[srp] implement AdvertisingProxy and define Dnssd platform APIs

This commit adds a generic SRP Advertising Proxy implementation to
OpenThread core, which uses a set of newly defined `otPlatDnssd`
platform APIs for DNS-SD (mDNS) support on infrastructure network on
a Border Router.

`Srp::Server` provides `ServiceUpdateHandler` callback mechanism that
allows platforms to implement their own advertising proxy function.
While this is still supported, the new generic advertising proxy
implementation makes it easier to port and support the proxy function
on new platforms. The platform needs to provide the DNS-SD platform
APIs, which are designed to be simple and easy to implement.

The `AdvertisingProxy` directly interacts with `Srp::Server` and its
registered `Host` and `Service` entries, tracking whether an entry
has been successfully advertised, is currently being advertised, or
has been replaced by a new registration.

The `AdvertisingProxy` ensures that consecutive SRP updates for the
same host or service are committed on the server in the order they
are received, even if their advertisements are finished in a
different order. This is important for SRP Replication support, as
the server may receive a large number of SRP updates back-to-back for
the same host.

This commit adds a detailed unit test `test_srp_adv_proxy` that
validates the `AdvertisingProxy` under many scenarios. The test
covers a range of cases, including delayed registration callbacks and
timeouts, new registrations replacing outstanding advertisements,
platform DNS-SD state changes and failures.

doc/ot_api_doc.h

@@ -184,6 +184,7 @@
  * @defgroup plat-toolchain           Toolchain
  * @defgroup plat-trel                TREL - Platform
  * @defgroup plat-infra-if            Infrastructure Interface
+ * @defgroup plat-dns-sd              DNS-SD (mDNS)
  *
  * @}
  *

etc/cmake/options.cmake

@@ -230,6 +230,7 @@ ot_option(OT_SERVICE OPENTHREAD_CONFIG_TMF_NETDATA_SERVICE_ENABLE "Network Data
 ot_option(OT_SETTINGS_RAM OPENTHREAD_SETTINGS_RAM "volatile-only storage of settings")
 ot_option(OT_SLAAC OPENTHREAD_CONFIG_IP6_SLAAC_ENABLE "SLAAC address")
 ot_option(OT_SNTP_CLIENT OPENTHREAD_CONFIG_SNTP_CLIENT_ENABLE "SNTP client")
+ot_option(OT_SRP_ADV_PROXY OPENTHREAD_CONFIG_SRP_SERVER_ADVERTISING_PROXY_ENABLE "SRP advertising proxy")
 ot_option(OT_SRP_CLIENT OPENTHREAD_CONFIG_SRP_CLIENT_ENABLE "SRP client")
 ot_option(OT_SRP_SERVER OPENTHREAD_CONFIG_SRP_SERVER_ENABLE "SRP server")
 ot_option(OT_TCP OPENTHREAD_CONFIG_TCP_ENABLE "TCP")

examples/platforms/simulation/CMakeLists.txt

@@ -61,6 +61,7 @@ add_library(openthread-simulation
     alarm.c
     crypto.c
     diag.c
+    dnssd.c
     dso_transport.c
     entropy.c
     flash.c

examples/platforms/simulation/dnssd.c

@@ -0,0 +1,85 @@
+/*
+ *  Copyright (c) 2023, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "platform-simulation.h"
+
+#include <openthread/platform/dnssd.h>
+
+#if OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE
+otPlatDnssdState otPlatDnssdGetState(otInstance *aInstance)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+
+    return OT_PLAT_DNSSD_STOPPED;
+}
+
+void otPlatDnssdRegisterService(otInstance                 *aInstance,
+                                const otPlatDnssdService   *aService,
+                                otPlatDnssdRequestId        aRequestId,
+                                otPlatDnssdRegisterCallback aCallback)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aService);
+    OT_UNUSED_VARIABLE(aRequestId);
+    OT_UNUSED_VARIABLE(aCallback);
+}
+
+void otPlatDnssdUnregisterService(otInstance                 *aInstance,
+                                  const otPlatDnssdService   *aService,
+                                  otPlatDnssdRequestId        aRequestId,
+                                  otPlatDnssdRegisterCallback aCallback)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aService);
+    OT_UNUSED_VARIABLE(aRequestId);
+    OT_UNUSED_VARIABLE(aCallback);
+}
+
+void otPlatDnssdRegisterHost(otInstance                 *aInstance,
+                             const otPlatDnssdHost      *aHost,
+                             otPlatDnssdRequestId        aRequestId,
+                             otPlatDnssdRegisterCallback aCallback)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aHost);
+    OT_UNUSED_VARIABLE(aRequestId);
+    OT_UNUSED_VARIABLE(aCallback);
+}
+
+void otPlatDnssdUnregisterHost(otInstance                 *aInstance,
+                               const otPlatDnssdHost      *aHost,
+                               otPlatDnssdRequestId        aRequestId,
+                               otPlatDnssdRegisterCallback aCallback)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aHost);
+    OT_UNUSED_VARIABLE(aRequestId);
+    OT_UNUSED_VARIABLE(aCallback);
+}
+
+#endif // OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE

include/openthread/BUILD.gn

@@ -89,6 +89,7 @@ source_set("openthread") {
     "platform/debug_uart.h",
     "platform/diag.h",
     "platform/dns.h",
+    "platform/dnssd.h",
     "platform/dso_transport.h",
     "platform/entropy.h",
     "platform/flash.h",

include/openthread/instance.h

@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (347)
+#define OPENTHREAD_API_VERSION (348)
 
 /**
  * @addtogroup api-instance