refactor: merge psiphonx and torx into tunnel (#287)

* refactor: merge psiphonx and torx into tunnel

This is a case where it seems that merging these three packages into
a single package will enable us to better the implementation.

The goal is still https://github.com/ooni/probe/issues/985.

The roadblock I'm trying to overcome is
https://github.com/ooni/probe-cli/pull/286#pullrequestreview-627460104.

* avoid duplicating logger for now

internal/engine/tunnel/tor.go

@@ -0,0 +1,138 @@
+package tunnel
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+	"path"
+	"strings"
+	"time"
+
+	"github.com/cretz/bine/control"
+	"github.com/cretz/bine/tor"
+)
+
+// torProcess is a running tor process
+type torProcess interface {
+	Close() error
+}
+
+// torTunnel is the Tor tunnel
+type torTunnel struct {
+	bootstrapTime time.Duration
+	instance      torProcess
+	proxy         *url.URL
+}
+
+// BootstrapTime is the bootstrsap time
+func (tt *torTunnel) BootstrapTime() (duration time.Duration) {
+	if tt != nil {
+		duration = tt.bootstrapTime
+	}
+	return
+}
+
+// SOCKS5ProxyURL returns the URL of the SOCKS5 proxy
+func (tt *torTunnel) SOCKS5ProxyURL() (url *url.URL) {
+	if tt != nil {
+		url = tt.proxy
+	}
+	return
+}
+
+// Stop stops the Tor tunnel
+func (tt *torTunnel) Stop() {
+	if tt != nil {
+		tt.instance.Close()
+	}
+}
+
+// torStartConfig contains the configuration for StartWithConfig
+type torStartConfig struct {
+	Sess          Session
+	Start         func(ctx context.Context, conf *tor.StartConf) (*tor.Tor, error)
+	EnableNetwork func(ctx context.Context, tor *tor.Tor, wait bool) error
+	GetInfo       func(ctrl *control.Conn, keys ...string) ([]*control.KeyVal, error)
+}
+
+// torStart starts the tor tunnel
+func torStart(ctx context.Context, sess Session) (Tunnel, error) {
+	return torStartWithConfig(ctx, torStartConfig{
+		Sess: sess,
+		Start: func(ctx context.Context, conf *tor.StartConf) (*tor.Tor, error) {
+			return tor.Start(ctx, conf)
+		},
+		EnableNetwork: func(ctx context.Context, tor *tor.Tor, wait bool) error {
+			return tor.EnableNetwork(ctx, wait)
+		},
+		GetInfo: func(ctrl *control.Conn, keys ...string) ([]*control.KeyVal, error) {
+			return ctrl.GetInfo(keys...)
+		},
+	})
+}
+
+// torStartWithConfig is a configurable torStart for testing
+func torStartWithConfig(ctx context.Context, config torStartConfig) (Tunnel, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err() // allows to write unit tests using this code
+	default:
+	}
+	logfile := LogFile(config.Sess)
+	extraArgs := append([]string{}, config.Sess.TorArgs()...)
+	extraArgs = append(extraArgs, "Log")
+	extraArgs = append(extraArgs, "notice stderr")
+	extraArgs = append(extraArgs, "Log")
+	extraArgs = append(extraArgs, fmt.Sprintf(`notice file %s`, logfile))
+	instance, err := config.Start(ctx, &tor.StartConf{
+		DataDir:   path.Join(config.Sess.TempDir(), "tor"),
+		ExtraArgs: extraArgs,
+		ExePath:   config.Sess.TorBinary(),
+		NoHush:    true,
+	})
+	if err != nil {
+		return nil, err
+	}
+	instance.StopProcessOnClose = true
+	start := time.Now()
+	if err := config.EnableNetwork(ctx, instance, true); err != nil {
+		instance.Close()
+		return nil, err
+	}
+	stop := time.Now()
+	// Adapted from <https://git.io/Jfc7N>
+	info, err := config.GetInfo(instance.Control, "net/listeners/socks")
+	if err != nil {
+		instance.Close()
+		return nil, err
+	}
+	if len(info) != 1 || info[0].Key != "net/listeners/socks" {
+		instance.Close()
+		return nil, fmt.Errorf("unable to get socks proxy address")
+	}
+	proxyAddress := info[0].Val
+	if strings.HasPrefix(proxyAddress, "unix:") {
+		instance.Close()
+		return nil, fmt.Errorf("tor returned unsupported proxy")
+	}
+	return &torTunnel{
+		bootstrapTime: stop.Sub(start),
+		instance:      instance,
+		proxy:         &url.URL{Scheme: "socks5", Host: proxyAddress},
+	}, nil
+}
+
+// LogFile returns the name of tor logs given a specific session. The file
+// is always located somewhere inside the sess.TempDir() directory.
+func LogFile(sess Session) string {
+	return path.Join(sess.TempDir(), "tor.log")
+}
+
+// newTorTunnel creates a new torTunnel
+func newTorTunnel(bootstrapTime time.Duration, instance torProcess, proxy *url.URL) *torTunnel {
+	return &torTunnel{
+		bootstrapTime: bootstrapTime,
+		instance:      instance,
+		proxy:         proxy,
+	}
+}