Modularize Compact Language Detector 2 (CLD2) data sources

components/translate/content/browser/data_file_browser_cld_data_provider.cc

Index: components/translate/content/browser/data_file_browser_cld_data_provider.cc
diff --git a/components/translate/content/browser/data_file_browser_cld_data_provider.cc b/components/translate/content/browser/data_file_browser_cld_data_provider.cc
new file mode 100644
index 0000000000000000000000000000000000000000..97764aa40ab09e2234055bf45ecf0d48140d8bef
--- /dev/null
+++ b/components/translate/content/browser/data_file_browser_cld_data_provider.cc
@@ -0,0 +1,224 @@
+// Copyright 2014 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 "data_file_browser_cld_data_provider.h"
+
+#include "base/basictypes.h"
+#include "base/files/file.h"
+#include "base/files/file_path.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/memory/weak_ptr.h"
+#include "base/path_service.h"
+#include "base/synchronization/lock.h"
+#include "base/task_runner.h"
+#include "components/translate/content/common/data_file_cld_data_provider_messages.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/render_view_host.h"
+#include "ipc/ipc_message.h"
+#include "ipc/ipc_message_macros.h"
+#include "ipc/ipc_platform_file.h"
+
+namespace {
+// The data file,  cached as long as the process stays alive.
+// We also track the offset at which the data starts, and its length.
+base::FilePath g_cached_filepath;  // guarded by g_file_lock_
+base::File* g_cached_file = NULL;  // guarded by g_file_lock_
+uint64 g_cached_data_offset = -1;  // guarded by g_file_lock_
+uint64 g_cached_data_length = -1;  // guarded by g_file_lock_
+
+// Guards g_cached_filepath
+base::LazyInstance<base::Lock> g_file_lock_;
+}  // namespace
+
+namespace translate {
+
+// Implementation of the static factory method from BrowserCldDataProvider,
+// hooking up this specific implementation for all of Chromium.
+BrowserCldDataProvider* CreateBrowserCldDataProviderFor(
+    content::RenderViewHost* render_view_host) {
+  return new DataFileBrowserCldDataProvider(render_view_host);
+}
+
+void DataFileBrowserCldDataProvider::SetCldDataFilePath(
+    const base::FilePath& path) {
+  VLOG(1) << "Setting CLD data file path to: " << path.value();
+  base::AutoLock lock(g_file_lock_.Get());
+  if (g_cached_filepath == path)
+    return;  // no change necessary
+  g_cached_filepath = path;
+  // For sanity, clean these other values up just in case.
+  g_cached_file = NULL;
+  g_cached_data_length = -1;
+  g_cached_data_offset = -1;
+}
+
+base::FilePath DataFileBrowserCldDataProvider::GetCldDataFilePath() {
+  base::AutoLock lock(g_file_lock_.Get());
+  return g_cached_filepath;
+}
+
+DataFileBrowserCldDataProvider::DataFileBrowserCldDataProvider(
+    content::RenderViewHost* render_view_host)
+    : render_view_host_(render_view_host), weak_pointer_factory_() {
+}
+
+DataFileBrowserCldDataProvider::~DataFileBrowserCldDataProvider() {
+}
+
+bool DataFileBrowserCldDataProvider::OnMessageReceived(
+    const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(DataFileBrowserCldDataProvider, message)
+  IPC_MESSAGE_HANDLER(ChromeViewHostMsg_NeedCldDataFile, OnCldDataRequest)
+  IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void DataFileBrowserCldDataProvider::OnCldDataRequest() {
+  // Quickly try to read g_cached_file. If valid, the file handle is
+  // cached and can be used immediately. Else, queue the caching task to the
+  // blocking pool.
+  VLOG(1) << "Received request for CLD data file.";
+  base::File* handle = NULL;
+  uint64 data_offset = 0;
+  uint64 data_length = 0;
+  {
+    base::AutoLock lock(g_file_lock_.Get());
+    handle = g_cached_file;
+    data_offset = g_cached_data_offset;
+    data_length = g_cached_data_length;
+  }
+
+  if (handle && handle->IsValid()) {
+    // Cached data available. Respond to the request.
+    VLOG(1) << "CLD data file is already cached, replying immediately.";
+    SendCldDataResponseInternal(handle, data_offset, data_length);
+    return;
+  }
+
+  if (weak_pointer_factory_.get() == NULL) {
+    weak_pointer_factory_.reset(
+        new base::WeakPtrFactory<DataFileBrowserCldDataProvider>(this));
+    weak_pointer_factory_.get()->GetWeakPtr().get();
+  }
+
+  // Else, we don't have the data file yet. Queue a caching attempt.
