WM: Add message type for remote downloader messages to message bus

We plan on using this for online assets (see blender/blender!130543), to
send status updates with a URL to identify the online library remote.
In future this can be expanded for multiple kinds of messages with
differing data, like progress reports, sub-resource download messages
(e.g. individual assets), etc.

While this will only be used for online assets for the start, I imagine
we'd want these same kind of status messages for other remote
resources. Hence the name `WM_MSG_TYPE_REMOTE_IO`.

Pull Request: https://projects.blender.org/blender/blender/pulls/144567

source/blender/windowmanager/CMakeLists.txt

@@ -57,6 +57,7 @@ set(SRC
   gizmo/intern/wm_gizmo_target_props.cc
   gizmo/intern/wm_gizmo_type.cc
   message_bus/intern/wm_message_bus.cc
+  message_bus/intern/wm_message_bus_remote_io.cc
   message_bus/intern/wm_message_bus_rna.cc
   message_bus/intern/wm_message_bus_static.cc
 

source/blender/windowmanager/message_bus/intern/wm_message_bus.cc

@@ -33,6 +33,7 @@ using wmMsgTypeInitFn = void (*)(wmMsgTypeInfo *);
 static wmMsgTypeInitFn wm_msg_init_fn[WM_MSG_TYPE_NUM] = {
     WM_msgtypeinfo_init_rna,
     WM_msgtypeinfo_init_static,
+    WM_msgtypeinfo_init_remote_io,
 };
 
 void WM_msgbus_types_init()

source/blender/windowmanager/message_bus/intern/wm_message_bus_remote_io.cc

@@ -0,0 +1,144 @@
+/* SPDX-FileCopyrightText: 2025 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup wm
+ */
+
+#include "CLG_log.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "BLI_ghash.h"
+#include "BLI_hash.h"
+#include "BLI_listbase.h"
+#include "BLI_string.h"
+#include "BLI_string_ref.hh"
+
+#include "WM_types.hh"
+#include "message_bus/intern/wm_message_bus_intern.hh"
+
+/* -------------------------------------------------------------------------- */
+
+static uint wm_msg_remote_io_gset_hash(const void *key_p)
+{
+  const wmMsgSubscribeKey_RemoteIO *key = static_cast<const wmMsgSubscribeKey_RemoteIO *>(key_p);
+  const wmMsgParams_RemoteIO *params = &key->msg.params;
+  uint k = BLI_hash_string(params->remote_url);
+  return k;
+}
+static bool wm_msg_remote_io_gset_cmp(const void *key_a_p, const void *key_b_p)
+{
+  const wmMsgParams_RemoteIO *params_a =
+      &(static_cast<const wmMsgSubscribeKey_RemoteIO *>(key_a_p))->msg.params;
+  const wmMsgParams_RemoteIO *params_b =
+      &(static_cast<const wmMsgSubscribeKey_RemoteIO *>(key_b_p))->msg.params;
+  return !STREQ(params_a->remote_url, params_b->remote_url);
+}
+
+static void *wm_msg_remote_io_gset_key_duplicate(const void *key_p)
+{
+  const wmMsgSubscribeKey_RemoteIO *key_src = static_cast<const wmMsgSubscribeKey_RemoteIO *>(
+      key_p);
+  wmMsgSubscribeKey_RemoteIO *key = MEM_dupallocN<wmMsgSubscribeKey_RemoteIO>(__func__, *key_src);
+  key->msg.params.remote_url = BLI_strdup(key_src->msg.params.remote_url);
+  return key;
+}
+static void wm_msg_remote_io_gset_key_free(void *key_p)
+{
+  wmMsgSubscribeKey_RemoteIO *key = static_cast<wmMsgSubscribeKey_RemoteIO *>(key_p);
+  MEM_freeN(key->msg.params.remote_url);
+  wmMsgSubscribeValueLink *msg_lnk_next;
+  for (wmMsgSubscribeValueLink *msg_lnk =
+           static_cast<wmMsgSubscribeValueLink *>(key->head.values.first);
+       msg_lnk;
+       msg_lnk = msg_lnk_next)
+  {
+    msg_lnk_next = msg_lnk->next;
+    BLI_remlink(&key->head.values, msg_lnk);
+    MEM_freeN(msg_lnk);
+  }
+  MEM_freeN(key);
+}
+
+static void wm_msg_remote_io_repr(FILE *stream, const wmMsgSubscribeKey *msg_key)
+{
+  const wmMsgSubscribeKey_RemoteIO *m = (wmMsgSubscribeKey_RemoteIO *)msg_key;
+  fprintf(stream,
+          "<wmMsg_RemoteIO %p, "
+          "id='%s', "
+          "values_len=%d\n",
+          m,
+          m->msg.head.id,
+          BLI_listbase_count(&m->head.values));
+}
+
+void WM_msgtypeinfo_init_remote_io(wmMsgTypeInfo *msgtype_info)
+{
+  msgtype_info->gset.hash_fn = wm_msg_remote_io_gset_hash;
+  msgtype_info->gset.cmp_fn = wm_msg_remote_io_gset_cmp;
+  msgtype_info->gset.key_duplicate_fn = wm_msg_remote_io_gset_key_duplicate;
+  msgtype_info->gset.key_free_fn = wm_msg_remote_io_gset_key_free;
+  msgtype_info->repr = wm_msg_remote_io_repr;
+}
+
+/* -------------------------------------------------------------------------- */
+
+wmMsgSubscribeKey_RemoteIO *WM_msg_lookup_remote_io(wmMsgBus *mbus,
+                                                    const wmMsgParams_RemoteIO *msg_key_params)
+{
+  wmMsgSubscribeKey_RemoteIO key_test;
+  key_test.msg.params = *msg_key_params;
+  return static_cast<wmMsgSubscribeKey_RemoteIO *>(
+      BLI_gset_lookup(mbus->messages_gset[WM_MSG_TYPE_REMOTE_IO], &key_test));
+}
+
+void WM_msg_publish_remote_io_params(wmMsgBus *mbus, const wmMsgParams_RemoteIO *msg_key_params)
+{
+  CLOG_DEBUG(WM_LOG_MSGBUS_PUB, "remote_io(remote_url=%s)", msg_key_params->remote_url);
+
+  wmMsgSubscribeKey_RemoteIO *key = WM_msg_lookup_remote_io(mbus, msg_key_params);
+  if (key) {
+    WM_msg_publish_with_key(mbus, &key->head);
+  }
+}
+
+void WM_msg_publish_remote_io(wmMsgBus *mbus, const blender::StringRef remote_url)
+{
+  wmMsgParams_RemoteIO params{};
+  params.remote_url = BLI_strdupn(remote_url.data(), remote_url.size());
+  WM_msg_publish_remote_io_params(mbus, &params);
+
+  /* Value was copied into the publish key. */
+  MEM_freeN(params.remote_url);
+}
+
+void WM_msg_subscribe_remote_io_params(wmMsgBus *mbus,
+                                       const wmMsgParams_RemoteIO *msg_key_params,
+                                       const wmMsgSubscribeValue *msg_val_params,
+                                       const char *id_repr)
+{
+  wmMsgSubscribeKey_RemoteIO msg_key_test{};
+
+  /* Use when added. */
+  msg_key_test.msg.head.id = id_repr;
+  msg_key_test.msg.head.type = WM_MSG_TYPE_REMOTE_IO;
+  /* For lookup. */
+  msg_key_test.msg.params = *msg_key_params;
+
+  WM_msg_subscribe_with_key(mbus, &msg_key_test.head, msg_val_params);
+}
+
+void WM_msg_subscribe_remote_io(wmMsgBus *mbus,
+                                const blender::StringRef remote_url,
+                                const wmMsgSubscribeValue *msg_val_params,
+                                const char *id_repr)
+{
+  wmMsgParams_RemoteIO params{};
+  params.remote_url = BLI_strdupn(remote_url.data(), remote_url.size());
+  WM_msg_subscribe_remote_io_params(mbus, &params, msg_val_params, id_repr);
+
+  /* Value was copied into the subscribe key. */
+  MEM_freeN(params.remote_url);
+}

