Add Socket::ReadIfReady()

net/socket/socket.h

 // Copyright (c) 2011 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 NET_SOCKET_SOCKET_H_
 #define NET_SOCKET_SOCKET_H_
 
 #include <stdint.h>
 
 #include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 class IOBuffer;
 
 // Represents a read/write socket.
 class NET_EXPORT Socket {
  public:
+  // Name of the field trial for using ReadyIfReady() instead of Read().
+  static const char kReadIfReadyTrialName[];
+
   virtual ~Socket() {}
 
   // Reads data, up to |buf_len| bytes, from the socket.  The number of bytes
   // read is returned, or an error is returned upon failure.
   // ERR_SOCKET_NOT_CONNECTED should be returned if the socket is not currently
   // connected.  Zero is returned once to indicate end-of-file; the return value
   // of subsequent calls is undefined, and may be OS dependent.  ERR_IO_PENDING
   // is returned if the operation could not be completed synchronously, in which
   // case the result will be passed to the callback when available. If the
   // operation is not completed immediately, the socket acquires a reference to
   // the provided buffer until the callback is invoked or the socket is
   // closed.  If the socket is Disconnected before the read completes, the
   // callback will not be invoked.
   virtual int Read(IOBuffer* buf, int buf_len,
                    const CompletionCallback& callback) = 0;
 
+  // Reads as much data as possible into |buf| without blocking. Default
+  // implementation returns ERR_READ_IF_READY_NOT_IMPLEMENTED. Caller should
+  // fall back to Read() if receives ERR_READ_IF_READY_NOT_IMPLEMENTED.
+  // Upon synchronous completion, returns the number of bytes read or an error
+  // code if an error happens; If read cannot be completed synchronously,
+  // returns ERR_IO_PENDING and does not hold on to |buf|. |callback| will be
+  // invoked with OK when data can be read, at which point, caller can call
+  // ReadIfReady() again; if an error occurs asynchronously, |callback| will be
+  // invoked with the error code.
+  virtual int ReadIfReady(IOBuffer* buf,
+                          int buf_len,
+                          const CompletionCallback& callback);
+
   // Writes data, up to |buf_len| bytes, to the socket.  Note: data may be
   // written partially.  The number of bytes written is returned, or an error
   // is returned upon failure.  ERR_SOCKET_NOT_CONNECTED should be returned if
   // the socket is not currently connected.  The return value when the
   // connection is closed is undefined, and may be OS dependent.  ERR_IO_PENDING
   // is returned if the operation could not be completed synchronously, in which
   // case the result will be passed to the callback when available.  If the
   // operation is not completed immediately, the socket acquires a reference to
   // the provided buffer until the callback is invoked or the socket is
   // closed.  Implementations of this method should not modify the contents
   // of the actual buffer that is written to the socket.  If the socket is
   // Disconnected before the write completes, the callback will not be invoked.
   virtual int Write(IOBuffer* buf, int buf_len,
                     const CompletionCallback& callback) = 0;
 
   // Set the receive buffer size (in bytes) for the socket.
   // Note: changing this value can affect the TCP window size on some platforms.
   // Returns a net error code.
   virtual int SetReceiveBufferSize(int32_t size) = 0;
 
   // Set the send buffer size (in bytes) for the socket.
   // Note: changing this value can affect the TCP window size on some platforms.
   // Returns a net error code.
   virtual int SetSendBufferSize(int32_t size) = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_SOCKET_H_