Blimp: Add BlobChannelReceiver and bindings interface.

blimp/net/blob_channel/blob_channel_receiver.h

Index: blimp/net/blob_channel/blob_channel_receiver.h
diff --git a/blimp/net/blob_channel/blob_channel_receiver.h b/blimp/net/blob_channel/blob_channel_receiver.h
new file mode 100644
index 0000000000000000000000000000000000000000..6b94cff7ff4f2c0074e99c74b722f5e23c19d667
--- /dev/null
+++ b/blimp/net/blob_channel/blob_channel_receiver.h
@@ -0,0 +1,94 @@
+// 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.
+
+#ifndef BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_
+#define BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
+#include "blimp/common/blob_cache/blob_cache.h"
+#include "blimp/net/blimp_message_processor.h"
+#include "blimp/net/blimp_net_export.h"
+#include "blimp/net/blob_channel/types.h"
+
+namespace blimp {
+
+class BlobCache;
+
+// Receives blobs from a remote sender.
+// The transport-specific details are provided by the caller using a Delegate
+// subclass.
+class BLIMP_NET_EXPORT BlobChannelReceiver {
+ public:
+  typedef base::Callback<void(const BlobId&, scoped_refptr<RefCountedVector>)>
+      BlobReceivedCallback;
+
+  class Delegate {
+   public:
+    Delegate();
+    ~Delegate();
+
+    // Requests the blob |id| from the sender. The delegate method
+    // OnBlobReceived() is triggered if and when the blob arrives.
+    virtual void Request(const BlobId& id) = 0;
+
+    // Calls OnBlobReceived() on the BlobChannelReceiver.
+    void OnBlobReceived(const BlobId& id, BlobData data);
+
+   private:
+    friend class BlobChannelReceiver;
+
+    // Sets the Receiver object to receive incoming blobs.
+    void SetReceiver(base::WeakPtr<BlobChannelReceiver> receiver);
+
+    // Using a WeakPtr so the BlobChannelReceiver can be destroyed before
+    // |this|.
+    base::WeakPtr<BlobChannelReceiver> receiver_;
+
+    DISALLOW_COPY_AND_ASSIGN(Delegate);
+  };
+
+  // Caller must ensure that |cache| and |delegate| outlive |this|.
+  BlobChannelReceiver(BlobCache* cache, Delegate* delegate);

[Wez, 2016/04/18 22:40:40]

Remind me why the receiver can't just "own" the cache object?

+  ~BlobChannelReceiver();
+
+  // Gets a blob from the BlobChannel, first pulling from a local cache and
+  // falling back to requesting the data from a remote cache.
+  // If blob |id| is already available, then it is returned synchronously and
+  // |callback| is discarded.
+  // If blob |id| has not yet been received, then a null refptr is returned,
+  // and |callback| is invoked later when the blob arrives.
+  // Can be called on any thread. Holds |lock_|.

[Wez, 2016/04/18 22:40:40]

Holds lock_ is an internal implementation detail.

I think what you want to say is that this is thread-safe?

+  BlobData Get(const BlobId& id, const BlobReceivedCallback& callback);

[Wez, 2016/04/18 22:40:41]

What is BlobData? I don't see it defined anywhere in this CL, nor the existing
codebase.

+
+ private:
+  friend class Delegate;
+
+  // Method called by |delegate_| when a blob arrives from the transport.
+  // Holds |lock_|.
+  void OnBlobReceived(const BlobId& id, BlobData data);
+
+  BlobCache* cache_ = nullptr;
+  Delegate* delegate_ = nullptr;

[Wez, 2016/04/18 22:56:11]

nit: You have no default ctor for this class, so no need for in-line init.

+
+  // Callbacks waiting to be invoked on read completion, keyed by blob ID.
+  std::multimap<BlobId, BlobReceivedCallback> active_read_callbacks_;
+
+  // Guards concurrent access to |cache_| and |active_read_callbacks_|.

[Wez, 2016/04/18 22:40:41]

Concurrent access by whom?  The delegates call the BlobChannelReceiver via a
WeakPtr, so those calls must all happen on the thread on which
BlobChannelReceiver is going to be torn down.

+  base::Lock lock_;
+
+  base::WeakPtrFactory<BlobChannelReceiver> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlobChannelReceiver);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_