derp: clean up derphttp client code, use contexts

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

derp/derp_server.go

@@ -97,10 +97,13 @@ func (s *Server) isClosed() bool {
 	return s.closed
 }
 
-// Accept adds a new connection to the server.
+// Accept adds a new connection to the server and serves it.
+//
 // The provided bufio ReadWriter must be already connected to nc.
 // Accept blocks until the Server is closed or the connection closes
 // on its own.
+//
+// Accept closes nc.
 func (s *Server) Accept(nc net.Conn, brw *bufio.ReadWriter) {
 	closed := make(chan struct{})
 

derp/derphttp/derphttp_client.go

@@ -12,16 +12,18 @@ package derphttp
 
 import (
 	"bufio"
-	"bytes"
 	"context"
 	"crypto/tls"
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
+	"log"
 	"net"
 	"net/http"
 	"net/url"
 	"sync"
+	"time"
 
 	"tailscale.com/derp"
 	"tailscale.com/types/key"
@@ -37,15 +39,15 @@ import (
 type Client struct {
 	privateKey key.Private
 	logf       logger.Logf
-	closed     chan struct{}
 	url        *url.URL
-	resp       *http.Response
 
-	netConnMu sync.Mutex
+	ctx       context.Context // closed via cancelCtx in Client.Close
-	netConn   net.Conn
+	cancelCtx context.CancelFunc
 
-	clientMu sync.Mutex
+	mu      sync.Mutex
-	client   *derp.Client
+	closed  bool
+	netConn io.Closer
+	client  *derp.Client
 }
 
 // NewClient returns a new DERP-over-HTTP client. It connects lazily.
@@ -55,12 +57,16 @@ func NewClient(privateKey key.Private, serverURL string, logf logger.Logf) (*Cli
 	if err != nil {
 		return nil, fmt.Errorf("derphttp.NewClient: %v", err)
 	}
-
+	if urlPort(u) == "" {
+		return nil, fmt.Errorf("derphttp.NewClient: invalid URL scheme %q", u.Scheme)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
 	c := &Client{
 		privateKey: privateKey,
 		logf:       logf,
 		url:        u,
-		closed:     make(chan struct{}),
+		ctx:        ctx,
+		cancelCtx:  cancel,
 	}
 	return c, nil
 }
@@ -72,71 +78,119 @@ func (c *Client) Connect(ctx context.Context) error {
 	return err
 }
 
+func urlPort(u *url.URL) string {
+	if p := u.Port(); p != "" {
+		return p
+	}
+	switch u.Scheme {
+	case "https":
+		return "443"
+	case "http":
+		return "80"
+	}
+	return ""
+}
+
 func (c *Client) connect(ctx context.Context, caller string) (client *derp.Client, err error) {
-	// TODO: use ctx for TCP+TLS+HTTP below
+	c.mu.Lock()
-	select {
+	defer c.mu.Unlock()
-	case <-c.closed:
+	if c.closed {
 		return nil, ErrClientClosed
-	default:
 	}
-
-	c.clientMu.Lock()
-	defer c.clientMu.Unlock()
-
 	if c.client != nil {
 		return c.client, nil
 	}
 
-	c.logf("%s: connecting", caller)
+	c.logf("%s: connecting to %v", caller, c.url)
+
+	// timeout is the fallback maximum time (if ctx doesn't limit
+	// it further) to do all of: DNS + TCP + TLS + HTTP Upgrade +
+	// DERP upgrade.
+	const timeout = 10 * time.Second
+	ctx, cancel := context.WithTimeout(ctx, timeout)
+	go func() {
+		select {
+		case <-ctx.Done():
+			log.Printf("XXXX normal")
+			// Either timeout fired (handled below), or
+			// we're returning via the defer cancel()
+			// below.
+		case <-c.ctx.Done():
+			log.Printf("XXXX dead2")
+			// Propagate a Client.Close call into
+			// cancelling this context.
+			cancel()
+		}
+	}()
+	defer cancel()
 
-	var netConn net.Conn
+	var tcpConn net.Conn
 	defer func() {
 		if err != nil {
-			err = fmt.Errorf("%s connect: %v", caller, err)
+			if ctx.Err() != nil {
-			if netConn != nil {
+				err = fmt.Errorf("%v: %v", ctx.Err(), err)
-				netConn.Close()
+			}
+			err = fmt.Errorf("%s connect to %v: %v", caller, c.url, err)
+			if tcpConn != nil {
+				go tcpConn.Close()
 			}
 		}
 	}()
 
-	if c.url.Scheme == "https" {
+	var d net.Dialer
-		port := c.url.Port()
+	log.Printf("Dialing: %q", net.JoinHostPort(c.url.Hostname(), urlPort(c.url)))
-		if port == "" {
+	tcpConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(c.url.Hostname(), urlPort(c.url)))
-			port = "443"
-		}
-		config := &tls.Config{}
-		var tlsConn *tls.Conn
-		tlsConn, err = tls.Dial("tcp", net.JoinHostPort(c.url.Host, port), config)
-		if tlsConn != nil {
-			netConn = tlsConn
-		}
-	} else {
-		netConn, err = net.Dial("tcp", c.url.Host)
-	}
 	if err != nil {
 		return nil, err
 	}
 
