SchemaRegistrySerde: Avro deserialization via topic name

Closes #882

Author: 1-alex98

api/src/main/java/io/kafbat/ui/serdes/builtin/sr/SchemaRegistrySerde.java

@@ -279,7 +279,7 @@ public Serializer serializer(String topic, Target type) {
   @Override
   public Deserializer deserializer(String topic, Target type) {
     return (headers, data) -> {
-      var schemaId = extractSchemaIdFromMsg(data);
+      int schemaId = getSchemaIdFromMessageOrTopic(data, topic, type);
       SchemaType format = getMessageFormatBySchemaId(schemaId);
       MessageFormatter formatter = schemaRegistryFormatters.get(format);
       return new DeserializeResult(
@@ -293,22 +293,30 @@ public Deserializer deserializer(String topic, Target type) {
     };
   }
 
+  private int getSchemaIdFromMessageOrTopic(byte[] data, String topic, Target type) {
+    return extractSchemaIdFromMsg(data).orElseGet(
+        () -> {
+          String subject = schemaSubject(topic, type);
+          return getSchemaBySubject(subject)
+              .map(SchemaMetadata::getId)
+              .orElseThrow(() -> new ValidationException(
+                  String.format("No schema for subject '%s' found and no magic byte in avro data", subject)));
+        }
+    );
+  }
+
   private SchemaType getMessageFormatBySchemaId(int schemaId) {
     return getSchemaById(schemaId)
         .map(ParsedSchema::schemaType)
         .flatMap(SchemaType::fromString)
         .orElseThrow(() -> new ValidationException(String.format("Schema for id '%d' not found ", schemaId)));
   }
 
-  private int extractSchemaIdFromMsg(byte[] data) {
+  private Optional<Integer> extractSchemaIdFromMsg(byte[] data) {
     ByteBuffer buffer = ByteBuffer.wrap(data);
     if (buffer.remaining() >= SR_PAYLOAD_PREFIX_LENGTH && buffer.get() == SR_PAYLOAD_MAGIC_BYTE) {
-      return buffer.getInt();
+      return Optional.of(buffer.getInt());
     }
-    throw new ValidationException(
-        String.format(
-            "Data doesn't contain magic byte and schema id prefix, so it can't be deserialized with %s serde",
-            name())
-    );
+    return Optional.empty();
   }
 }

api/src/test/java/io/kafbat/ui/serdes/builtin/sr/SchemaRegistrySerdeTest.java

@@ -130,6 +130,39 @@ void deserializeReturnsJsonAvroMsgJsonRepresentation() throws RestClientExceptio
         .contains(Map.entry("schemaId", schemaId));
   }
 
+  @Test
+  void deserializeReturnsJsonAvroMsgJsonRepresentationViaTopicNameOnly() throws RestClientException, IOException {
+    AvroSchema schema = new AvroSchema(
+        "{"
+            + "  \"type\": \"record\","
+            + "  \"name\": \"TestAvroRecord1\","
+            + "  \"fields\": ["
+            + "    {"
+            + "      \"name\": \"field1\","
+            + "      \"type\": \"string\""
+            + "    },"
+            + "    {"
+            + "      \"name\": \"field2\","
+            + "      \"type\": \"int\""
+            + "    }"
+            + "  ]"
+            + "}"
+    );
+    String jsonValue = "{ \"field1\":\"testStr\", \"field2\": 123 }";
+
+    String topic = "test";
+    int schemaId = registryClient.register(topic + "-value", schema);
+
+    byte[] data = jsonToAvro(jsonValue, schema); // No magic byte no schema id registered
+    var result = serde.deserializer(topic, Serde.Target.VALUE).deserialize(null, data);
+
+    assertJsonsEqual(jsonValue, result.getResult());
+    assertThat(result.getType()).isEqualTo(DeserializeResult.Type.JSON);
+    assertThat(result.getAdditionalProperties())
+        .contains(Map.entry("type", "AVRO"))
+        .contains(Map.entry("schemaId", schemaId));
+  }
+
   @Nested
   class SerdeWithDisabledSubjectExistenceCheck {