我创建了一个简单的控制台应用程序,使用new ASP.NET Core 2.1 HttpClientFactory从archive.org下载单个(PDF)文件。
对于该程序中使用的特定URL,我总是得到TaskCanceledException
。如果您尝试运行此代码,您可能会得到相同的异常。它适用于archive.org上的其他URL。使用wget从完全相同的URL(wget https://archive.org/download/1952-03_IF/1952-03_IF.pdf --output-document=IF.pdf
)下载文件时
下载成功。
但是当我使用HttpClient
时,我得到以下异常。
我可能做错什么?
以下是简单的代码:
using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using System.IO;
using System.Diagnostics;
namespace test2
{
public class Program
{
public static async Task Main(string[] args)
{
var serviceCollection = new ServiceCollection();
serviceCollection.AddHttpClient("archive", c =>
{
c.BaseAddress = new Uri("https://archive.org/download/");
c.DefaultRequestHeaders.Add("Accept", "application/pdf");
})
.AddTypedClient<ArchiveClient>();
var services = serviceCollection.BuildServiceProvider();
var archive = services.GetRequiredService<ArchiveClient>();
await archive.Get();
}
private class ArchiveClient
{
public ArchiveClient(HttpClient httpClient)
{
HttpClient = httpClient;
}
public HttpClient HttpClient { get; }
public async Task Get()
{
var request = new HttpRequestMessage(HttpMethod.Get, "1952-03_IF/1952-03_IF.pdf");
var response = await HttpClient.SendAsync(request).ConfigureAwait(false);
response.EnsureSuccessStatusCode();
using (Stream contentStream = await response.Content.ReadAsStreamAsync(),
fileStream = new FileStream("Worlds of IF 1952-03.pdf", FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
{
var totalRead = 0L;
var totalReads = 0L;
var buffer = new byte[8192];
var isMoreToRead = true;
do
{
var read = await contentStream.ReadAsync(buffer, 0, buffer.Length);
if (read == 0)
{
isMoreToRead = false;
}
else
{
await fileStream.WriteAsync(buffer, 0, read);
totalRead += read;
totalReads += 1;
if (totalReads % 2000 == 0)
{
Console.WriteLine(string.Format("bytes downloaded: {0:n0}", totalRead));
}
}
}
while (isMoreToRead);
}
}
}
}
}
这是我得到的完整例外:
Unhandled Exception: System.Threading.Tasks.TaskCanceledException: The operation was canceled.
---> System.IO.IOException: Unable to read data from the transport connection: Operation canceled.
---> System.Net.Sockets.SocketException: Operation canceled
--- End of inner exception stack trace ---
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error)
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.GetResult(Int16 token)
at System.Net.Security.SslStreamInternal.<FillBufferAsync>g__InternalFillBufferAsync|38_0[TReadAdapter](TReadAdapter adap, ValueTask`1 task, Int32 min, Int32 initial)
at System.Net.Security.SslStreamInternal.ReadAsyncInternal[TReadAdapter](TReadAdapter adapter, Memory`1 buffer)
at System.Net.Http.HttpConnection.FillAsync()
at System.Net.Http.HttpConnection.CopyToExactLengthAsync(Stream destination, UInt64 length, CancellationToken cancellationToken)
at System.Net.Http.HttpConnection.ContentLengthReadStream.CompleteCopyToAsync(Task copyTask, CancellationToken cancellationToken)
--- End of inner exception stack trace ---
at System.Net.Http.HttpConnection.ContentLengthReadStream.CompleteCopyToAsync(Task copyTask, CancellationToken cancellationToken)
at System.Net.Http.HttpConnection.HttpConnectionResponseContent.SerializeToStreamAsync(Stream stream, TransportContext context, CancellationToken cancellationToken)
at System.Net.Http.HttpContent.LoadIntoBufferAsyncCore(Task serializeToStreamTask, MemoryStream tempBuffer) at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
at test2.Program.ArchiveClient.Get() in /Users/Foo/Temp/test3/Program.cs:line 42
at test2.Program.Main(String[] args) in /Users/Foo/Temp/test3/Program.cs:line 27
at test2.Program.<Main>(String[] args)
答案 0 :(得分:1)
在您的情况下,似乎是问题所在。我想尝试的另一件事是通过
HttpCompletionOption.ResponseHeadersRead
SendPsync()中的作为第二个参数。发生的情况是,您的方法在读取标头后立即返回。响应不再在MemoryStream缓冲区中进行缓冲,而是直接从套接字读取。这意味着您可以在流传输整个对象之前开始流传输。从性能角度来看,它要快得多,在您的情况下,速度可能至关重要。
请记住要处理响应消息,否则连接将不会被释放。