我正在对文件流执行复制异步操作。我注意到如果在操作期间发生错误，我不会收到任何错误异常。
使用大文件进行测试，在复制操作过程中，我突然关闭了网络连接。
经过一段时间后，测试结束了。
我希望能够捕获复制操作期间发生的任何错误。
我在下面复制..代码示例，只是请一些帮助。
BR Alex
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using static Microsoft.VisualStudio.TestTools.UnitTesting.Assert;
using static System.Console;
namespace CopyAsync
{
[TestClass]
public class UnitTest
{
public int BufferSize = 10;
[TestMethod]
public void CopyFileAsyncSouldCopyFile()
{
BufferSize = 10;
const string source = @"..\..\UnitTest.cs";
var destination = Path.GetRandomFileName();
WriteLine($"Start...");
var task = CopyAsync(source, destination, action: (total) => WriteLine($"Copying... {total}"));
var bytes = task.Result;
WriteLine($"Bytes copied... {bytes}");
IsTrue(File.Exists(destination));
AreEqual((new FileInfo(source)).Length, bytes);
File.Delete(destination);
}
[TestMethod]
public void CopyFileAsyncCancelledSouldCancelCopyFile()
{
BufferSize = 10;
const string source = @"..\..\UnitTest.cs";
var destination = Path.GetRandomFileName();
var cts = new CancellationTokenSource();
WriteLine($"Start...");
var task = CopyAsync(source, destination, cts.Token,
(total) =>
{
WriteLine($"Copying... {total}");
if (total > 1677)
return;
cts.Cancel();
WriteLine($"Canceled...");
});
try
{
var bytes = task.Result; // exception WILL BE thrown here
WriteLine($"Bytes copied... {bytes}"); // WON'T BE executed
}
catch (AggregateException ex) when (ex.InnerException.GetType() == typeof(TaskCanceledException))
{
WriteLine($"TaskCanceledException...");
File.Delete(destination);
}
}
[TestMethod]
// Exception not captured
// missed: System.AggregateException: One or more errors occurred. ---> System.IO.IOException: The network path was not found.
public void CopyFileAsyncNetworkErrorShouldFail()
{
const string source = @"..\..\verybigfile.iso";
var destination = Path.GetRandomFileName();
BufferSize = 4096;
WriteLine($"Start...");
var task = CopyAsync(source, destination, action: (total) => WriteLine($"Copying... {total}"));
var bytes = task.Result; // exception WON'T BE thrown here
WriteLine($"Bytes copied... {bytes}"); // WILL BE executed
}
public async Task<int> CopyAsync(string input, string output, CancellationToken token = default(CancellationToken), Action<long> action = null)
{
using (var source = new FileStream(input, FileMode.Open, FileAccess.Read, FileShare.Read, BufferSize, true))
using (var destination = new FileStream(output, FileMode.Create, FileAccess.Write, FileShare.None, BufferSize, true))
{
int bytes;
var total = 0;
var buffer = new byte[BufferSize];
while ((bytes = await source.ReadAsync(buffer, 0, buffer.Length, token)) > 0)
{
await destination.WriteAsync(buffer, 0, bytes, token);
total += bytes;
action?.Invoke(total);
}
return total;
}
}
}
}
答案 0 :(得分：0)
这里我改变了一段代码，但这里是工作代码..
（但实际上我无法理解为什么现在正在运作，因为工作流程或多或少相同）
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using static Microsoft.VisualStudio.TestTools.UnitTesting.Assert;
using static System.Console;
namespace CopyAsync
{
[TestClass]
public class UnitTest
{
private int _bufferSize = 4096;
[TestMethod]
public void CopyFileAsyncSouldCopyFile()
{
_bufferSize = 100;
const string source = @"..\..\UnitTest.cs";
var destination = Path.GetRandomFileName();
WriteLine($"Start...");
var task = FileCopyAsync(source, destination, action: total => WriteLine($"Copying... {total}"));
var bytes = task.Result;
WriteLine($"Bytes copied... {bytes}");
IsTrue(File.Exists(destination));
AreEqual((new FileInfo(source)).Length, bytes);
File.Delete(destination);
}
[TestMethod]
public void CopyFileAsyncCancelledSouldCancelCopyFile()
{
_bufferSize = 100;
const string source = @"..\..\UnitTest.cs";
var destination = Path.GetRandomFileName();
var cts = new CancellationTokenSource();
WriteLine($"Start...");
var task = FileCopyAsync(source, destination,
token: cts.Token,
action: total =>
{
WriteLine($"Copying... {total}");
if (total < 2000)
return;
cts.Cancel();
WriteLine($"Canceled... at {total}");
});
try
{
task.Wait(); // exception WILL BE thrown here... PERFECT!!!!
}
catch (AggregateException ex) when (ex.InnerException.GetType() == typeof(TaskCanceledException))
{
WriteLine($"TaskCanceledException...");
File.Delete(destination);
}
}
[TestMethod]
public void CopyFileAsyncNetworkErrorShouldFail()
{
_bufferSize = 4096;
const string source = @"\\server\sharedfolder\bigfile.iso"; // to test close network connection while copying...
var destination = Path.GetRandomFileName();
WriteLine($"Start...");
var task = FileCopyAsync(source, destination, action: total => WriteLine($"Copying... {total}"));
try
{
task.Wait(); // exception WILL BE thrown here... PERFECT!!!! more than PERFECT
}
catch (AggregateException ex) when (ex.InnerException.GetType() == typeof(IOException))
{
WriteLine($"IOException...");
File.Delete(destination);
}
}
// ##########################
public async Task<int> FileCopyAsync(string sourceFileName, string destFileName, bool overwrite = false, CancellationToken token = default(CancellationToken), Action<long> action = null)
{
if (string.Equals(sourceFileName, destFileName, StringComparison.InvariantCultureIgnoreCase))
throw new IOException($"Source {sourceFileName} and destination {destFileName} are the same");
using (var sourceStream = new FileStream(sourceFileName, FileMode.Open, FileAccess.Read, FileShare.Read, _bufferSize, true))
using (var destStream = new FileStream(destFileName, FileMode.Create, FileAccess.Write, FileShare.None, _bufferSize, true))
{
var bytesCopied = await StreamCopyAsync(sourceStream, destStream, token, action);
if (bytesCopied != (new FileInfo(sourceFileName)).Length)
throw new IOException($"Source {sourceFileName} and destination {destFileName} don't match");
return bytesCopied;
}
}
public async Task<int> StreamCopyAsync(Stream sourceStream, Stream destStream, CancellationToken token = default(CancellationToken), Action<long> action = null)
{
if (Equals(sourceStream, destStream))
throw new ApplicationException("Source and destination are the same");
using (var reg = token.Register(() => Close(sourceStream, destStream))) // disposes registration for token cancellation callback
{
int bytes;
var bytesCopied = 0;
var buffer = new byte[_bufferSize];
while ((bytes = await sourceStream.ReadAsync(buffer, 0, buffer.Length, token)) > 0)
{
if (token.IsCancellationRequested)
break;
await destStream.WriteAsync(buffer, 0, bytes, token);
bytesCopied += bytes;
action?.Invoke(bytesCopied);
}
return bytesCopied;
}
}
private static void Close(Stream source, Stream destination) // fires on token cancellation
{
source.Close();
destination.Close();
}
}
}