HttpClient SendAsync 无法访问已释放的对象 ResponseHeadersRead

Question

我正在研究一些将 Http 请求中继到另一个 URL 的遗留代码的问题。它是一个 API 控制器，它读取请求并将其异步转发到另一个地址。

极少情况下，它会引发“无法访问已处置的对象”异常 - 本问题后面会显示完整的堆栈跟踪。它似乎在 HttpClient 调用 SendAsync 方法的地方。我认为这可能是 ResponseHeadersRead 选项 - 我怀疑它正在发送一个大数据包并且它被关闭，因为它刚刚读取了标题并退出。只是想我会和你们一起理智地检查一下，为了你们的想法。我会将选项更改为 ResponseContentsRead 选项，看看效果如何（但错误可能需要很长时间才能浮出水面）。

代码如下：

        using (var client = new HttpClient())
        {
            var request = BuildRelayHttpRequest(Request);
            await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
        }


        private static HttpRequestMessage BuildRelayHttpRequest(HttpRequestMessage incomingRequest)
        {
            var forwardToUrl = new Uri(ConfigurationManager.AppSettings["ForwardFeedURL"]);
            var relayRequest = new HttpRequestMessage(incomingRequest.Method, forwardToUrl);
            if (incomingRequest.Method != HttpMethod.Get && incomingRequest.Content != null)
            {
                relayRequest.Content = incomingRequest.Content;
            }

            //Copies contents
            relayRequest.Content = incomingRequest.Content;
            return relayRequest;
        }

这里是个例外：

System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'System.Web.Http.WebHost.HttpControllerHandler+LazyStreamContent'.
   at System.Net.Http.HttpContent.CheckDisposed()
   at System.Net.Http.HttpContent.CopyToAsync(Stream stream, TransportContext context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at CHO.Web.Services.ETrains.Controllers.ETrainsApiController.<CopyandForwardFeedAsyn>d__18.MoveNext() in \Controllers\MyAPIController.cs:line 289

注意，第 289 行是“await client.SendAsync”代码行

Answer 1

很可能是服务器设置了错误代码。

使用封装在 Try Catch 块中的 response.EnsureSuccessStatusCode(); 跟踪您的代码：

try
{
    var request = BuildRelayHttpRequest(Request);
    await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
    response.EnsureSuccessStatusCode();
    // Handle success
}
catch (HttpRequestException)
{
    // Handle failure
}