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/psiphon.go

@@ -0,0 +1,124 @@
+package tunnel
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/url"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/ooni/psiphon/oopsi/github.com/Psiphon-Labs/psiphon-tunnel-core/ClientLibrary/clientlib"
+)
+
+// psiphonDependencies contains dependencies for psiphonStart
+type psiphonDependencies interface {
+	MkdirAll(path string, perm os.FileMode) error
+	RemoveAll(path string) error
+	Start(ctx context.Context, config []byte,
+		workdir string) (*clientlib.PsiphonTunnel, error)
+}
+
+type defaultDependencies struct{}
+
+func (defaultDependencies) MkdirAll(path string, perm os.FileMode) error {
+	return os.MkdirAll(path, perm)
+}
+
+func (defaultDependencies) RemoveAll(path string) error {
+	return os.RemoveAll(path)
+}
+
+func (defaultDependencies) Start(
+	ctx context.Context, config []byte, workdir string) (*clientlib.PsiphonTunnel, error) {
+	return clientlib.StartTunnel(ctx, config, "", clientlib.Parameters{
+		DataRootDirectory: &workdir}, nil, nil)
+}
+
+// psiphonConfig contains the settings for psiphonStart. The empty config object implies
+// that we will be using default settings for starting the tunnel.
+type psiphonConfig struct {
+	// Dependencies contains dependencies for Start.
+	Dependencies psiphonDependencies
+
+	// WorkDir is the directory where Psiphon should store
+	// its configuration database.
+	WorkDir string
+}
+
+// psiphonTunnel is a psiphon tunnel
+type psiphonTunnel struct {
+	tunnel   *clientlib.PsiphonTunnel
+	duration time.Duration
+}
+
+func makeworkingdir(config psiphonConfig) (string, error) {
+	const testdirname = "oonipsiphon"
+	workdir := filepath.Join(config.WorkDir, testdirname)
+	if err := config.Dependencies.RemoveAll(workdir); err != nil {
+		return "", err
+	}
+	if err := config.Dependencies.MkdirAll(workdir, 0700); err != nil {
+		return "", err
+	}
+	return workdir, nil
+}
+
+// psiphonStart starts the psiphon tunnel.
+func psiphonStart(
+	ctx context.Context, sess Session, config psiphonConfig) (Tunnel, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err() // simplifies unit testing this code
+	default:
+	}
+	if config.Dependencies == nil {
+		config.Dependencies = defaultDependencies{}
+	}
+	if config.WorkDir == "" {
+		config.WorkDir = sess.TempDir()
+	}
+	configJSON, err := sess.FetchPsiphonConfig(ctx)
+	if err != nil {
+		return nil, err
+	}
+	workdir, err := makeworkingdir(config)
+	if err != nil {
+		return nil, err
+	}
+	start := time.Now()
+	tunnel, err := config.Dependencies.Start(ctx, configJSON, workdir)
+	if err != nil {
+		return nil, err
+	}
+	stop := time.Now()
+	return &psiphonTunnel{tunnel: tunnel, duration: stop.Sub(start)}, nil
+}
+
+// Stop is an idempotent method that shuts down the tunnel
+func (t *psiphonTunnel) Stop() {
+	if t != nil {
+		t.tunnel.Stop()
+	}
+}
+
+// SOCKS5ProxyURL returns the SOCKS5 proxy URL.
+func (t *psiphonTunnel) SOCKS5ProxyURL() (proxyURL *url.URL) {
+	if t != nil {
+		proxyURL = &url.URL{
+			Scheme: "socks5",
+			Host: net.JoinHostPort(
+				"127.0.0.1", fmt.Sprintf("%d", t.tunnel.SOCKSProxyPort)),
+		}
+	}
+	return
+}
+
+// BootstrapTime returns the bootstrap time
+func (t *psiphonTunnel) BootstrapTime() (duration time.Duration) {
+	if t != nil {
+		duration = t.duration
+	}
+	return
+}