C#記一次http協議multipart/form-data的boundary問題

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1.問題描述

使用post方法調用上級聯網廠傢接口，返回http狀態碼415，返回信息Content type ‘application/x-www-form-urlencoded’ not supported

測試上級聯網廠傢接口使用的是Postman工具，工具下載地址：https://www.getpostman.com/downloads/

使用application/x-www-form-urlencoded調用接口，返回http狀態碼415，如圖：

既然服務器無法處理請求附帶的媒體格式，那麼改用multipart/form-data試試？

測試後發現可以調用成功，如圖：

我們都知道ContentType為application/x-www-form-urlencoded的請求頭、體如何構造，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的請求頭與請求體該如何構造呢？像下面這樣？

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();
}

顯然不對，捕獲到瞭"遠程服務器返回錯誤:(500)內部服務器錯誤。"異常，那麼我們該怎麼辦呢？

2.解決思路

既然Postman工具使用ContentType為multipart/form-data類型post數據可以成功，那麼我們寫的C#程序應該也可以呀！那怎麼辦呢？。。。。沒錯！！就是抓包！

首先想到的是，用fiddler抓Postman的數據包，然後C#程序構造同樣的數據包即可。

觀察數據包Headers選項卡，如圖：

發現Content-Type: multipart/form-data;後面跟瞭一個boundary=—————————-183584948778966847113836

並且TextView選項卡如下：

WebForms選項卡如下：

所以，可以按照Headers和TextView選項卡內容構造post請求，就可以解決我們的問題瞭！

3.解決步驟

將ContentType加上boundary=boundary————————-xxxxxxxxxxxxxx

並且構造參數，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();
}

值得註意的是，“boundary————————-xxxxxxxxxxxxxx”

這麼長一串東西，隻是作為分隔符出現的，不必太在意它是什麼東西，我將它理解為分割文本參數的這麼一個東西，並且通過仔細觀察發現可以發現header中contenttype的橫線數量比參數中橫線數量少兩個且必須少兩個？

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。 

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