C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法

针对你提出的问题，我会按照以下步骤进行回答：

1. 标题：C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法

2. 内容：

1）HttpWebRequest概述

在C#中，我们可以通过HttpWebRequest对象来进行HTTP请求。HttpWebRequest是Web请求的一种方法，它提供了对HTTP协议和其他互联网协议的灵活、可扩展的支持。这个对象使得我们能够进行HTTP/HTTPS请求，并支持向远程源发送数据。使用它，我们可以发送GET、POST、PUT、DELETE等类型的请求。

2）保持会话上传文件

在HTTP请求中，我们常常需要保持会话，这样可以避免每次请求都需要重新验证。当我们需要上传文件时，我们需要保持会话，并将文件上传到服务器。下面我们来看一下如何通过C#的HttpWebRequest来实现保持会话上传文件的步骤：

① 首先我们需要创建一个HttpWebRequest对象，并设置请求的属性，如下：

    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
    CookieContainer cookieContainer = new CookieContainer();
    request.CookieContainer = cookieContainer;
    request.Method = "POST";
    request.Timeout = 120000;
    request.ContentType = "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW";

② 然后，我们需要通过该对象的GetResponse方法来获取响应流，并获取其中的Cookie：

    request.GetResponse();
    CookieCollection cookies = request.CookieContainer.GetCookies(new Uri(url));

这样，我们就可以获取到保持会话所需要的Cookie。

③ 我们还需要读取要上传的文件并将其写入HttpWebRequest的请求流中：

    using (var stream = request.GetRequestStream())
    {
        using (var fileStream = new FileStream(file, FileMode.Open))
        {
            var buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                stream.Write(buffer, 0, bytesRead);
            }
        }
    }

④ 最后，我们需要发起HTTP请求，并获取返回的响应结果：

    using (var response = (HttpWebResponse)request.GetResponse())
    {
        using (var reader = new StreamReader(response.GetResponseStream()))
        {
            responseText = reader.ReadToEnd();
        }
    }

至此，我们就完成了一个保持会话上传文件的操作。

3）代码示例

下面，我提供两个示例，一个是通过表单来上传文件，一个是直接上传文件。这两个示例都可以通过C#的HttpWebRequest来实现：

① 通过表单上传文件：

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    CookieContainer cookieContainer = new CookieContainer();
    request.CookieContainer = cookieContainer;
    request.Method = "POST";
    request.Timeout = 120000;
    request.ContentType = "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW";

    string boundary = "------WebKitFormBoundary7MA4YWxkTrZu0gW";
    string formdataTemplate = "--{0}\r\nContent-Disposition: form-data; name=\"{1}\"\r\n\r\n{2}\r\n";
    string formItem = string.Format(formdataTemplate, boundary, "testField", "value");
    byte[] formBytes = Encoding.UTF8.GetBytes(formItem);
    request.ContentLength = formBytes.Length;

    using (Stream requestStream = request.GetRequestStream())
    {
        requestStream.Write(formBytes, 0, formBytes.Length);
        MemoryStream fileStream = new MemoryStream(File.ReadAllBytes(filePath));//read file data into byte array
        byte[] buffer = new byte[fileStream.Length];//new byte array
        fileStream.Read(buffer, 0, buffer.Length);//read to end
        string fileHeader = string.Format(formdataTemplate, boundary, "file", "test.txt");
        byte[] headerBytes = Encoding.UTF8.GetBytes(fileHeader);
        requestStream.Write(headerBytes, 0, headerBytes.Length);
        requestStream.Write(buffer, 0, buffer.Length);//write the data
        byte[] footBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");//upload file end
        requestStream.Write(footBytes, 0, footBytes.Length);
        fileStream.Close();
    }

    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    Stream myResponseStream = response.GetResponseStream();
    StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
    string result = myStreamReader.ReadToEnd();
    myStreamReader.Close();
    myResponseStream.Close();
    response.Close();

② 直接上传文件：

    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
    CookieContainer cookieContainer = new CookieContainer();
    request.CookieContainer = cookieContainer;
    request.Method = "POST";
    request.Timeout = 120000;
    request.ContentType = "application/octet-stream";
    request.ContentLength = new FileInfo(filePath).Length;

    using (Stream requestStream = request.GetRequestStream())
    {
        using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
        {
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                requestStream.Write(buffer, 0, bytesRead);
            }
        }
    }

    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
    {
        using (StreamReader reader = new StreamReader(response.GetResponseStream()))
        {
            string responseText = reader.ReadToEnd();
        }
    }

1. 结束语

希望以上内容能够帮助你，如果你还有其他问题需要解决，请随时提出。