protocol-native: extend v3 protocol with message footers

Extend version 3 protocol with message footers, which are for passing
around global state data that is not addressed to a specific object.

The extension is backward compatible with previous v3 clients, and won't
e.g. result to error spam in logs.

The footer is a single SPA POD, appended after the main message POD.
Because both the protocol message and the message POD record their
length, it's possible to append trailing data. Earlier clients will
ignore any data trailing the message POD.

The footer POD contains a sequence [Id opcode, Struct {...}]*,
so there is room to extend with new opcodes later as necessary.

There are separate marshal/demarshal routines for messages aimed at
resources and proxies.

src/modules/meson.build

@@ -197,6 +197,7 @@ pipewire_module_protocol_native = shared_library('pipewire-module-protocol-nativ
     'module-protocol-native/portal-screencast.c',
     'module-protocol-native/protocol-native.c',
     'module-protocol-native/v0/protocol-native.c',
+    'module-protocol-native/protocol-footer.c',
     'module-protocol-native/connection.c' ],
   include_directories : [configinc],
   install : true,

src/modules/module-protocol-native.c

@@ -57,6 +57,7 @@
 
 #include "modules/module-protocol-native/connection.h"
 #include "modules/module-protocol-native/defs.h"
+#include "modules/module-protocol-native/protocol-footer.h"
 
 
 #define NAME "protocol-native"
@@ -115,6 +116,8 @@ struct client {
 
 	int ref;
 
+	struct footer_proxy_global_state footer_state;
+
 	unsigned int connected:1;
 	unsigned int disconnecting:1;
 	unsigned int need_flush:1;
@@ -151,6 +154,8 @@ struct client_data {
 	struct pw_protocol_native_connection *connection;
 	struct spa_hook conn_listener;
 
+	struct footer_resource_global_state footer_state;
+
 	unsigned int busy:1;
 	unsigned int need_flush:1;
 
@@ -164,7 +169,7 @@ static void debug_msg(const char *prefix, const struct pw_protocol_native_messag
 		      "%s: id:%d op:%d size:%d seq:%d", prefix,
 		      msg->id, msg->opcode, msg->size, msg->seq);
 
-	if ((pod = spa_pod_from_data(msg->data, msg->size, 0, msg->size)) != NULL)
+	if ((pod = get_first_pod_from_data(msg->data, msg->size, 0)) != NULL)
 		spa_debug_pod(0, NULL, pod);
 	else
 		hex = true;
@@ -172,6 +177,49 @@ static void debug_msg(const char *prefix, const struct pw_protocol_native_messag
 		spa_debug_mem(0, msg->data, msg->size);
 }
 
+static void pre_demarshal(struct pw_protocol_native_connection *conn,
+		const struct pw_protocol_native_message *msg,
+		void *object, const struct footer_demarshal *opcodes, size_t n_opcodes)
+{
+	struct spa_pod *footer = NULL;
+	struct spa_pod_parser parser;
+	struct spa_pod_frame f[2];
+	uint32_t opcode;
+	int ret;
+
+	footer = pw_protocol_native_connection_get_footer(conn, msg);
+	if (footer == NULL)
+		return;   /* No valid footer. Ignore silently. */
+
+	/*
+	 * Version 3 footer
+	 *
+	 * spa_pod Struct { [Id opcode, Struct { ... }]* }
+	 */
+
+	spa_pod_parser_pod(&parser, footer);
+	if (spa_pod_parser_push_struct(&parser, &f[0]) < 0) {
+		pw_log_error("malformed message footer");
+		return;
+	}
+
+	while (1) {
+		if (spa_pod_parser_get_id(&parser, &opcode) < 0)
+			break;
+		if (spa_pod_parser_push_struct(&parser, &f[1]) < 0)
+			break;
+		if (opcode < n_opcodes) {
+			if ((ret = opcodes[opcode].demarshal(object, &parser)) < 0)
+				pw_log_error("failed processing message footer (opcode %u): %d (%s)",
+						opcode, ret, spa_strerror(ret));
+		} else {
+			/* Ignore (don't log errors), in case we need to extend this later. */
+			pw_log_debug("unknown message footer opcode %u", opcode);
+		}
+		spa_pod_parser_pop(&parser, &f[1]);
+	}
+}
+
 static int
 process_messages(struct client_data *data)
 {
@@ -249,6 +297,8 @@ process_messages(struct client_data *data)
 		}
 
