Dart RawSocketOption

last modified April 4, 2025

The RawSocketOption class in Dart provides low-level access to socket configuration options. It's used with RawSocket for custom network protocol implementations.

RawSocketOption allows setting platform-specific socket options not exposed through higher-level APIs. It's part of Dart's dart:io library.

Basic Definition

RawSocketOption represents a socket option that can be set or queried on a RawSocket. It encapsulates both the option level and name.

Key properties include option level (SOL_SOCKET, IPPROTO_TCP etc.), option name, and value type. Options affect socket behavior at the OS level.

Enabling Socket Reuse

This example demonstrates enabling SO_REUSEADDR to allow address reuse.

import 'dart:io';

void main() async {
  var socket = await RawSocket.connect('localhost', 8080);
  
  var reuseAddr = RawSocketOption.fromInt(
    SocketOption.SOL_SOCKET,
    SocketOption.SO_REUSEADDR,
    1 // enable
  );
  
  socket.setOption(reuseAddr);
  print('SO_REUSEADDR set to 1');
  
  socket.close();
}

We create a socket and enable SO_REUSEADDR to allow binding to addresses in TIME_WAIT state. This is useful for server sockets that restart frequently.

$ dart main.dart
SO_REUSEADDR set to 1

Setting TCP Keepalive

This example configures TCP keepalive to detect dead connections.

import 'dart:io';

void main() async {
  var socket = await RawSocket.connect('google.com', 80);
  
  var keepAlive = RawSocketOption.fromInt(
    SocketOption.SOL_SOCKET,
    SocketOption.SO_KEEPALIVE,
    1 // enable
  );
  
  socket.setOption(keepAlive);
  print('TCP Keepalive enabled');
  
  socket.close();
}

We enable SO_KEEPALIVE which causes TCP to periodically verify the connection is still alive. This helps detect network failures without application traffic.

$ dart main.dart
TCP Keepalive enabled

Configuring Receive Buffer Size

This example sets the socket receive buffer size for better performance.

import 'dart:io';

void main() async {
  var socket = await RawSocket.connect('example.com', 80);
  
  var rcvBuf = RawSocketOption.fromInt(
    SocketOption.SOL_SOCKET,
    SocketOption.SO_RCVBUF,
    65536 // 64KB buffer
  );
  
  socket.setOption(rcvBuf);
  print('Receive buffer size set to 64KB');
  
  socket.close();
}

We configure SO_RCVBUF to increase the kernel receive buffer size. Larger buffers improve throughput for high-bandwidth connections.

$ dart main.dart
Receive buffer size set to 64KB

Disabling Nagle's Algorithm

This example disables Nagle's algorithm for low-latency communication.

import 'dart:io';

void main() async {
  var socket = await RawSocket.connect('localhost', 9000);
  
  var noDelay = RawSocketOption.fromInt(
    SocketOption.IPPROTO_TCP,
    SocketOption.TCP_NODELAY,
    1 // disable Nagle
  );
  
  socket.setOption(noDelay);
  print('Nagle\'s algorithm disabled');
  
  socket.close();
}

TCP_NODELAY disables Nagle's algorithm which buffers small packets. This reduces latency for interactive applications at the cost of more packets.

$ dart main.dart
Nagle's algorithm disabled

Querying Socket Options

This example shows how to query current socket option values.

import 'dart:io';

void main() async {
  var socket = await RawSocket.connect('example.com', 80);
  
  var queryRcvBuf = RawSocketOption(
    SocketOption.SOL_SOCKET,
    SocketOption.SO_RCVBUF,
    4 // buffer for int result
  );
  
  var bufSize = socket.getOption(queryRcvBuf);
  print('Current receive buffer size: ${bufSize.getInt32(0)} bytes');
  
  socket.close();
}

We create a RawSocketOption with a buffer to hold the result, then call getOption to retrieve the current value. The buffer must be large enough.

$ dart main.dart
Current receive buffer size: 87380 bytes

Best Practices

• Platform awareness: Options may behave differently across OSes
• Error handling: Check setOption/getOption return values
• Documentation: Consult OS docs for option specifics
• Testing: Verify option effects in your environment

Source

Dart RawSocketOption Documentation

This tutorial covered Dart's RawSocketOption class with practical examples showing common socket configurations for performance and reliability tuning.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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