upstream.go

package main

import (
	"context"
	"flag"
	"fmt"
	"io"
	"net"
	"net/http"
	"time"
)

var (
	address string
)

func main() {
	flag.StringVar(&address, "address", "208.76.14.119:0", "address")
	flag.Parse()

	addr, err := net.ResolveTCPAddr("tcp", address)
	if err != nil {
		panic(err)
	}

	dialer := &net.Dialer{LocalAddr: addr}

	dialContext := func(ctx context.Context, network, addr string) (net.Conn, error) {
		conn, err := dialer.Dial(network, addr)
		return conn, err
	}

	client := &http.Client{
		Timeout: time.Second * 5,
		Transport: &http.Transport{
			DialContext: dialContext,
		},
	}

	resp, err := client.Get("https://checkip.amazonaws.com")
	if err != nil {
		panic(err)
	}
	fmt.Printf("status: %s\n", resp.Status)
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		panic(err)
	}
	_ = resp.Body.Close()
	fmt.Printf(string(body))
}