 		pw_protocol_native_connection_enter(conn);
+		pre_demarshal(conn, msg, resource, footer_resource_demarshal,
+				SPA_N_ELEMENTS(footer_resource_demarshal));
 		res = demarshal[msg->opcode].func(resource, msg);
 		pw_protocol_native_connection_leave(conn);
 		if (res < 0) {
@@ -794,6 +844,8 @@ process_remote(struct client *impl)
 		}
 		proxy->refcount++;
 		pw_protocol_native_connection_enter(conn);
+		pre_demarshal(conn, msg, proxy, footer_proxy_demarshal,
+				SPA_N_ELEMENTS(footer_proxy_demarshal));
 		res = demarshal[msg->opcode].func(proxy, msg);
 		pw_protocol_native_connection_leave(conn);
 		pw_proxy_unref(proxy);
@@ -1230,6 +1282,7 @@ static int impl_ext_end_proxy(struct pw_proxy *proxy,
 {
 	struct pw_core *core = proxy->core;
 	struct client *impl = SPA_CONTAINER_OF(core->conn, struct client, this);
+	marshal_proxy_footers(&impl->footer_state, proxy, builder);
 	return core->send_seq = pw_protocol_native_connection_end(impl->connection, builder);
 }
 
@@ -1257,6 +1310,7 @@ static int impl_ext_end_resource(struct pw_resource *resource,
 {
 	struct client_data *data = resource->client->user_data;
 	struct pw_impl_client *client = resource->client;
+	marshal_resource_footers(&data->footer_state, resource, builder);
 	return client->send_seq = pw_protocol_native_connection_end(data->connection, builder);
 }
 static const struct pw_protocol_native_ext protocol_ext_impl = {

src/modules/module-protocol-native/connection.c

@@ -45,6 +45,7 @@ PW_LOG_TOPIC_EXTERN(mod_topic_connection);
 #include <spa/debug/pod.h>
 
 #include "connection.h"
+#include "defs.h"
 
 #define MAX_BUFFER_SIZE (1024 * 32)
 #define MAX_FDS 1024u
@@ -598,6 +599,38 @@ pw_protocol_native_connection_get_next(struct pw_protocol_native_connection *con
 	return 1;
 }
 
+/** Get footer data from the tail of the current packet.
+ *
+ * \param conn the connection
+ * \param msg current message
+ * \return footer POD, or NULL if no valid footer present
+ *
+ * \memberof pw_protocol_native_connection
+ */
+struct spa_pod *pw_protocol_native_connection_get_footer(struct pw_protocol_native_connection *conn,
+		const struct pw_protocol_native_message *msg)
+{
+	struct impl *impl = SPA_CONTAINER_OF(conn, struct impl, this);
+	struct spa_pod *pod;
+
+	if (impl->version != 3)
+		return NULL;
+
+	/*
+	 * Protocol version 3 footer: a single SPA POD
+	 */
+
+	/* Footer immediately follows the message POD, if it is present */
+	if ((pod = get_first_pod_from_data(msg->data, msg->size, 0)) == NULL)
+		return NULL;
+	pod = get_first_pod_from_data(msg->data, msg->size, SPA_POD_SIZE(pod));
+	if (pod == NULL)
+		return NULL;
+	pw_log_trace("connection %p: recv message footer, size:%zu",
+			conn, (size_t)SPA_POD_SIZE(pod));
+	return pod;
+}
+
 static inline void *begin_write(struct pw_protocol_native_connection *conn, uint32_t size)
 {
 	struct impl *impl = SPA_CONTAINER_OF(conn, struct impl, this);

src/modules/module-protocol-native/connection.h

@@ -102,6 +102,9 @@ pw_protocol_native_connection_clear(struct pw_protocol_native_connection *conn);
 void pw_protocol_native_connection_enter(struct pw_protocol_native_connection *conn);
 void pw_protocol_native_connection_leave(struct pw_protocol_native_connection *conn);
 
