i3bar: Don't start child unless status_command

If a command is passed to `start_child` which is NULL, such as in the
case when there is no `status_command` specified in the bar config, do
not start a child process to listen on stdin.

fixes #1140

i3bar/src/child.c

@@ -452,10 +452,16 @@ void child_write_output(void) {
 /*
  * Start a child-process with the specified command and reroute stdin.
  * We actually start a $SHELL to execute the command so we don't have to care
- * about arguments and such
+ * about arguments and such.
+ *
+ * If `command' is NULL, such as in the case when no `status_command' is given
+ * in the bar config, no child will be started.
  *
  */
 void start_child(char *command) {
+    if (command == NULL)
+        return;
+
     /* Allocate a yajl parser which will be used to parse stdin. */
     memset(&callbacks, '\0', sizeof(yajl_callbacks));
     callbacks.yajl_map_key = stdin_map_key;
@@ -478,7 +484,6 @@ void start_child(char *command) {
     gen = yajl_gen_alloc(NULL);
 #endif
 
-    if (command != NULL) {
     int pipe_in[2]; /* pipe we read from */
     int pipe_out[2]; /* pipe we write to */
 
@@ -515,7 +520,6 @@ void start_child(char *command) {
 
             break;
     }
-    }
 
     /* We set O_NONBLOCK because blocking is evil in event-driven software */
     fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK);

i3bar/src/config.c

@@ -127,10 +127,6 @@ static int config_string_cb(void *params_, const unsigned char *val, unsigned in
     }
 
     if (!strcmp(cur_key, "status_command")) {
-        /* We cannot directly start the child here, because start_child() also
-         * needs to be run when no command was specified (to setup stdin).
-         * Therefore we save the command in 'config' and access it later in
-         * got_bar_config() */
         DLOG("command = %.*s\n", len, val);
         sasprintf(&config.command, "%.*s", len, val);
         return 1;

i3bar/src/ipc.c

@@ -100,9 +100,6 @@ void got_bar_config(char *reply) {
     /* Resolve color strings to colorpixels and save them, then free the strings. */
     init_colors(&(config.colors));
 
-    /* The name of this function is actually misleading. Even if no command is
-     * specified, this function initiates the watchers to listen on stdin and
-     * react accordingly */
     start_child(config.command);
     FREE(config.command);
 }