Make URLFetcherFileWriter::Finish() skip closing file when there is an error

net/url_request/url_fetcher_core.cc

Index: net/url_request/url_fetcher_core.cc
diff --git a/net/url_request/url_fetcher_core.cc b/net/url_request/url_fetcher_core.cc
index d83f52f2ccbc15532d8c314e0142176ba4901b52..2337cb5b4256703b7d7a6abf489151561e6da8ed 100644
--- a/net/url_request/url_fetcher_core.cc
+++ b/net/url_request/url_fetcher_core.cc
@@ -477,6 +477,7 @@ void URLFetcherCore::OnReadCompleted(URLRequest* request,
 
     // No more data to write.
     const int result = response_writer_->Finish(
+        bytes_read > 0 ? OK : bytes_read,

[mmenke, 2016/10/18 20:20:01]

Hrm...I'd normally ask for an integration test that runs into the problem, but
I'd actually really like to fix URLRequest so that this can't happen.  Fixing
the API would break the test.  (And I'd like to fix the API sooner rather than
later)

[xunjieli, 2016/10/18 21:18:07]

I see. So in the future URLRequest::Delegate::OnReadCompleted() won't be called
with an net error (bytes_read < 0)?

[mmenke, 2016/10/18 21:40:46]

No, in the future, I want it not to call into the Delegate with an error unless
there's a pending read/start operation, which I think this the only case this
happens in?

Cancellation through the URLFetcher interface goes through a different path, and
doesn't run into this problem, I believe.  And this code doesn't currently
open/write to the file while trying to read remote data.

[xunjieli, 2016/10/19 12:00:21]

Acknowledged. Thanks for explaining!

         base::Bind(&URLFetcherCore::DidFinishWriting, this));
     if (result != ERR_IO_PENDING)
       DidFinishWriting(result);
@@ -861,7 +862,7 @@ int URLFetcherCore::WriteBuffer(scoped_refptr<DrainableIOBuffer> data) {
 void URLFetcherCore::DidWriteBuffer(scoped_refptr<DrainableIOBuffer> data,
                                     int result) {
   if (result < 0) {  // Handle errors.
-    response_writer_->Finish(base::Bind(&EmptyCompletionCallback));
+    response_writer_->Finish(result, base::Bind(&EmptyCompletionCallback));
     CancelRequestAndInformDelegate(result);
     return;
   }