message-params: use JSON instead of custom format

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/525>

doc/messaging_api.txt

@@ -4,26 +4,18 @@ The message API allows any object within pulseaudio to register a message
 handler. A message handler is a function that can be called by clients using
 PA_COMMAND_SEND_OBJECT_MESSAGE. A message consists at least of an object path
 and a message command, both specified as strings. Additional parameters can
-be specified using a single string, but are not mandatory. The message handler
-returns an error number as defined in def.h and also returns a string in
-the "response" variable. If the string is not empty it consists of elements.
-Curly braces are used to separate elements. Each element can itself contain
-further elements. For example consider a message that returns multiple elements
-which each contain an integer and an array of float. A response string would
-look like that:
-{{Integer} {{1st float} {2nd float} ...}}{...}
-Any characters that are not enclosed in curly braces are ignored (all characters
-between { and {, between } and } and between } and {). The same syntax is used
-to specify message parameters. The reference further down lists available messages,
-their parameters and return values. If a return value is enclosed in {}, this
-means that multiple elements of the same type may be returned.
+be specified using a single string in JSON format, but are not mandatory.
 
-For string parameters that contain curly braces or backslashes, those characters
-must be escaped by adding a "\" before them.
+The message handler returns an error number as defined in def.h and also returns
+a string in the "response" variable. Non-empty response will be in JSON format.
+
+The reference further down lists available messages, their parameters
+and return values.
 
 Reference:
 
 Object path: /core
 Message: list-handlers
 Parameters: None
-Return value: {{{Handler name} {Description}} ...}
+Return value: JSON array of handler description objects
+    [{"name":"Handler name","description":"Description"} ...]

src/modules/bluetooth/module-bluez5-device.c

@@ -27,6 +27,7 @@
 
 #include <arpa/inet.h>
 
+#include <pulse/json.h>
 #include <pulse/rtclock.h>
 #include <pulse/timeval.h>
 #include <pulse/utf8.h>
@@ -2458,7 +2459,7 @@ static char *list_codecs(struct userdata *u) {
     const pa_a2dp_codec_capabilities *a2dp_capabilities;
     const pa_a2dp_codec_id *key;
     pa_hashmap *a2dp_endpoints;
-    pa_message_params *param;
+    pa_json_encoder *encoder;
     unsigned int i;
     bool is_a2dp_sink;
     void *state;
@@ -2467,9 +2468,9 @@ static char *list_codecs(struct userdata *u) {
 
     a2dp_endpoints = is_a2dp_sink ? u->device->a2dp_sink_endpoints : u->device->a2dp_source_endpoints;
 
-    param = pa_message_params_new();
+    encoder = pa_json_encoder_new();
 
-    pa_message_params_begin_list(param);
+    pa_json_encoder_begin_element_array(encoder);
 
     PA_HASHMAP_FOREACH_KV(key, a2dp_capabilities, a2dp_endpoints, state) {
         for (i = 0; i < pa_bluetooth_a2dp_codec_count(); i++) {
@@ -2479,23 +2480,23 @@ static char *list_codecs(struct userdata *u) {
 
             if (memcmp(key, &a2dp_codec->id, sizeof(pa_a2dp_codec_id)) == 0) {
                 if (a2dp_codec->can_be_supported(is_a2dp_sink)) {
-                    pa_message_params_begin_list(param);
+                    pa_json_encoder_begin_element_object(encoder);
 
-                    pa_message_params_write_string(param, a2dp_codec->name);
-                    pa_message_params_write_string(param, a2dp_codec->description);
+                    pa_json_encoder_add_member_string(encoder, "name", a2dp_codec->name);
+                    pa_json_encoder_add_member_string(encoder, "description", a2dp_codec->description);
 
-                    pa_message_params_end_list(param);
+                    pa_json_encoder_end_object(encoder);
                 }
             }
         }
     }
 
-    pa_message_params_end_list(param);
+    pa_json_encoder_end_array(encoder);
 
-    return pa_message_params_to_string_free(param);
+    return pa_json_encoder_to_string_free(encoder);
 }
 
