From 0619c7e435b53477f5f9ace0b4b4621cb8435f04 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 3 Apr 2026 19:58:59 +0530
Subject: [PATCH] More work on DnD protocol

---
 kitty/dnd.c    | 20 +++++++++++++++++++-
 kitty/dnd.h    |  1 +
 kitty/screen.c |  3 +++
 kitty/state.h  |  3 ++-
 4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/kitty/dnd.c b/kitty/dnd.c
index 2fea78b06..7f68dd8f1 100644
--- a/kitty/dnd.c
+++ b/kitty/dnd.c
@@ -867,6 +867,7 @@ drag_free_offer(Window *w) {
         free(ds.items);
     }
     ds.num_mimes = 0;
+    ds.pre_sent_total_sz = 0;
 }
 
 void
@@ -901,8 +902,25 @@ drag_add_mimes(Window *w, int allowed_operations, const char *data, size_t sz, b
                 p += strlen(p) + 1;
             } else p++;
         }
+        ds.pre_sent_total_sz = 0;
     }
-#undef abrt
 }
 
+void
+drag_add_pre_sent_data(Window *w, unsigned idx, const uint8_t *payload, size_t sz) {
+    if (!ds.offer_being_built || idx >= ds.num_mimes) abrt(EINVAL);
+    if (sz + ds.pre_sent_total_sz > 64 * 1024 * 1024) abrt(EFBIG);
+    ds.pre_sent_total_sz += sz;
+    DragSourceItem *item = ds.items + idx;
+    if (item->data_capacity < sz + item->data_size) {
+        size_t newcap = MAX(item->data_size * 2, sz + item->data_size);
+        item->optional_data = realloc(item->optional_data, newcap);
+        if (!item->optional_data) abrt(ENOMEM);
+        item->data_capacity = newcap;
+    }
+    memcpy(item->optional_data + item->data_size, payload, sz);
+    item->data_size += sz;
+}
+
+#undef abrt
 #undef ds
diff --git a/kitty/dnd.h b/kitty/dnd.h
index 0dadb71dd..646d78006 100644
--- a/kitty/dnd.h
+++ b/kitty/dnd.h
@@ -25,3 +25,4 @@ void dnd_set_test_write_func(PyObject *func);
 
 void drag_free_offer(Window *w);
 void drag_add_mimes(Window *w, int allowed_operations, const char *data, size_t sz, bool has_more);
+void drag_add_pre_sent_data(Window *w, unsigned idx, const uint8_t *payload, size_t sz);
diff --git a/kitty/screen.c b/kitty/screen.c
index b8572f8b7..101497f93 100644
--- a/kitty/screen.c
+++ b/kitty/screen.c
@@ -1548,6 +1548,9 @@ screen_handle_dnd_command(Screen *self, const DnDCommand *cmd, const uint8_t *pa
                 cancel_current_drag_source();
             }
         } break;
+        case 'p': {
+            if (cmd->cell_x >= 0) drag_add_pre_sent_data(w, cmd->cell_x, payload, cmd->payload_sz);
+        } break;
     }
 }
 
diff --git a/kitty/state.h b/kitty/state.h
index 7bda02504..7524d0eb8 100644
--- a/kitty/state.h
+++ b/kitty/state.h
@@ -236,7 +236,7 @@ typedef struct DirHandle {
 typedef struct DragSourceItem {
     const char *mime_type;
     char *optional_data;
-    size_t data_size;
+    size_t data_size, data_capacity;
 } DragSourceItem;
 
 typedef struct Window {
@@ -296,6 +296,7 @@ typedef struct Window {
         struct { double x, y; monotonic_t at; } initial_left_press;
         char *mimes_buf; size_t num_mimes, bufsz;
         DragSourceItem *items;
+        size_t pre_sent_total_sz;
         int allowed_operations;
         bool offer_being_built;
     } drag_source;