This patch extends the client subscription API, so that signals sent from
PulseAudio can be processed. Within PulseAudio, a signal can be emitted
using pa_signal_post(). The interface can be used to notify the client of
events that are not covered by the subscription API (for example a button
press event on a bluetooth headset).

Setting up signal notification is very similar to using subscriptions.
First the client needs to subscribe with pa_context_subscribe_signals()
and then sets up a signal handler using pa_context_set_signal_callback().

The signal handler will receive three arguments in addition to the usual
context and userdata:
object_path - string that specifies the origin of the signal
signal - string that specifies the type of the signal
signal_parameters - optional string for additional information
---
 PROTOCOL                        |  6 ++++
 src/map-file                    |  2 ++
 src/pulse/def.h                 |  6 ++++
 src/pulse/internal.h            |  2 ++
 src/pulse/subscribe.c           | 71 +++++++++++++++++++++++++++++++++++++----
 src/pulse/subscribe.h           |  9 ++++++
 src/pulsecore/core.h            |  1 +
 src/pulsecore/message-handler.c | 16 ++++++++++
 src/pulsecore/message-handler.h | 13 ++++++++
 src/pulsecore/native-common.h   |  3 ++
 src/pulsecore/pdispatch.c       |  1 +
 src/pulsecore/protocol-native.c | 56 ++++++++++++++++++++++++++++++++
 12 files changed, 180 insertions(+), 6 deletions(-)

diff --git a/PROTOCOL b/PROTOCOL
index f693cd3d..d20f48c6 100644
--- a/PROTOCOL
+++ b/PROTOCOL
@@ -434,6 +434,12 @@ parameters:
 
 The command returns a string.
 
+Added signal sending capability and command PA_COMMAND_SUBSCRIBE_SIGNALS.
+This command allows clients to subscribe to signals that PulseAudio sends.
+
+parameters:
+    uint64_t facility_mask - subscription mask
+
 #### If you just changed the protocol, read this
 ## module-tunnel depends on the sink/source/sink-input/source-input protocol
 ## internals, so if you changed these, you might have broken module-tunnel.
diff --git a/src/map-file b/src/map-file
index 88d892ef..e3f86bf9 100644
--- a/src/map-file
+++ b/src/map-file
@@ -94,6 +94,7 @@ pa_context_set_default_sink;
 pa_context_set_default_source;
 pa_context_set_event_callback;
 pa_context_set_name;
+pa_context_set_signal_callback;
 pa_context_set_sink_input_mute;
 pa_context_set_sink_input_volume;
 pa_context_set_sink_mute_by_index;
@@ -114,6 +115,7 @@ pa_context_set_state_callback;
 pa_context_set_subscribe_callback;
 pa_context_stat;
 pa_context_subscribe;
+pa_context_subscribe_signals;
 pa_context_suspend_sink_by_index;
 pa_context_suspend_sink_by_name;
 pa_context_suspend_source_by_index;
diff --git a/src/pulse/def.h b/src/pulse/def.h
index 100df5b5..964fa9fa 100644
--- a/src/pulse/def.h
+++ b/src/pulse/def.h
@@ -615,6 +615,11 @@ typedef enum pa_subscription_event_type {
     PA_SUBSCRIPTION_EVENT_REMOVE = 0x0020U,
     /**< An object was removed */
 
+/** \cond fulldocs */
+    PA_SUBSCRIPTION_EVENT_SIGNAL = 0x0040U,
+    /** A signal was issued. Only used internally. */
+/** \endcond */
+
     PA_SUBSCRIPTION_EVENT_TYPE_MASK = 0x0030U
     /**< A mask to extract the event operation from an event value */
 
