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// Copyright 2013 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_TCP_SOCKET_H_
#define NET_SOCKET_TCP_SOCKET_H_
#include "build/build_config.h"
#include "net/base/net_export.h"
#include "net/socket/socket_descriptor.h"
#if defined(OS_WIN)
#include "net/socket/tcp_socket_win.h"
#elif defined(OS_POSIX)
#include "net/socket/tcp_socket_posix.h"
#endif
namespace net {
// TCPSocket provides a platform-independent interface for TCP sockets.
//
// It is recommended to use TCPClientSocket/TCPServerSocket instead of this
// class, unless a clear separation of client and server socket functionality is
// not suitable for your use case (e.g., a socket needs to be created and bound
// before you know whether it is a client or server socket).
#if defined(OS_WIN)
typedef TCPSocketWin TCPSocket;
#elif defined(OS_POSIX)
typedef TCPSocketPosix TCPSocket;
#endif
// Check if TCP FastOpen is supported by the OS.
bool IsTCPFastOpenSupported();
// Check if TCP FastOpen is enabled by the user.
bool IsTCPFastOpenUserEnabled();
// Checks if TCP FastOpen is supported by the kernel. Also enables TFO for all
// connections if indicated by user.
// Not thread safe. Must be called during initialization/startup only.
NET_EXPORT void CheckSupportAndMaybeEnableTCPFastOpen(bool user_enabled);
// This function enables/disables buffering in the kernel. By default, on Linux,
// TCP sockets will wait up to 200ms for more data to complete a packet before
// transmitting. After calling this function, the kernel will not wait. See
// TCP_NODELAY in `man 7 tcp`.
//
// For Windows:
//
// The Nagle implementation on Windows is governed by RFC 896. The idea
// behind Nagle is to reduce small packets on the network. When Nagle is
// enabled, if a partial packet has been sent, the TCP stack will disallow
// further *partial* packets until an ACK has been received from the other
// side. Good applications should always strive to send as much data as
// possible and avoid partial-packet sends. However, in most real world
// applications, there are edge cases where this does not happen, and two
// partial packets may be sent back to back. For a browser, it is NEVER
// a benefit to delay for an RTT before the second packet is sent.
//
// As a practical example in Chromium today, consider the case of a small
// POST. I have verified this:
// Client writes 649 bytes of header (partial packet #1)
// Client writes 50 bytes of POST data (partial packet #2)
// In the above example, with Nagle, a RTT delay is inserted between these
// two sends due to nagle. RTTs can easily be 100ms or more. The best
// fix is to make sure that for POSTing data, we write as much data as
// possible and minimize partial packets. We will fix that. But disabling
// Nagle also ensure we don't run into this delay in other edge cases.
// See also:
// http://technet.microsoft.com/en-us/library/bb726981.aspx
//
// This function returns true if it succeeds to set the TCP_NODELAY option,
// otherwise returns false.
NET_EXPORT_PRIVATE bool SetTCPNoDelay(SocketDescriptor socket, bool no_delay);
} // namespace net
#endif // NET_SOCKET_TCP_SOCKET_H_
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