Add detection for dnd protocol

Author: kovidgoyal

docs/dnd-protocol.rst

@@ -25,7 +25,7 @@ Only the first chunk is guaranteed to have metadata other than the ``m`` key.
 Subsequent chunks may optionally omit all
 metadata except the ``m`` and ``i`` keys. While a chunked transfer is in
 progress it is a protocol error to for the sending side to
-send any protocol related escape codes other than chunked ones.
+send any protocol related escape codes other than chunked ones or query (``t=q|Q``) ones.
 In particular, this means that the receiving side should use the metadata from
 the first chunk in a chain of chunks only.
 
@@ -438,6 +438,31 @@ inform the client of it with::
 The error code for too many resources is ``EMFILE`` for IO errors is ``EIO``
 and so on.
 
+Detecting support for this protocol
+-------------------------------------
+
+Clients can query the terminal emulator for support of this protocol
+using::
+
+    OSC _dnd_code ; t=q:i=optional ST
+    OSC _dnd_code ; t=Q:i=optional ST
+
+The former queries support for drag and the latter for drop. The ``i`` key is
+optional, if present it will be echoed back in the responses from the terminal.
+A terminal supporting this protocol **must** respond with::
+
+    OSC _dnd_code ; t=q:i=echoed ; payload ST
+    OSC _dnd_code ; t=Q:i=echoed ; payload ST
+
+Here, ``payload`` is a colon separated list of ``key=value`` pairs. These
+specify support for optional/future parts of this protocol. Currently the
+payload is empty, but that might change as the protocol evolves.
+
+The client should send these escape codes followed by a request for the `primary device
+attributes <https://vt100.net/docs/vt510-rm/DA1.html>`_. If a response for the
+device attributes is received before a response for the queries, then the
+terminal does not support this protocol.
+
 Multiplexers
 -----------------
 
@@ -469,6 +494,8 @@ Key      Value                 Default    Description
                                           ``e`` - a drag offer event occurred
                                           ``E`` - a drag offer data error occurred
                                           ``k`` - data for uri-list items in drag offer
+                                          ``q`` - query support for drag
+                                          ``Q`` - query support for drop
 
 ``m``    Chunking indicator    ``0``      ``0`` or ``1``
 

gen/apc_parsers.py

@@ -333,7 +333,7 @@ def parsers() -> None:
     write_header(text, 'kitty/parse-multicell-command.h')
 
     keymap = {
-        't': ('type', flag('aAmMrRopPeEk')),
+        't': ('type', flag('aAmMrRopPqQeEk')),
         'm': ('more', 'uint'),
         'i': ('client_id', 'uint'),
         'o': ('operation', 'uint'),

kitty/dnd.c

@@ -294,6 +294,13 @@ queue_payload_to_child(id_type id, uint32_t client_id, PendingData *pending, con
     if (pending->count) check_for_pending_writes();
 }
 
+void
+dnd_query(Window *w, uint32_t client_id, bool for_drag) {
+    char buf[64];
+    ssize_t header_size = snprintf(buf, sizeof(buf), "\x1b]%d;t=%c", DND_CODE, for_drag ? 'q' : 'Q');
+    send_payload_to_child(w->id, client_id, buf, header_size, NULL, 0, false);
+}
+
 static bool
 is_same_machine(const char *client_machine_id, size_t sz) {
     if (!sz || !client_machine_id) return true;

kitty/dnd.h

@@ -8,6 +8,7 @@
 
 #include "state.h"
 
+void dnd_query(Window *w, uint32_t client_id, bool for_drag);
 
 void drop_register_window(Window *w, const uint8_t *payload, size_t payload_sz, bool on, uint32_t client_id, bool more);
 void drop_register_machine_id(Window *w, const uint8_t *machine_id, size_t sz);

kitty/parse-dnd-command.h

@@ -87,8 +87,9 @@ static inline void parse_dnd_code(PS *self, uint8_t *parser_buf,
       case type: {
         g.type = parser_buf[pos++];
         if (g.type != 'A' && g.type != 'E' && g.type != 'M' && g.type != 'P' &&
-            g.type != 'R' && g.type != 'a' && g.type != 'e' && g.type != 'k' &&
-            g.type != 'm' && g.type != 'o' && g.type != 'p' && g.type != 'r') {
+            g.type != 'Q' && g.type != 'R' && g.type != 'a' && g.type != 'e' &&
+            g.type != 'k' && g.type != 'm' && g.type != 'o' && g.type != 'p' &&
+            g.type != 'q' && g.type != 'r') {
           REPORT_ERROR("Malformed DnDCommand control block, unknown flag value "
                        "for type: 0x%x",
                        g.type);

kitty/screen.c

@@ -1583,6 +1583,9 @@ screen_handle_dnd_command(Screen *self, const DnDCommand *cmd_, const uint8_t *p
             drag_remote_file_data(
                 w, cmd->cell_x, cmd->cell_y, cmd->pixel_x, cmd->pixel_y, cmd->more != 0, payload, cmd->payload_sz);
         } break;
+        case 'q': case 'Q': {
+            dnd_query(w, cmd->client_id, cmd->type == 'q');
+        } break;
     }
 }