notify: try to read the daemon assigned notification ID from stdout

And document the things we recognize in the notification helper's
stdout.

doc/foot.ini.5.scd

@@ -496,6 +496,21 @@ Note: do not set *TERM* here; use the *term* option in the main
 		reporting the XDG activation token in any way. This means
 		window activation will not work by default.
 	
+	Stdout
+		Foot recognizes the following things from the notification
+		helper's stdout:
+		
+		- _nnn_: integer in base 10, daemon assigned notification ID
+		- _id=nnn_: same as plain _nnn_.
+		- _default_: the 'default' action was triggered
+		- _action=default_: same as _default_
+		- _xdgtoken=xyz_: XDG activation token.
+		
+		Example:
+			17++
+action=default++
+xdgtoken=95ebdfe56e4f47ddb5bba9d7dc3a2c35
+
 	Default: _notify-send --wait --app-name ${app-id} --icon ${icon} --urgency ${urgency} --action ${action-name}=${action-label} --print-id -- ${title} ${body}_.
 
 

notify.c

@@ -34,6 +34,27 @@ notify_free(struct terminal *term, struct notification *notif)
     free(notif->stdout_data);
 }
 
+static bool
+to_integer(const char *line, size_t len, uint32_t *res)
+{
+    bool is_id = true;
+    uint32_t maybe_id = 0;
+
+    for (size_t i = 0; i < len; i++) {
+        char digit = line[i];
+        if (digit < '0' || digit > '9') {
+            is_id = false;
+            break;
+        }
+
+        maybe_id *= 10;
+        maybe_id += digit - '0';
+    }
+
+    *res = maybe_id;
+    return is_id;
+}
+
 static void
 consume_stdout(struct notification *notif, bool eof)
 {
@@ -54,10 +75,26 @@ consume_stdout(struct notification *notif, bool eof)
         } else if (!eof)
             break;
 
-        if (strcmp(line, "default") == 0)
-            notif->activated = true;
+        uint32_t maybe_id = 0;
 
-        /* Check for 'xdgtoken=xyz' */
+        /* Check for daemon assigned ID, either '123', or 'id=123' */
+        if (to_integer(line, len, &maybe_id) ||
+            (len > 3 && memcmp(line, "id=", 3) == 0 &&
+             to_integer(&line[3], len - 3, &maybe_id)))
+        {
+            notif->external_id = maybe_id;
+            LOG_DBG("external ID: %u", notif->external_id);
+        }
+
+        /* Check for triggered action, either 'default' or 'action=default' */
+        else if ((len == 7 && memcmp(line, "default", 7) == 0) ||
+                 (len == 7 + 7 && memcmp(line, "action=default", 7 + 7) == 0))
+        {
+            notif->activated = true;
+            LOG_DBG("notification's default action was triggered");
+        }
+
+        /* Check for XDG activation token, 'xdgtoken=xyz' */
         else if (len > 9 && memcmp(line, "xdgtoken=", 9) == 0) {
             notif->xdg_token = xstrndup(&line[9], len - 9);
             LOG_DBG("XDG token: \"%s\"", notif->xdg_token);

notify.h

@@ -45,6 +45,7 @@ struct notification {
      * Used internally by notify
      */
 
+    uint32_t external_id;  /* Daemon assigned notification ID */
     bool activated;        /* User 'activated' the notification */
     char *xdg_token;       /* XDG activation token, from daemon */