Fix VNC WebSocket connection hanging after initial RFB handshake

- Implement bidirectional pipe communication for VNC sessions
- Replace single pipe with separate stdin/stdout pipes
- Fix child process redirection to properly handle both input and output
- Add enhanced debug logging for VNC data flow
- Update resource cleanup in vnc_free_session()

This resolves the issue where VNC connections would hang after exchanging
the first 12 bytes (RFB protocol version strings) because input from
noVNC WebSocket wasn't reaching the wsssht process.

wssshd2/vnc.c

@@ -117,16 +117,22 @@ vnc_session_t *vnc_create_session(const wssshd_config_t *config, const char *cli
     session->debug_vnc = debug_vnc;
     pthread_mutex_init(&session->output_mutex, NULL);
 
-    // Create pipe for communication
-    int pipefd[2];
-    if (pipe(pipefd) < 0) {
+    // Create pipes for bidirectional communication
+    int stdout_pipe[2]; // parent reads from child stdout
+    int stdin_pipe[2];  // parent writes to child stdin
+
+    if (pipe(stdout_pipe) < 0 || pipe(stdin_pipe) < 0) {
+        if (stdout_pipe[0] >= 0) close(stdout_pipe[0]);
+        if (stdout_pipe[1] >= 0) close(stdout_pipe[1]);
+        if (stdin_pipe[0] >= 0) close(stdin_pipe[0]);
+        if (stdin_pipe[1] >= 0) close(stdin_pipe[1]);
         free(session->output_buffer);
         free(session);
         return NULL;
     }
 
-    session->read_fd = pipefd[0];  // read end
-    session->write_fd = pipefd[1]; // write end
+    session->read_fd = stdout_pipe[0];  // parent reads from child stdout
+    session->write_fd = stdin_pipe[1];  // parent writes to child stdin
 
     // Build command: wsssht --pipe --wssshd-port 9898 vnc://{client_id}@mbetter.nexlab.net
     char command[1024];
@@ -137,25 +143,33 @@ vnc_session_t *vnc_create_session(const wssshd_config_t *config, const char *cli
     // Fork and execute
     pid_t pid = fork();
     if (pid < 0) {
-        close(pipefd[0]);
-        close(pipefd[1]);
+        close(stdout_pipe[0]);
+        close(stdout_pipe[1]);
+        close(stdin_pipe[0]);
+        close(stdin_pipe[1]);
         free(session->output_buffer);
         free(session);
         return NULL;
     }
 
     if (pid == 0) { // Child process
-        // Redirect stdout to pipe
-        dup2(pipefd[1], 1);
-        close(pipefd[0]);
-        close(pipefd[1]);
+        // Redirect stdout to stdout_pipe
+        dup2(stdout_pipe[1], 1);
+        // Redirect stdin from stdin_pipe
+        dup2(stdin_pipe[0], 0);
+        close(stdout_pipe[0]);
+        close(stdout_pipe[1]);
+        close(stdin_pipe[0]);
+        close(stdin_pipe[1]);
 
         // Execute command
         execl("/bin/sh", "sh", "-c", command, NULL);
         _exit(1); // Should not reach here
     }
 
-    // Parent process keeps both ends: read_fd for reading from child, write_fd for writing to child
+    // Parent process
+    close(stdout_pipe[1]); // close write end of stdout pipe
+    close(stdin_pipe[0]);  // close read end of stdin pipe
     session->proc_pid = pid;
 
     // Start output reading thread
@@ -171,13 +185,16 @@ void vnc_free_session(vnc_session_t *session) {
 
     if (session->read_fd >= 0) {
         close(session->read_fd);
+        session->read_fd = -1;
     }
     if (session->write_fd >= 0) {
         close(session->write_fd);
+        session->write_fd = -1;
     }
 
     if (session->output_buffer) {
         free(session->output_buffer);
+        session->output_buffer = NULL;
     }
     pthread_mutex_destroy(&session->output_mutex);