Pass error messages from native messaging to web-app.

remoting/host/native_messaging/log_message_handler.cc

+// Copyright 2015 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 "remoting/host/native_messaging/log_message_handler.h"
+
+#include "base/bind.h"
+#include "base/lazy_instance.h"
+#include "base/strings/string_util.h"
+#include "base/synchronization/lock.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/tracked_objects.h"
+
+namespace remoting {
+
+namespace {
+// Log message handler registration and deregistration is not thread-safe.
+// This lock must be held in order to set or restore a log message handler,
+// and when accessing the weak pointer to the LogMessageHandler instance.

[Sergey Ulanov, 2015/08/17 23:06:24]

update the comment - it's not weak anymore.

[Jamie, 2015/08/18 00:05:20]

Done.

+base::LazyInstance<base::Lock>::Leaky g_lock = LAZY_INSTANCE_INITIALIZER;

[Sergey Ulanov, 2015/08/17 23:06:25]

nit: maybe rename this to g_log_message_handler_lock to make it clear that it
needs to be locked to access g_log_message_handler.

[Jamie, 2015/08/18 00:05:20]

Done.

+
+// The singleton LogMessageHandler instance, or null if log messages are
+// not being intercepted. It must be dereferenced and updated under a lock.

[Sergey Ulanov, 2015/08/17 23:06:25]

s/a lock/the lock/

[Jamie, 2015/08/18 00:05:20]

Done.

+LogMessageHandler* g_log_message_handler = nullptr;
+}  // namespace
+
+LogMessageHandler::LogMessageHandler(
+    const Delegate& delegate)
+    : delegate_(delegate),
+      suppress_logging_(false),
+      caller_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      weak_ptr_factory_(this) {
+  base::AutoLock lock(g_lock.Get());
+  if (g_log_message_handler) {
+    LOG(FATAL) << "LogMessageHandler is already registered. Only one instance "
+               << "per process is allowed.";
+  }
+  previous_log_message_handler_ = logging::GetLogMessageHandler();
+  logging::SetLogMessageHandler(&LogMessageHandler::OnLogMessage);
+  g_log_message_handler = this;
+}
+
+LogMessageHandler::~LogMessageHandler() {
+  base::AutoLock lock(g_lock.Get());
+  if (logging::GetLogMessageHandler() != &LogMessageHandler::OnLogMessage) {
+    LOG(FATAL) << "LogMessageHandler is not the top-most message handler. "
+               << "Cannot unregister.";
+  }
+  logging::SetLogMessageHandler(previous_log_message_handler_);
+  g_log_message_handler = nullptr;
+}
+
+// static
+bool LogMessageHandler::OnLogMessage(
+    logging::LogSeverity severity,
+    const char* file,
+    int line,
+    size_t message_start,
+    const std::string& str) {
+  base::AutoLock lock(g_lock.Get());
+  if (g_log_message_handler) {
+    g_log_message_handler->PostLogMessageToCorrectThread(
+        severity, file, line, message_start, str);
+  }
+  return false;
+}
+
+void LogMessageHandler::PostLogMessageToCorrectThread(
+    logging::LogSeverity severity,
+    const char* file,
+    int line,
+    size_t message_start,
+    const std::string& str) {
+  // Don't process this message if we're already logging and on the caller
+  // thread. This guards against an infinite loop if any code called by this
+  // class logs something.
+  if (suppress_logging_ && caller_task_runner_->BelongsToCurrentThread()) {
+    return;
+  }
+
+  // This method is always called under the global lock, so post a task to
+  // handle the log message, even if we're already on the correct thread.
+  // This alows the lock to be released quickly.
+  //
+  // Note that this means that LOG(FATAL) messages will be lost because the
+  // process will exit before the message is sent to the client.
+  caller_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&LogMessageHandler::SendLogMessageToClient,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 severity, file, line, message_start, str));
+}
+
+void LogMessageHandler::SendLogMessageToClient(
+    logging::LogSeverity severity,
+    const char* file,
+    int line,
+    size_t message_start,
+    const std::string& str) {
+  suppress_logging_ = true;
+
+  std::string severity_string = "log";
+  switch (severity) {
+    case logging::LOG_WARNING:
+      severity_string = "warn";
+      break;
+    case logging::LOG_FATAL:
+    case logging::LOG_ERROR:
+      severity_string = "error";
+      break;
+  }
+
+  std::string message = str.substr(message_start);
+  base::TrimWhitespaceASCII(message, base::TRIM_ALL, &message);
+
+  scoped_ptr<base::DictionaryValue> dictionary(new base::DictionaryValue);
+  dictionary->SetString("type", "_debug_log");
+  dictionary->SetString("severity", severity_string);
+  dictionary->SetString("message", message);
+  dictionary->SetString("file", file);
+  dictionary->SetInteger("line", line);
+
+  delegate_.Run(dictionary.Pass());
+
+  suppress_logging_ = false;
+}
+
+}  // namespace remoting