@@ -650,6 +655,7 @@ typedef enum pa_subscription_event_type {
 #define PA_SUBSCRIPTION_EVENT_NEW PA_SUBSCRIPTION_EVENT_NEW
 #define PA_SUBSCRIPTION_EVENT_CHANGE PA_SUBSCRIPTION_EVENT_CHANGE
 #define PA_SUBSCRIPTION_EVENT_REMOVE PA_SUBSCRIPTION_EVENT_REMOVE
+#define PA_SUBSCRIPTION_EVENT_SIGNAL PA_SUBSCRIPTION_EVENT_SIGNAL
 #define PA_SUBSCRIPTION_EVENT_TYPE_MASK PA_SUBSCRIPTION_EVENT_TYPE_MASK
 /** \endcond */
 
diff --git a/src/pulse/internal.h b/src/pulse/internal.h
index 0d18aa71..a1b4957e 100644
--- a/src/pulse/internal.h
+++ b/src/pulse/internal.h
@@ -95,6 +95,8 @@ struct pa_context {
     void *subscribe_userdata;
     pa_context_event_cb_t event_callback;
     void *event_userdata;
+    pa_context_signal_cb_t signal_callback;
+    void *signal_userdata;
 
     pa_mempool *mempool;
 
diff --git a/src/pulse/subscribe.c b/src/pulse/subscribe.c
index e7cce2e3..fa5567fb 100644
--- a/src/pulse/subscribe.c
+++ b/src/pulse/subscribe.c
@@ -32,7 +32,6 @@
 void pa_command_subscribe_event(pa_pdispatch *pd, uint32_t command, uint32_t 
tag, pa_tagstruct *t, void *userdata) {
     pa_context *c = userdata;
     pa_subscription_event_type_t e;
-    uint32_t idx;
 
     pa_assert(pd);
     pa_assert(command == PA_COMMAND_SUBSCRIBE_EVENT);
@@ -42,15 +41,44 @@ void pa_command_subscribe_event(pa_pdispatch *pd, uint32_t 
command, uint32_t tag
 
     pa_context_ref(c);
 
-    if (pa_tagstruct_getu32(t, &e) < 0 ||
-        pa_tagstruct_getu32(t, &idx) < 0 ||
-        !pa_tagstruct_eof(t)) {
+    if (pa_tagstruct_getu32(t, &e) < 0) {
         pa_context_fail(c, PA_ERR_PROTOCOL);
         goto finish;
     }
 
-    if (c->subscribe_callback)
-        c->subscribe_callback(c, e, idx, c->subscribe_userdata);
+    if (e != PA_SUBSCRIPTION_EVENT_SIGNAL) {
+        uint32_t idx;
+
+        if (pa_tagstruct_getu32(t, &idx) < 0 ||
+            !pa_tagstruct_eof(t)) {
+            pa_context_fail(c, PA_ERR_PROTOCOL);
+            goto finish;
+        }
+
+        if (c->subscribe_callback)
+            c->subscribe_callback(c, e, idx, c->subscribe_userdata);
+
+    } else {
+        const char *object_path;
+        const char *signal;
+        const char *signal_parameters;
+
+        if (pa_tagstruct_gets(t, &object_path) < 0 ||
+            pa_tagstruct_gets(t, &signal) < 0 ||
+            pa_tagstruct_gets(t, &signal_parameters) < 0 ||
+            !pa_tagstruct_eof(t)) {
+            pa_context_fail(c, PA_ERR_PROTOCOL);
+            goto finish;
+        }
+
+        if (c->signal_callback) {
+            char *signal_parameter_copy;
+
+            signal_parameter_copy = pa_xstrdup(signal_parameters);
+            c->signal_callback(c, object_path, signal, signal_parameter_copy, 
c->signal_userdata);
+            pa_xfree(signal_parameter_copy);
+        }
+    }
 
