grpc-swift/Sources/GRPCCore/Transport/ServerTransport.swift

/*
 * 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 type that provides a bidirectional communication channel with a client.
///
/// The server transport is responsible for handling connections created by a client and
/// the multiplexing of those connections into streams corresponding to RPCs.
///
/// gRPC provides an in-process transport in the `GRPCInProcessTransport` module and HTTP/2
/// transport built on top of SwiftNIO in the https://github.com/grpc/grpc-swift-nio-transport
/// package.
public protocol ServerTransport: Sendable {
  typealias Inbound = RPCAsyncSequence<RPCRequestPart, any Error>
  typealias Outbound = RPCWriter<RPCResponsePart>.Closable

  /// Starts the transport.
  ///
  /// Implementations will typically bind to a listening port when this function is called
  /// and start accepting new connections. Each accepted inbound RPC stream will be handed over to
  /// the provided `streamHandler` to handle accordingly.
  ///
  /// You can call ``beginGracefulShutdown()`` to stop the transport from accepting new streams. Existing
  /// streams must be allowed to complete naturally. However, transports may also enforce a grace
  /// period after which any open streams may be cancelled. You can also cancel the task running
  /// ``listen(streamHandler:)`` to abruptly close connections and streams.
  func listen(
    streamHandler: @escaping @Sendable (
      _ stream: RPCStream<Inbound, Outbound>,
      _ context: ServerContext
    ) async -> Void
  ) async throws

  /// Indicates to the transport that no new streams should be accepted.
  ///
  /// Existing streams are permitted to run to completion. However, the transport may also enforce
  /// a grace period, after which remaining streams are cancelled.
  func beginGracefulShutdown()
}