoader::Create(std::move(request),
                                                 traffic_annotation);

     fetcher_->DownloadToString(
         loader_factory_dispenser_.Run(),
         base::BindOnce(&PrinterConfigCacheImpl::FinishNetworkedFetch,
                        weak_factory_.GetWeakPtr(), std::move(context)),
         network::SimpleURLLoader::kMaxBoundedStringDownloadSize);
   }

   // 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.
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

     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);
       base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
           FROM_HERE, base::BindOnce(std::move(context->cb),
                                     FetchResult::Success(
                                         context->key, newly_inserted.contents,
                                         newly_inserted.time_of_fetch)));
     } else {
       base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
           FROM_HERE, base::BindOnce(std::move(context->cb),
                                     FetchResult::Failure(context->key)));
     }

     fetcher_.reset();
     TryToStartNetworkedFetch();
   }

   // 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.
   raw_ptr<const base::Clock> clock_;

   // Dispenses fresh URLLoaderFactory instances; see header comment
   // on Create().
   base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
       loader_factory_dispenser_;

   // 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_;

   // Determines the address of the server.
   const bool use_localhost_as_root_;

   SEQUENCE_CHECKER(sequence_checker_);

   // 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,
     base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
         loader_factory_dispenser,
     bool use_localhost_as_root) {
   return std::make_unique<PrinterConfigCacheImpl>(
       clock, std::move(loader_factory_dispenser), use_localhost_as_root);
 }

 }  // namespace chromeos
	// Copyright 2020 The Chromium Authors
	// 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 <optional>
	#include <string_view>
	#include <utility>
	#include <vector>

	#include "base/containers/queue.h"
	#include "base/functional/callback.h"
	#include "base/location.h"
	#include "base/memory/raw_ptr.h"
	#include "base/memory/weak_ptr.h"
	#include "base/sequence_checker.h"
	#include "base/strings/strcat.h"
	#include "base/task/sequenced_task_runner.h"
	#include "base/time/clock.h"
	#include "base/time/time.h"
	#include "net/base/load_flags.h"
	#include "net/base/net_errors.h"
	#include "services/network/public/cpp/resource_request.h"
	#include "services/network/public/cpp/simple_url_loader.h"
	#include "url/gurl.h"

	namespace chromeos {

	namespace {

	// Defines the serving root in which all PPDs and PPD metadata reside.
	constexpr char kServingRoot[] =
	"https://printerconfigurations.googleusercontent.com/"
	"chromeos_printing/";
	constexpr char kLocalhostRoot[] = "http://localhost:7002/";

	// Prepends the serving root to \|name\|, returning the result.
	std::string PrependServingRoot(const std::string& name,
	bool use_localhost_as_root) {
	if (use_localhost_as_root) {
	return base::StrCat({kLocalhostRoot, name});
	}
	return base::StrCat({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,
	bool use_localhost_as_root) {
	GURL full_url(PrependServingRoot(path, use_localhost_as_root));
	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(),
	base::Time()};
	}

	// 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 {
	public:
	explicit PrinterConfigCacheImpl(
	const base::Clock* clock,
	base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
	loader_factory_dispenser,
	bool use_localhost_as_root)
	: clock_(clock),
	loader_factory_dispenser_(std::move(loader_factory_dispenser)),
	use_localhost_as_root_(use_localhost_as_root),
	weak_factory_(this) {}

	~PrinterConfigCacheImpl() override {
	DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
	}

	void Fetch(const std::string& key,
	base::TimeDelta expiration,
	FetchCallback cb) override {
	DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

	// 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()) {
	base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
	FROM_HERE, base::BindOnce(std::move(cb), FetchResult::Success(
	key, entry.contents,
	entry.time_of_fetch)));
	return;
	}
	}

	// 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));
	fetch_queue_.push(std::move(context));
	TryToStartNetworkedFetch();
	}

	void Drop(const std::string& key) override {
	DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
	cache_.erase(key);
	}

	private:
	// 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()) {
	return;
	}

	std::unique_ptr<FetchContext> context = std::move(fetch_queue_.front());
	fetch_queue_.pop();
	auto request = FormRequest(context->key, use_localhost_as_root_);

	// Create traffic annotation tag.
	net::NetworkTrafficAnnotationTag traffic_annotation =
	net::DefineNetworkTrafficAnnotation("printer_config_fetch", R"(
	semantics {
	sender: "Printer Configuration"
	description:
	"This component sends requests to the Chrome OS Printing "
	"serving root during printer configuration. This can return "
	"two pieces of information, depending on the request: "
	"PostScript Printer Description (PPD) files for a specified "
	"printer, and PPD file metadata to help locate the desired PPD "
	"file."
	trigger: "On printer setup in ChromeOS."
	data: "Printer names (comprising of make and/or model)."
	user_data: {
	type: OTHER
	}
	destination: GOOGLE_OWNED_SERVICE
	internal: {
	contacts: {
	email: "bmgordon@google.com"
	}
	}
	last_reviewed: "2023-01-18"
	}
	policy {
	cookies_allowed: NO
	setting:
	"Admins must disable access to both enterprise and "
	"non-enterprise printers. Enterprise printers should be left "
	"empty under 'Devices > Chrome > Printers'. Non-enterprise "
	"printers can be disabled under 'Devices > Chrome > Settings > "
	"Printer management' by setting to: 'Do not allow users to add "
	"new printers'."
	chrome_policy {
	UserPrintersAllowed {
	UserPrintersAllowed: false
	}
	PrintersBulkConfiguration: {
	PrintersBulkConfiguration: ""
	}
	}
	chrome_device_policy {
	# DevicePrinters
	device_printers: {
	external_policy: ""
	}
	}
	})");
	fetcher_ = network::SimpleURLLoader::Create(std::move(request),
	traffic_annotation);

	fetcher_->DownloadToString(
	loader_factory_dispenser_.Run(),
	base::BindOnce(&PrinterConfigCacheImpl::FinishNetworkedFetch,
	weak_factory_.GetWeakPtr(), std::move(context)),
	network::SimpleURLLoader::kMaxBoundedStringDownloadSize);
	}

	// 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.
	DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

	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);
	base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
	FROM_HERE, base::BindOnce(std::move(context->cb),
	FetchResult::Success(
	context->key, newly_inserted.contents,
	newly_inserted.time_of_fetch)));
	} else {
	base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
	FROM_HERE, base::BindOnce(std::move(context->cb),
	FetchResult::Failure(context->key)));
	}

	fetcher_.reset();
	TryToStartNetworkedFetch();
	}

	// 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.
	raw_ptr<const base::Clock> clock_;

	// Dispenses fresh URLLoaderFactory instances; see header comment
	// on Create().
	base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
	loader_factory_dispenser_;

	// 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_;

	// Determines the address of the server.
	const bool use_localhost_as_root_;

	SEQUENCE_CHECKER(sequence_checker_);

	// 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,
	base::RepeatingCallback<network::mojom::URLLoaderFactory*()>
	loader_factory_dispenser,
	bool use_localhost_as_root) {
	return std::make_unique<PrinterConfigCacheImpl>(
	clock, std::move(loader_factory_dispenser), use_localhost_as_root);
	}

	} // namespace chromeos