 finish:
     pa_context_unref(c);
@@ -86,3 +114,34 @@ void pa_context_set_subscribe_callback(pa_context *c, 
pa_context_subscribe_cb_t
     c->subscribe_callback = cb;
     c->subscribe_userdata = userdata;
 }
+
+void pa_context_set_signal_callback(pa_context *c, pa_context_signal_cb_t cb, 
void *userdata) {
+    pa_assert(c);
+    pa_assert(PA_REFCNT_VALUE(c) >= 1);
+
+    if (c->state == PA_CONTEXT_TERMINATED || c->state == PA_CONTEXT_FAILED)
+        return;
+
+    c->signal_callback = cb;
+    c->signal_userdata = userdata;
+}
+
+pa_operation* pa_context_subscribe_signals(pa_context *c, uint64_t 
signal_mask, pa_context_success_cb_t cb, void *userdata) {
+    pa_operation *o;
+    pa_tagstruct *t;
+    uint32_t tag;
+
+    pa_assert(c);
+    pa_assert(PA_REFCNT_VALUE(c) >= 1);
+
+    PA_CHECK_VALIDITY_RETURN_NULL(c, c->state == PA_CONTEXT_READY, 
PA_ERR_BADSTATE);
+
+    o = pa_operation_new(c, NULL, (pa_operation_cb_t) cb, userdata);
+
+    t = pa_tagstruct_command(c, PA_COMMAND_SUBSCRIBE_SIGNALS, &tag);
+    pa_tagstruct_putu64(t, signal_mask);
+    pa_pstream_send_tagstruct(c->pstream, t);
+    pa_pdispatch_register_reply(c->pdispatch, tag, DEFAULT_TIMEOUT, 
pa_context_simple_ack_callback, pa_operation_ref(o), (pa_free_cb_t) 
pa_operation_unref);
+
+    return o;
+}
diff --git a/src/pulse/subscribe.h b/src/pulse/subscribe.h
index b43c8ea4..e0117655 100644
--- a/src/pulse/subscribe.h
+++ b/src/pulse/subscribe.h
@@ -72,12 +72,21 @@ PA_C_DECL_BEGIN
 /** Subscription event callback prototype */
 typedef void (*pa_context_subscribe_cb_t)(pa_context *c, 
pa_subscription_event_type_t t, uint32_t idx, void *userdata);
 
+/** Signal event callback prototype, \since 13.0 */
+typedef void (*pa_context_signal_cb_t)(pa_context *c, const char *object_path, 
const char *signal, char *signal_parameters, void *userdata);
+
 /** Enable event notification */
 pa_operation* pa_context_subscribe(pa_context *c, pa_subscription_mask_t m, 
pa_context_success_cb_t cb, void *userdata);
 
+/** Enable signal notification, \since 13.0 */
+pa_operation* pa_context_subscribe_signals(pa_context *c, uint64_t 
signal_mask, pa_context_success_cb_t cb, void *userdata);
+
 /** Set the context specific call back function that is called whenever the 
state of the daemon changes */
 void pa_context_set_subscribe_callback(pa_context *c, 
pa_context_subscribe_cb_t cb, void *userdata);
 
+/** Set the context specific call back function that is called whenever 
pulseaudio sends a signal, \since 13.0 */
+void pa_context_set_signal_callback(pa_context *c, pa_context_signal_cb_t cb, 
void *userdata);
+
 PA_C_DECL_END
 
 #endif
diff --git a/src/pulsecore/core.h b/src/pulsecore/core.h
index d03897c4..1f342184 100644
--- a/src/pulsecore/core.h
+++ b/src/pulsecore/core.h
@@ -142,6 +142,7 @@ typedef enum pa_core_hook {
     PA_CORE_HOOK_SAMPLE_CACHE_NEW,
     PA_CORE_HOOK_SAMPLE_CACHE_CHANGED,
     PA_CORE_HOOK_SAMPLE_CACHE_UNLINK,
+    PA_CORE_HOOK_SEND_SIGNAL,
     PA_CORE_HOOK_MAX
 } pa_core_hook_t;
 
diff --git a/src/pulsecore/message-handler.c b/src/pulsecore/message-handler.c
index 860f3b8e..75310667 100644
--- a/src/pulsecore/message-handler.c
+++ b/src/pulsecore/message-handler.c
@@ -146,3 +146,19 @@ int pa_message_handler_set_description(pa_core *c, const 
char *object_path, cons
 
