Add authentication.

Other code fixing:
- Fixed bugs in get32.
- Fix code for parsing display string (as a new function).
- Fix code for connecting to X server. The old code only work
  if the server is listening to TCP port, otherwise it doesn't
  work (at least in my PC).

R=nigeltao_golang, rsc, jhh
CC=golang-dev
https://golang.org/cl/183111

src/pkg/xgb/auth.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xgb
+
+import (
+	"bufio"
+	"io"
+	"os"
+)
+
+func getU16BE(r io.Reader, b []byte) (uint16, os.Error) {
+	_, err := io.ReadFull(r, b[0:2])
+	if err != nil {
+		return 0, err
+	}
+	return uint16(b[0])<<8 + uint16(b[1]), nil
+}
+
+func getBytes(r io.Reader, b []byte) ([]byte, os.Error) {
+	n, err := getU16BE(r, b)
+	if err != nil {
+		return nil, err
+	}
+	if int(n) > len(b) {
+		return nil, os.NewError("bytes too long for buffer")
+	}
+	_, err = io.ReadFull(r, b[0:n])
+	if err != nil {
+		return nil, err
+	}
+	return b[0:n], nil
+}
+
+func getString(r io.Reader, b []byte) (string, os.Error) {
+	b, err := getBytes(r, b)
+	if err != nil {
+		return "", err
+	}
+	return string(b), nil
+}
+
+// readAuthority reads the X authority file for the DISPLAY.
+// If hostname == "" or hostname == "localhost",
+// readAuthority uses the system's hostname (as returned by os.Hostname) instead.
+func readAuthority(hostname, display string) (name string, data []byte, err os.Error) {
+	// b is a scratch buffer to use and should be at least 256 bytes long
+	// (i.e. it should be able to hold a hostname).
+	var b [256]byte
+
+	// As per /usr/include/X11/Xauth.h.
+	const familyLocal = 256
+
+	if len(hostname) == 0 || hostname == "localhost" {
+		hostname, err = os.Hostname()
+		if err != nil {
+			return "", nil, err
+		}
+	}
+
+	fname := os.Getenv("XAUTHORITY")
+	if len(fname) == 0 {
+		home := os.Getenv("HOME")
+		if len(home) == 0 {
+			err = os.NewError("Xauthority not found: $XAUTHORITY, $HOME not set")
+			return "", nil, err
+		}
+		fname = home + "/.Xauthority"
+	}
+
+	r, err := os.Open(fname, os.O_RDONLY, 0444)
+	if err != nil {
+		return "", nil, err
+	}
+	defer r.Close()
+
+	br := bufio.NewReader(r)
+	for {
+		family, err := getU16BE(br, b[0:2])
+		if err != nil {
+			return "", nil, err
+		}
+
+		addr, err := getString(br, b[0:])
+		if err != nil {
+			return "", nil, err
+		}
+
+		disp, err := getString(br, b[0:])
+		if err != nil {
+			return "", nil, err
+		}
+
+		name0, err := getString(br, b[0:])
+		if err != nil {
+			return "", nil, err
+		}
+
+		data0, err := getBytes(br, b[0:])
+		if err != nil {
+			return "", nil, err
+		}
+
+		if family == familyLocal && addr == hostname && disp == display {
+			return name0, data0, nil
+		}
+	}
+	panic("unreachable")
+}

src/pkg/xgb/xgb.go

@@ -18,12 +18,14 @@ import (
 // A Conn represents a connection to an X server.
 // Only one goroutine should use a Conn's methods at a time.
 type Conn struct {
+	host          string
 	conn          net.Conn
 	nextId        Id
 	nextCookie    Cookie
 	replies       map[Cookie][]byte
 	events        queue
 	err           os.Error
+	display       string
 	defaultScreen int
 	scratch       [32]byte
 	Setup         SetupInfo
@@ -89,7 +91,7 @@ func get32(buf []byte) uint32 {
 	v := uint32(buf[0])
 	v |= uint32(buf[1]) << 8
 	v |= uint32(buf[2]) << 16
-	v |= uint32(buf[3]) << 32
+	v |= uint32(buf[3]) << 24
 	return v
 }
 