-static int bluez5_device_message_handler(const char *object_path, const char *message, char *message_parameters, char **response, void *userdata) {
+static int bluez5_device_message_handler(const char *object_path, const char *message, const pa_json_object *parameters, char **response, void *userdata) {
     char *message_handler_path;
     pa_hashmap *capabilities_hashmap;
     pa_bluetooth_profile_t profile;
@@ -2503,8 +2504,6 @@ static int bluez5_device_message_handler(const char *object_path, const char *me
     const char *codec_name;
     struct userdata *u;
     bool is_a2dp_sink;
-    void *state = NULL;
-    int err;
 
     pa_assert(u = (struct userdata *)userdata);
     pa_assert(message);
@@ -2539,9 +2538,17 @@ static int bluez5_device_message_handler(const char *object_path, const char *me
     }
 
     if (pa_streq(message, "switch-codec")) {
-        err = pa_message_params_read_string(message_parameters, &codec_name, &state);
-        if (err < 0)
-            return err;
+        if (!parameters) {
+            pa_log_info("Codec switching operation requires codec name string parameter");
+            return -PA_ERR_INVALID;
+        }
+
+        if (pa_json_object_get_type(parameters) != PA_JSON_TYPE_STRING) {
+            pa_log_info("Codec name object parameter must be a string");
+            return -PA_ERR_INVALID;
+        }
+
+        codec_name = pa_json_object_get_string(parameters);
 
         if (u->a2dp_codec && pa_streq(codec_name, u->a2dp_codec->name)) {
             pa_log_info("Requested codec is currently selected codec");
@@ -2599,15 +2606,13 @@ static int bluez5_device_message_handler(const char *object_path, const char *me
         *response = list_codecs(u);
         return PA_OK;
     } else if (pa_streq(message, "get-codec")) {
-        pa_message_params *param;
-        param = pa_message_params_new();
+        pa_json_encoder *encoder;
+        encoder = pa_json_encoder_new();
 
         if (u->a2dp_codec)
-            pa_message_params_write_string(param, u->a2dp_codec->name);
-        else
-            pa_message_params_write_string(param, "none");
+            pa_json_encoder_add_element_string(encoder, u->a2dp_codec->name);
 
-        *response = pa_message_params_to_string_free(param);
+        *response = pa_json_encoder_to_string_free(encoder);
 
         return PA_OK;
     }

src/pulsecore/core.c

@@ -66,29 +66,27 @@ static void core_free(pa_object *o);
 
 /* Returns a list of handlers. */
 static char *message_handler_list(pa_core *c) {
-    pa_message_params *param;
+    pa_json_encoder *encoder;
     void *state = NULL;
     struct pa_message_handler *handler;
 
-    param = pa_message_params_new();
+    encoder = pa_json_encoder_new();
 
-    pa_message_params_begin_list(param);
+    pa_json_encoder_begin_element_array(encoder);
     PA_HASHMAP_FOREACH(handler, c->message_handlers, state) {
-        pa_message_params_begin_list(param);
+        pa_json_encoder_begin_element_object(encoder);
 
-        /* object_path cannot contain characters that need escaping, therefore
-         * pa_message_params_write_raw() can safely be used here. */
-        pa_message_params_write_raw(param, handler->object_path, true);
-        pa_message_params_write_string(param, handler->description);
+        pa_json_encoder_add_member_string(encoder, "name", handler->object_path);
+        pa_json_encoder_add_member_string(encoder, "description", handler->description);
 
-        pa_message_params_end_list(param);
+        pa_json_encoder_end_object(encoder);
     }
-    pa_message_params_end_list(param);
+    pa_json_encoder_end_array(encoder);
 
-    return pa_message_params_to_string_free(param);
+    return pa_json_encoder_to_string_free(encoder);
 }
 
-static int core_message_handler(const char *object_path, const char *message, char *message_parameters, char **response, void *userdata) {
+static int core_message_handler(const char *object_path, const char *message, const pa_json_object *parameters, char **response, void *userdata) {
     pa_core *c;
 
     pa_assert(c = (pa_core *) userdata);

src/pulsecore/message-handler.c

@@ -105,7 +105,8 @@ void pa_message_handler_unregister(pa_core *c, const char *object_path) {
 int pa_message_handler_send_message(pa_core *c, const char *object_path, const char *message, const char *message_parameters, char **response) {
     struct pa_message_handler *handler;
     int ret;
-    char *parameter_copy, *path_copy;
+    char *path_copy;
+    pa_json_object *parameters = NULL;
 
     pa_assert(c);
     pa_assert(object_path);
@@ -125,14 +126,21 @@ int pa_message_handler_send_message(pa_core *c, const char *object_path, const c
         return -PA_ERR_NOENTITY;
     }
 