     return PA_OK;
 }
+
+/* Send a signal */
+void pa_signal_post(pa_core *c, const char *object_path, uint64_t facility, 
const char *signal, const char *signal_parameters) {
+    struct pa_signal_descriptor sd;
+
+    pa_assert(object_path);
+    pa_assert(facility);
+    pa_assert(signal);
+
+    sd.object_path = object_path;
+    sd.facility = facility;
+    sd.signal = signal;
+    sd.parameters = signal_parameters;
+
+    pa_hook_fire(&c->hooks[PA_CORE_HOOK_SEND_SIGNAL], &sd);
+}
diff --git a/src/pulsecore/message-handler.h b/src/pulsecore/message-handler.h
index 38b24e1b..9aadde6a 100644
--- a/src/pulsecore/message-handler.h
+++ b/src/pulsecore/message-handler.h
@@ -47,4 +47,17 @@ int pa_message_handler_send_message(pa_core *c, const char 
*object_path, const c
 
 /* Set handler description */
 int pa_message_handler_set_description(pa_core *c, const char *object_path, 
const char *description);
+
+/* Signals */
+
+/* Structure to pass signal information */
+struct pa_signal_descriptor {
+    const char *object_path;
+    const char *signal;
+    const char *parameters;
+    uint64_t facility;
+};
+
+/* Send a signal */
+void pa_signal_post(pa_core *c, const char *object_path, uint64_t facility, 
const char *signal, const char *signal_parameters);
 #endif
diff --git a/src/pulsecore/native-common.h b/src/pulsecore/native-common.h
index 561746d7..58a91546 100644
--- a/src/pulsecore/native-common.h
+++ b/src/pulsecore/native-common.h
@@ -190,6 +190,9 @@ enum {
     /* Supported since protocol v33 (13.0) */
     PA_COMMAND_SEND_OBJECT_MESSAGE,
 
+    /* Supported since protocol v33 (13.0) */
+    PA_COMMAND_SUBSCRIBE_SIGNALS,
+
     PA_COMMAND_MAX
 };
 
diff --git a/src/pulsecore/pdispatch.c b/src/pulsecore/pdispatch.c
index 9f9dc981..3be43e38 100644
--- a/src/pulsecore/pdispatch.c
+++ b/src/pulsecore/pdispatch.c
@@ -85,6 +85,7 @@ static const char *command_names[PA_COMMAND_MAX] = {
     [PA_COMMAND_GET_SOURCE_OUTPUT_INFO] = "GET_SOURCE_OUTPUT_INFO",
     [PA_COMMAND_GET_SOURCE_OUTPUT_INFO_LIST] = "GET_SOURCE_OUTPUT_INFO_LIST",
     [PA_COMMAND_SUBSCRIBE] = "SUBSCRIBE",
+    [PA_COMMAND_SUBSCRIBE_SIGNALS] = "SUBSCRIBE_SIGNALS",
 
     [PA_COMMAND_SET_SINK_VOLUME] = "SET_SINK_VOLUME",
     [PA_COMMAND_SET_SINK_INPUT_VOLUME] = "SET_SINK_INPUT_VOLUME",
diff --git a/src/pulsecore/protocol-native.c b/src/pulsecore/protocol-native.c
index 4e35d406..7364e8ea 100644
--- a/src/pulsecore/protocol-native.c
+++ b/src/pulsecore/protocol-native.c
@@ -187,6 +187,7 @@ struct pa_native_connection {
     pa_idxset *record_streams, *output_streams;
     uint32_t rrobin_index;
     pa_subscription *subscription;
+    uint64_t signal_mask;
     pa_time_event *auth_timeout_event;
     pa_srbchannel *srbpending;
 };
@@ -204,6 +205,8 @@ struct pa_native_protocol {
     pa_hook hooks[PA_NATIVE_HOOK_MAX];
 
     pa_hashmap *extensions;
+
+    pa_hook_slot *signal_hook_slot;
 };
 
 enum {
@@ -3722,6 +3725,26 @@ static void command_subscribe(pa_pdispatch *pd, uint32_t 
command, uint32_t tag,
     pa_pstream_send_simple_ack(c->pstream, tag);
 }
 
