Add enhanced socket debugging and validation

- Added fcntl() check to validate socket before sending data
- Enhanced error reporting with socket descriptor and errno details
- Added detailed send operation logging for troubleshooting
- Improved socket state validation to prevent bad file descriptor errors
- Added errno reporting for better error diagnosis
- Enhanced debugging output for socket operations
- Added socket validity checks using file descriptor flags
- Improved error messages with more context information

wssshtools/tunnel.c

@@ -438,12 +438,24 @@ void handle_tunnel_data(SSL *ssl __attribute__((unused)), const char *request_id
     // Check if target socket is valid
     if (target_sock < 0) {
         if (debug) {
-            printf("[DEBUG] Target socket not ready yet, ignoring tunnel_data\n");
+            printf("[DEBUG] Target socket not ready yet (sock=%d), ignoring tunnel_data\n", target_sock);
             fflush(stdout);
         }
         pthread_mutex_unlock(&tunnel_mutex);
         return;
     }
+
+    // Double-check socket validity with fcntl
+    int socket_flags = fcntl(target_sock, F_GETFL);
+    if (socket_flags == -1) {
+        if (debug) {
+            printf("[DEBUG] Socket %d is invalid (fcntl failed), ignoring tunnel_data\n", target_sock);
+            fflush(stdout);
+        }
+        pthread_mutex_unlock(&tunnel_mutex);
+        return;
+    }
+
     pthread_mutex_unlock(&tunnel_mutex);
 
     // Validate hex data length
@@ -493,12 +505,23 @@ void handle_tunnel_data(SSL *ssl __attribute__((unused)), const char *request_id
         pthread_mutex_unlock(&tunnel_mutex);
     } else {
         // wsssh/wssshc: Send directly to target socket
+        if (debug) {
+            printf("[DEBUG] Attempting to send %zu bytes to socket %d\n", data_len, target_sock);
+            fflush(stdout);
+        }
         ssize_t sent = send(target_sock, data, data_len, 0);
-        if (sent < 0 && debug) {
-            printf("[DEBUG] Failed to send %zu bytes to target socket: %s\n", data_len, strerror(errno));
+        if (sent < 0) {
+            if (debug) {
+                printf("[DEBUG] Failed to send %zu bytes to target socket %d: %s (errno=%d)\n",
+                       data_len, target_sock, strerror(errno), errno);
                 fflush(stdout);
-        } else if (debug && (size_t)sent != data_len) {
-            printf("[DEBUG] Partial send: sent %zd of %zu bytes\n", sent, data_len);
+            }
+        } else if (debug) {
+            if ((size_t)sent != data_len) {
+                printf("[DEBUG] Partial send: sent %zd of %zu bytes to socket %d\n", sent, data_len, target_sock);
+            } else {
+                printf("[DEBUG] Successfully sent %zu bytes to socket %d\n", data_len, target_sock);
+            }
             fflush(stdout);
         }
     }