GUACAMOLE-313: Add function for sending "key" instructions.

src/libguac/guacamole/protocol.h

@@ -106,6 +106,32 @@ int guac_protocol_send_disconnect(guac_socket* socket);
 int guac_protocol_send_error(guac_socket* socket, const char* error,
         guac_protocol_status status);
 
+/**
+ * Sends a key instruction over the given guac_socket connection.
+ *
+ * If an error occurs sending the instruction, a non-zero value is
+ * returned, and guac_error is set appropriately.
+ *
+ * @param socket
+ *     The guac_socket connection to use.
+ *
+ * @param keysym
+ *     The X11 keysym of the key that was pressed or released.
+ *
+ * @param pressed
+ *     Non-zero if the key represented by the given keysym is currently
+ *     pressed, zero if it is released.
+ *
+ * @param timestamp
+ *     The server timestamp (in milliseconds) at the point in time this key
+ *     event was acknowledged.
+ *
+ * @return
+ *     Zero on success, non-zero on error.
+ */
+int guac_protocol_send_key(guac_socket* socket, int keysym, int pressed,
+        guac_timestamp timestamp);
+
 /**
  * Sends a log instruction over the given guac_socket connection. This is
  * mainly useful in debugging.

src/libguac/protocol.c

@@ -615,6 +615,24 @@ int guac_protocol_send_identity(guac_socket* socket, const guac_layer* layer) {
 
 }
 
+int guac_protocol_send_key(guac_socket* socket, int keysym, int pressed,
+        guac_timestamp timestamp) {
+
+    int ret_val;
+
+    guac_socket_instruction_begin(socket);
+    ret_val =
+           guac_socket_write_string(socket, "3.key,")
+        || __guac_socket_write_length_int(socket, keysym)
+        || guac_socket_write_string(socket, pressed ? ",1.1," : ",1.0,")
+        || __guac_socket_write_length_int(socket, timestamp)
+        || guac_socket_write_string(socket, ";");
+
+    guac_socket_instruction_end(socket);
+    return ret_val;
+
+}
+
 int guac_protocol_send_lfill(guac_socket* socket,
         guac_composite_mode mode, const guac_layer* layer,
         const guac_layer* srcl) {