Add an EncodeEmptyList helper on AttributeValueEncoder. (#13135)

Fixes #12850

examples/all-clusters-app/all-clusters-common/src/bridged-actions-stub.cpp

@@ -53,13 +53,13 @@ constexpr uint16_t BridgedActionsAttrAccess::ClusterRevision;
 CHIP_ERROR BridgedActionsAttrAccess::ReadActionListAttribute(EndpointId endpoint, AttributeValueEncoder & aEncoder)
 {
     // Just return an empty list
-    return aEncoder.Encode(DataModel::List<BridgedActions::Structs::ActionStruct::Type>());
+    return aEncoder.EncodeEmptyList();
 }
 
 CHIP_ERROR BridgedActionsAttrAccess::ReadEndpointListAttribute(EndpointId endpoint, AttributeValueEncoder & aEncoder)
 {
     // Just return an empty list
-    return aEncoder.Encode(DataModel::List<BridgedActions::Structs::EndpointListStruct::Type>());
+    return aEncoder.EncodeEmptyList();
 }
 
 CHIP_ERROR BridgedActionsAttrAccess::ReadSetupUrlAttribute(EndpointId endpoint, AttributeValueEncoder & aEncoder)

src/app/AttributeAccessInterface.cpp

@@ -55,7 +55,7 @@ CHIP_ERROR AttributeReportBuilder::FinishAttribute(AttributeReportIBs::Builder &
     return aAttributeReportIBsBuilder.GetAttributeReport().EndOfAttributeReportIB().GetError();
 }
 
-CHIP_ERROR AttributeValueEncoder::EncodeEmptyList()
+CHIP_ERROR AttributeValueEncoder::EnsureListStarted()
 {
     if (mCurrentEncodingListIndex == kInvalidListIndex)
     {

src/app/AttributeAccessInterface.h

@@ -177,6 +177,15 @@ class AttributeValueEncoder
         return Encode(DataModel::Nullable<uint8_t>());
     }
 
+    /**
+     * Encode an explicit empty list.
+     */
+    CHIP_ERROR EncodeEmptyList()
+    {
+        // Doesn't matter what type List we use here.
+        return Encode(DataModel::List<uint8_t>());
+    }
+
     /**
      * aCallback is expected to take a const auto & argument and Encode() on it as many times as needed to encode all the list
      * elements one by one.  If any of those Encode() calls returns failure, aCallback must stop encoding and return failure.  When
@@ -200,7 +209,7 @@ class AttributeValueEncoder
         // EmptyList acts as the beginning of the whole array type attribute report.
         // An empty list is encoded iff both mCurrentEncodingListIndex and mEncodeState.mCurrentEncodingListIndex are invalid
         // values. After encoding the empty list, mEncodeState.mCurrentEncodingListIndex and mCurrentEncodingListIndex are set to 0.
-        ReturnErrorOnFailure(EncodeEmptyList());
+        ReturnErrorOnFailure(EnsureListStarted());
         ReturnErrorOnFailure(aCallback(ListEncodeHelper(*this)));
         // The Encode procedure finished without any error, clear the state.
         mEncodeState = AttributeEncodeState();
@@ -226,7 +235,7 @@ class AttributeValueEncoder
     template <typename... Ts>
     CHIP_ERROR EncodeListItem(Ts &&... aArgs)
     {
-        // EncodeListItem must be called after EncodeEmptyList(), thus mCurrentEncodingListIndex and
+        // EncodeListItem must be called after EnsureListStarted(), thus mCurrentEncodingListIndex and
         // mEncodeState.mCurrentEncodingListIndex are not invalid values.
         if (mCurrentEncodingListIndex < mEncodeState.mCurrentEncodingListIndex)
         {
@@ -273,7 +282,8 @@ class AttributeValueEncoder
     }
 
     /**
-     * EncodeEmptyList encodes the first item of one report with lists (an empty list).
+     * EnsureListStarted encodes the first item of one report with lists (an
+     * empty list), as needed.
      *
      * If internal state indicates we have already encoded the empty list, this function will encode nothing, set
      * mCurrentEncodingListIndex to 0 and return CHIP_NO_ERROR.
@@ -282,7 +292,7 @@ class AttributeValueEncoder
      * after it returns, because at that point we will be encoding the list
      * items.
      */
-    CHIP_ERROR EncodeEmptyList();
+    CHIP_ERROR EnsureListStarted();
 
     bool mTriedEncode = false;
     AttributeReportIBs::Builder & mAttributeReportIBsBuilder;

src/app/clusters/access-control-server/access-control-server.cpp

@@ -371,7 +371,7 @@ CHIP_ERROR AccessControlAttribute::ReadAcl(AttributeValueEncoder & aEncoder)
 
