Added cancelation token support for the operation of asynchronously r…

…eading a string from a stream. (#156)

CodeJam.Main.Tests/IO/StreamTests.cs

@@ -0,0 +1,101 @@
+#if NET45_OR_GREATER || TARGETS_NETSTANDARD || TARGETS_NETCOREAPP // PUBLIC_API_CHANGES
+
+using NUnit.Framework;
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace CodeJam.IO
+{
+	[TestFixture(Category = "Assertions")]
+	[SuppressMessage("ReSharper", "NotResolvedInText")]
+	public class StreamTests
+	{
+		[Test]
+		public void TestStreamReadingCanceled()
+		{
+			using var file = new FileStreamSlowWrapper(1, 3, 0);
+			var input = Encoding.UTF8.GetBytes(Guid.NewGuid().ToString());
+
+			file.Write(input, 0, input.Length);
+			file.Flush();
+
+			var cancellationTokenSource = new CancellationTokenSource();
+			var cancellationToken = cancellationTokenSource.Token;
+
+			file.Position = 0;
+			var task = file.ReadAsStringAsync(Encoding.UTF8, cancellationToken);
+
+			cancellationTokenSource.Cancel();
+			Assert.ThrowsAsync<OperationCanceledException>(() => task);
+		}
+
+		internal class FileStreamSlowWrapper : Stream
+		{
+			private FileStream fileStream;
+
+			private TimeSpan readDelay;
+
+			private TimeSpan writeDelay;
+
+			public FileStreamSlowWrapper(
+				int bufferSize = 4096,
+				double readDelaySeconds = 0,
+				double writeDelaySeconds = 0)
+			{
+				readDelay = TimeSpan.FromSeconds(readDelaySeconds);
+				writeDelay = TimeSpan.FromSeconds(writeDelaySeconds);
+
+				var filePath = System.IO.Path.Combine(
+					System.IO.Path.GetTempPath(),
+					Guid.NewGuid() + ".tmp");
+				fileStream = new FileStream(
+					filePath,
+					FileMode.CreateNew,
+					FileAccess.ReadWrite,
+					FileShare.Read,
+					bufferSize,
+					FileOptions.DeleteOnClose);
+			}
+
+			public override bool CanRead => fileStream.CanRead;
+
+			public override bool CanSeek => fileStream.CanSeek;
+
+			public override bool CanWrite => fileStream.CanWrite;
+
+			public override long Length => fileStream.Length;
+
+			public override long Position { get => fileStream.Position; set => fileStream.Position = value; }
+
+			public override void Flush() => fileStream.Flush();
+
+			public override long Seek(long offset, SeekOrigin origin) => fileStream.Seek(offset, origin);
+
+			public override void SetLength(long value) => fileStream.SetLength(value);
+
+			public override void Close() => fileStream.Close();
+
+			protected override void Dispose(bool disposing) => fileStream.Dispose();
+
+			public override int Read(byte[] buffer, int offset, int count)
+			{
+				Task.Delay(readDelay).Wait();
+				return fileStream.Read(buffer, offset, count);
+			}
+
+			public override void Write(byte[] buffer, int offset, int count)
+			{
+				Task.Delay(writeDelay).Wait();
+				fileStream.Write(buffer, offset, count);
+			}
+		}
+	}
+}
+
+#endif

CodeJam.Main/IO/StreamExtensions.cs

@@ -2,6 +2,7 @@
 using System;
 using System.IO;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 
 using JetBrains.Annotations;
@@ -110,6 +111,32 @@ public static async Task<string> ReadAsStringAsync(
 				return await reader.ReadToEndAsync().ConfigureAwait(false);
 		}
 
+		/// <summary>
+		/// Returns content of the stream as a string.
+		/// </summary>
+		/// <param name="stream">The stream to read.</param>
+		/// <param name="encoding">The character encoding to use.</param>
+		/// <param name="cancellationToken">Token of cancellation of the operation.</param>
+		public static async Task<string> ReadAsStringAsync(
+			this Stream stream,
+			Encoding? encoding = null,
+			CancellationToken cancellationToken = default)
+		{
+			Code.NotNull(stream, nameof(stream));
+			using var register = cancellationToken.Register(() => stream.Close());
+
+			try
+			{
+				using var reader = stream.ToStreamReader(encoding, true);
+				return await reader.ReadToEndAsync().ConfigureAwait(false);
+			}
+			catch
+			{
+				if (!cancellationToken.IsCancellationRequested) throw;
+				throw new OperationCanceledException(cancellationToken);
+			}
+		}
+
 		/// <summary>
 		/// Returns content of the stream as a byte array.
 		/// </summary>