client: handle x11 channel open requests with callbacks

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/callbacks.h

@@ -94,6 +94,19 @@ typedef void (*ssh_status_callback) (ssh_session session, float status,
 typedef void (*ssh_global_request_callback) (ssh_session session,
                                         ssh_message message, void *userdata);
 
+/**
+ * @brief Handles an SSH new channel open X11 request. This happens when the server
+ * sends back an X11 connection attempt. This is a client-side API
+ * @param session current session handler
+ * @param userdata Userdata to be passed to the callback function.
+ * @returns a valid ssh_channel handle if the request is to be allowed
+ * @returns NULL if the request should not be allowed
+ * @warning The channel pointer returned by this callback must be closed by the application.
+ */
+typedef ssh_channel (*ssh_channel_open_request_x11_callback) (ssh_session session,
+      const char * originator_address, int originator_port, void *userdata);
+
+
 /**
  * The structure to replace libssh functions with appropriate callbacks.
  */
@@ -121,6 +134,10 @@ struct ssh_callbacks_struct {
    * This function will be called each time a global request is received.
    */
   ssh_global_request_callback global_request_function;
+  /** This function will be called when an incoming X11 request is received.
+   */
+  ssh_channel_open_request_x11_callback channel_open_request_x11_function;
+
 };
 typedef struct ssh_callbacks_struct *ssh_callbacks;
 
@@ -185,7 +202,6 @@ typedef int (*ssh_service_request_callback) (ssh_session session, const char *se
  */
 typedef ssh_channel (*ssh_channel_open_request_session_callback) (ssh_session session, void *userdata);
 
-
 /**
  * This structure can be used to implement a libssh server, with appropriate callbacks.
  */

src/messages.c

@@ -130,6 +130,19 @@ static int ssh_execute_server_callbacks(ssh_session session, ssh_message msg){
 						ssh_message_reply_default(msg);
 					}
 					return SSH_OK;
+				} else if (msg->channel_request_open.type == SSH_CHANNEL_X11){
+				  if(ssh_callbacks_exists(session->common.callbacks, channel_open_request_x11_function)){
+				    channel = session->common.callbacks->channel_open_request_x11_function (session,
+				        msg->channel_request_open.originator, msg->channel_request_open.originator_port,
+				        session->common.callbacks->userdata);
+				    if(channel != NULL) {
+				      rc = ssh_message_channel_request_open_reply_accept_channel(msg, channel);
+				      return SSH_OK;
+				    } else {
+				      ssh_message_reply_default(msg);
+				    }
+				    return SSH_OK;
+				  }
 				}
 			}
 			break;