[srp-server] allow disabling "Fast Start Mode" via auto-enable (#11319)

This commit updates the `Srp::Server` so that Fast Start Mode can be
disabled by a call to `otSrpServerSetAutoEnableMode()`, in addition
to the existing method of calling `otSrpServerSetEnabled()`.

The `test_srp_server` unit test is updated to validate this new
behavior.

include/openthread/instance.h

@@ -52,7 +52,7 @@ extern "C" {
  *
  * @note This number versions both OpenThread platform and user APIs.
  */
-#define OPENTHREAD_API_VERSION (482)
+#define OPENTHREAD_API_VERSION (483)
 
 /**
  * @addtogroup api-instance

include/openthread/srp_server.h

@@ -301,8 +301,12 @@ bool otSrpServerIsAutoEnableMode(otInstance *aInstance);
  * The Fast Start Mode can be enabled when the device is in the detached or disabled state, the SRP server is currently
  * disabled, and "auto-enable mode" is not in use (i.e., `otSrpServerIsAutoEnableMode()` returns `false`).
  *
- * After successfully enabling Fast Start Mode, it can be disabled by a direct call to `otSrpServerSetEnabled()`,
- * explicitly enabling or disabling the SRP server function.
+ * After successfully enabling Fast Start Mode, it can be disabled either by a call to `otSrpServerSetEnabled()`,
+ * explicitly enabling or disabling the SRP server, or by a call to `otSrpServerSetAutoEnableMode()`, enabling or
+ * disabling the auto-enable mode. If the Fast Start Mode (while active) enables the SRP server, upon disabling
+ * Fast Start Mode (regardless of how it is done), the SRP server will also be stopped, and the use of the
+ * `OT_SRP_SERVER_ADDRESS_MODE_UNICAST_FORCE_ADD` address mode will be stopped, and the address mode will be
+ * automatically reverted back to its previous setting before Fast Start Mode was enabled.
  *
  * @param[in] aInstance             A pointer to the OpenThread instance.
  *

src/core/net/srp_server.cpp

@@ -128,7 +128,7 @@ void Server::SetEnabled(bool aEnabled)
     mAutoEnable = false;
 #endif
 #if OPENTHREAD_CONFIG_SRP_SERVER_FAST_START_MODE_ENABLE
-    mFastStartMode = false;
+    DisableFastStartMode();
 #endif
 
     if (aEnabled)
@@ -144,6 +144,15 @@ void Server::SetEnabled(bool aEnabled)
 void Server::Enable(void)
 {
     VerifyOrExit(mState == kStateDisabled);
+
+#if OPENTHREAD_CONFIG_SRP_SERVER_FAST_START_MODE_ENABLE
+    if (mFastStartMode)
+    {
+        mPrevAddressMode = mAddressMode;
+        IgnoreError(SetAddressMode(kAddressModeUnicastForceAdd));
+    }
+#endif
+
     mState = kStateStopped;
 
     // Request publishing of "DNS/SRP Address Service" entry in the
@@ -199,6 +208,13 @@ void Server::Disable(void)
     Stop();
     mState = kStateDisabled;
 
+#if OPENTHREAD_CONFIG_SRP_SERVER_FAST_START_MODE_ENABLE
+    if (mFastStartMode)
+    {
+        IgnoreError(SetAddressMode(mPrevAddressMode));
+    }
+#endif
+
 exit:
     return;
 }
@@ -206,6 +222,10 @@ exit:
 #if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
 void Server::SetAutoEnableMode(bool aEnabled)
 {
+#if OPENTHREAD_CONFIG_SRP_SERVER_FAST_START_MODE_ENABLE
+    DisableFastStartMode();
+#endif
+
     VerifyOrExit(mAutoEnable != aEnabled);
     mAutoEnable = aEnabled;
 
@@ -236,6 +256,18 @@ exit:
     return error;
 }
 
+void Server::DisableFastStartMode(void)
+{
+    VerifyOrExit(mFastStartMode);
+
+    Disable();
+    mFastStartMode = false;
+    LogInfo("FastStartMode disabled");
+
+exit:
+    return;
+}
+
 void Server::HandleNotifierEvents(Events aEvents)
 {
     VerifyOrExit(mFastStartMode);
@@ -248,9 +280,6 @@ void Server::HandleNotifierEvents(Events aEvents)
         if (!NetDataContainsOtherSrpServers())
         {
             LogInfo("FastStartMode - No SRP server in NetData");
-
-            mPrevAddressMode = mAddressMode;
-            IgnoreError(SetAddressMode(kAddressModeUnicastForceAdd));
             Enable();
         }
     }
@@ -261,9 +290,7 @@ void Server::HandleNotifierEvents(Events aEvents)
         if (NetDataContainsOtherSrpServers())
         {
             LogInfo("FastStartMode - New SRP server entry in NetData");
-
             Disable();
-            IgnoreError(SetAddressMode(mPrevAddressMode));
         }
     }
 

src/core/net/srp_server.hpp

@@ -949,6 +949,7 @@ private:
 #endif
 
 #if OPENTHREAD_CONFIG_SRP_SERVER_FAST_START_MODE_ENABLE
+    void DisableFastStartMode(void);
     void HandleNotifierEvents(Events aEvents);
     bool NetDataContainsOtherSrpServers(void) const;
 #endif

tests/unit/test_srp_server.cpp

@@ -1367,6 +1367,22 @@ void TestSrpServerFastStartMode(void)
     VerifyOrQuit(srpServer->IsFastStartModeEnabled());
     VerifyOrQuit(srpServer->GetState() == Srp::Server::kStateRunning);
 
+    //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    // Start auto-enable mode and ensure "fast start mode" is turned
+    // off and the original AddressMode is restored on the SRP server.
+
+#if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
+    srpServer->SetAutoEnableMode(true);
+
+    VerifyOrQuit(!srpServer->IsFastStartModeEnabled());
+    VerifyOrQuit(srpServer->IsAutoEnableMode());
+
+    VerifyOrQuit(srpServer->GetState() == Srp::Server::kStateDisabled);
+    VerifyOrQuit(srpServer->GetAddressMode() == Srp::Server::kAddressModeUnicast);
+
+    VerifyOrQuit(srpServer->EnableFastStartMode() == kErrorInvalidState);
+#endif
+
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // Finalize OT instance and validate all heap allocations are freed.