make error no display error more clear

auth.go

@@ -2,15 +2,16 @@ package main
 
 import (
 	"fmt"
+	"net"
 	"os"
 	"os/exec"
 	"path"
 	"strconv"
 	"strings"
-	"net"
+	"x11proxy/x11probe"
 )
 
-func resolveDisplay(display string) (ConnType, string) {
+func resolveDisplay(display string) (x11probe.ConnType, string) {
 	var dispNum int
 	var err error
 
@@ -26,25 +27,21 @@ func resolveDisplay(display string) (ConnType, string) {
 
 	unixPath := path.Join("/tmp/.X11-unix", fmt.Sprintf("X%d", dispNum))
 	if _, err := os.Stat(unixPath); err == nil {
-        return Unix, unixPath
+		return x11probe.Unix, unixPath
 	}
 
 	tcpAddr := fmt.Sprintf("127.0.0.1:%d", 6000+dispNum)
 	conn, err := net.Dial("tcp", tcpAddr)
 	if err == nil {
 		conn.Close()
-        return TCP, tcpAddr
+		return x11probe.TCP, tcpAddr
 	}
 
-    return Unix, unixPath
+	return x11probe.Unix, unixPath
 }
 
 func getXAuthCookie(display string) ([]byte, error) {
-    out, err := exec.Command("xauth", "list").Output()
+	// Extract display number
-    if err != nil {
-        return nil, err
-    }
-
 	var dispNum string
 	if strings.HasPrefix(display, ":") {
 		dispNum = strings.Split(display[1:], ".")[0]
@@ -53,22 +50,56 @@ func getXAuthCookie(display string) ([]byte, error) {
 		dispNum = strings.Split(parts[1], ".")[0]
 	}
 
+	// Query only entries for that display
+	out, err := exec.Command("xauth", "list", ":"+dispNum).Output()
+	if err != nil {
+		return nil, fmt.Errorf("xauth list failed: %w", err)
+	}
+
 	lines := strings.Split(string(out), "\n")
+	var bestMatch string
+	var bestCookie string
+	var bestScore int
+
 	for _, line := range lines {
 		fields := strings.Fields(line)
-        if len(fields) >= 3 && fields[1] == "MIT-MAGIC-COOKIE-1" {
+		if len(fields) < 3 || fields[1] != "MIT-MAGIC-COOKIE-1" {
+			continue
+		}
+
 		entry := fields[0]
-            if strings.Contains(entry, ":"+dispNum) {
+		cookie := fields[2]
-                fmt.Printf("Using XAuth cookie from entry: %s\n", entry)
+
-                return parseHexCookie(fields[2]), nil
+		// Score based on specificity
+		score := 0
+		switch {
+		case strings.HasPrefix(entry, os.Getenv("HOSTNAME")+"/unix:"):
+			score = 100
+		case strings.HasPrefix(entry, "unix:"):
+			score = 90
+		case strings.Contains(entry, "/unix:"):
+			score = 80
+		case strings.HasPrefix(entry, "#ffff#"):
+			score = 70
+		default:
+			score = 50
+		}
+
+		if score > bestScore {
+			bestMatch = entry
+			bestCookie = cookie
+			bestScore = score
 		}
 	}
+
+	if bestCookie != "" {
+		fmt.Printf("Using XAuth cookie from entry: %s\n", bestMatch)
+		return parseHexCookie(bestCookie), nil
 	}
 
 	return nil, fmt.Errorf("no matching cookie found for display %s", display)
 }
 
-
 func parseHexCookie(hexStr string) []byte {
 	var cookie []byte
 	for i := 0; i < len(hexStr); i += 2 {
@@ -113,4 +144,3 @@ func PatchAuth(data []byte, cookie []byte) []byte {
 
 	return patched
 }
-

main.go

@@ -6,6 +6,8 @@ import (
 	"log"
 	"os"
 	"strings"
+	"time"
+	"x11proxy/x11probe"
 )
 
 const version = "0.1"
@@ -37,17 +39,36 @@ func main() {
 		display = *overrideDisplay
 	}
 
+	if display == "" {
+		log.Fatalf("No DISPLAY environment variable set and no override provided. Please set DISPLAY or use --display.")
+	}
+
 	connType, target := resolveDisplay(display)
 	fmt.Printf("Proxying to %s (%s)\n", target, connTypeString(connType))
 
