Introduce method descriptor

packages/protobuf/src/service-type.ts

@@ -143,3 +143,64 @@ export enum MethodIdempotency {
    */
   Idempotent = 2,
 }
+
+interface mtShared {
+  readonly localName: string;
+  readonly service: Omit<ServiceType, "methods">;
+}
+
+/**
+ * A unary method: rpc (Input) returns (Output)
+ */
+export interface MethodTypeUnary<I extends Message<I>, O extends Message<O>>
+  extends mtShared,
+    MethodInfoUnary<I, O> {}
+
+/**
+ * A server streaming method: rpc (Input) returns (stream Output)
+ */
+export interface MethodTypeServerStreaming<
+  I extends Message<I>,
+  O extends Message<O>,
+> extends mtShared,
+    MethodInfoServerStreaming<I, O> {}
+
+/**
+ * A client streaming method: rpc (stream Input) returns (Output)
+ */
+export interface MethodTypeClientStreaming<
+  I extends Message<I>,
+  O extends Message<O>,
+> extends mtShared,
+    MethodInfoClientStreaming<I, O> {}
+
+/**
+ * A method that streams bi-directionally: rpc (stream Input) returns (stream Output)
+ */
+export interface MethodTypeBiDiStreaming<
+  I extends Message<I>,
+  O extends Message<O>,
+> extends mtShared,
+    MethodInfoBiDiStreaming<I, O> {}
+
+/**
+ * MethodType represents a self-contained method type. It must contain
+ * references to the service that implements it.
+ *
+ * - "name": The original name of the protobuf rpc.
+ * - "I": The input message type.
+ * - "O": The output message type.
+ * - "kind": The method type.
+ * - "idempotency": User-provided indication whether the method will cause
+ *   the same effect every time it is called.
+ * - "localName": The local name of the method, safe to use in ECMAScript.
+ * - "service": The service that implements the method, without methods.
+ */
+export type MethodType<
+  I extends Message<I> = AnyMessage,
+  O extends Message<O> = AnyMessage,
+> =
+  | MethodTypeUnary<I, O>
+  | MethodTypeServerStreaming<I, O>
+  | MethodTypeClientStreaming<I, O>
+  | MethodTypeBiDiStreaming<I, O>;