Intercept a HTTP Call

main.go

package main

import (
	"bytes"
	"context"
	"io"
	"net"
	"net/http"
	"os"
	"time"
)

func main() {
	(&http.Client{Transport: &test{}}).Get("http://google.com")
}

type test struct {

}

type ConnWrapper struct {
	c net.Conn
	w io.Writer
}

func (c *ConnWrapper) Read(b []byte) (n int, err error) {
	read, err := c.c.Read(b)
	_, _ = io.Copy(os.Stdout, bytes.NewReader(b))
	return read, err
}

func (c *ConnWrapper) Write(b []byte) (n int, err error) {
	return c.w.Write(b)
}

func (c *ConnWrapper) Close() error {
	return c.c.Close()
}

func (c *ConnWrapper) LocalAddr() net.Addr {
	return c.c.LocalAddr()
}

func (c *ConnWrapper) RemoteAddr() net.Addr {
	return c.c.RemoteAddr()
}

func (c *ConnWrapper) SetDeadline(t time.Time) error {
	return c.c.SetDeadline(t)
}

func (c *ConnWrapper) SetReadDeadline(t time.Time) error {
	return c.c.SetReadDeadline(t)
}

func (c *ConnWrapper) SetWriteDeadline(t time.Time) error {
	return c.c.SetWriteDeadline(t)
}

func (t *test) RoundTrip(req *http.Request) (*http.Response, error) {
	c := http.Client{
	}

	transport := http.DefaultTransport.(*http.Transport)
	transport.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
		d := &net.Dialer{
			Timeout:   30 * time.Second,
			KeepAlive: 30 * time.Second,
			DualStack: true,
		}

		conn, err := d.DialContext(ctx, network, addr)
		if err != nil {
			return nil, err
		}

		return &ConnWrapper{
			c: conn,
			w: io.MultiWriter(conn, os.Stdout),
		}, nil
	}
	return c.Do(req)
}


var (
	_ http.RoundTripper = (*test)(nil)
)