C# HTTP POST（System.Net.WebException：请求已中止：请求已被取消）

一.问题描述

最近在使用c# http post请求时，遇见了这种异常，大概异常提示如下

System.Net.WebException：请求已中止：请求已被取消，在数据写入前关闭了数据流

错误代码如下：

        /// <summary>/// 向指定URL发送POST请求/// </summary>/// <param name="url">发送请求的URL</param>/// <param name="jsonData">请求参数，请求参数应该是Json格式字符串的形式</param>/// <param name="contenType"><设置响应信息的编码格式，如utf-8/param>/// <param name="header">请求头</param>/// <returns>所代表远程资源的响应结果</returns>public static string SendPost(string url,string jsonData,Encoding encoding,string contenType="application/json",Dictionary<string,string>header=null){string result =string.Empty;try{CookieContainer cookie = new CookieContainer();HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url);request.Method = "POST";if(null != header && 0 < header.Count()){foreach(var item in header.Keys){request.Headers.Add(item, header[item]);}}request.ServicePoint.Expect100Continue = false;request.ContentType = contenType;request.ContentLength = Encoding.UTF8.GetByteCount(jsonData);request.CookieContainer = cookie;using (StreamWriter writer = new StreamWriter(request.GetRequestStream(), encoding)){writer.Write(jsonData);}HttpWebResponse response = (HttpWebResponse)request.GetResponse();response.Cookies = cookie.GetCookies(response.ResponseUri);using (Stream responseStream=response.GetResponseStream()){using(StreamReader reader= new StreamReader(responseStream,encoding)){result = reader.ReadToEnd();reader.Close();}responseStream.Close();}response.Close();response = null;request = null;}catch (Exception ex){string msg = ex.Message;}return result;}

通过代码调试，出问题的大致位置在这里：

 using (StreamWriter writer = new StreamWriter(request.GetRequestStream(), encoding)){writer.Write(jsonData);}

二.问题分析

在Write时，数据流意外关闭了，触发了http数据传输异常，为什么会出现这种情况，使用其它接口时不会出现这种问题，通过分析代码以及查阅资料发现了出问题的原因，我在调用接口函数时是这样的：

SendPost(url, jsonData, Encoding.Default, contenType, header);

这里我指定了编码格式为Encoding.Default，在函数内部计算request.ContentLength 长度的时候却指定了UTF8编码，如下：

request.ContentLength = Encoding.UTF8.GetByteCount(jsonData);

这种情况如果当前默认刚好是UTF8编码，则不会出问题，如果是其它编码，则数据流读取时会出问题（编码解析规则），导致意外结束，分析问题大概是这样

三.问题修改

修改后的代码如下，使用前后一致的编码格式

        /// <summary>/// 向指定URL发送POST请求/// </summary>/// <param name="url">发送请求的URL</param>/// <param name="jsonData">请求参数，请求参数应该是Json格式字符串的形式</param>/// <param name="contenType"><设置响应信息的编码格式，如utf-8/param>/// <param name="header">请求头</param>/// <returns>所代表远程资源的响应结果</returns>public static string SendPost(string url,string jsonData,Encoding encoding,string contenType="application/json",Dictionary<string,string>header=null){string result =string.Empty;try{CookieContainer cookie = new CookieContainer();HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url);request.Method = "POST";if(null != header && 0 < header.Count()){foreach(var item in header.Keys){request.Headers.Add(item, header[item]);}}request.ServicePoint.Expect100Continue = false;request.ContentType = contenType;request.ContentLength = encoding.GetByteCount(jsonData);request.CookieContainer = cookie;using (StreamWriter writer = new StreamWriter(request.GetRequestStream(), encoding)){writer.Write(jsonData);}HttpWebResponse response = (HttpWebResponse)request.GetResponse();response.Cookies = cookie.GetCookies(response.ResponseUri);using (Stream responseStream=response.GetResponseStream()){using(StreamReader reader= new StreamReader(responseStream,encoding)){result = reader.ReadToEnd();reader.Close();}responseStream.Close();}response.Close();response = null;request = null;}catch (Exception ex){string msg = ex.Message;}return result;}