Make WebDataConsumerHandleImpl return OK while zero-length reading of closed pipe.

content/child/web_data_consumer_handle_impl.cc

 // 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 "content/child/web_data_consumer_handle_impl.h"
 
 #include <stdint.h>
 
 #include <limits>
 #include <utility>
@@ skipping 38 matching lines @@
                                                    size_t size,
                                                    Flags flags,
                                                    size_t* read_size) {
   // We need this variable definition to avoid a link error.
   const Flags kNone = FlagNone;
   DCHECK_EQ(flags, kNone);
   DCHECK_LE(size, std::numeric_limits<uint32_t>::max());
 
   *read_size = 0;
 
+  if (!size) {
+    // Even if there is unread data available, mojo::ReadDataRaw() returns
+    // FAILED_PRECONDITION when |size| is 0 and the producer handle was closed.
+    // But in this case, WebDataConsumerHandle::Reader::read() must return Ok.
+    // So we use mojo::Wait() with 0 deadline to check whether readable or not.
+    return HandleReadResult(mojo::Wait(
+        context_->handle().get(), MOJO_HANDLE_SIGNAL_READABLE, 0, nullptr));
+  }
+
   uint32_t size_to_pass = size;
   MojoReadDataFlags flags_to_pass = MOJO_READ_DATA_FLAG_NONE;
   MojoResult rv = mojo::ReadDataRaw(context_->handle().get(), data,
                                     &size_to_pass, flags_to_pass);
   if (rv == MOJO_RESULT_OK)
     *read_size = size_to_pass;
 
   return HandleReadResult(rv);
 }
 
@@ skipping 60 matching lines @@
 std::unique_ptr<blink::WebDataConsumerHandle::Reader>
 WebDataConsumerHandleImpl::obtainReader(Client* client) {
   return base::WrapUnique(new ReaderImpl(context_, client));
 }
 
 const char* WebDataConsumerHandleImpl::debugName() const {
   return "WebDataConsumerHandleImpl";
 }
 
 }  // namespace content