content/browser/font_access/font_enumeration_cache.h

// 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.

#ifndef CONTENT_BROWSER_FONT_ACCESS_FONT_ENUMERATION_CACHE_H_
#define CONTENT_BROWSER_FONT_ACCESS_FONT_ENUMERATION_CACHE_H_

#include <memory>
#include <optional>
#include <string>

#include "base/memory/read_only_shared_memory_region.h"
#include "base/memory/scoped_refptr.h"
#include "base/sequence_checker.h"
#include "base/synchronization/atomic_flag.h"
#include "base/task/deferred_sequenced_task_runner.h"
#include "base/task/sequenced_task_runner.h"
#include "base/thread_annotations.h"
#include "base/threading/sequence_bound.h"
#include "base/types/pass_key.h"
#include "content/common/content_export.h"
#include "third_party/blink/public/common/font_access/font_enumeration_table.pb.h"
#include "third_party/blink/public/mojom/font_access/font_access.mojom.h"

namespace content {

class FontEnumerationDataSource;

struct CONTENT_EXPORT FontEnumerationData {
  blink::mojom::FontEnumerationStatus status;

  // Stores a serialized blink::FontEnumerationTable proto.
  //
  // Valid iff `status` is kOk.
  base::ReadOnlySharedMemoryRegion font_data;
};

// Caches font enumeration data, and serves it as a ReadOnlySharedMemoryRegion.
//
// This class is not thread-safe. Each instance must be accessed from a single
// sequence, which must allow blocking.
class CONTENT_EXPORT FontEnumerationCache {
 public:
  // Factory method for production instances.
  static base::SequenceBound<FontEnumerationCache> Create();

  // Factory method with dependency injection support for testing.
  //
  // `task_runner` must allow blocking.
  static base::SequenceBound<FontEnumerationCache> CreateForTesting(
      scoped_refptr<base::SequencedTaskRunner> task_runner,
      std::unique_ptr<FontEnumerationDataSource> data_source,
      std::optional<std::string> locale_override);

  // Exposed for base::SequenceBound. Instances must be obtained from one of
  // the Create*() factory methods.
  FontEnumerationCache(std::unique_ptr<FontEnumerationDataSource> data_source,
                       std::optional<std::string> locale_override,
                       base::PassKey<FontEnumerationCache>);

  FontEnumerationCache(const FontEnumerationCache&) = delete;
  FontEnumerationCache& operator=(const FontEnumerationCache&) = delete;
  ~FontEnumerationCache();

  FontEnumerationData GetFontEnumerationData();

 private:
  // Build the cache given a properly formed enumeration cache table.
  void BuildEnumerationCache(blink::FontEnumerationTable& table);

  SEQUENCE_CHECKER(sequence_checker_);

  // Guaranteed to be non-null.
  const std::unique_ptr<FontEnumerationDataSource> data_source_
      GUARDED_BY_CONTEXT(sequence_checker_);

  // nullopt in production. Only set in testing.
  const std::optional<std::string> locale_override_;

  bool initialized_ GUARDED_BY_CONTEXT(sequence_checker_) = false;

  // Valid only if `initialized_` is true.
  FontEnumerationData data_ GUARDED_BY_CONTEXT(sequence_checker_);
};

}  // namespace content

#endif  // CONTENT_BROWSER_FONT_ACCESS_FONT_ENUMERATION_CACHE_H_