+static void command_signal_subscribe(pa_pdispatch *pd, uint32_t command, 
uint32_t tag, pa_tagstruct *t, void *userdata) {
+    pa_native_connection *c = PA_NATIVE_CONNECTION(userdata);
+    uint64_t m;
+
+    pa_native_connection_assert_ref(c);
+    pa_assert(t);
+
+    if (pa_tagstruct_getu64(t, &m) < 0 ||
+        !pa_tagstruct_eof(t)) {
+        protocol_error(c);
+        return;
+    }
+
+    CHECK_VALIDITY(c->pstream, c->authorized, tag, PA_ERR_ACCESS);
+
+    c->signal_mask = m;
+
+    pa_pstream_send_simple_ack(c->pstream, tag);
+}
+
 static void command_set_volume(
         pa_pdispatch *pd,
         uint32_t command,
@@ -4921,6 +4944,7 @@ static const pa_pdispatch_cb_t 
command_table[PA_COMMAND_MAX] = {
     [PA_COMMAND_GET_SAMPLE_INFO_LIST] = command_get_info_list,
     [PA_COMMAND_GET_SERVER_INFO] = command_get_server_info,
     [PA_COMMAND_SUBSCRIBE] = command_subscribe,
+    [PA_COMMAND_SUBSCRIBE_SIGNALS] = command_signal_subscribe,
 
     [PA_COMMAND_SET_SINK_VOLUME] = command_set_volume,
     [PA_COMMAND_SET_SINK_INPUT_VOLUME] = command_set_volume,
@@ -5269,6 +5293,33 @@ void pa_native_protocol_disconnect(pa_native_protocol 
*p, pa_module *m) {
             native_connection_unlink(c);
 }
 
+static pa_hook_result_t native_protocol_signal_hook(pa_core *core, struct 
pa_signal_descriptor *sd, pa_native_protocol *p) {
+    pa_native_connection *c;
+    uint32_t idx;
+
+    pa_assert(p);
+    pa_assert(sd);
+
+    PA_IDXSET_FOREACH(c, p->connections, idx) {
+        if (sd->facility & c->signal_mask) {
+            pa_tagstruct *t;
+
+            pa_native_connection_assert_ref(c);
+
+            t = pa_tagstruct_new();
+            pa_tagstruct_putu32(t, PA_COMMAND_SUBSCRIBE_EVENT);
+            pa_tagstruct_putu32(t, (uint32_t) -1);
+            pa_tagstruct_putu32(t, PA_SUBSCRIPTION_EVENT_SIGNAL);
+            pa_tagstruct_puts(t, sd->object_path);
+            pa_tagstruct_puts(t, sd->signal);
+            pa_tagstruct_puts(t, sd->parameters);
+            pa_pstream_send_tagstruct(c->pstream, t);
+        }
+    }
+
+    return PA_HOOK_OK;
+}
+
 static pa_native_protocol* native_protocol_new(pa_core *c) {
     pa_native_protocol *p;
     pa_native_hook_t h;
@@ -5287,6 +5338,8 @@ static pa_native_protocol* native_protocol_new(pa_core 
*c) {
     for (h = 0; h < PA_NATIVE_HOOK_MAX; h++)
         pa_hook_init(&p->hooks[h], p);
 
+    p->signal_hook_slot = pa_hook_connect(&c->hooks[PA_CORE_HOOK_SEND_SIGNAL], 
PA_HOOK_NORMAL, (pa_hook_cb_t) native_protocol_signal_hook, p);
+
     pa_assert_se(pa_shared_set(c, "native-protocol", p) >= 0);
 
     return p;
@@ -5327,6 +5380,9 @@ void pa_native_protocol_unref(pa_native_protocol *p) {
 
     pa_strlist_free(p->servers);
 
+    if (p->signal_hook_slot)
+        pa_hook_slot_free(p->signal_hook_slot);
+
     for (h = 0; h < PA_NATIVE_HOOK_MAX; h++)
         pa_hook_done(&p->hooks[h]);
 
-- 
2.14.1

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