这里有另一个我的评论的工作示例:

        List<MimePart> mimeParts = new List<MimePart>();

        try
        {
            foreach (string key in form.AllKeys)
            {
                StringMimePart part = new StringMimePart();

                part.Headers["Content-Disposition"] = "form-data; name=\"" + key + "\"";
                part.StringData = form[key];

                mimeParts.Add(part);
            }

            int nameIndex = 0;

            foreach (UploadFile file in files)
            {
                StreamMimePart part = new StreamMimePart();

                if (string.IsNullOrEmpty(file.FieldName))
                    file.FieldName = "file" + nameIndex++;

                part.Headers["Content-Disposition"] = "form-data; name=\"" + file.FieldName + "\"; filename=\"" + file.FileName + "\"";
                part.Headers["Content-Type"] = file.ContentType;

                part.SetStream(file.Data);

                mimeParts.Add(part);
            }

            string boundary = "----------" + DateTime.Now.Ticks.ToString("x");

            req.ContentType = "multipart/form-data; boundary=" + boundary;
            req.Method = "POST";

            long contentLength = 0;

            byte[] _footer = Encoding.UTF8.GetBytes("--" + boundary + "--\r\n");

            foreach (MimePart part in mimeParts)
            {
                contentLength += part.GenerateHeaderFooterData(boundary);
            }

            req.ContentLength = contentLength + _footer.Length;

            byte[] buffer = new byte[8192];
            byte[] afterFile = Encoding.UTF8.GetBytes("\r\n");
            int read;

            using (Stream s = req.GetRequestStream())
            {
                foreach (MimePart part in mimeParts)
                {
                    s.Write(part.Header, 0, part.Header.Length);

                    while ((read = part.Data.Read(buffer, 0, buffer.Length)) > 0)
                        s.Write(buffer, 0, read);

                    part.Data.Dispose();

                    s.Write(afterFile, 0, afterFile.Length);
                }

                s.Write(_footer, 0, _footer.Length);
            }

            return (HttpWebResponse)req.GetResponse();
        }
        catch
        {
            foreach (MimePart part in mimeParts)
                if (part.Data != null)
                    part.Data.Dispose();

            throw;
        }

这里有一个使用的例子:

            UploadFile[] files = new UploadFile[] 
            { 
                new UploadFile(@"C:\2.jpg","new_file","image/jpeg") //new_file is id of upload field
            };

            NameValueCollection form = new NameValueCollection();

            form["id_hidden_input"] = "value_hidden_inpu"; //there is additional param (hidden fields on page)


            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(full URL of action);

            // set credentials/cookies etc. 
            req.CookieContainer = hrm.CookieContainer; //hrm is my class. i copied all cookies from last request to current (for auth)
            HttpWebResponse resp = HttpUploadHelper.Upload(req, files, form);

            using (Stream s = resp.GetResponseStream())
            using (StreamReader sr = new StreamReader(s))
            {
                string response = sr.ReadToEnd();
            }
             //profit!

对于我来说，下面的作品(主要是受到以下所有回答的启发)，我从Elad的回答开始，修改/简化事情以符合我的需要(删除不是文件形式输入，只有一个文件，……)

希望它能帮助到一些人:)

(PS:我知道异常处理没有实现，并且假设它是在一个类中编写的，所以我可能需要一些集成工作…)

private void uploadFile()
    {
        Random rand = new Random();
        string boundary = "----boundary" + rand.Next().ToString();
        Stream data_stream;
        byte[] header = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\nContent-Disposition: form-data; name=\"file_path\"; filename=\"" + System.IO.Path.GetFileName(this.file) + "\"\r\nContent-Type: application/octet-stream\r\n\r\n");
        byte[] trailer = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");

        // Do the request
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(MBF_URL);
        request.UserAgent = "My Toolbox";
        request.Method = "POST";
        request.KeepAlive = true;
        request.ContentType = "multipart/form-data; boundary=" + boundary;
        data_stream = request.GetRequestStream();
        data_stream.Write(header, 0, header.Length);
        byte[] file_bytes = System.IO.File.ReadAllBytes(this.file);
        data_stream.Write(file_bytes, 0, file_bytes.Length);
        data_stream.Write(trailer, 0, trailer.Length);
        data_stream.Close();

        // Read the response
        WebResponse response = request.GetResponse();
        data_stream = response.GetResponseStream();
        StreamReader reader = new StreamReader(data_stream);
        this.url = reader.ReadToEnd();

        if (this.url == "") { this.url = "No response :("; }

        reader.Close();
        data_stream.Close();
        response.Close();
    }

我最近不得不处理这个问题——另一种方法是使用WebClient是可继承的这一事实，并从那里改变底层的WebRequest:

http://msdn.microsoft.com/en-us/library/system.net.webclient.getwebrequest (VS.80) . aspx

我更喜欢c#，但如果你坚持使用VB，结果将是这样的:

Public Class BigWebClient
    Inherits WebClient
    Protected Overrides Function GetWebRequest(ByVal address As System.Uri) As System.Net.WebRequest
        Dim x As WebRequest = MyBase.GetWebRequest(address)
        x.Timeout = 60 * 60 * 1000
        Return x
    End Function
End Class

'Use BigWebClient here instead of WebClient

我的ASP。NET上传常见问题解答中有一篇关于这方面的文章，有示例代码:使用HttpWebRequest/WebClient的RFC 1867 POST请求上传文件。此代码不将文件加载到内存中(与上面的代码相反)，支持多个文件，并支持表单值、设置凭据和cookie等。