+  // The caching attempt happens in the blocking pool because it may involve
+  // arbitrary filesystem access.
+  // After the caching attempt is made, we call MaybeSendCLDDataAvailable
+  // to pass the file handle to the renderer. This only results in an IPC
+  // message if the caching attempt was successful.
+  VLOG(1) << "CLD data file not yet cached, deferring lookup";
+  content::BrowserThread::PostBlockingPoolTaskAndReply(
+      FROM_HERE,
+      base::Bind(&DataFileBrowserCldDataProvider::OnCldDataRequestInternal),
+      base::Bind(&DataFileBrowserCldDataProvider::SendCldDataResponse,
+                 weak_pointer_factory_.get()->GetWeakPtr()));
+}
+
+void DataFileBrowserCldDataProvider::SendCldDataResponse() {
+  base::File* handle = NULL;
+  uint64 data_offset = 0;
+  uint64 data_length = 0;
+  {
+    base::AutoLock lock(g_file_lock_.Get());
+    handle = g_cached_file;
+    data_offset = g_cached_data_offset;
+    data_length = g_cached_data_length;
+  }
+
+  if (handle && handle->IsValid())
+    SendCldDataResponseInternal(handle, data_offset, data_length);
+}
+
+void DataFileBrowserCldDataProvider::SendCldDataResponseInternal(
+    const base::File* handle,
+    const uint64 data_offset,
+    const uint64 data_length) {
+  VLOG(1) << "Sending CLD data file response.";
+  // Data available, respond to the request.
+  IPC::PlatformFileForTransit ipc_platform_file =
+      IPC::GetFileHandleForProcess(handle->GetPlatformFile(),
+                                   render_view_host_->GetProcess()->GetHandle(),
+                                   false);
+  // In general, sending a response from within the code path that is processing
+  // a request is discouraged because there is potential for deadlock (if the
+  // methods are sent synchronously) or loops (if the response can trigger a
+  // new request). Neither of these concerns is relevant in this code, so
+  // sending the response from within the code path of the request handler is
+  // safe.
+  render_view_host_->Send(
+      new ChromeViewMsg_CldDataFileAvailable(render_view_host_->GetRoutingID(),
+                                             ipc_platform_file,
+                                             data_offset,
+                                             data_length));
+}
+
+void DataFileBrowserCldDataProvider::OnCldDataRequestInternal() {
+  // Because this function involves arbitrary file system access, it must run
+  // on the blocking pool.
+  DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::IO));
+  DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  VLOG(1) << "CLD data file caching attempt starting.";
+
+  {
+    base::AutoLock lock(g_file_lock_.Get());
+    if (g_cached_file) {
+      VLOG(1) << "CLD data file is already cached, aborting caching attempt";
+      return;  // Already done, duplicate request
+    }
+  }
+
+  const base::FilePath path = GetCldDataFilePath();
+  if (path.empty()) {
+    VLOG(1) << "CLD data file does not yet have a known location.";
+    return;
+  }
+
+  // If the file exists, we can send an IPC-safe construct back to the
+  // renderer process immediately; otherwise, nothing to do here.
+  if (!base::PathExists(path)) {
+    VLOG(1) << "CLD data file does not exist.";
+    return;
+  }
+
+  // Attempt to open the file for reading.
+  scoped_ptr<base::File> file(
+      new base::File(path, base::File::FLAG_OPEN | base::File::FLAG_READ));
+  if (!file->IsValid()) {
+    LOG(WARNING) << "CLD data file exists but cannot be opened";
+    return;
+  }
+
+  base::File::Info file_info;
+  if (!file->GetInfo(&file_info)) {
+    LOG(WARNING) << "CLD data file exists but cannot be inspected";
+    return;
+  }
+
+  // For now, our offset and length are simply 0 and the length of the file,
+  // respectively. If we later decide to include the CLD2 data file inside of
+  // a larger binary context, these params can be twiddled appropriately.
+  const uint64 data_offset = 0;
+  const uint64 data_length = file_info.size;
+
+  {
+    base::AutoLock lock(g_file_lock_.Get());
+    if (g_cached_file) {
+      // Idempotence: Racing another request on the blocking pool, abort.
+      VLOG(1) << "Another thread finished caching first, aborting.";
+    } else {
+      // Else, this request has taken care of it all. Cache all info.
+      VLOG(1) << "Caching CLD data file information.";
+      g_cached_file = file.release();
+      g_cached_data_offset = data_offset;
+      g_cached_data_length = data_length;
+    }
+  }
+}
+
+}  // namespace translate