tls-autodetect: put most of the server code in place

So far we act up when it is the client who initializes the shutdown.

prototypes/tls-autodetect.go

@@ -13,12 +13,17 @@
 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 //
 
+//
 // This is an example TLS-autodetecting chat server.
 //
-// You may connect to it either using:
+// You may connect to it using either of these:
+//  ncat -C localhost 1234
+//  ncat -C --ssl localhost 1234
+//
+// These clients are unable to properly shutdown the connection:
 //  telnet localhost 1234
-// or
 //  openssl s_client -connect localhost:1234
+//
 package main
 
 import (
@@ -37,6 +42,7 @@ import (
 
 // --- Utilities ---------------------------------------------------------------
 
+//
 // Trivial SSL/TLS autodetection. The first block of data returned by Recvfrom
 // must be at least three octets long for this to work reliably, but that should
 // not pose a problem in practice. We might try waiting for them.
@@ -46,8 +52,7 @@ import (
 //  SSL3/TLS:    <22>    |    <3>    | xxxx xxxx
 //            (handshake)|  (protocol version)
 //
-func detectTLS(sysconn syscall.RawConn) bool {
-	isTLS := false
+func detectTLS(sysconn syscall.RawConn) (isTLS bool) {
 	sysconn.Read(func(fd uintptr) (done bool) {
 		var buf [3]byte
 		n, _, err := syscall.Recvfrom(int(fd), buf[:], syscall.MSG_PEEK)
@@ -78,21 +83,27 @@ type client struct {
 	transport  net.Conn       // underlying connection
 	tls        *tls.Conn      // TLS, if detected
 	conn       connCloseWrite // high-level connection
-	connReady  bool           // conn is safe to read from the main goroutine
 	inQ        []byte         // unprocessed input
 	outQ       []byte         // unprocessed output
 	writing    bool           // whether a writing goroutine is running
 	inShutdown bool           // whether we're closing connection
+	killTimer  *time.Timer    // timeout
+}
+
+type preparedEvent struct {
+	client *client
+	host   string // client's hostname or literal IP address
+	isTLS  bool   // the client seems to use TLS
 }
 
 type readEvent struct {
-	client *client // client
+	client *client
 	data   []byte // new data from the client
 	err    error  // read error
 }
 
 type writeEvent struct {
-	client  *client // client
+	client  *client
 	written int   // amount of bytes written
 	err     error // write error
 }
@@ -100,8 +111,10 @@ type writeEvent struct {
 var (
 	sigs     = make(chan os.Signal, 1)
 	conns    = make(chan net.Conn)
+	prepared = make(chan preparedEvent)
 	reads    = make(chan readEvent)
 	writes   = make(chan writeEvent)
+	timeouts = make(chan *client)
 
 	tlsConf       *tls.Config
 	clients       = make(map[*client]bool)
@@ -122,6 +135,7 @@ func broadcast(line string, except *client) {
 	}
 }
 
+// Initiate a clean shutdown of the whole daemon.
 func initiateShutdown() {
 	log.Println("shutting down")
 	if err := listener.Close(); err != nil {
@@ -135,7 +149,12 @@ func initiateShutdown() {
 	inShutdown = true
 }
 
+// Forcefully tear down all connections.
 func forceShutdown(reason string) {
+	if !inShutdown {
+		log.Fatalln("forceShutdown called without initiateShutdown")
+	}
+
 	log.Printf("forced shutdown (%s)\n", reason)
 	for c := range clients {
 		c.destroy()
@@ -151,67 +170,84 @@ func (c *client) send(line string) {
 	}
 }
 
-func (c *client) shutdown() {
+// Tear down the client connection, trying to do so in a graceful manner.
+func (c *client) kill() {
 	if c.inShutdown {
-		log.Println("client double shutdown")
+		return
+	}
+	if c.conn == nil {
+		c.destroy()
 		return
 	}
 
-	// TODO: We must set a timer and destroy the client on timeout. Since we
-	//   have a central event loop, we probably need an event. Since we also
-	//   seem to need an event for TLS autodetection because of conn, we might
-	//   want to send an enumeration value.
-	c.inShutdown = true
-	c.conn.CloseWrite()
-}
-
-// Tear down the client connection, trying to do so in a graceful manner.
-func (c *client) kill() {
-	if c.connReady {
+	// Since we send this goodbye, we don't need to call CloseWrite.
 	c.send("Goodbye")
-		c.shutdown()
-	} else {
-		c.destroy()
-	}
+	c.killTimer = time.AfterFunc(3*time.Second, func() {
+		timeouts <- c
+	})
+
+	c.inShutdown = true
 }
 
 // Close the connection and forget about the client.
 func (c *client) destroy() {
 	// Try to send a "close notify" alert if the TLS object is ready,
 	// otherwise just tear down the transport.
-	if c.connReady {
+	if c.conn != nil {
 		_ = c.conn.Close()
 	} else {
 		_ = c.transport.Close()
 	}
 
+	// Clean up the goroutine, although a spurious event may still be sent.
+	if c.killTimer != nil {
+		c.killTimer.Stop()
+	}
+
 	delete(clients, c)
 }
 
+// Handle the results from initializing the client's connection.
+func (c *client) onPrepared(host string, isTLS bool) {
+	if isTLS {
+		c.tls = tls.Server(c.transport, tlsConf)
+		c.conn = c.tls
+	} else {
+		c.conn = c.transport.(connCloseWrite)
+	}
+
+	// TODO: Save the host in the client structure.
+	go read(c)
+}
+
 // Handle the results from trying to read from the client connection.
 func (c *client) onRead(data []byte, readErr error) {
 	c.inQ = append(c.inQ, data...)
 	for {
 		advance, token, _ := bufio.ScanLines(c.inQ, false /* atEOF */)
-		c.inQ = c.inQ[advance:]
 		if advance == 0 {
 			break
 		}
 