-    err := StartProxy(*overrideSocket, target, connType, display)
+	timeout := 10 * time.Second
+	status, err := x11probe.ProbeX11Socket(connType, target, timeout)
 	if err != nil {
-        log.Fatalf("Proxy error: %v", err)
+		log.Fatalf("Connection probe error: %v", err)
+	}
+
+	switch status {
+	case x11probe.X11Live:
+		log.Println("X11 socket is live and accepting connections")
+	case x11probe.X11AuthRequired:
+		log.Println("X11 socket is live but requires authentication")
+	case x11probe.X11Dead:
+		log.Fatalf("Target connection is dead or unreachable")
+	}
+
+	err2 := StartProxy(*overrideSocket, target, connType, display)
+	if err2 != nil {
+		log.Fatalf("Proxy error: %v", err2)
 	}
 }
 
-func connTypeString(t ConnType) string {
+func connTypeString(t x11probe.ConnType) string {
-    if t == Unix {
+	if t == x11probe.Unix {
 		return "Unix socket"
 	}
 	return "TCP"

proxy.go

@@ -8,16 +8,11 @@ import (
 	"log"
 	"net"
 	"os"
+	"time"
+	"x11proxy/x11probe"
 )
 
-type ConnType int
+func StartProxy(proxyPath, target string, connType x11probe.ConnType, display string) error {
-
-const (
-    Unix ConnType = iota
-    TCP
-)
-
-func StartProxy(proxyPath, target string, connType ConnType, display string) error {
 	os.Remove(proxyPath)
 	listener, err := net.Listen("unix", proxyPath)
 	if err != nil {
@@ -36,11 +31,18 @@ func StartProxy(proxyPath, target string, connType ConnType, display string) err
 		go handleConnection(clientConn, connType, target, display)
 	}
 }
-
 func readAndPatchHandshake(r io.Reader, cookie []byte) ([]byte, error) {
-    // Step 1: Read fixed-length header
+	// If r is a net.Conn, set a read deadline
+	if conn, ok := r.(net.Conn); ok {
+		deadline := time.Now().Add(3 * time.Second)
+		conn.SetReadDeadline(deadline)
+	}
+
+	// Step 1: Read fixed-length header manually
 	header := make([]byte, 12)
-    if _, err := io.ReadFull(r, header); err != nil {
+	n, err := io.ReadFull(r, header)
+	if err != nil {
+		log.Printf("Handshake header read failed after %d bytes: %v", n, err)
 		return nil, fmt.Errorf("failed to read handshake header: %w", err)
 	}
 
@@ -58,13 +60,19 @@ func readAndPatchHandshake(r io.Reader, cookie []byte) ([]byte, error) {
 	authProtoLen := read16(header[6:8])
 	authDataLen := read16(header[8:10])
 
-    // Step 3: Read remaining fields
+	// Step 3 A: Read remaining fields
-    totalLen := int(authProtoLen+authDataLen)
+	totalLen := padLen(int(authProtoLen)) + padLen(int(authDataLen))
-    totalLen += padLen(int(authProtoLen)) + padLen(int(authDataLen))
 	extra := make([]byte, totalLen)
-    if _, err := io.ReadFull(r, extra); err != nil {
+
+	n, err = io.ReadFull(r, extra)
+	if err != nil {
+		log.Printf("Handshake auth read failed after %d bytes: %v", n, err)
 		return nil, fmt.Errorf("failed to read handshake auth fields: %w", err)
 	}
+	// Step 3 B: clear timeout/deadline
+	if conn, ok := r.(net.Conn); ok {
+		conn.SetReadDeadline(time.Time{})
+	}
 
 	// Step 4: Decide whether to patch
 	patch := authProtoLen == 0 || authDataLen == 0
@@ -82,7 +90,6 @@ func readAndPatchHandshake(r io.Reader, cookie []byte) ([]byte, error) {
 	newAuthProtoLen := uint16(len(authProto))
 	newAuthDataLen := uint16(len(authData))
 
-	// Patch header in-place
 	if isLittle {
 		binary.LittleEndian.PutUint16(header[6:8], newAuthProtoLen)
 		binary.LittleEndian.PutUint16(header[8:10], newAuthDataLen)
@@ -113,12 +120,12 @@ func binaryOrder(isLittle bool) binary.ByteOrder {
 	return binary.BigEndian
 }
 
-
+func handleConnection(client net.Conn, connType x11probe.ConnType, target string, display string) {
-func handleConnection(client net.Conn, connType ConnType, target string, display string) {
 	var serverConn net.Conn
 	var err error
+	var patch bool
 
