Add server request and response objects (#1667)

Sources/GRPCCore/Call/ServerRequest.swift

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2023, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/// A namespace for request message types used by servers.
+public enum ServerRequest {}
+
+extension ServerRequest {
+  /// A request received at the server containing a single message.
+  public struct Single<Message: Sendable>: Sendable {
+    /// Metadata received from the client at the start of the RPC.
+    ///
+    /// The metadata contains gRPC and transport specific entries in addition to user-specified
+    /// metadata.
+    public var metadata: Metadata
+
+    /// The message received from the client.
+    public var message: Message
+
+    /// Create a new single server request.
+    ///
+    /// - Parameters:
+    ///   - metadata: Metadata received from the client.
+    ///   - messages: The message received from the client.
+    public init(metadata: Metadata, message: Message) {
+      self.metadata = metadata
+      self.message = message
+    }
+  }
+}
+
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension ServerRequest {
+  /// A request received at the server containing a stream of messages.
+  public struct Stream<Message: Sendable>: Sendable {
+    /// Metadata received from the client at the start of the RPC.
+    ///
+    /// The metadata contains gRPC and transport specific entries in addition to user-specified
+    /// metadata.
+    public var metadata: Metadata
+
+    /// A sequence of messages received from the client.
+    ///
+    /// The sequence may be iterated at most once.
+    public var messages: RPCAsyncSequence<Message>
+
+    /// Create a new streaming request.
+    ///
+    /// - Parameters:
+    ///   - metadata: Metadata received from the client.
+    ///   - messages: A sequence of messages received from the client.
+    public init(metadata: Metadata, messages: RPCAsyncSequence<Message>) {
+      self.metadata = metadata
+      self.messages = messages
+    }
+  }
+}
+
+// MARK: - Conversion
+
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension ServerRequest.Stream {
+  @_spi(Testing)
+  public init(single request: ServerRequest.Single<Message>) {
+    self.init(metadata: request.metadata, messages: .one(request.message))
+  }
+}