请求需要缓冲数据才能成功 HttpClient

Question

我正在尝试使用POST 方法将字典内容发送到服务器

public async Task<T> postConnection(string GETParam, Dictionary<string, string> values, bool isRegistration = false)
{
    HttpResponseMessage response;
    string responseString;
    try
    { 
        using (var client = new HttpClient() { MaxResponseContentBufferSize = 256000 }) 
        {
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", tocken);
            var content = new FormUrlEncodedContent(values);
            response = await client.PostAsync(url, content);
            responseString = await response.Content.ReadAsStringAsync();
        }
    }

但是当我运行代码时，它给了我错误
WebException: The request requires buffering data to succeed HttpClient。

我不想使用WebRequest 或WebClient 发出请求，我只想使用HttpClient。

question 已经存在，但在尝试发送 head request 时发生相同的异常，表示该问题仅发生在 Xamarin 项目上，但尚未回答该问题。刚才提到他用WebRequest解决了这个问题。

Xamarin.Forms 上的此代码有什么错误？以及如何使用HttpClient 解决？

编辑

完全例外

{System.Net.WebException: The request requires buffering data to succeed.
  at System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult) [0x0005e] in /Users/builder/data/lanes/3540/1cf254db/source/mono/mcs/class/System/System.Net/HttpWebRequest.cs:1005 
  at System.Threading.Tasks.TaskFactory`1[TResult].FromAsyncCoreLogic (IAsyncResult iar, System.Func`2 endFunction, System.Action`1 endAction, System.Threading.Tasks.Task`1 promise, Boolean requiresSynchronization) [0x00014] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/threading/Tasks/FutureFactory.cs:550 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128 
  at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:535 
  at System.Net.Http.HttpClientHandler+<SendAsync>c__async0.MoveNext () [0x003d6] in /Users/builder/data/lanes/3540/1cf254db/source/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClientHandler.cs:372 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128 
  at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:535 
  at System.Net.Http.HttpClient+<SendAsyncWorker>c__async0.MoveNext () [0x000a9] in /Users/builder/data/lanes/3540/1cf254db/source/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:276 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3540/1cf254db/source/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:357 
  at HuraApp.API.Connection`1+<postConnection>d__1[T].MoveNext () [0x0011c] in C:\Users\Nullsky\documents\visual studio 2015\Projects\HuraApp\HuraApp\HuraApp\API\Connection.cs:43 }

Answer 1

对于您在发出头部请求时链接的相同问题，请参阅下面的链接，其中在 xamarin 论坛中给出了其中一个解决方案，他们在向 Google url 发出 POST 请求 (200) 时遇到了同样的问题。

在这种情况下，解决方案是将 URL 更改为实际页面，而不是重定向。

这是链接Solution for the issue

希望对你有帮助。

Answer 2

根据 HttpWebRequest 的 Mono 源代码，看起来服务器正在发出重定向，而 HttpWebRequest（由 HttpClient 在幕后使用）没有处理该问题。

我不确定正在使用哪个版本的 Mono 源，但这看起来很可能是候选者： https://github.com/mono/mono/blob/cc3f4c60379c3839dd4259e171bb4539d21f2157/mcs/class/System/System.Net/HttpWebRequest.cs

该版本在 HttpWebRequest.EndGetResponse 的第 1005 行有一个“抛出”，它与您看到的异常堆栈相匹配。异常中的字符串“请求需要缓冲数据才能成功”来自 HttpWebRequest.Redirect。

下一步是使用 Fiddler（或类似工具）复制 Xamarin 客户端尝试查看它从服务器获得的响应的确切 POST 消息。

Answer 3

很遗憾

var response = await client.PostAsync(url, content);

在完成之前下载整个响应，因此它不使用任何缓冲。唯一的选择是使用，

var request = new HttpRequestMessage(url);
request.Content = content;
var response = await client.SendAsync(request, 
      HttpCompletionOption.ResponseHeadersRead);

HttpCompletionOption.ResponseHeadersRead 选项使HttpClient 在下载标头后从SendAsync 返回。您可以等待阅读内容。

Answer 4

这是否发生在 iOS 和/或 Android 上？

我会尝试将 HttpClient 处理程序更改为本机处理程序。这解决了很多问题，涉及很多主题（TLS 是一个很大的问题）。对于 iOS，使用 NSUrlSession 处理程序，对于 Android，尝试使用 AndroidClientHandler。您应该能够将 HttpClient 用于 Xamarin 的所有内容。