csi: in-band window resize notifications, private mode 2048

This implements
https://gist.github.com/rockorager/e695fb2924d36b2bcf1fff4a3704bd83,
in-band window resize notifications.

When user enables private mode 2048 (in-band resize
notifications), *always* send current size, even if the mode is
already active.

This ensures applications can rely on getting a reply from the
terminal.

CHANGELOG.md

@@ -67,6 +67,9 @@
   i.e. color palette stack ([#856][856]).
 * Log output now respects the [`NO_COLOR`](http://no-color.org/)
   environment variable ([#1771][1771]).
+* Support for [in-band window resize
+  notifications](https://gist.github.com/rockorager/e695fb2924d36b2bcf1fff4a3704bd83),
+  private mode `2048`.
 
 [1707]: https://codeberg.org/dnkl/foot/issues/1707
 [1738]: https://codeberg.org/dnkl/foot/issues/1738

csi.c

@@ -562,6 +562,13 @@ decset_decrst(struct terminal *term, unsigned param, bool enable)
         term->grapheme_shaping = enable;
         break;
 
+    case 2048:
+        if (enable)
+            term_enable_size_notifications(term);
+        else
+            term_disable_size_notifications(term);
+        break;
+
     case 8452:
         term->sixel.cursor_right_of_graphics = enable;
         break;
@@ -649,6 +656,7 @@ decrqm(const struct terminal *term, unsigned param)
     case 2027: return term->conf->tweak.grapheme_width_method != GRAPHEME_WIDTH_DOUBLE
         ? DECRPM_PERMANENTLY_RESET
         : decrpm(term->grapheme_shaping);
+    case 2048: return decrpm(term->size_notifications);
     case 8452: return decrpm(term->sixel.cursor_right_of_graphics);
     case 737769: return decrpm(term_ime_is_enabled(term));
     }
@@ -693,6 +701,7 @@ xtsave(struct terminal *term, unsigned param)
     case 2004: term->xtsave.bracketed_paste = term->bracketed_paste; break;
     case 2026: term->xtsave.app_sync_updates = term->render.app_sync_updates.enabled; break;
     case 2027: term->xtsave.grapheme_shaping = term->grapheme_shaping; break;
+    case 2048: term->xtsave.size_notifications = term->size_notifications; break;
     case 8452: term->xtsave.sixel_cursor_right_of_graphics = term->sixel.cursor_right_of_graphics; break;
     case 737769: term->xtsave.ime = term_ime_is_enabled(term); break;
     }
@@ -736,6 +745,7 @@ xtrestore(struct terminal *term, unsigned param)
     case 2004: enable = term->xtsave.bracketed_paste; break;
     case 2026: enable = term->xtsave.app_sync_updates; break;
     case 2027: enable = term->xtsave.grapheme_shaping; break;
+    case 2048: enable = term->xtsave.size_notifications; break;
     case 8452: enable = term->xtsave.sixel_cursor_right_of_graphics; break;
     case 737769: enable = term->xtsave.ime; break;
 

doc/foot-ctlseqs.7.scd

@@ -337,6 +337,9 @@ that corresponds to one of the following modes:
 |  2027
 :  contour
 :  Grapheme cluster processing
+|  2048
+:  TODO
+:  In-band window resize notifications
 |  8452
 :  xterm
 :  Position cursor to the right of sixels, instead of on the next line

render.c

@@ -4072,6 +4072,8 @@ tiocswinsz(struct terminal *term)
         {
             LOG_ERRNO("TIOCSWINSZ");
         }
+
+        term_send_size_notification(term);
     }
 }
 

terminal.c

@@ -44,6 +44,7 @@
 #include "util.h"
 #include "vt.h"
 #include "xmalloc.h"
+#include "xsnprintf.h"
 
 #define PTMX_TIMING 0
 
@@ -4240,3 +4241,37 @@ term_set_user_mouse_cursor(struct terminal *term, const char *cursor)
         : NULL;
     term_xcursor_update(term);
 }
+
+void
+term_enable_size_notifications(struct terminal *term)
+{
+    /* Note: always send current size upon activation, regardless of
+       previous state */
+    term->size_notifications = true;
+    term_send_size_notification(term);
+}
+
+void
+term_disable_size_notifications(struct terminal *term)
+{
+    if (!term->size_notifications)
+        return;
+
+    term->size_notifications = false;
+}
+
+void
+term_send_size_notification(struct terminal *term)
+{
+    if (!term->size_notifications)
+        return;
+
+    const int height = term->height - term->margins.top - term->margins.bottom;
+    const int width = term->width - term->margins.left - term->margins.right;
+
+    char buf[128];
+    const int n = xsnprintf(
+        buf, sizeof(buf), "\033[48;%d;%d;%d;%dt",
+        term->rows, term->cols, height, width);
+    term_to_slave(term, buf, n);
+}

terminal.h

@@ -541,6 +541,8 @@ struct terminal {
         bool app_sync_updates:1;
         bool grapheme_shaping:1;
 
+        bool size_notifications:1;
+
         bool sixel_display_mode:1;
         bool sixel_private_palette:1;
         bool sixel_cursor_right_of_graphics:1;
@@ -800,6 +802,7 @@ struct terminal {
     char *cwd;
 
     bool grapheme_shaping;
+    bool size_notifications;
 };
 
 struct config;
@@ -946,6 +949,10 @@ void term_osc8_close(struct terminal *term);
 bool term_ptmx_pause(struct terminal *term);
 bool term_ptmx_resume(struct terminal *term);
 
+void term_enable_size_notifications(struct terminal *term);
+void term_disable_size_notifications(struct terminal *term);
+void term_send_size_notification(struct terminal *term);
+
 static inline void term_reset_grapheme_state(struct terminal *term)
 {
 #if defined(FOOT_GRAPHEME_CLUSTERING)