-	c.netConnMu.Lock()
+	// Now that we have a TCP connection, force close it.
-	c.netConn = netConn
+	done := make(chan struct{})
-	c.netConnMu.Unlock()
+	defer close(done)
+	go func() {
+		select {
+		case <-done:
+			// Normal path. Upgrade occurred in time.
+		case <-ctx.Done():
+			select {
+			case <-done:
+				// Normal path. Upgrade occurred in time.
+				// But the ctx.Done() is also done because
+				// the "defer cancel()" above scheduled
+				// before this goroutine.
+			default:
+				// The TLS or HTTP or DERP exchanges didn't complete
+				// in time. Force close the TCP connection to force
+				// them to fail quickly.
+				tcpConn.Close()
+			}
+		}
+	}()
+
+	var httpConn net.Conn // a TCP conn or a TLS conn; what we speak HTTP to
+	if c.url.Scheme == "https" {
+		httpConn = tls.Client(tcpConn, &tls.Config{ServerName: c.url.Host})
+	} else {
+		httpConn = tcpConn
+	}
 
-	conn := bufio.NewReadWriter(bufio.NewReader(netConn), bufio.NewWriter(netConn))
+	brw := bufio.NewReadWriter(bufio.NewReader(httpConn), bufio.NewWriter(httpConn))
 
 	req, err := http.NewRequest("GET", c.url.String(), nil)
 	if err != nil {
 		return nil, err
 	}
-	req.Header.Set("Upgrade", "WebSocket")
+	req.Header.Set("Upgrade", "DERP")
 	req.Header.Set("Connection", "Upgrade")
-	if err := req.Write(conn); err != nil {
+
+	if err := req.Write(brw); err != nil {
 		return nil, err
 	}
-	if err := conn.Flush(); err != nil {
+	if err := brw.Flush(); err != nil {
 		return nil, err
 	}
 
-	resp, err := http.ReadResponse(conn.Reader, req)
+	resp, err := http.ReadResponse(brw.Reader, req)
 	if err != nil {
 		return nil, err
 	}
@@ -145,14 +199,14 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
 		resp.Body.Close()
 		return nil, fmt.Errorf("GET failed: %v: %s", err, b)
 	}
-	resp.Body = ioutil.NopCloser(bytes.NewReader([]byte{}))
 
-	derpClient, err := derp.NewClient(c.privateKey, netConn, conn, c.logf)
+	derpClient, err := derp.NewClient(c.privateKey, httpConn, brw, c.logf)
 	if err != nil {
 		return nil, err
 	}
-	c.resp = resp
+
 	c.client = derpClient
+	c.netConn = tcpConn
 	return c.client, nil
 }
 
@@ -162,7 +216,7 @@ func (c *Client) Send(dstKey key.Public, b []byte) error {
 		return err
 	}
 	if err := client.Send(dstKey, b); err != nil {
-		c.close()
+		c.Close()
 	}
 	return err
 }
@@ -174,7 +228,7 @@ func (c *Client) Recv(b []byte) (derp.ReceivedMessage, error) {
 	}
 	m, err := client.Recv(b)
 	if err != nil {
-		c.close()
+		c.Close()
 	}
 	return m, err
 }
@@ -182,35 +236,20 @@ func (c *Client) Recv(b []byte) (derp.ReceivedMessage, error) {
 // Close closes the client. It will not automatically reconnect after
 // being closed.
 func (c *Client) Close() error {
-	select {
+	c.cancelCtx() // not in lock, so it can cancel Connect, which holds mu
-	case <-c.closed:
-		return ErrClientClosed
-	default:
-	}
-	close(c.closed)
-	c.close()
-	return nil
-}
 
-func (c *Client) close() {
+	c.mu.Lock()
-	c.netConnMu.Lock()
+	defer c.mu.Unlock()
-	netConn := c.netConn
+	if c.closed {
-	c.netConnMu.Unlock()
+		return ErrClientClosed
-
-	if netConn != nil {
-		netConn.Close()
 	}
-
+	c.closed = true
-	c.clientMu.Lock()
+	if c.netConn != nil {
-	defer c.clientMu.Unlock()
+		c.netConn.Close()
-	if c.client == nil {
+		c.netConn = nil
-		return
 	}
-	c.resp = nil
 	c.client = nil
-	c.netConnMu.Lock()
+	return nil
-	c.netConn = nil
-	c.netConnMu.Unlock()
 }
 
 var ErrClientClosed = errors.New("derphttp.Client closed")

derp/derphttp/derphttp_server.go

@@ -5,6 +5,7 @@
 package derphttp
 
 import (
+	"log"
 	"net/http"
 
 	"tailscale.com/derp"
@@ -12,11 +13,11 @@ import (
 
 func Handler(s *derp.Server) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if r.Header.Get("Upgrade") != "WebSocket" {
+		if p := r.Header.Get("Upgrade"); p != "WebSocket" && p != "DERP" {
 			http.Error(w, "DERP requires connection upgrade", http.StatusUpgradeRequired)
 			return
 		}
-		w.Header().Set("Upgrade", "WebSocket")
+		w.Header().Set("Upgrade", "DERP")
 		w.Header().Set("Connection", "Upgrade")
 		w.WriteHeader(http.StatusSwitchingProtocols)
 
@@ -27,6 +28,7 @@ func Handler(s *derp.Server) http.Handler {
 		}
 		netConn, conn, err := h.Hijack()
 		if err != nil {
+			log.Printf("Hijack failed: %v", err)
 			http.Error(w, "HTTP does not support general TCP support", 500)
 			return
 		}