 CHIP_ERROR AccessControlAttribute::ReadExtension(AttributeValueEncoder & aEncoder)
 {
-    return aEncoder.EncodeList([&](const auto & encoder) -> CHIP_ERROR { return CHIP_NO_ERROR; });
+    return aEncoder.EncodeEmptyList();
 }
 
 CHIP_ERROR AccessControlAttribute::Write(const ConcreteDataAttributePath & aPath, AttributeValueDecoder & aDecoder)

src/app/clusters/descriptor/descriptor.cpp

@@ -79,7 +79,7 @@ CHIP_ERROR DescriptorAttrAccess::ReadPartsAttribute(EndpointId endpoint, Attribu
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<EndpointId>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;

src/app/clusters/fixed-label-server/fixed-label-server.cpp

@@ -68,7 +68,7 @@ CHIP_ERROR FixedLabelAttrAccess::ReadLabelList(EndpointId endpoint, AttributeVal
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<Structs::LabelStruct::Type>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;

src/app/clusters/general-diagnostics-server/general-diagnostics-server.cpp

@@ -101,7 +101,7 @@ CHIP_ERROR GeneralDiagosticsAttrAccess::ReadListIfSupported(CHIP_ERROR (Diagnost
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<uint8_t>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;
@@ -127,7 +127,7 @@ CHIP_ERROR GeneralDiagosticsAttrAccess::ReadNetworkInterfaces(AttributeValueEnco
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<EndpointId>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;

src/app/clusters/mode-select-server/mode-select-server.cpp

@@ -59,7 +59,7 @@ CHIP_ERROR ModeSelectAttrAccess::Read(const ConcreteReadAttributePath & aPath, A
             gSupportedModeManager->getModeOptionsProvider(aPath.mEndpointId);
         if (modeOptionsProvider.begin() == nullptr)
         {
-            aEncoder.Encode(DataModel::List<ModeSelect::Structs::ModeOptionStruct::Type>());
+            aEncoder.EncodeEmptyList();
             return CHIP_NO_ERROR;
         }
         CHIP_ERROR err;

src/app/clusters/software-diagnostics-server/software-diagnostics-server.cpp

@@ -119,7 +119,7 @@ CHIP_ERROR SoftwareDiagosticsAttrAccess::ReadThreadMetrics(AttributeValueEncoder
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<EndpointId>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;

src/app/clusters/user-label-server/user-label-server.cpp

@@ -72,7 +72,7 @@ CHIP_ERROR UserLabelAttrAccess::ReadLabelList(EndpointId endpoint, AttributeValu
     }
     else
     {
-        err = aEncoder.Encode(DataModel::List<Structs::LabelStruct::Type>());
+        err = aEncoder.EncodeEmptyList();
     }
 
     return err;

src/app/tests/TestAttributeValueEncoder.cpp

@@ -216,30 +216,39 @@ void TestEncodeListOfBools2(nlTestSuite * aSuite, void * aContext)
     VERIFY_BUFFER_STATE(aSuite, test, expected);
 }
 
-void TestEncodeEmptyList(nlTestSuite * aSuite, void * aContext)
+constexpr uint8_t emptyListExpected[] = {
+    // clang-format off
+    0x15, 0x36, 0x01, // Test overhead, Start Anonymous struct + Start 1 byte Tag Array + Tag (01)
+    0x15, // Start anonymous struct
+      0x35, 0x01, // Start 1 byte tag struct + Tag (01)
+        0x24, 0x00, 0x99, // Tag (00) Value (1 byte uint) 0x99 (Attribute Version)
+        0x37, 0x01, // Start 1 byte tag list + Tag (01) (Attribute Path)
+          0x24, 0x02, 0x55, // Tag (02) Value (1 byte uint) 0x55
+          0x24, 0x03, 0xaa, // Tag (03) Value (1 byte uint) 0xaa
+          0x24, 0x04, 0xcc, // Tag (04) Value (1 byte uint) 0xcc
+        0x18, // End of container
+        // Intended empty array
+        0x36, 0x02, // Start 1 byte tag array + Tag (02) (Attribute Value)
+        0x18, // End of container
+      0x18, // End of container
+    0x18, // End of container
+    // clang-format on
+};
+
+void TestEncodeEmptyList1(nlTestSuite * aSuite, void * aContext)
 {
     TestSetup test(aSuite);
     CHIP_ERROR err = test.encoder.EncodeList([](const auto & encoder) -> CHIP_ERROR { return CHIP_NO_ERROR; });
     NL_TEST_ASSERT(aSuite, err == CHIP_NO_ERROR);
-    const uint8_t expected[] = {
-        // clang-format off
-        0x15, 0x36, 0x01, // Test overhead, Start Anonymous struct + Start 1 byte Tag Array + Tag (01)
-        0x15, // Start anonymous struct
-          0x35, 0x01, // Start 1 byte tag struct + Tag (01)
-            0x24, 0x00, 0x99, // Tag (00) Value (1 byte uint) 0x99 (Attribute Version)
-            0x37, 0x01, // Start 1 byte tag list + Tag (01) (Attribute Path)
-              0x24, 0x02, 0x55, // Tag (02) Value (1 byte uint) 0x55
-              0x24, 0x03, 0xaa, // Tag (03) Value (1 byte uint) 0xaa
-              0x24, 0x04, 0xcc, // Tag (04) Value (1 byte uint) 0xcc
-            0x18, // End of container
-            // Intended empty array
-            0x36, 0x02, // Start 1 byte tag array + Tag (02) (Attribute Value)
-            0x18, // End of container
-          0x18, // End of container
-        0x18, // End of container
-        // clang-format on
-    };
-    VERIFY_BUFFER_STATE(aSuite, test, expected);
+    VERIFY_BUFFER_STATE(aSuite, test, emptyListExpected);
+}
+
+void TestEncodeEmptyList2(nlTestSuite * aSuite, void * aContext)
+{
+    TestSetup test(aSuite);
+    CHIP_ERROR err = test.encoder.EncodeEmptyList();
+    NL_TEST_ASSERT(aSuite, err == CHIP_NO_ERROR);
+    VERIFY_BUFFER_STATE(aSuite, test, emptyListExpected);
 }
 
