reactive/Ix.NET/Source/System.Interactive.Async/Catch.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.ExceptionServices;
using System.Threading;
using System.Threading.Tasks;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TSource> Catch<TSource, TException>(this IAsyncEnumerable<TSource> source, Func<TException, IAsyncEnumerable<TSource>> handler)
            where TException : Exception
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (handler == null)
                throw new ArgumentNullException(nameof(handler));

            return CreateEnumerable(
                () =>
                {
                    var e = source.GetEnumerator();

                    var cts = new CancellationTokenDisposable();
                    var a = new AssignableDisposable
                    {
                        Disposable = e
                    };
                    var d = Disposable.Create(cts, a);
                    var done = false;

                    var f = default(Func<CancellationToken, Task<bool>>);
                    f = async ct =>
                        {
                            if (!done)
                            {
                                try
                                {
                                    return await e.MoveNext(ct)
                                                  .ConfigureAwait(false);
                                }
                                catch (TException ex)
                                {
                                    var err = handler(ex)
                                        .GetEnumerator();
                                    e = err;
                                    a.Disposable = e;
                                    done = true;
                                    return await f(ct)
                                               .ConfigureAwait(false);
                                }
                            }
                            return await e.MoveNext(ct)
                                          .ConfigureAwait(false);
                        };

                    return CreateEnumerator(
                        f,
                        () => e.Current,
                        d.Dispose,
                        a
                    );
                });
        }

        public static IAsyncEnumerable<TSource> Catch<TSource>(this IEnumerable<IAsyncEnumerable<TSource>> sources)
        {
            if (sources == null)
                throw new ArgumentNullException(nameof(sources));

            return sources.Catch_();
        }

        public static IAsyncEnumerable<TSource> Catch<TSource>(params IAsyncEnumerable<TSource>[] sources)
        {
            if (sources == null)
                throw new ArgumentNullException(nameof(sources));

            return sources.Catch_();
        }

        public static IAsyncEnumerable<TSource> Catch<TSource>(this IAsyncEnumerable<TSource> first, IAsyncEnumerable<TSource> second)
        {
            if (first == null)
                throw new ArgumentNullException(nameof(first));
            if (second == null)
                throw new ArgumentNullException(nameof(second));

            return new[] {first, second}.Catch_();
        }

        private static IAsyncEnumerable<TSource> Catch_<TSource>(this IEnumerable<IAsyncEnumerable<TSource>> sources)
        {
            return CreateEnumerable(
                () =>
                {
                    var se = sources.GetEnumerator();
                    var e = default(IAsyncEnumerator<TSource>);

                    var cts = new CancellationTokenDisposable();
                    var a = new AssignableDisposable();
                    var d = Disposable.Create(cts, se, a);

                    var error = default(ExceptionDispatchInfo);

                    var f = default(Func<CancellationToken, Task<bool>>);
                    f = async ct =>
                        {
                            if (e == null)
                            {
                                if (se.MoveNext())
                                {
                                    e = se.Current.GetEnumerator();
                                }
                                else
                                {
                                    error?.Throw();
                                    return false;
                                }

                                error = null;

                                a.Disposable = e;
                            }

                            try
                            {
                                return await e.MoveNext(ct)
                                              .ConfigureAwait(false);
                            }
                            catch (Exception exception)
                            {
                                e.Dispose();
                                e = null;
                                error = ExceptionDispatchInfo.Capture(exception);
                                return await f(ct)
                                           .ConfigureAwait(false);
                            }
                        };

                    return CreateEnumerator(
                        f,
                        () => e.Current,
                        d.Dispose,
                        a
                    );
                });
        }
    }
}