Add mojo interface to load hyphenation dictionaries on Android

content/browser/hyphenation/hyphenation_impl.cc

+// Copyright 2016 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 "content/browser/hyphenation/hyphenation_impl.h"
+
+#include <algorithm>
+#include <map>
+#include <utility>
+
+#include "base/files/file.h"
+#include "base/files/file_path.h"
+#include "base/strings/stringprintf.h"
+#include "mojo/public/cpp/system/platform_handle.h"
+
+namespace {
+
+using DictionaryFileMap = std::unordered_map<std::string, base::File>;
+
+static bool IsValidLocale(const std::string& locale) {
+  return std::all_of(locale.cbegin(), locale.cend(),
+                     [](const char ch) { return isalpha(ch) || ch == '-'; });
+}
+
+static base::File& GetDictionaryFile(const std::string& locale) {
+  // Keep Files open in the cache for subsequent calls.
+  CR_DEFINE_STATIC_LOCAL(DictionaryFileMap, cache, ());
+
+  // TODO(kojii): Replace find+insert with emplace()+std::piecewise_construct
+  // when std::map::emplace() is fully supported on all configurations.

[dcheng, 2016/07/13 02:56:28]

FWIW, the C++ style owners don't really like piecewise_construct for readability
reasons:
https://groups.google.com/a/chromium.org/d/msg/cxx/nCdjQqnouO4/l4mbaQiXEQAJ

[kojii, 2016/07/13 05:02:28]

Oh, thanks for the info. Removed the TODO. I originally used it in PS1, only to
figure out it fails on some compiler.

+  const auto& it = cache.find(locale);
+  if (it != cache.end())
+    return it->second;
+  base::File file_on_stack;
+  const auto& inserted = cache.insert(
+      std::make_pair(locale, std::move(file_on_stack)));

[dcheng, 2016/07/13 02:56:29]

Slightly shorter to write:
const auto& inserted = cache.insert(std::make_pair(locale, base::File()))

since we don't use |file_on_stack| after this anyway.

[kojii, 2016/07/13 05:02:29]

Thought some compiler complained, but it looks like it was my misunderstanding,
done.

+  base::File& file = inserted.first->second;
+  DCHECK(!file.IsValid());
+
+#if defined(OS_ANDROID)
+  base::FilePath dir("/system/usr/hyphen-data");
+#else
+#error "This configuration is not supported."
+#endif
+  std::string filename = base::StringPrintf("hyph-%s.hyb", locale.c_str());
+  base::FilePath path = dir.AppendASCII(filename);
+  file.Initialize(path, base::File::FLAG_OPEN | base::File::FLAG_READ);
+  return file;
+}
+
+}  // namespace
+
+namespace hyphenation {
+
+HyphenationImpl::HyphenationImpl(blink::mojom::HyphenationRequest request)
+    : binding_(this, std::move(request)) {}
+
+HyphenationImpl::~HyphenationImpl() {}
+
+// static
+void HyphenationImpl::Create(blink::mojom::HyphenationRequest request) {
+  new HyphenationImpl(std::move(request));
+}
+
+void HyphenationImpl::OpenDictionary(const mojo::String& locale,
+                                     const OpenDictionaryCallback& callback) {
+  mojo::ScopedHandle handle;
+  if (IsValidLocale(locale)) {
+    base::File& file = GetDictionaryFile(locale);
+    if (file.IsValid())
+      handle = mojo::WrapPlatformFile(file.Duplicate().TakePlatformFile());
+  }
+  callback.Run(std::move(handle));
+}
+
+}  // namespace hyphenation