Testing TCP Endpoints with Go

README.md

This gist demonstrates how to test the availability of a TCP endponit using Golang. The following example checks if an endpoint is available and responding to both TCP and TLS connections. To run the example, simply open a command line and execute the following:

$ curl -sSL https://goo.gl/ENx9d8 > tcp-tls-ping.go && go run tcp-tls-ping.go
tcp success
tls success

The program shows that the specified endpoint (defaults to google.com:443) is available and responding to TCP and TLS connection attempts. To illustrate the error that occurs when an endpoint presents an invalid TLS certificate, execute the following:

$ curl -sSL https://goo.gl/ENx9d8 > tcp-tls-ping.go && go run tcp-tls-ping.go www.pcwebshop.co.uk:443
tcp success
tls error: x509: certificate is valid for *.secure-secure.co.uk, secure-secure.co.uk, not www.pcwebshop.co.uk
exit status 1

Finally, the program can also demonstrate that a TCP endpoint is unavailable:

$ curl -sSL https://goo.gl/ENx9d8 > tcp-tls-ping.go && go run tcp-tls-ping.go google.com:444
tcp error: dial tcp [2607:f8b0:4000:80a::200e]:444: i/o timeout
exit status 1

main.go

package main

import (
	"crypto/tls"
	"fmt"
	"net"
	"os"
	"time"
)

func main() {
	var (
		proto    = "tcp"
		endpoint = "google.com:443"
		dialer   = &net.Dialer{Timeout: time.Second * 1}
	)
	switch len(os.Args) {
	case 2:
		endpoint = os.Args[1]
	case 3:
		proto = os.Args[1]
		endpoint = os.Args[2]
	}
	if _, err := dialer.Dial(proto, endpoint); err != nil {
		fmt.Printf("tcp error: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("tcp success")
	if _, err := tls.DialWithDialer(
		dialer, proto, endpoint, &tls.Config{}); err != nil {
		fmt.Printf("tls error: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("tls success")
}