FIN vs RST Experiment

experiment.go

package main

import (
	"log"
	"net"
	"os"
	"time"
)

// FIN vs RST Experiment
// ---
// Demonstrates how to trigger a connection reset by peer on close
// using SetLinger.
// ---
// $ go run experiment.go
// 2019/01/02 08:29:36 connect err: EOF
// exit status 1
// $ go run experiment.go rst
// 2019/01/02 08:29:40 connect err: read tcp 127.0.0.1:50361->127.0.0.1:4444: read: connection reset by peer
// exit status 1

func main() {
	rst := len(os.Args) >= 2 && os.Args[1] == "rst"

	// Start a listener that accepts one connection and then immediately closes it.
	go func() {
		err := listen(rst)
		if err != nil {
			log.Fatalf("listen err: %s", err)
		}
	}()

	// Wait for listener to start.
	time.Sleep(time.Second)

	// Connect and report error on close.
	err := connect()
	if err != nil {
		log.Fatalf("connect err: %s", err)
	}
}

func listen(rst bool) error {
	ln, err := net.Listen("tcp", "localhost:4444")
	if err != nil {
		return err
	}

	// Accept one connection.
	conn, err := ln.Accept()
	if err != nil {
		return err
	}

	// Force an RST if flag is set.
	// Close with normal FIN if flag is not set.
	if rst {
		tcpConn := conn.(*net.TCPConn)
		tcpConn.SetLinger(0)
	}
	return conn.Close()
}

func connect() error {
	conn, err := net.Dial("tcp", "localhost:4444")
	if err != nil {
		return err
	}
	// Block until close.
	buf := make([]byte, 1)
	_, err = conn.Read(buf)
	return err
}