@@ -284,49 +286,39 @@ func (c *Conn) PollForEvent() (Event, os.Error) {
 }
 
 // Dial connects to the X server given in the 'display' string.
-// The display string is typically taken from os.Getenv("DISPLAY").
+// If 'display' is empty it will be taken from os.Getenv("DISPLAY").
+//
+// Examples:
+//	Dial(":1")                 // connect to net.Dial("unix", "", "/tmp/.X11-unix/X1")
+//	Dial("/tmp/launch-123/:0") // connect to net.Dial("unix", "", "/tmp/launch-123/:0")
+//	Dial("hostname:2.1")       // connect to net.Dial("tcp", "", "hostname:6002")
+//	Dial("tcp/hostname:1.0")   // connect to net.Dial("tcp", "", "hostname:6001")
 func Dial(display string) (*Conn, os.Error) {
-	var err os.Error
-
-	c := new(Conn)
-
-	if display[0] == '/' {
-		c.conn, err = net.Dial("unix", "", display)
+	c, err := connect(display)
 	if err != nil {
-			fmt.Printf("cannot connect: %v\n", err)
 		return nil, err
 	}
-	} else {
-		parts := strings.Split(display, ":", 2)
-		host := parts[0]
-		port := 0
-		if len(parts) > 1 {
-			parts = strings.Split(parts[1], ".", 2)
-			port, _ = strconv.Atoi(parts[0])
-			if len(parts) > 1 {
-				c.defaultScreen, _ = strconv.Atoi(parts[1])
-			}
-		}
-		display = fmt.Sprintf("%s:%d", host, port+6000)
-		c.conn, err = net.Dial("tcp", "", display)
+
+	// Get authentication data
+	authName, authData, err := readAuthority(c.host, c.display)
 	if err != nil {
-			fmt.Printf("cannot connect: %v\n", err)
 		return nil, err
 	}
-	}
 
-	// TODO: get these from .Xauthority
-	var authName, authData []byte
+	// Assume that the authentication protocol is "MIT-MAGIC-COOKIE-1".
+	if authName != "MIT-MAGIC-COOKIE-1" || len(authData) != 16 {
+		return nil, os.NewError("unsupported auth protocol " + authName)
+	}
 
 	buf := make([]byte, 12+pad(len(authName))+pad(len(authData)))
-	buf[0] = 'l'
+	buf[0] = 0x6c
 	buf[1] = 0
 	put16(buf[2:], 11)
 	put16(buf[4:], 0)
 	put16(buf[6:], uint16(len(authName)))
 	put16(buf[8:], uint16(len(authData)))
 	put16(buf[10:], 0)
-	copy(buf[12:], authName)
+	copy(buf[12:], strings.Bytes(authName))
 	copy(buf[12+pad(len(authName)):], authData)
 	if _, err = c.conn.Write(buf); err != nil {
 		return nil, err
@@ -396,3 +388,77 @@ func getClientMessageData(b []byte, v *ClientMessageData) int {
 	}
 	return 20
 }
+
+func connect(display string) (*Conn, os.Error) {
+	if len(display) == 0 {
+		display = os.Getenv("DISPLAY")
+	}
+
+	display0 := display
+	if len(display) == 0 {
+		return nil, os.NewError("empty display string")
+	}
+
+	colonIdx := strings.LastIndex(display, ":")
+	if colonIdx < 0 {
+		return nil, os.NewError("bad display string: " + display0)
+	}
+
+	var protocol, socket string
+	c := new(Conn)
+
+	if display[0] == '/' {
+		socket = display[0:colonIdx]
+	} else {
+		slashIdx := strings.LastIndex(display, "/")
+		if slashIdx >= 0 {
+			protocol = display[0:slashIdx]
+			c.host = display[slashIdx+1 : colonIdx]
+		} else {
+			c.host = display[0:colonIdx]
+		}
+	}
+
+	display = display[colonIdx+1 : len(display)]
+	if len(display) == 0 {
+		return nil, os.NewError("bad display string: " + display0)
+	}
+
+	var scr string
+	dotIdx := strings.LastIndex(display, ".")
+	if dotIdx < 0 {
+		c.display = display[0:]
+	} else {
+		c.display = display[0:dotIdx]
+		scr = display[dotIdx+1:]
+	}
+
+	dispnum, err := strconv.Atoui(c.display)
+	if err != nil {
+		return nil, os.NewError("bad display string: " + display0)
+	}
+
+	if len(scr) != 0 {
+		c.defaultScreen, err = strconv.Atoi(scr)
+		if err != nil {
+			return nil, os.NewError("bad display string: " + display0)
+		}
+	}
+
+	// Connect to server
+	if len(socket) != 0 {
+		c.conn, err = net.Dial("unix", "", socket+":"+c.display)
+	} else if len(c.host) != 0 {
+		if protocol == "" {
+			protocol = "tcp"
+		}
+		c.conn, err = net.Dial(protocol, "", c.host+":"+strconv.Uitoa(6000+dispnum))
+	} else {
+		c.conn, err = net.Dial("unix", "", "/tmp/.X11-unix/X"+c.display)
+	}
+
+	if err != nil {
+		return nil, os.NewError("cannot connect to " + display0 + ": " + err.String())
+	}
+	return c, nil
+}