Add Catch.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/Operators/Catch.cs

@@ -0,0 +1,228 @@
+// 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.Collections.Generic;
+using System.Reactive.Disposables;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    // TODO: Implement tail call behavior to flatten Catch chains.
+
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> Catch<TSource, TException>(this IAsyncObservable<TSource> source, Func<TException, IAsyncObservable<TSource>> handler)
+            where TException : Exception
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (handler == null)
+                throw new ArgumentNullException(nameof(handler));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sink, inner) = AsyncObserver.Catch(observer, handler);
+
+                var subscription = await source.SubscribeAsync(sink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(subscription, inner);
+            });
+        }
+
+        public static IAsyncObservable<TSource> Catch<TSource, TException>(this IAsyncObservable<TSource> source, Func<TException, Task<IAsyncObservable<TSource>>> handler)
+            where TException : Exception
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (handler == null)
+                throw new ArgumentNullException(nameof(handler));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sink, inner) = AsyncObserver.Catch(observer, handler);
+
+                var subscription = await source.SubscribeAsync(sink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(subscription, inner);
+            });
+        }
+
+        public static IAsyncObservable<TSource> Catch<TSource>(this IAsyncObservable<TSource> first, IAsyncObservable<TSource> second)
+        {
+            if (first == null)
+                throw new ArgumentNullException(nameof(first));
+            if (second == null)
+                throw new ArgumentNullException(nameof(second));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sink, inner) = AsyncObserver.Catch(observer, second);
+
+                var subscription = await first.SubscribeAsync(sink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(subscription, inner);
+            });
+        }
+
+        public static IAsyncObservable<TSource> Catch<TSource>(params IAsyncObservable<TSource>[] sources) => Catch<TSource>((IEnumerable<IAsyncObservable<TSource>>)sources);
+
+        public static IAsyncObservable<TSource> Catch<TSource>(this IEnumerable<IAsyncObservable<TSource>> sources)
+        {
+            if (sources == null)
+                throw new ArgumentNullException(nameof(sources));
+
+            return Create<TSource>(async observer =>
+            {
+                var enumerator = sources.GetEnumerator();
+
+                if (!enumerator.MoveNext())
+                {
+                    return AsyncDisposable.Nop;
+                }
+
+                var source = enumerator.Current;
+
+                var (sink, inner) = AsyncObserver.Catch(observer, enumerator);
+
+                var subscription = await source.SubscribeAsync(sink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(subscription, inner);
+            });
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static (IAsyncObserver<TSource>, IAsyncDisposable) Catch<TSource, TException>(IAsyncObserver<TSource> observer, Func<TException, IAsyncObservable<TSource>> handler)
+            where TException : Exception
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (handler == null)
+                throw new ArgumentNullException(nameof(handler));
+
+            return Catch<TSource, TException>(observer, ex => Task.FromResult(handler(ex)));
+        }
+
+        public static (IAsyncObserver<TSource>, IAsyncDisposable) Catch<TSource, TException>(IAsyncObserver<TSource> observer, Func<TException, Task<IAsyncObservable<TSource>>> handler)
+            where TException : Exception
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (handler == null)
+                throw new ArgumentNullException(nameof(handler));
+
+            var subscription = new SingleAssignmentAsyncDisposable();
+
+            var sink = Create<TSource>(
+                observer.OnNextAsync,
+                async ex =>
+                {
+                    if (ex is TException error)
+                    {
+                        IAsyncObservable<TSource> handlerObservable;
+
+                        try
+                        {
+                            handlerObservable = await handler(error).ConfigureAwait(false);
+                        }
+                        catch (Exception err)
+                        {
+                            await observer.OnErrorAsync(err).ConfigureAwait(false);
+                            return;
+                        }
+
+                        var handlerSubscription = await handlerObservable.SubscribeAsync(observer).ConfigureAwait(false);
+
+                        await subscription.AssignAsync(handlerSubscription).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                    }
+                },
+                observer.OnCompletedAsync
+            );
+
+            return (sink, subscription);
+        }
+
+        public static (IAsyncObserver<TSource>, IAsyncDisposable) Catch<TSource>(IAsyncObserver<TSource> observer, IAsyncObservable<TSource> second)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (second == null)
+                throw new ArgumentNullException(nameof(second));
+
+            var subscription = new SingleAssignmentAsyncDisposable();
+
+            var sink = Create<TSource>(
+                observer.OnNextAsync,
+                async ex =>
+                {
+                    var secondSubscription = await second.SubscribeAsync(observer).ConfigureAwait(false);
+
+                    await subscription.AssignAsync(secondSubscription).ConfigureAwait(false);
+                },
+                observer.OnCompletedAsync
+            );
+
+            return (sink, subscription);
+        }
+
+        public static (IAsyncObserver<TSource>, IAsyncDisposable) Catch<TSource>(IAsyncObserver<TSource> observer, IEnumerator<IAsyncObservable<TSource>> handlers)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (handlers == null)
+                throw new ArgumentNullException(nameof(handlers));
+
+            var innerSubscription = new SerialAsyncDisposable();
+
+            IAsyncObserver<TSource> sink = null;
+
+            sink = Create<TSource>(
+                observer.OnNextAsync,
+                async ex =>
+                {
+                    var handler = default(IAsyncObservable<TSource>);
+
+                    try
+                    {
+                        if (handlers.MoveNext())
+                        {
+                            handler = handlers.Current;
+                        }
+                    }
+                    catch (Exception err)
+                    {
+                        await observer.OnErrorAsync(err).ConfigureAwait(false);
+                        return;
+                    }
+
+                    if (handler == null)
+                    {
+                        await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                        return;
+                    }
+
+                    var handlerSubscription = await handler.SubscribeAsync(sink).ConfigureAwait(false);
+
+                    await innerSubscription.AssignAsync(handlerSubscription).ConfigureAwait(false);
+                },
+                observer.OnCompletedAsync
+            );
+
+            var disposeEnumerator = AsyncDisposable.Create(() =>
+            {
+                handlers.Dispose();
+                return Task.CompletedTask;
+            });
+
+            var subscription = StableCompositeAsyncDisposable.Create(innerSubscription, disposeEnumerator);
+
+            return (sink, subscription);
+        }
+    }
+}