// -=-=- StartHere -=-=-
//
// # Chapter I: TLS parroting
//
// In this chapter we will write together a `main.go` file that
// uses netxlite to establish a new TCP connection and then performs
// a TLS handshake using the established connection.
//
// Rather than using the Go standard library, like we did in the
// previous chapter, we will use the `gitlab.com/yawning/utls.git`
// library to customize the ClientHello to look like Firefox.
//
// (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 the previous chapter,
// so there is not much to say about it.
//
// ```Go
package main

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

	"github.com/apex/log"
	"github.com/ooni/probe-cli/v3/internal/netxlite"
	utls "gitlab.com/yawning/utls.git"
)

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()
	tlsConfig := &tls.Config{
		ServerName: *sni,
		NextProtos: []string{"h2", "http/1.1"},
		RootCAs:    netxlite.NewDefaultCertPool(),
	}
	conn, state, err := dialTLS(ctx, *address, tlsConfig)
	if err != nil {
		fatal(err)
	}
	log.Infof("Conn type          : %T", conn)
	log.Infof("Cipher suite       : %s", netxlite.TLSCipherSuiteString(state.CipherSuite))
	log.Infof("Negotiated protocol: %s", state.NegotiatedProtocol)
	log.Infof("TLS version        : %s", netxlite.TLSVersionString(state.Version))
	conn.Close()
}

func dialTCP(ctx context.Context, address string) (net.Conn, error) {
	d := netxlite.NewDialerWithoutResolver(log.Log)
	return d.DialContext(ctx, "tcp", address)
}

func handshakeTLS(ctx context.Context, tcpConn net.Conn,
	config *tls.Config) (net.Conn, tls.ConnectionState, error) {
	// ```
	//
	// The following line of code is where we diverge from the
	// previous chapter. Here we're creating a TLS handshaker
	// that uses `gitlab.com/yawning/utls.git` and sets the
	// ClientHello to look like Firefox 55. (This is also
	// know as TLS parroting because we're parroting what this
	// version of Firefox would do.)
	//
	// Note that, when you use parroting, some settings inside
	// the `tls.Config` (such as the ALPN) may be ignored
	// if they conflict with what the parroted browser would do.
	//
	// ```Go
	th := netxlite.NewTLSHandshakerUTLS(log.Log, &utls.HelloFirefox_55)
	// ```
	//
	// The rest of the program is exactly like the one in the
	// previous chapter, so we won't add further comments.
	//
	// ```Go
	return th.Handshake(ctx, tcpConn, config)
}

func dialTLS(ctx context.Context, address string,
	config *tls.Config) (net.Conn, tls.ConnectionState, error) {
	tcpConn, err := dialTCP(ctx, address)
	if err != nil {
		return nil, tls.ConnectionState{}, err
	}
	tlsConn, state, err := handshakeTLS(ctx, tcpConn, config)
	if err != nil {
		tcpConn.Close()
		return nil, tls.ConnectionState{}, err
	}
	return tlsConn, state, 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
//
// You can now run this code as follows:
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter03
// ```
//
// You will see debug logs describing what is happening along with timing info.
//
// ### Connect timeout
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter03 -address 8.8.4.4:1
// ```
//
// should cause a connect timeout error. Try lowering the timout adding, e.g.,
// the `-timeout 5s` flag to the command line.
//
// ### Connection refused
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter03 -address '[::1]:1'
// ```
//
// should give you a connection refused error in most cases. (We are quoting
// the `::1` IPv6 address using `[` and `]` here.)
//
// ### SNI mismatch
//
// ```bash
// go run -race ./internal/tutorial/netxlite/chapter03 -sni example.com
// ```
//
// should give you a TLS invalid hostname error (for historical reasons
// named `ssl_invalid_hostname`).
//
// ### TLS handshake reset
//
// If you're on Linux, build Jafar (`go build -v ./internal/cmd/jafar`)
// and then run:
//
// ```bash
// sudo ./jafar -iptables-reset-keyword dns.google
// ```
//
// Then run in another terminal
//
// ```bash
// go run ./internal/tutorial/netxlite/chapter03
// ```
//
// Then you can interrupt Jafar using ^C.
//
// ### TLS handshake timeout
//
// If you're on Linux, build Jafar (`go build -v ./internal/cmd/jafar`)
// and then run:
//
// ```bash
// sudo ./jafar -iptables-drop-keyword dns.google
// ```
//
// Then run in another terminal
//
// ```bash
// go run ./internal/tutorial/netxlite/chapter03
// ```
//
// Then you can interrupt Jafar using ^C.
//
// ## Conclusions
//
// We have seen how to use netxlite to establish a TCP connection
// and perform a TLS handshake using such a connection with a specific
// configuration that parrots Firefox v55's ClientHello.