+struct spa_pod *pw_protocol_native_connection_get_footer(struct pw_protocol_native_connection *conn,
+		const struct pw_protocol_native_message *msg);
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif

src/modules/module-protocol-native/defs.h

@@ -30,3 +30,14 @@ int pw_protocol_native_connect_portal_screencast(struct pw_protocol_client *clie
 					    const struct spa_dict *props,
 					    void (*done_callback) (void *data, int res),
 					    void *data);
+
+static inline void *get_first_pod_from_data(void *data, size_t maxsize, off_t offset)
+{
+	void *pod;
+	if (offset + sizeof(struct spa_pod) > maxsize)
+		return NULL;
+	pod = SPA_PTROFF(data, offset, void);
+	if (offset + SPA_POD_SIZE(pod) > maxsize)
+		return NULL;
+	return pod;
+}

src/modules/module-protocol-native/protocol-footer.c

@@ -0,0 +1,94 @@
+/* PipeWire
+ *
+ * Copyright © 2018 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+
+#include <spa/pod/builder.h>
+#include <spa/pod/parser.h>
+#include <spa/utils/result.h>
+
+#include <pipewire/private.h>
+
+#include "connection.h"
+#include "protocol-footer.h"
+#include "defs.h"
+
+PW_LOG_TOPIC_EXTERN(mod_topic);
+#define PW_LOG_TOPIC_DEFAULT mod_topic
+
+struct footer_builder {
+	struct spa_pod_builder *builder;
+	struct spa_pod_frame outer;
+	struct spa_pod_frame inner;
+	unsigned int started:1;
+};
+
+#define FOOTER_BUILDER_INIT(builder) (struct footer_builder) { builder }
+
+static void start_footer_entry(struct footer_builder *fb, uint32_t opcode)
+{
+	if (!fb->started) {
+		spa_pod_builder_push_struct(fb->builder, &fb->outer);
+		fb->started = true;
+	}
+
+	spa_pod_builder_id(fb->builder, opcode);
+	spa_pod_builder_push_struct(fb->builder, &fb->inner);
+}
+
+static void end_footer_entry(struct footer_builder *fb)
+{
+	spa_pod_builder_pop(fb->builder, &fb->inner);
+}
+
+static void end_footer(struct footer_builder *fb)
+{
+	if (!fb->started)
+		return;
+
+	spa_pod_builder_pop(fb->builder, &fb->outer);
+}
+
+void marshal_proxy_footers(struct footer_proxy_global_state *state, struct pw_proxy *proxy,
+		struct spa_pod_builder *builder)
+{
+	struct footer_builder fb = FOOTER_BUILDER_INIT(builder);
+
+	end_footer(&fb);
+}
+
+void marshal_resource_footers(struct footer_resource_global_state *state, struct pw_resource *resource,
+		struct spa_pod_builder *builder)
+{
+	struct footer_builder fb = FOOTER_BUILDER_INIT(builder);
+
+	end_footer(&fb);
+}
+
+const struct footer_demarshal footer_proxy_demarshal[FOOTER_PROXY_OPCODE_LAST] = {
+};
+
+const struct footer_demarshal footer_resource_demarshal[FOOTER_RESOURCE_OPCODE_LAST] = {
+};

src/modules/module-protocol-native/protocol-footer.h

@@ -0,0 +1,56 @@
+/* PipeWire
+ *
+ * Copyright © 2018 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * Protocol footer.
+ *
+ * For passing around general state data that is not associated with
+ * messages sent to objects.
+ */
+
+enum {
+	FOOTER_PROXY_OPCODE_LAST = 0,
+};
+
+enum {
+	FOOTER_RESOURCE_OPCODE_LAST = 0,
+};
+
+struct footer_proxy_global_state {
+};
+
+struct footer_resource_global_state {
+};
+
+struct footer_demarshal {
+	int (*demarshal)(void *object, struct spa_pod_parser *parser);
+};
+
+extern const struct footer_demarshal footer_proxy_demarshal[FOOTER_PROXY_OPCODE_LAST];
+extern const struct footer_demarshal footer_resource_demarshal[FOOTER_RESOURCE_OPCODE_LAST];
+
+void marshal_proxy_footers(struct footer_proxy_global_state *state, struct pw_proxy *proxy,
+		struct spa_pod_builder *builder);
+void marshal_resource_footers(struct footer_resource_global_state *state, struct pw_resource *resource,
+		struct spa_pod_builder *builder);