C#记一次http协议multipart/form-data的boundary

1.问题描述

使用post方法调用上级联网厂家接口，返回http状态码415，返回信息Content type ‘application/x-www-form-urlencoded’ not supported

测试上级联网厂家接口使用的是Postman工具，工具下载地址：https://www.getpostman.com/downloads/
使用application/x-www-form-urlencoded调用接口，返回http状态码415，如图：

既然服务器无法处理请求附带的媒体格式，那么改用multipart/form-data试试？
测试后发现可以调用成功，如图：

我们都知道ContentType为application/x-www-form-urlencoded的请求头、体如何构造，如：

HttpWebRequest request = WebRequest.Create(new Uri(url)) as HttpWebRequest;
request.Method = "POST";
request.Host = Properties.Settings.Default.IP;
request.ContentType = "application/x-www-form-urlencoded; charset=UTF-8";
request.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko";
request.Accept = "*/*";
request.CookieContainer = cc;
request.KeepAlive = true;
string postData = string.Format("action=cx&hphm={0}&hpzl=&jclb=&detlsh=&clpp=&clxh=&rlzl=&pfbz=&jcff=&evl=&staName={1}&detLineId=&syxz=&rqyi={2}&rqer={3}&RQXZ=JCRQ&CXJL=Jiance&cllb=&clgs=&zcrq=&zzl=&clsbdh=&syr=&ccdjrq=&page={4}&rows=10", hphm, staName, rqyi, rqer, page);
byte[] postdatabyte = Encoding.GetEncoding("utf-8").GetBytes(postData);
request.ContentLength = postdatabyte.Length;
using (Stream stream = request.GetRequestStream())
{
	stream.Write(postdatabyte, 0, postdatabyte.Length);
}
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("utf-8")))
{
	string temp = reader.ReadToEnd();
}

但是！multipart/form-data的请求头与请求体该如何构造呢？像下面这样？

string url = "http://112.17.158.12:8180/intf/services/query";
HttpWebRequest request = WebRequest.Create(new Uri(url)) as HttpWebRequest;
request.Method = "POST";
request.Host = "112.17.158.12:8180";
request.ContentType = "multipart/form-data; ";
request.UserAgent = "PostmanRuntime/7.17.1";
request.Accept = "*/*";
request.KeepAlive = true;
string postData = @"jkuser=33088102&jkpasswd=33088102&jsondata={""jkid"":""R10"",""requestTime"":""20190919110603"",""body"":[{""inspstationcode"":""33088102""}]}";
byte[] postdatabyte = Encoding.GetEncoding("utf-8").GetBytes(postData);
request.ContentLength = postdatabyte.Length;
using (Stream stream = request.GetRequestStream())
{
	stream.Write(postdatabyte, 0, postdatabyte.Length);
}
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("utf-8")))
{
	string temp = reader.ReadToEnd();
}

显然不对，捕获到了"远程服务器返回错误:(500)内部服务器错误。"异常，那么我们该怎么办呢？

2.解决思路

既然Postman工具使用ContentType为multipart/form-data类型post数据可以成功，那么我们写的C#程序应该也可以呀！那怎么办呢？。。。。没错！！就是抓包！

首先想到的是，用fiddler抓Postman的数据包，然后C#程序构造同样的数据包即可。
观察数据包Headers选项卡，如图：

发现Content-Type: multipart/form-data;后面跟了一个boundary=----------------------------183584948778966847113836，并且TextView选项卡如下：

WebForms选项卡如下：
所以，可以按照Headers和TextView选项卡内容构造post请求，就可以解决我们的问题了！

3.解决步骤

将ContentType加上boundary=boundary-------------------------xxxxxxxxxxxxxx，并且构造参数，如下：

string url = "http://112.17.158.12:8180/intf/services/query";
string boundary = "--------------------------" + DateTime.Now.Ticks.ToString("x");
string boundary2 = "--" + boundary;

HttpWebRequest request = WebRequest.Create(new Uri(url)) as HttpWebRequest;
request.Method = "POST";
request.Host = "112.17.158.12:8180";
request.ContentType = "multipart/form-data; boundary=" + boundary;
request.UserAgent = "PostmanRuntime/7.17.1";
request.Accept = "*/*";
request.KeepAlive = true;
StringBuilder sb = new StringBuilder();
sb.Append(boundary2 + "\r\n");
sb.Append(@"Content-Disposition: form-data; name=""jkuser""" + "\r\n\r\n");
sb.Append("33088102" + "\r\n");
sb.Append(boundary2 + "\r\n");
sb.Append(@"Content-Disposition: form-data; name=""jkpasswd""" + "\r\n\r\n");
sb.Append("33088102" + "\r\n");
sb.Append(boundary2 + "\r\n");
sb.Append(@"Content-Disposition: form-data; name=""jsondata""" + "\r\n\r\n");
sb.Append(@"{""jkid"":""R10"",""requestTime"":""20190919110603"",""body"":[{""inspstationcode"":""33088102""}]}" + "\r\n");
sb.Append(boundary2 + "--" + "\r\n");

string postData = sb.ToString();
byte[] postdatabyte = Encoding.GetEncoding("utf-8").GetBytes(postData);
request.ContentLength = postdatabyte.Length;
using (Stream stream = request.GetRequestStream())
{
    stream.Write(postdatabyte, 0, postdatabyte.Length);
}
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("utf-8")))
{
    string temp = reader.ReadToEnd();
}

值得注意的是，“boundary-------------------------xxxxxxxxxxxxxx”这么长一串东西，只是作为分隔符出现的，不必太在意它是什么东西，我将它理解为分割文本参数的这么一个东西，并且通过仔细观察发现可以发现header中contenttype的横线数量比参数中横线数量少两个且必须少两个？