-    parameter_copy = pa_xstrdup(message_parameters);
+    pa_xfree(path_copy);
+
+    if (message_parameters) {
+        parameters = pa_json_parse(message_parameters);
+
+        if (!parameters)
+            return -PA_ERR_INVALID;
+    }
 
     /* The handler is expected to return an error code and may also
        return an error string in response */
-    ret = handler->callback(handler->object_path, message, parameter_copy, response, handler->userdata);
+    ret = handler->callback(handler->object_path, message, parameters, response, handler->userdata);
 
-    pa_xfree(parameter_copy);
-    pa_xfree(path_copy);
+    if (parameters)
+        pa_json_object_free(parameters);
     return ret;
 }
 

src/pulsecore/message-handler.h

@@ -19,6 +19,7 @@
 ***/
 
 #include <pulsecore/core.h>
+#include <pulse/json.h>
 
 /* Message handler types and functions */
 
@@ -26,7 +27,7 @@
 typedef int (*pa_message_handler_cb_t)(
         const char *object_path,
         const char *message,
-        char *message_parameters,
+        const pa_json_object *parameters,
         char **response,
         void *userdata);
 

src/utils/pactl.c

@@ -37,6 +37,7 @@
 #include <pulse/pulseaudio.h>
 #include <pulse/message-params.h>
 #include <pulse/ext-device-restore.h>
+#include <pulse/json.h>
 
 #include <pulsecore/i18n.h>
 #include <pulsecore/macro.h>
@@ -897,10 +898,10 @@ static void send_message_callback(pa_context *c, int success, char *response, vo
 }
 
 static void list_handlers_callback(pa_context *c, int success, char *response, void *userdata) {
-    void *state = NULL;
-    char *handler_list;
-    char *handler_struct;
     int err;
+    pa_json_object *o;
+    int i;
+    const pa_json_object *v, *path, *description;
 
     if (!success) {
         pa_log(_("list-handlers message failed: %s"), pa_strerror(pa_context_errno(c)));
@@ -908,29 +909,45 @@ static void list_handlers_callback(pa_context *c, int success, char *response, v
         return;
     }
 
-    if (pa_message_params_read_raw(response, &handler_list, &state) <= 0) {
+    o = pa_json_parse(response);
+
+    if (!o) {
         pa_log(_("list-handlers message response could not be parsed correctly"));
+        pa_json_object_free(o);
         quit(1);
         return;
     }
 
-    state = NULL;
-    while ((err = pa_message_params_read_raw(handler_list, &handler_struct, &state)) > 0) {
-        void *state2 = NULL;
-        const char *path;
-        const char *description;
+    if (pa_json_object_get_type(o) != PA_JSON_TYPE_ARRAY) {
+        pa_log(_("list-handlers message response is not a JSON array"));
+        pa_json_object_free(o);
+        quit(1);
+        return;
+    }
 
-        if (pa_message_params_read_string(handler_struct, &path, &state2) <= 0) {
+    err = 0;
+
+    for (i = 0; i < pa_json_object_get_array_length(o); ++i) {
+        v = pa_json_object_get_array_member(o, i);
+        if (pa_json_object_get_type(v) != PA_JSON_TYPE_OBJECT) {
+            pa_log(_("list-handlers message response array element %d is not a JSON object"), i);
             err = -1;
             break;
         }
-        if (pa_message_params_read_string(handler_struct, &description, &state2) <= 0) {
+
+        path = pa_json_object_get_object_member(v, "name");
+        if (!path || pa_json_object_get_type(path) != PA_JSON_TYPE_STRING) {
+            err = -1;
+            break;
+        }
+        description = pa_json_object_get_object_member(v, "description");
+        if (!description || pa_json_object_get_type(description) != PA_JSON_TYPE_STRING) {
             err = -1;
             break;
         }
 
         if (short_list_format)
-            printf("%s\n", path);
+            printf("%s\n", pa_json_object_get_string(path));
         else {
             if (nl)
                 printf("\n");
@@ -938,17 +955,20 @@ static void list_handlers_callback(pa_context *c, int success, char *response, v
 
             printf("Message Handler %s\n"
                    "\tDescription: %s\n",
-                   path,
-                   description);
+                   pa_json_object_get_string(path),
+                   pa_json_object_get_string(description));
         }
     }
 
     if (err < 0) {
         pa_log(_("list-handlers message response could not be parsed correctly"));
+        pa_json_object_free(o);
         quit(1);
         return;
     }
 
+    pa_json_object_free(o);
+
     complete_action();
 }