-    if connType == Unix {
+	if connType == x11probe.Unix {
 		serverConn, err = net.Dial("unix", target)
 	} else {
 		serverConn, err = net.Dial("tcp", target)
@@ -130,15 +137,15 @@ func handleConnection(client net.Conn, connType ConnType, target string, display
 	}
 
 	log.Printf("New connection from %v", client.RemoteAddr())
+	patch = true
 
 	cookie, err := getXAuthCookie(display)
 	if err != nil || cookie == nil {
-        log.Printf("Failed to get XAuth cookie")
+		patch = false
-        client.Close()
+		log.Printf("Failed to get XAuth cookie, try forwarding without patching")
-        serverConn.Close()
-        return
 	}
 
+	if patch {
 		log.Printf("About to read the handshake")
 		patched, err := readAndPatchHandshake(client, cookie)
 		if err != nil {
@@ -148,7 +155,6 @@ func handleConnection(client net.Conn, connType ConnType, target string, display
 			serverConn.Close()
 			return
 		}
-	
 		_, err = serverConn.Write(patched)
 		if err != nil {
 			log.Printf("Initial write failed: %v", err)
@@ -156,7 +162,7 @@ func handleConnection(client net.Conn, connType ConnType, target string, display
 			serverConn.Close()
 			return
 		}
-
+	}
 	done := make(chan struct{}, 2)
 
 	go inspectAndForward(serverConn, client, "client→server", done)

x11probe/probe.go

@@ -0,0 +1,125 @@
+package x11probe
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"strings"
+	"time"
+)
+
+type ConnType int
+
+const (
+	Unix ConnType = iota
+	TCP
+)
+
+// X11Status represents the result of probing an X11 socket.
+type X11Status int
+
+const (
+	X11Dead X11Status = iota
+	X11Live
+	X11AuthRequired
+)
+
+func ProbeX11Socket(connType ConnType, target string, timeout time.Duration) (X11Status, error) {
+	var (
+		conn net.Conn
+		err  error
+	)
+
+	switch connType {
+	case Unix:
+		conn, err = net.DialTimeout("unix", target, timeout)
+		if err != nil {
+			return X11Dead, fmt.Errorf("unix dial failed: %w", err)
+		}
+	case TCP:
+		addr := parseTCPAddress(target)
+		conn, err = net.DialTimeout("tcp", addr, timeout)
+		if err != nil {
+			return X11Dead, fmt.Errorf("TCP dial failed: %w", err)
+		}
+	}
+
+	defer conn.Close()
+	log.Printf("Successfully connected to %s", target)
+
+	if err := performHandshake(conn); err != nil {
+		return X11Dead, err
+	}
+
+	status, err := readResponse(conn, timeout)
+	if err != nil {
+		return X11Dead, err
+	}
+
+	return status, nil
+}
+
+func parseTCPAddress(target string) string {
+	parts := strings.SplitN(target, ":", 2)
+
+	ipPart := parts[0]
+	portPart := "0"
+
+	if len(parts) == 2 && portPart != "" {
+		portPart = parts[1]
+	}
+
+	return fmt.Sprintf("%s:%s", ipPart, portPart)
+}
+
+func performHandshake(conn net.Conn) error {
+	// Minimal valid handshake with correct padding
+	handshake := []byte{
+		'l', 0, // Byte order
+		0, 11, 0, 0, // Protocol major/minor
+		0, 0, // Auth name length
+		0, 0, // Auth data length
+		0, 0, 0, 0, // Padding
+	}
+
+	if _, err := conn.Write(handshake); err != nil {
+		return fmt.Errorf("write failed: %w", err)
+	}
+	return nil
+}
+
+func readResponse(conn net.Conn, timeout time.Duration) (X11Status, error) {
+	buf := make([]byte, 1)
+
+	deadline := time.Now().Add(timeout)
+	if err := conn.SetReadDeadline(deadline); err != nil {
+		return X11Dead, fmt.Errorf("SetReadDeadline failed: %w", err)
+	}
+
+	n, err := conn.Read(buf)
+	if err != nil {
+		if err == io.EOF {
+			return X11AuthRequired, nil
+		}
+		return X11Dead, fmt.Errorf("read failed: %w", err)
+	}
+
+	if n == 0 {
+		return X11Dead, fmt.Errorf("read returned 0 bytes")
+	}
+
+	switch buf[0] {
+	case 0x01:
+		return X11Live, nil
+	case 0x02:
+		return X11AuthRequired, nil
+	case 0x00:
+		fmt.Printf("X11 handshake rejected (value %x)\n", buf[0])
+		return X11AuthRequired, nil
+	default:
+		fmt.Printf("unexpected value %x\n", buf[0])
+		return X11Dead, nil
+	}
+
+}