[cronet] make startNetLogToFile write to correct file

components/cronet/ios/cronet_environment.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 "components/cronet/ios/cronet_environment.h"
 
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
@@ skipping 128 matching lines @@
   DCHECK(!base::MessageLoop::current());
   DCHECK(!g_main_message_loop);
   g_main_message_loop = new base::MessageLoopForUI();
   base::MessageLoopForUI::current()->Attach();
   // The network change notifier must be initialized so that registered
   // delegates will receive callbacks.
   DCHECK(!g_network_change_notifier);
   g_network_change_notifier = net::NetworkChangeNotifier::Create();
 }
 
-void CronetEnvironment::StartNetLog(base::FilePath::StringType file_name,
+bool CronetEnvironment::StartNetLog(base::FilePath::StringType file_name,
                                     bool log_bytes) {
-  DCHECK(file_name.length());
-  PostToNetworkThread(FROM_HERE,
-                      base::Bind(&CronetEnvironment::StartNetLogOnNetworkThread,
-                                 base::Unretained(this), file_name, log_bytes));
+  if (!file_name.length())
+    return false;
+
+  base::FilePath full_path(file_name);
+
+  if (!full_path.IsAbsolute()) {
+    if (!PathService::Get(base::DIR_HOME, &full_path))

[kapishnikov, 2016/11/10 20:52:17]

What is the value of base::DIR_HOME on iOS? Can application write into it? Do we
expect that some other code rather than Cronet.cc will be calling this method?

[lilyhoughton, 2016/11/16 16:04:10]

iOS apps definitely can't write to it, per bug 616918; I left the if-clause here
so as to not break other functions that might want the old behavior, but if that
isn't used anywhere, then this should definitely be removed.

+      return false;
+
+    full_path = full_path.Append(file_name);
+  }
+
+  base::ScopedFILE file(base::OpenFile(full_path, "w"));
+  if (!file) {
+    LOG(ERROR) << "Can not start NetLog to " << full_path.value();
+    return false;
+  }
+
+  LOG(WARNING) << "Starting NetLog to " << full_path.value();
+  PostToNetworkThread(
+      FROM_HERE,
+      base::Bind(&CronetEnvironment::StartNetLogOnNetworkThread,
+                 base::Unretained(this), base::Passed(&file), log_bytes));

[kapishnikov, 2016/11/10 20:52:17]

Why do we need base::Passes here?

[lilyhoughton, 2016/11/16 16:04:10]

Because `base::Bind` will not accept an undecorated `std::unique_ptr` (which is
what a ScopedFILE is)

+
+  return true;
 }
 
-void CronetEnvironment::StartNetLogOnNetworkThread(
-    const base::FilePath::StringType& file_name,
-    bool log_bytes) {
-  DCHECK(file_name.length());
+void CronetEnvironment::StartNetLogOnNetworkThread(base::ScopedFILE file,
+                                                   bool log_bytes) {
   DCHECK(net_log_);
 
   if (net_log_observer_)
     return;
 
-  base::FilePath files_root;
-  if (!PathService::Get(base::DIR_HOME, &files_root))
-    return;
-
-  base::FilePath full_path = files_root.Append(file_name);
-  base::ScopedFILE file(base::OpenFile(full_path, "w"));
-  if (!file) {
-    LOG(ERROR) << "Can not start NetLog to " << full_path.value();
-    return;
-  }
-
   net::NetLogCaptureMode capture_mode =
       log_bytes ? net::NetLogCaptureMode::IncludeSocketBytes()
                 : net::NetLogCaptureMode::Default();
 
   net_log_observer_.reset(new net::WriteToFileNetLogObserver());
   net_log_observer_->set_capture_mode(capture_mode);
   net_log_observer_->StartObserving(main_context_->net_log(), std::move(file),
                                     nullptr, main_context_.get());
-  LOG(WARNING) << "Started NetLog to " << full_path.value();
+
+  LOG(WARNING) << "Started NetLog";

[kapishnikov, 2016/11/10 20:52:17]

We already logging a message in StartNetLog(). I think we should remove this
message or reduce the level to debug/verbose.

[lilyhoughton, 2016/11/16 16:04:10]

I wanted to include both whether or not `startNetLog()` succeeded and what file
it is writing too.  I think ideally the format is

Starting NetLog to <file>...OK

or

Starting NetLog to <file>...FAIL

but I don't know how to make LOG() continue on the same line.

[kapishnikov, 2016/11/18 22:17:27]

If StartNetLogOnNetworkThread is called, this line is printed unconditionally
(unless net_log_observer_ is NULL). I don't see value in this LOG since we print
the result in StartNetLog. I agree that we need to log if there is an unexpected
failure.

 }
 
 void CronetEnvironment::StopNetLog() {
   base::WaitableEvent log_stopped_event(
       base::WaitableEvent::ResetPolicy::MANUAL,
       base::WaitableEvent::InitialState::NOT_SIGNALED);
   PostToNetworkThread(FROM_HERE,
                       base::Bind(&CronetEnvironment::StopNetLogOnNetworkThread,
                                  base::Unretained(this), &log_stopped_event));
   log_stopped_event.Wait();
@@ skipping 198 matching lines @@
 
 std::vector<uint8_t> CronetEnvironment::GetHistogramDeltas() {
   base::StatisticsRecorder::Initialize();
   std::vector<uint8_t> data;
   if (!HistogramManager::GetInstance()->GetDeltas(&data))
     return std::vector<uint8_t>();
   return data;
 }
 
 }  // namespace cronet