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; }四.其它解决该异常的方法
这种异常问题触发原因估计有很多，这里收集一些其它的解决方法
1.添加：request.KeepAlive = false
2.注释掉：request.ContentLength = data.Length;