grpc-swift/Sources/GRPC/AsyncAwaitSupport/GRPCAsyncUnaryCall.swift

/*
 * Copyright 2021, 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.
 */
import NIOHPACK

/// A unary gRPC call. The request is sent on initialization.
///
/// Note: while this object is a `struct`, its implementation delegates to ``Call``. It therefore
/// has reference semantics.
@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
public struct GRPCAsyncUnaryCall<Request: Sendable, Response: Sendable>: Sendable {
  private let call: Call<Request, Response>
  private let responseParts: UnaryResponseParts<Response>

  /// The options used to make the RPC.
  public var options: CallOptions {
    self.call.options
  }

  /// The path used to make the RPC.
  public var path: String {
    self.call.path
  }

  /// Cancel this RPC if it hasn't already completed.
  public func cancel() {
    self.call.cancel(promise: nil)
  }

  // MARK: - Response Parts

  private func withRPCCancellation<R: Sendable>(_ fn: () async throws -> R) async rethrows -> R {
    return try await withTaskCancellationHandler(operation: fn) {
      self.cancel()
    }
  }

  /// The initial metadata returned from the server.
  ///
  /// - Important: The initial metadata will only be available when the response has been received.
  public var initialMetadata: HPACKHeaders {
    get async throws {
      try await self.withRPCCancellation {
        try await self.responseParts.initialMetadata.get()
      }
    }
  }

  /// The response message returned from the service if the call is successful. This may be throw
  /// if the call encounters an error.
  ///
  /// Callers should rely on the `status` of the call for the canonical outcome.
  public var response: Response {
    get async throws {
      try await self.withRPCCancellation {
        try await self.responseParts.response.get()
      }
    }
  }

  /// The trailing metadata returned from the server.
  ///
  /// - Important: Awaiting this property will suspend until the responses have been consumed.
  public var trailingMetadata: HPACKHeaders {
    get async throws {
      try await self.withRPCCancellation {
        try await self.responseParts.trailingMetadata.get()
      }
    }
  }

  /// The final status of the the RPC.
  ///
  /// - Important: Awaiting this property will suspend until the responses have been consumed.
  public var status: GRPCStatus {
    get async {
      // force-try acceptable because any error is encapsulated in a successful GRPCStatus future.
      await self.withRPCCancellation {
        try! await self.responseParts.status.get()
      }
    }
  }

  private init(
    call: Call<Request, Response>,
    _ request: Request
  ) {
    self.call = call
    self.responseParts = UnaryResponseParts(on: call.eventLoop)
    self.call.invokeUnaryRequest(
      request,
      onStart: {},
      onError: self.responseParts.handleError(_:),
      onResponsePart: self.responseParts.handle(_:)
    )
  }

  /// We expose this as the only non-private initializer so that the caller
  /// knows that invocation is part of initialisation.
  internal static func makeAndInvoke(
    call: Call<Request, Response>,
    _ request: Request
  ) -> Self {
    Self(call: call, request)
  }
}