[NaCl SDK] nacl_io: Add flow control the JavaScript pipes.

native_client_sdk/src/libraries/nacl_io/devfs/jspipe_node.h

 // 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.
 
 #ifndef LIBRARIES_NACL_IO_DEVFS_JSPIPE_NODE_H_
 #define LIBRARIES_NACL_IO_DEVFS_JSPIPE_NODE_H_
 
-#include "nacl_io/pipe/pipe_node.h"
+#include <ppapi/c/pp_var.h>
+#include <string>
 
-#include <string>
+#include "nacl_io/devfs/jspipe_event_emitter.h"
+#include "nacl_io/stream/stream_node.h"
 
 namespace nacl_io {
 
-class JSPipeNode : public PipeNode {
+class MessagingInterface;
+class VarInterface;
+class VarArrayInterface;
+class VarArrayBufferInterface;
+class VarDictionaryInterface;
+
+/**
+ * JSPipeNode represents a two-way channel for communicating with JavaScript
+ * via calls to PostMessage.  In order to use these some amount of logic on
+ * the JavaScript side is also required.  The protocol to the communication
+ * looks the same in both directions and consists of two message types:
+ * 'write' and 'ack'.
+ * The messages are formated as JavaScript dictionary objects and take the
+ * following form:
+ * {
+ *   pipe: <pipe_name>,
+ *   operation: <operation_name>,
+ *   payload: <operations_payload>
+ * }
+ * The payload for 'write' message is a ArrayBuffer containing binary data.
+ * The payload for 'ack' messages is the total number of bytes recieved at
+ * the other end.
+ * For example: { pipe: 'jspipe1', operation: 'ack', payload: 234 }
+ *
+ * Messages coming from JavaScript must be delivered using the
+ * NACL_IOC_HANDLEMESSAGE ioctl on the file handle.
+ */
+class JSPipeNode : public Node {
  public:
-  explicit JSPipeNode(Filesystem* filesystem) : PipeNode(filesystem) {}
+  explicit JSPipeNode(Filesystem* filesystem);
+
+  virtual void Destroy() { LOG_TRACE("JSPipeNode: Destroy"); };
+
+  virtual JSPipeEventEmitter* GetEventEmitter();
 
   virtual Error VIoctl(int request, va_list args);
 
-  // Writes go directly to PostMessage, reads come from a pipe
-  // that gets populated by incoming messages
+  virtual Error Read(const HandleAttr& attr,
+                     void* buf,
+                     size_t count,
+                     int* out_bytes);
   virtual Error Write(const HandleAttr& attr,
                       const void* buf,
                       size_t count,
                       int* out_bytes);
 
- private:
-  std::string name_;
+ protected:
+  Error SendAck();
+
+  ScopedJSPipeEventEmitter pipe_;
 };
 
 }  // namespace nacl_io
 
 #endif  // LIBRARIES_NACL_IO_DEVFS_JSPIPE_NODE_H_