HTTP POST 返回错误:417“期望失败". [英] HTTP POST Returns Error: 417 "Expectation Failed."

问题描述

当我尝试 POST 到一个 URL 时，它会导致以下异常:

When I try to POST to a URL it results in the following exception:

远程服务器返回错误:(417) 期望失败.

The remote server returned an error: (417) Expectation Failed.

这是一个示例代码:

var client = new WebClient();

var postData = new NameValueCollection();
postData.Add("postParamName", "postParamValue");

byte[] responseBytes = client.UploadValues("http://...", postData);
string response = Encoding.UTF8.GetString(responseBytes); // (417) Expectation Failed.

使用 HttpWebRequest/HttpWebResponse 对或 HttpClient 没有区别.

Using an HttpWebRequest/HttpWebResponse pair or an HttpClient doesn't make a difference.

是什么导致了这个异常?

What's causing this exception?

推荐答案

System.Net.HttpWebRequest 向每个请求添加标头 'HTTP header "Expect: 100-Continue"' 除非您通过设置 这个静态属性为假:

System.Net.HttpWebRequest adds the header 'HTTP header "Expect: 100-Continue"' to every request unless you explicitly ask it not to by setting this static property to false:

System.Net.ServicePointManager.Expect100Continue = false;

某些服务器阻塞在该标头上并发回您看到的 417 错误.

Some servers choke on that header and send back the 417 error you're seeing.

试一试.

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