Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/mojo/blob_channel_service.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 "blimp/engine/mojo/blob_channel_service.h"
 
 #include "blimp/net/blob_channel/blob_channel_sender.h"
+#include "mojo/public/cpp/system/buffer.h"
 
 namespace blimp {
 namespace engine {
 
 BlobChannelService::BlobChannelService(BlobChannelSender* blob_channel_sender,
                                        mojom::BlobChannelRequest request)
     : binding_(this, std::move(request)),
       blob_channel_sender_(blob_channel_sender) {
   DCHECK(blob_channel_sender_);
 }
 
 BlobChannelService::~BlobChannelService() {}
 
 void BlobChannelService::PutBlob(const mojo::String& id,
-                                 const mojo::String& data) {
-  blob_channel_sender_->PutBlob(id, new BlobData(data));
+                                 mojo::ScopedSharedBufferHandle data,
+                                 uint32_t size) {
+  // Map |data| into the address space and copy out its contents.
+  if (!data.is_valid()) {
+    LOG(ERROR) << "Invalid data handle received from renderer process.";

[Wez, 2016/07/01 01:06:56]

Not for this CL: We should work out how in general to turn these sorts of
failures into renderer teardowns, since they indicate the renderer violating the
protocol.

[Kevin M, 2016/07/18 16:35:16]

Filed crbug.com/629096

+    return;
+  }
+
+  if (size > kMaxBlobSizeBytes) {
+    LOG(ERROR) << "Blob size too big: " << size;
+    return;
+  }
+
+  scoped_refptr<BlobData> new_blob(new BlobData);
+  auto mapping = data->Map(size);

[Wez, 2016/07/01 01:06:56]

nit: Don't use auto here, since it's not obvious to the reader what the
resulting type will be without looking up the Map() API, and the explicit type
name won't make the code too verbose.

[dcheng, 2016/07/01 02:04:28]

I missed this, but we need to check that the Map() call succeeds (it will return
nullptr on failure)

[Kevin M, 2016/07/18 16:35:16]

Done.

[Kevin M, 2016/07/18 16:35:16]

Done.

+  new_blob->data.assign(reinterpret_cast<const char*>(mapping.get()), size);
+  blob_channel_sender_->PutBlob(id, std::move(new_blob));
 }
 
 void BlobChannelService::DeliverBlob(const mojo::String& id) {
   blob_channel_sender_->DeliverBlob(id);
 }
 
 // static
 void BlobChannelService::Create(
     BlobChannelSender* blob_channel_sender,
     mojo::InterfaceRequest<mojom::BlobChannel> request) {
   // Object lifetime is managed by BlobChannelService's StrongBinding
   // |binding_|.
   new BlobChannelService(blob_channel_sender, std::move(request));
 }
 
 }  // namespace engine
 }  // namespace blimp