[ncp] integrate SRP Server and Advertising Proxy for NCP (#2624)

This commit integrates the mDNS Publisher with NcpHost to make
advertising proxy work under NCP mode.

The commit adds an expect test to verify the advertising proxy
function under NCP mode. To do the test, `avahi-browser` is used. So
it's added into the bootstrap of the CI for ncp_mode.

As an abstraction: 
1. The commit adds `NcpSpinel::SrpServerSetEnabled` and
   `NcpSpinel::SrpServerSetAutoEnableMode` to control the SRP server
   on the NCP.
2. The commit adds the handling of `SPINEL_PROP_DNSSD_HOST`,
   `SPINEL_PROP_DNSSD_SERVICE` and `SPINEL_PROP_DNSSD_KEY_RECORD` to
   help NCP to publish the dnssd entries (by using the mDNSPublisher
   on the host).

.github/workflows/ncp_mode.yml

@@ -53,7 +53,7 @@ jobs:
         OTBR_MDNS: ${{ matrix.mdns }}
         OTBR_COVERAGE: 1
         OTBR_VERBOSE: 1
-        OTBR_OPTIONS: "-DCMAKE_BUILD_TYPE=Debug -DOT_THREAD_VERSION=1.4 -DOTBR_COVERAGE=ON -DOTBR_DBUS=ON -DOTBR_FEATURE_FLAGS=ON -DOTBR_TELEMETRY_DATA_API=ON -DOTBR_UNSECURE_JOIN=ON -DOTBR_TREL=ON -DBUILD_TESTING=OFF"
+        OTBR_OPTIONS: "-DCMAKE_BUILD_TYPE=Debug -DOT_THREAD_VERSION=1.4 -DOTBR_COVERAGE=ON -DOTBR_DBUS=ON -DOTBR_FEATURE_FLAGS=ON -DOTBR_TELEMETRY_DATA_API=ON -DOTBR_UNSECURE_JOIN=ON -DOTBR_TREL=ON -DOTBR_SRP_ADVERTISING_PROXY=ON -DBUILD_TESTING=OFF"
     steps:
     - uses: actions/checkout@v4
       with:
@@ -76,6 +76,6 @@ jobs:
             --build-arg OTBR_OPTIONS="${OTBR_OPTIONS}"
     - name: Run
       run: |
-       top_builddir="./build/temp" tests/scripts/ncp_mode build_ot_sim expect
+        top_builddir="./build/temp" tests/scripts/ncp_mode build_ot_sim expect
     - name: Codecov
       uses: codecov/codecov-action@v5

src/agent/application.cpp

@@ -288,14 +288,22 @@ void Application::DeinitRcpMode(void)
 
 void Application::InitNcpMode(void)
 {
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+    otbr::Ncp::NcpHost &ncpHost = static_cast<otbr::Ncp::NcpHost &>(mHost);
+    ncpHost.SetMdnsPublisher(mPublisher.get());
+    mMdnsStateSubject.AddObserver(ncpHost);
+    mPublisher->Start();
+#endif
 #if OTBR_ENABLE_DBUS_SERVER
     mDBusAgent->Init(*mBorderAgent);
 #endif
 }
 
 void Application::DeinitNcpMode(void)
 {
-    /* empty */
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+    mPublisher->Stop();
+#endif
 }
 
 } // namespace otbr

src/agent/application.hpp

@@ -44,6 +44,7 @@
 #if OTBR_ENABLE_BORDER_AGENT
 #include "border_agent/border_agent.hpp"
 #endif
+#include "ncp/ncp_host.hpp"
 #include "ncp/rcp_host.hpp"
 #if OTBR_ENABLE_BACKBONE_ROUTER
 #include "backbone_router/backbone_agent.hpp"

src/ncp/ncp_host.cpp

@@ -38,7 +38,6 @@
 #include <openthread/openthread-system.h>
 
 #include "lib/spinel/spinel_driver.hpp"
-
 #include "ncp/async_task.hpp"
 
 namespace otbr {
@@ -134,6 +133,16 @@ void NcpHost::Init(void)
     {
         mInfraIf.SetInfraIf(mConfig.mBackboneInterfaceName);
     }
+
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+#if OTBR_ENABLE_SRP_SERVER_AUTO_ENABLE_MODE
+    // Let SRP server use auto-enable mode. The auto-enable mode delegates the control of SRP server to the Border
+    // Routing Manager. SRP server automatically starts when bi-directional connectivity is ready.
+    mNcpSpinel.SrpServerSetAutoEnableMode(/* aEnabled */ true);
+#else
+    mNcpSpinel.SrpServerSetEnabled(/* aEnabled */ true);
+#endif
+#endif
 }
 
 void NcpHost::Deinit(void)
@@ -264,5 +273,17 @@ void NcpHost::Update(MainloopContext &aMainloop)
     mNetif.UpdateFdSet(&aMainloop);
 }
 
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+void NcpHost::SetMdnsPublisher(Mdns::Publisher *aPublisher)
+{
+    mNcpSpinel.SetMdnsPublisher(aPublisher);
+}
+
+void NcpHost::HandleMdnsState(Mdns::Publisher::State aState)
+{
+    mNcpSpinel.DnssdSetState(aState);
+}
+#endif
+
 } // namespace Ncp
 } // namespace otbr

src/ncp/ncp_host.hpp

@@ -72,7 +72,13 @@ class NcpNetworkProperties : virtual public NetworkProperties, public PropsObser
     otOperationalDatasetTlvs mDatasetActiveTlvs;
 };
 
-class NcpHost : public MainloopProcessor, public ThreadHost, public NcpNetworkProperties
+class NcpHost : public MainloopProcessor,
+                public ThreadHost,
+                public NcpNetworkProperties
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+    ,
+                public Mdns::StateObserver
+#endif
 {
 public:
     /**
@@ -119,7 +125,15 @@ class NcpHost : public MainloopProcessor, public ThreadHost, public NcpNetworkPr
     void Update(MainloopContext &aMainloop) override;
     void Process(const MainloopContext &aMainloop) override;
 
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+    void SetMdnsPublisher(Mdns::Publisher *aPublisher);
+#endif
+
 private:
+#if OTBR_ENABLE_SRP_ADVERTISING_PROXY
+    void HandleMdnsState(Mdns::Publisher::State aState) override;
+#endif
+
     ot::Spinel::SpinelDriver &mSpinelDriver;
     otPlatformConfig          mConfig;
     NcpSpinel                 mNcpSpinel;