编辑:看起来好像是Axosoft把这个页面删除了。谢谢你的家伙。

它仍然可以通过archive.org访问。

采用上面的代码并修复，因为它抛出内部服务器错误500。\r\n的位置和空格等存在一些问题。应用内存流重构，直接写入请求流。结果如下:

    public static void HttpUploadFile(string url, string file, string paramName, string contentType, NameValueCollection nvc) {
        log.Debug(string.Format("Uploading {0} to {1}", file, url));
        string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
        byte[] boundarybytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

        HttpWebRequest wr = (HttpWebRequest)WebRequest.Create(url);
        wr.ContentType = "multipart/form-data; boundary=" + boundary;
        wr.Method = "POST";
        wr.KeepAlive = true;
        wr.Credentials = System.Net.CredentialCache.DefaultCredentials;

        Stream rs = wr.GetRequestStream();

        string formdataTemplate = "Content-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}";
        foreach (string key in nvc.Keys)
        {
            rs.Write(boundarybytes, 0, boundarybytes.Length);
            string formitem = string.Format(formdataTemplate, key, nvc[key]);
            byte[] formitembytes = System.Text.Encoding.UTF8.GetBytes(formitem);
            rs.Write(formitembytes, 0, formitembytes.Length);
        }
        rs.Write(boundarybytes, 0, boundarybytes.Length);

        string headerTemplate = "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: {2}\r\n\r\n";
        string header = string.Format(headerTemplate, paramName, file, contentType);
        byte[] headerbytes = System.Text.Encoding.UTF8.GetBytes(header);
        rs.Write(headerbytes, 0, headerbytes.Length);

        FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Read);
        byte[] buffer = new byte[4096];
        int bytesRead = 0;
        while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0) {
            rs.Write(buffer, 0, bytesRead);
        }
        fileStream.Close();

        byte[] trailer = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
        rs.Write(trailer, 0, trailer.Length);
        rs.Close();

        WebResponse wresp = null;
        try {
            wresp = wr.GetResponse();
            Stream stream2 = wresp.GetResponseStream();
            StreamReader reader2 = new StreamReader(stream2);
            log.Debug(string.Format("File uploaded, server response is: {0}", reader2.ReadToEnd()));
        } catch(Exception ex) {
            log.Error("Error uploading file", ex);
            if(wresp != null) {
                wresp.Close();
                wresp = null;
            }
        } finally {
            wr = null;
        }
    }

以及示例用法:

    NameValueCollection nvc = new NameValueCollection();
    nvc.Add("id", "TTR");
    nvc.Add("btn-submit-photo", "Upload");
    HttpUploadFile("http://your.server.com/upload", 
         @"C:\test\test.jpg", "file", "image/jpeg", nvc);

可以扩展它来处理多个文件，或者对每个文件多次调用它。但它适合你的需要。

基于上面提供的代码，我添加了对多个文件的支持，也可以直接上传流，而不需要有本地文件。

要将文件上传到包含一些post参数的特定url，请执行以下操作:

RequestHelper.PostMultipart(
    "http://www.myserver.com/upload.php", 
    new Dictionary<string, object>() {
        { "testparam", "my value" },
        { "file", new FormFile() { Name = "image.jpg", ContentType = "image/jpeg", FilePath = "c:\\temp\\myniceimage.jpg" } },
        { "other_file", new FormFile() { Name = "image2.jpg", ContentType = "image/jpeg", Stream = imageDataStream } },
    });

为了进一步增强这一点，可以从给定的文件本身确定名称和mime类型。

public class FormFile 
{
    public string Name { get; set; }

    public string ContentType { get; set; }

    public string FilePath { get; set; }

    public Stream Stream { get; set; }
}

public class RequestHelper
{

    public static string PostMultipart(string url, Dictionary<string, object> parameters) {

        string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
        byte[] boundaryBytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.ContentType = "multipart/form-data; boundary=" + boundary;
        request.Method = "POST";
        request.KeepAlive = true;
        request.Credentials = System.Net.CredentialCache.DefaultCredentials;

        if(parameters != null && parameters.Count > 0) {

            using(Stream requestStream = request.GetRequestStream()) {

                foreach(KeyValuePair<string, object> pair in parameters) {

                    requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);
                    if(pair.Value is FormFile) {
                        FormFile file = pair.Value as FormFile;
                        string header = "Content-Disposition: form-data; name=\"" + pair.Key + "\"; filename=\"" + file.Name + "\"\r\nContent-Type: " + file.ContentType + "\r\n\r\n";
                        byte[] bytes = System.Text.Encoding.UTF8.GetBytes(header);
                        requestStream.Write(bytes, 0, bytes.Length);
                        byte[] buffer = new byte[32768];
                        int bytesRead;
                        if(file.Stream == null) {
                            // upload from file
                            using(FileStream fileStream = File.OpenRead(file.FilePath)) {
                                while((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                                    requestStream.Write(buffer, 0, bytesRead);
                                fileStream.Close();
                            }
                        }
                        else {
                            // upload from given stream
                            while((bytesRead = file.Stream.Read(buffer, 0, buffer.Length)) != 0)
                                requestStream.Write(buffer, 0, bytesRead);
                        }
                    }
                    else {
                        string data = "Content-Disposition: form-data; name=\"" + pair.Key + "\"\r\n\r\n" + pair.Value;
                        byte[] bytes = System.Text.Encoding.UTF8.GetBytes(data);
                        requestStream.Write(bytes, 0, bytes.Length);
                    }
                }

                byte[] trailer = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
                requestStream.Write(trailer, 0, trailer.Length);
                requestStream.Close();
            }
        }

        using(WebResponse response = request.GetResponse()) {
            using(Stream responseStream = response.GetResponseStream())
            using(StreamReader reader = new StreamReader(responseStream))
                return reader.ReadToEnd();
        }


    }
}