src/csharp/Grpc.Core/Internal/AsyncCallServer.cs

#region Copyright notice and license

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// modification, are permitted provided that the following conditions are
// met:
// 
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
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// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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#endregion

using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using Grpc.Core.Internal;
using Grpc.Core.Utils;

namespace Grpc.Core.Internal
{
    /// <summary>
    /// Manages server side native call lifecycle.
    /// </summary>
    internal class AsyncCallServer<TRequest, TResponse> : AsyncCallBase<TResponse, TRequest>
    {
        readonly TaskCompletionSource<object> finishedServersideTcs = new TaskCompletionSource<object>();
        readonly CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
        readonly Server server;

        public AsyncCallServer(Func<TResponse, byte[]> serializer, Func<byte[], TRequest> deserializer, GrpcEnvironment environment, Server server) : base(serializer, deserializer, environment)
        {
            this.server = GrpcPreconditions.CheckNotNull(server);
        }

        public void Initialize(CallSafeHandle call)
        {
            call.Initialize(environment.CompletionRegistry, environment.CompletionQueue);

            server.AddCallReference(this);
            InitializeInternal(call);
        }

        /// <summary>
        /// Only for testing purposes.
        /// </summary>
        public void InitializeForTesting(INativeCall call)
        {
            server.AddCallReference(this);
            InitializeInternal(call);
        }

        /// <summary>
        /// Starts a server side call.
        /// </summary>
        public Task ServerSideCallAsync()
        {
            lock (myLock)
            {
                GrpcPreconditions.CheckNotNull(call);

                started = true;

                call.StartServerSide(HandleFinishedServerside);
                return finishedServersideTcs.Task;
            }
        }

        /// <summary>
        /// Sends a streaming response. Only one pending send action is allowed at any given time.
        /// completionDelegate is called when the operation finishes.
        /// </summary>
        public void StartSendMessage(TResponse msg, WriteFlags writeFlags, AsyncCompletionDelegate<object> completionDelegate)
        {
            StartSendMessageInternal(msg, writeFlags, completionDelegate);
        }

        /// <summary>
        /// Receives a streaming request. Only one pending read action is allowed at any given time.
        /// </summary>
        public Task<TRequest> ReadMessageAsync()
        {
            return ReadMessageInternalAsync();
        }

        /// <summary>
        /// Initiates sending a initial metadata. 
        /// Even though C-core allows sending metadata in parallel to sending messages, we will treat sending metadata as a send message operation
        /// to make things simpler.
        /// completionDelegate is invoked upon completion.
        /// </summary>
        public void StartSendInitialMetadata(Metadata headers, AsyncCompletionDelegate<object> completionDelegate)
        {
            lock (myLock)
            {
                GrpcPreconditions.CheckNotNull(headers, "metadata");
                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");

                GrpcPreconditions.CheckState(!initialMetadataSent, "Response headers can only be sent once per call.");
                GrpcPreconditions.CheckState(streamingWritesCounter == 0, "Response headers can only be sent before the first write starts.");
                CheckSendingAllowed(allowFinished: false);

                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");

                using (var metadataArray = MetadataArraySafeHandle.Create(headers))
                {
                    call.StartSendInitialMetadata(HandleSendFinished, metadataArray);
                }

                this.initialMetadataSent = true;
                sendCompletionDelegate = completionDelegate;
            }
        }

        /// <summary>
        /// Sends call result status, indicating we are done with writes.
        /// Sending a status different from StatusCode.OK will also implicitly cancel the call.
        /// </summary>
        public Task SendStatusFromServerAsync(Status status, Metadata trailers, Tuple<TResponse, WriteFlags> optionalWrite)
        {
            byte[] payload = optionalWrite != null ? UnsafeSerialize(optionalWrite.Item1) : null;
            var writeFlags = optionalWrite != null ? optionalWrite.Item2 : default(WriteFlags);

            lock (myLock)
            {
                GrpcPreconditions.CheckState(started);
                GrpcPreconditions.CheckState(!disposed);
                GrpcPreconditions.CheckState(!halfcloseRequested, "Can only send status from server once.");

                using (var metadataArray = MetadataArraySafeHandle.Create(trailers))
                {
                    call.StartSendStatusFromServer(HandleSendStatusFromServerFinished, status, metadataArray, !initialMetadataSent,
                        payload, writeFlags);
                }
                halfcloseRequested = true;
                initialMetadataSent = true;
                sendStatusFromServerTcs = new TaskCompletionSource<object>();
                if (optionalWrite != null)
                {
                    streamingWritesCounter++;
                }
                return sendStatusFromServerTcs.Task;
            }
        }

        /// <summary>
        /// Gets cancellation token that gets cancelled once close completion
        /// is received and the cancelled flag is set.
        /// </summary>
        public CancellationToken CancellationToken
        {
            get
            {
                return cancellationTokenSource.Token;
            }
        }

        public string Peer
        {
            get
            {
                return call.GetPeer();
            }
        }

        protected override bool IsClient
        {
            get { return false; }
        }

        protected override void OnAfterReleaseResources()
        {
            server.RemoveCallReference(this);
        }

        /// <summary>
        /// Handles the server side close completion.
        /// </summary>
        private void HandleFinishedServerside(bool success, bool cancelled)
        {
            // NOTE: because this event is a result of batch containing GRPC_OP_RECV_CLOSE_ON_SERVER,
            // success will be always set to true.
            lock (myLock)
            {
                finished = true;
                if (streamingReadTcs == null)
                {
                    // if there's no pending read, readingDone=true will dispose now.
                    // if there is a pending read, we will dispose once that read finishes.
                    readingDone = true;
                    streamingReadTcs = new TaskCompletionSource<TRequest>();
                    streamingReadTcs.SetResult(default(TRequest));
                }
                ReleaseResourcesIfPossible();
            }

            if (cancelled)
            {
                cancellationTokenSource.Cancel();
            }

            finishedServersideTcs.SetResult(null);
        }
    }
}