From c7ab7b353996634c61abd7cd66d32459a6e3da4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Thu, 2 Jan 2025 08:58:48 +0100
Subject: [PATCH] term: limit app-id to 2048 characters

Unsure if the protocol imposes a limit (haven't found any
documentation), or if the issue is in the libwayland implementation,
or wlroots (triggers in at least sway+river).

The issue is that setting a too long app-id causes the
compositor (river at least) to peg the CPU at 100%, and stop sending
e.g. frame callbacks to foot.

Closes #1897
---
 CHANGELOG.md |  7 +++++++
 terminal.c   | 15 +++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c824b82e..bdc1828b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -59,6 +59,13 @@
 ## Unreleased
 ### Added
 ### Changed
+
+* Runtime changes to the app-id (OSC-176) now limits the app-id string
+  to 2048 characters ([#1897][1897]).
+
+[1897]: https://codeberg.org/dnkl/foot/issues/1897
+
+
 ### Deprecated
 ### Removed
 ### Fixed
diff --git a/terminal.c b/terminal.c
index a4963bc8..5a74631a 100644
--- a/terminal.c
+++ b/terminal.c
@@ -3588,8 +3588,10 @@ term_set_app_id(struct terminal *term, const char *app_id)
 {
     if (app_id != NULL && *app_id == '\0')
         app_id = NULL;
+
     if (term->app_id == NULL && app_id == NULL)
         return;
+
     if (term->app_id != NULL && app_id != NULL && streq(term->app_id, app_id))
         return;
 
@@ -3604,6 +3606,19 @@ term_set_app_id(struct terminal *term, const char *app_id)
     } else {
         term->app_id = NULL;
     }
+
+    const size_t length = strlen(app_id);
+    if (length > 2048) {
+        /*
+         * Not sure if there's a limit in the protocol, or the
+         * libwayland implementation, or e.g. wlroots, but too long
+         * app-id's (not e.g. title) causes at least river and sway to
+         * peg the CPU at 100%, and stop sending e.g. frame callbacks.
+         *
+         */
+        term->app_id[2048] = '\0';
+    }
+
     render_refresh_app_id(term);
     render_refresh_icon(term);
 }