Remove Serde#schema. This is a leftover from a previous design, and i…

…t's currently unused. It might look different in future.

sdk-api-kotlin/src/main/kotlin/dev/restate/sdk/kotlin/Service.kt

@@ -121,13 +121,7 @@ private constructor(
       private val LOG = LogManager.getLogger()
     }
 
-    fun toHandlerDefinition() =
-        HandlerDefinition(
-            handlerSignature.name,
-            handlerType,
-            handlerSignature.requestSerde.schema(),
-            handlerSignature.responseSerde.schema(),
-            this)
+    fun toHandlerDefinition() = HandlerDefinition(handlerSignature.name, handlerType, this)
 
     override fun handle(
         syscalls: Syscalls,

sdk-api/src/main/java/dev/restate/sdk/Service.java

@@ -132,12 +132,7 @@ public BiFunction<Context, REQ, RES> getRunner() {
     }
 
     public HandlerDefinition<Service.Options> toHandlerDefinition() {
-      return new HandlerDefinition<>(
-          this.handlerSignature.name,
-          this.handlerType,
-          this.handlerSignature.requestSerde.schema(),
-          this.handlerSignature.responseSerde.schema(),
-          this);
+      return new HandlerDefinition<>(this.handlerSignature.name, this.handlerType, this);
     }
 
     @Override

sdk-common/src/main/java/dev/restate/sdk/common/Serde.java

@@ -14,7 +14,11 @@
 import java.util.Objects;
 import org.jspecify.annotations.Nullable;
 
-/** Interface defining serialization and deserialization of concrete types. */
+/**
+ * Interface defining serialization and deserialization of concrete types.
+ *
+ * <p>You can create a custom one using {@link #using(String, ThrowingFunction, ThrowingFunction)}.
+ */
 public interface Serde<T> {
 
   byte[] serialize(@Nullable T value);
@@ -30,20 +34,20 @@ default T deserialize(ByteString byteString) {
     return deserialize(byteString.toByteArray());
   }
 
+  // --- Metadata about the serialized/deserialized content
+
   /**
-   * @return the schema of this object.
+   * Content-type to use in request/responses.
+   *
+   * <p>If null, the SDK assumes the produced output is empty. This might change in the future.
    */
-  default @Nullable Object schema() {
-    return null;
-  }
-
   default @Nullable String contentType() {
-    return null;
+    return "application/octet-stream";
   }
 
   /**
-   * Create a {@link Serde} from {@code serializer}/{@code deserializer} lambdas. Before invoking
-   * the serializer, we check that {@code value} is non-null.
+   * Like {@link #using(String, ThrowingFunction, ThrowingFunction)}, using content-type {@code
+   * application/octet-stream}.
    */
   static <T> Serde<T> using(
       ThrowingFunction<T, byte[]> serializer, ThrowingFunction<byte[], T> deserializer) {
@@ -59,4 +63,59 @@ public T deserialize(byte[] value) {
       }
     };
   }
+
+  /**
+   * Create a {@link Serde} from {@code serializer}/{@code deserializer} lambdas, tagging with
+   * {@code contentType}. Before invoking the serializer, we check that {@code value} is non-null.
+   */
+  static <T> Serde<T> using(
+      String contentType,
+      ThrowingFunction<T, byte[]> serializer,
+      ThrowingFunction<byte[], T> deserializer) {
+    return new Serde<>() {
+      @Override
+      public byte[] serialize(T value) {
+        return serializer.asFunction().apply(Objects.requireNonNull(value));
+      }
+
+      @Override
+      public T deserialize(byte[] value) {
+        return deserializer.asFunction().apply(value);
+      }
+
+      @Override
+      public @Nullable String contentType() {
+        return contentType;
+      }
+    };
+  }
+
+  static <T> Serde<T> withContentType(String contentType, Serde<T> inner) {
+    return new Serde<>() {
+      @Override
+      public byte[] serialize(@Nullable T value) {
+        return inner.serialize(value);
+      }
+
+      @Override
+      public ByteString serializeToByteString(@Nullable T value) {
+        return inner.serializeToByteString(value);
+      }
+
+      @Override
+      public T deserialize(ByteString byteString) {
+        return inner.deserialize(byteString);
+      }
+
+      @Override
+      public T deserialize(byte[] value) {
+        return inner.deserialize(value);
+      }
+
+      @Override
+      public @Nullable String contentType() {
+        return contentType;
+      }
+    };
+  }
 }

sdk-common/src/main/java/dev/restate/sdk/common/syscalls/HandlerDefinition.java

@@ -14,20 +14,11 @@
 public final class HandlerDefinition<O> {
   private final String name;
   private final HandlerType handlerType;
-  private final Object inputSchema;
-  private final Object outputSchema;
   private final InvocationHandler<O> handler;
 
-  public HandlerDefinition(
-      String name,
-      HandlerType handlerType,
-      Object inputSchema,
-      Object outputSchema,
-      InvocationHandler<O> handler) {
+  public HandlerDefinition(String name, HandlerType handlerType, InvocationHandler<O> handler) {
     this.name = name;
     this.handlerType = handlerType;
-    this.inputSchema = inputSchema;
-    this.outputSchema = outputSchema;
     this.handler = handler;
   }
 
@@ -39,14 +30,6 @@ public HandlerType getHandlerType() {
     return handlerType;
   }
 
-  public Object getInputSchema() {
-    return inputSchema;
-  }
-
-  public Object getOutputSchema() {
-    return outputSchema;
-  }
-
   public InvocationHandler<O> getHandler() {
     return handler;
   }
@@ -56,14 +39,11 @@ public boolean equals(Object object) {
     if (this == object) return true;
     if (object == null || getClass() != object.getClass()) return false;
     HandlerDefinition<?> that = (HandlerDefinition<?>) object;
-    return Objects.equals(name, that.name)
-        && Objects.equals(inputSchema, that.inputSchema)
-        && Objects.equals(outputSchema, that.outputSchema)
-        && Objects.equals(handler, that.handler);
+    return Objects.equals(name, that.name) && Objects.equals(handler, that.handler);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name, inputSchema, outputSchema, handler);
+    return Objects.hash(name, handler);
   }
 }

sdk-core/src/test/java/dev/restate/sdk/core/ComponentDiscoveryHandlerTest.java

@@ -32,9 +32,7 @@ void handleWithMultipleServices() {
                 new ServiceDefinition<>(
                     "MyGreeter",
                     ServiceType.SERVICE,
-                    List.of(
-                        new HandlerDefinition<>(
-                            "greet", HandlerType.EXCLUSIVE, null, null, null)))));
+                    List.of(new HandlerDefinition<>("greet", HandlerType.EXCLUSIVE, null)))));
 
     DeploymentManifestSchema manifest = deploymentManifest.manifest();