+		c.inQ = c.inQ[advance:]
 		line := string(token)
 		fmt.Println(line)
 		broadcast(line, c)
 	}
 
 	// TODO: Inform the client about the inQ overrun in the farewell message.
+	// TODO: We should stop receiving any more data from this client.
 	if len(c.inQ) > 8192 {
 		c.kill()
 		return
 	}
 
 	if readErr == io.EOF {
-		// TODO: What if we're already in shutdown?
-		c.shutdown()
+		if c.inShutdown {
+			c.destroy()
+		} else {
+			c.kill()
+		}
 	} else if readErr != nil {
 		log.Println(readErr)
 		c.destroy()
@@ -221,7 +257,7 @@ func (c *client) onRead(data []byte, readErr error) {
 // Spawn a goroutine to flush the outQ if possible and necessary.  If the
 // connection is not ready yet, it needs to be retried as soon as it becomes.
 func (c *client) flushOutQ() {
-	if c.connReady && !c.writing {
+	if c.conn != nil && !c.writing {
 		go write(c, c.outQ)
 		c.writing = true
 	}
@@ -238,41 +274,77 @@ func (c *client) onWrite(written int, writeErr error) {
 	} else if len(c.outQ) > 0 {
 		c.flushOutQ()
 	} else if c.inShutdown {
+		if c.conn != nil {
+			// FIXME: This is only correct for when /we/ initiate the shutdown,
+			// otherwise we should perhaps just Close. Though even if we
+			// Close, there's a/ no writer to fail on it, and b/ the reader
+			// has already exited, too, which is why the client stays alive
+			// up until the timeout. It seems that in that case we need to
+			// call c.destroy().
+			c.conn.CloseWrite()
+		} else {
 			c.destroy()
 		}
 	}
+}
 
 // --- Worker goroutines -------------------------------------------------------
 
 func accept(ln net.Listener) {
-	// TODO: Consider specific cases in error handling, some errors
-	//   are transitional while others are fatal.
 	for {
 		if conn, err := ln.Accept(); err != nil {
+			// TODO: Consider specific cases in error handling, some errors
+			// are transitional while others are fatal.
 			log.Println(err)
+			break
 		} else {
 			conns <- conn
 		}
 	}
 }
 
-func read(client *client) {
-	// TODO: Either here or elsewhere we need to set a timeout.
-
-	client.conn = client.transport.(connCloseWrite)
-	if sysconn, err := client.transport.(syscall.Conn).SyscallConn(); err != nil {
-		// This is just for the TLS detection and doesn't need to be fatal.
-		log.Println(err)
-	} else if detectTLS(sysconn) {
-		client.tls = tls.Server(client.transport, tlsConf)
-		client.conn = client.tls
+func prepare(client *client) {
+	conn := client.transport
+	host, _, err := net.SplitHostPort(conn.RemoteAddr().String())
+	if err != nil {
+		// In effect, we require TCP/UDP, as they have port numbers.
+		log.Fatalln(err)
 	}
 
-	// TODO: Signal the main goroutine that conn is ready. In fact, the upper
-	//   part could be mostly moved to the main goroutine and we'd only spawn
-	//   a thin wrapper around detectTLS, sending back {*client, bool}. Heck,
-	//   I could get rid of connReady.
+	// The Cgo resolver doesn't pthread_cancel getnameinfo threads, so not
+	// bothering with pointless contexts.
+	ch := make(chan string)
+	go func() {
+		defer close(ch)
+		if names, err := net.LookupAddr(host); err != nil {
+			log.Println(err)
+		} else {
+			ch <- names[0]
+		}
+	}()
 
+	// While we can't cancel it, we still want to set a timeout on it.
+	select {
+	case <-time.After(5 * time.Second):
+	case resolved, ok := <-ch:
+		if ok {
+			host = resolved
+		}
+	}
+
+	isTLS := false
+	if sysconn, err := conn.(syscall.Conn).SyscallConn(); err != nil {
+		// This is just for the TLS detection and doesn't need to be fatal.
+		log.Println(err)
+	} else {
+		isTLS = detectTLS(sysconn)
+	}
+
+	prepared <- preparedEvent{client, host, isTLS}
+
+}
+
+func read(client *client) {
 	// A new buffer is allocated each time we receive some bytes, because of
 	// thread-safety. Therefore the buffer shouldn't be too large, or we'd
 	// need to copy it each time into a precisely sized new buffer.
@@ -312,7 +384,13 @@ func processOneEvent() {
 		log.Println("accepted client connection")
 		c := &client{transport: conn}
 		clients[c] = true
-		go read(c)
+		go prepare(c)
+
+	case ev := <-prepared:
+		log.Println("client is ready:", ev.host)
+		if _, ok := clients[ev.client]; ok {
+			ev.client.onPrepared(ev.host, ev.isTLS)
+		}
 
 	case ev := <-reads:
 		log.Println("received data from client")
@@ -325,6 +403,12 @@ func processOneEvent() {
 		if _, ok := clients[ev.client]; ok {
 			ev.client.onWrite(ev.written, ev.err)
 		}
+
+	case c := <-timeouts:
+		if _, ok := clients[c]; ok {
+			log.Println("client timeouted")
+			c.destroy()
+		}
 	}
 }