ooni-probe-cli/internal/tutorial/netxlite/chapter08/main.go

// -=-=- StartHere -=-=-
//
// # Chapter I: HTTP GET with QUIC sess
//
// In this chapter we will write together a `main.go` file that
// uses netxlite to establish a QUIC session to a remote endpoint
// and then fetches a webpage from it using GET.
//
// This file is basically the same as the one used in chapter04
// with the small addition of the code to perform the GET.
//
// (This file is auto-generated from the corresponding source file,
// so make sure you don't edit it manually.)
//
// ## The main.go file
//
// We define `main.go` file using `package main`.
//
// The beginning of the program is equal to chapter04,
// so there is not much to say about it.
//
// ```Go
package main

import (
	"context"
	"crypto/tls"
	"errors"
	"flag"
	"net/http"
	"net/url"
	"os"
	"time"

	"github.com/apex/log"
	"github.com/lucas-clemente/quic-go"
	"github.com/ooni/probe-cli/v3/internal/netxlite"
)

func main() {
	log.SetLevel(log.DebugLevel)
	address := flag.String("address", "8.8.4.4:443", "Remote endpoint address")
	sni := flag.String("sni", "dns.google", "SNI to use")
	timeout := flag.Duration("timeout", 60*time.Second, "Timeout")
	flag.Parse()
	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
	defer cancel()
	config := &tls.Config{
		ServerName: *sni,
		NextProtos: []string{"h3"},
		RootCAs:    netxlite.NewDefaultCertPool(),
	}
	sess, _, err := dialQUIC(ctx, *address, config)
	if err != nil {
		fatal(err)
	}
	log.Infof("Sess type  : %T", sess)
	// ```
	//
	// This is where things diverge. We create an HTTP client
	// using a transport created with `netxlite.NewHTTP3Transport`.
	//
	// This transport will use a "single use" QUIC dialer.
	// What does this mean? Well, we create such a QUICDialer
	// using the session we already established. The first
	// time the HTTP code dials for QUIC, the QUICDialer will
	// return the session we passed to its constructor
	// immediately. Every subsequent QUIC dial attempt will fail.
	//
	// The result is an HTTPTransport suitable for performing
	// a single request using the given QUIC sess.
	//
	// (A similar construct allows to create an HTTPTransport that
	// uses a cleartext TCP connection. In the previous chapter we've
	// seen how to do the same using TLS conns.)
	//
	// ```Go
	clnt := &http.Client{Transport: netxlite.NewHTTP3Transport(
		log.Log, netxlite.NewSingleUseQUICDialer(sess), &tls.Config{},
	)}
	// ```
	//
	// Once we have the proper transport and client, the rest of
	// the code is basically standard Go for fetching a webpage
	// using the GET method.
	//
	// ```Go
	log.Infof("Transport  : %T", clnt.Transport)
	defer clnt.CloseIdleConnections()
	resp, err := clnt.Get(
		(&url.URL{Scheme: "https", Host: *sni, Path: "/"}).String())
	if err != nil {
		fatal(err)
	}
	log.Infof("Status code: %d", resp.StatusCode)
	resp.Body.Close()
}

// ```
//
// We won't comment on the rest of the program because it is
// exactly like what we've seen in chapter04.
//
// ```Go

func dialQUIC(ctx context.Context, address string,
	config *tls.Config) (quic.EarlySession, tls.ConnectionState, error) {
	ql := netxlite.NewQUICListener()
	d := netxlite.NewQUICDialerWithoutResolver(ql, log.Log)
	sess, err := d.DialContext(ctx, "udp", address, config, &quic.Config{})
	if err != nil {
		return nil, tls.ConnectionState{}, err
	}
	return sess, sess.ConnectionState().TLS.ConnectionState, nil
}

func fatal(err error) {
	var ew *netxlite.ErrWrapper
	if !errors.As(err, &ew) {
		log.Fatal("cannot get ErrWrapper")
	}
	log.Warnf("error string    : %s", err.Error())
	log.Warnf("OONI failure    : %s", ew.Failure)
	log.Warnf("failed operation: %s", ew.Operation)
	log.Warnf("underlying error: %+v", ew.WrappedErr)
	os.Exit(1)
}

// ```
//
// ## Running the code
//
// ### Vanilla run
//
// You can now run this code as follows:
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter08
// ```
//
// You will see debug logs describing what is happening along with timing info.
//
// ### QUIC handshake timeout
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter08 -address 8.8.4.4:1
// ```
//
// should cause a QUIC handshake timeout error. Try lowering the timout adding, e.g.,
// the `-timeout 5s` flag to the command line.
//
// ### SNI mismatch
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter08 -sni example.com
// ```
//
// should give you an error mentioning the certificate is invalid.
//
// ## Conclusions
//
// We have seen how to establish a QUIC session with a website
// and then how to GET a webpage using such a session.