source/blender/windowmanager/message_bus/wm_message_bus.hh

@@ -8,6 +8,8 @@
 
 #pragma once
 
+#include "BLI_string_ref.hh"
+
 #include "DNA_listBase.h"
 
 #include "RNA_prototypes.hh"
@@ -35,8 +37,11 @@ using wmMsgSubscribeValueUpdateIdFn =
 enum {
   WM_MSG_TYPE_RNA = 0,
   WM_MSG_TYPE_STATIC = 1,
+  /** Messages relating to some remote resources, like progress reporting for online asset
+   * downloads. */
+  WM_MSG_TYPE_REMOTE_IO = 2,
 };
-#define WM_MSG_TYPE_NUM 2
+#define WM_MSG_TYPE_NUM 3
 
 struct wmMsgTypeInfo {
   struct {
@@ -167,6 +172,39 @@ void WM_msg_subscribe_static(wmMsgBus *mbus,
                              const wmMsgSubscribeValue *msg_val_params,
                              const char *id_repr);
 
+/* -------------------------------------------------------------------------- */
+/* `wm_message_bus_remote_io.cc` */
+
+struct wmMsgParams_RemoteIO {
+  /* Owned, needs freeing with `MEM_freeN()`. */
+  const char *remote_url;
+};
+
+struct wmMsg_RemoteIO {
+  wmMsg head; /* Keep first. */
+  wmMsgParams_RemoteIO params;
+};
+
+struct wmMsgSubscribeKey_RemoteIO {
+  wmMsgSubscribeKey head;
+  wmMsg_RemoteIO msg;
+};
+
+void WM_msgtypeinfo_init_remote_io(wmMsgTypeInfo *msgtype_info);
+
+wmMsgSubscribeKey_RemoteIO *WM_msg_lookup_remote_io(wmMsgBus *mbus,
+                                                    const wmMsgParams_RemoteIO *msg_key_params);
+void WM_msg_publish_remote_io_params(wmMsgBus *mbus, const wmMsgParams_RemoteIO *msg_key_params);
+void WM_msg_publish_remote_io(wmMsgBus *mbus, blender::StringRef remote_url);
+void WM_msg_subscribe_remote_io_params(wmMsgBus *mbus,
+                                       const wmMsgParams_RemoteIO *msg_key_params,
+                                       const wmMsgSubscribeValue *msg_val_params,
+                                       const char *id_repr);
+void WM_msg_subscribe_remote_io(wmMsgBus *mbus,
+                                blender::StringRef remote_url,
+                                const wmMsgSubscribeValue *msg_val_params,
+                                const char *id_repr);
+
 /* -------------------------------------------------------------------------- */
 /* `wm_message_bus_rna.cc` */