refactor: move tunnel pkg down one level (#358)

* refactor: move tunnel pkg down one level

While there, reduce unnecessary dependency on external packages.

* file I forgot to commit

internal/engine/tunnel/fake.go

@@ -1,80 +0,0 @@
-package tunnel
-
-import (
-	"context"
-	"net"
-	"net/url"
-	"sync"
-	"time"
-
-	"github.com/armon/go-socks5"
-)
-
-// fakeTunnel is a fake tunnel.
-type fakeTunnel struct {
-	addr          net.Addr
-	bootstrapTime time.Duration
-	listener      net.Listener
-	once          sync.Once
-}
-
-// BootstrapTime implements Tunnel.BootstrapTime.
-func (t *fakeTunnel) BootstrapTime() time.Duration {
-	return t.bootstrapTime
-}
-
-// Stop implements Tunnel.Stop.
-func (t *fakeTunnel) Stop() {
-	// Implementation note: closing the listener causes
-	// the socks5 server.Serve to return an error
-	t.once.Do(func() { t.listener.Close() })
-}
-
-// SOCKS5ProxyURL returns the SOCKS5 proxy URL.
-func (t *fakeTunnel) SOCKS5ProxyURL() *url.URL {
-	return &url.URL{
-		Scheme: "socks5",
-		Host:   t.addr.String(),
-	}
-}
-
-// fakeStart starts the fake tunnel.
-func fakeStart(ctx context.Context, config *Config) (Tunnel, error) {
-	// do the same things other tunnels do:
-	//
-	// 1. abort if context is cancelled
-	//
-	// 2. check for tunnelDir being not empty
-	//
-	// 3. attempt to create tunnelDir
-	//
-	// after that, it's all fake and we just create a simple
-	// socks5 server that we can use
-	select {
-	case <-ctx.Done():
-		return nil, ctx.Err() // simplifies unit testing this code
-	default:
-	}
-	if config.TunnelDir == "" {
-		return nil, ErrEmptyTunnelDir
-	}
-	if err := config.mkdirAll(config.TunnelDir, 0700); err != nil {
-		return nil, err
-	}
-	server, err := config.socks5New(&socks5.Config{})
-	if err != nil {
-		return nil, err
-	}
-	start := time.Now()
-	listener, err := config.netListen("tcp", "127.0.0.1:0")
-	if err != nil {
-		return nil, err
-	}
-	bootstrapTime := time.Since(start)
-	go server.Serve(listener)
-	return &fakeTunnel{
-		addr:          listener.Addr(),
-		bootstrapTime: bootstrapTime,
-		listener:      listener,
-	}, nil
-}