c# - 来自 webclient C# 的空答案

Question

我正在尝试从压缩器接收数据，但它的答案始终为空。这是我的代码:

WebClient client = new WebClient();
client.Headers[HttpRequestHeader.ContentType]= "application/x-www-form-urlencoded";
string question = "online_pressure"; 
string URL = "http://10.0.163.51/getVar.cgi"; 
string answer = client.UploadString(URL, "POST", question);
Console.WriteLine(answer);

当我将此代码用于另一个只有 2 个字符串不同的压缩器时，效果很好，我可以在控制台中看到答案:

string question = "QUESTION=300201"; 
string URL = "http://10.0.163.50/cgi-bin/mkv.cgi";

VBS 中的代码适用于两种压缩器。我可以在第一和第二个压缩器的 MsgBox 中看到答案:

Dim objHTTP
strToSend = "online_pressure"
Set objHTTP = CreateObject("Microsoft.XMLHTTP")
Call objHTTP.Open("POST", "http://10.0.163.51/getVar.cgi", false)
objHTTP.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
objHTTP.Send strToSend
MsgBox(objHTTP.ResponseText)

HttpRequest 代码也仅适用于第二个压缩器:

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    request.ContentLength = data.Length;
    StreamWriter requestWriter = new StreamWriter(request.GetRequestStream(), System.Text.Encoding.ASCII);
    requestWriter.Write(data);
    requestWriter.Close();

    try
    {
        // get the response
        WebResponse webResponse = request.GetResponse();
        Stream webStream = webResponse.GetResponseStream();
        StreamReader responseReader = new StreamReader(webStream);
        string response = responseReader.ReadToEnd();
        responseReader.Close();
        Console.WriteLine(response);
    }
    catch (WebException we)
    {
        string webExceptionMessage = we.Message;
    }

我还可以尝试从 C# 中的第一个压缩器获取数据吗？

Answer 1

我比较了 Fiddler 4 中的三个请求，并意识到 vbs 脚本和 WebClient 之间的唯一区别(除了一些不会影响行为的其他 header )
和 HttpWebRequest 是，托管 API 发送 Expect: 100-continue header 和 vbs 脚本没有。

如果压缩机设备上运行的软件不支持此功能，则可能会出现此问题。

请尝试以下操作，它告诉 HttpWebRequest 不发送此 header :

对于 HttpWebRequest，您可以简单地通过以下方式阻止发送:

 request.ServicePoint.Expect100Continue = false;

注意:对于 WebClient，分配需要访问内部使用的 HttpWebRequest 对象，但这具有“ protected ”访问修饰符，可以解决。

在设置此值之前:

POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: oguzozgul.com.tr
Content-Length: 15
Expect: 100-continue
Connection: Keep-Alive

online_pressure 

设置此值后:

POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: oguzozgul.com.tr
Content-Length: 15
Connection: Keep-Alive

online_pressure

我还想将 vb 脚本请求放在这里，以便您也可以看到其他差异。默认情况下也不发送 Accept-Encoding 和其他一些 header :

POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Accept: */*
Content-Type: application/x-www-form-urlencoded
Accept-Language: tr,en-US;q=0.8,en-GB;q=0.7,en;q=0.5,zh-Hans-CN;q=0.3,zh-Hans;q=0.2
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.3; Win64; x64; Trident/7.0; .NET4.0E; .NET4.0C; Tablet PC 2.0; .NET CLR 3.5.30729; .NET CLR 2.0.50727; .NET CLR 3.0.30729; wbx 1.0.0; Zoom 3.6.0; wbxapp 1.0.0)
Host: oguzozgul.com.tr
Content-Length: 15
Connection: Keep-Alive
Pragma: no-cache

online_pressure