 void TestEncodeFabricScoped(nlTestSuite * aSuite, void * aContext)
@@ -375,17 +384,20 @@ void TestEncodeListChunking(nlTestSuite * aSuite, void * aContext)
     }
 }
 
-#undef VERIFY_STATE
+#undef VERIFY_BUFFER_STATE
 
 } // anonymous namespace
 
 namespace {
-const nlTest sTests[] = {
-    NL_TEST_DEF("TestEncodeNothing", TestEncodeNothing),           NL_TEST_DEF("TestEncodeBool", TestEncodeBool),
-    NL_TEST_DEF("TestEncodeEmptyList", TestEncodeEmptyList),       NL_TEST_DEF("TestEncodeListOfBools1", TestEncodeListOfBools1),
-    NL_TEST_DEF("TestEncodeListOfBools2", TestEncodeListOfBools2), NL_TEST_DEF("TestEncodeListChunking", TestEncodeListChunking),
-    NL_TEST_DEF("TestEncodeFabricScoped", TestEncodeFabricScoped), NL_TEST_SENTINEL()
-};
+const nlTest sTests[] = { NL_TEST_DEF("TestEncodeNothing", TestEncodeNothing),
+                          NL_TEST_DEF("TestEncodeBool", TestEncodeBool),
+                          NL_TEST_DEF("TestEncodeEmptyList1", TestEncodeEmptyList1),
+                          NL_TEST_DEF("TestEncodeEmptyList2", TestEncodeEmptyList2),
+                          NL_TEST_DEF("TestEncodeListOfBools1", TestEncodeListOfBools1),
+                          NL_TEST_DEF("TestEncodeListOfBools2", TestEncodeListOfBools2),
+                          NL_TEST_DEF("TestEncodeListChunking", TestEncodeListChunking),
+                          NL_TEST_DEF("TestEncodeFabricScoped", TestEncodeFabricScoped),
+                          NL_TEST_SENTINEL() };
 }
 
 int TestAttributeValueEncoder()

src/include/platform/internal/GenericConnectivityManagerImpl_NoThread.h

@@ -152,7 +152,7 @@ inline CHIP_ERROR GenericConnectivityManagerImpl_NoThread<ImplClass>::_WriteThre
     case app::Clusters::ThreadNetworkDiagnostics::Attributes::SecurityPolicy::Id:
     case app::Clusters::ThreadNetworkDiagnostics::Attributes::OperationalDatasetComponents::Id:
     case app::Clusters::ThreadNetworkDiagnostics::Attributes::ActiveNetworkFaultsList::Id: {
-        err = encoder.Encode(app::DataModel::List<EndpointId>());
+        err = encoder.EncodeEmptyList();
         break;
     }
     default: {

src/platform/Linux/ThreadStackManagerImpl.cpp

@@ -486,7 +486,7 @@ CHIP_ERROR ThreadStackManagerImpl::_WriteThreadNetworkDiagnosticAttributeToTlv(A
     case ThreadNetworkDiagnostics::Attributes::SecurityPolicy::Id:
     case ThreadNetworkDiagnostics::Attributes::OperationalDatasetComponents::Id:
     case ThreadNetworkDiagnostics::Attributes::ActiveNetworkFaultsList::Id: {
-        err = encoder.Encode(DataModel::List<EndpointId>());
+        err = encoder.EncodeEmptyList();
         break;
     }
     default: {