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();
        }


    }
}

我想你在寻找更像WebClient的东西。

具体来说,还是()。

类似这样的代码很接近:(未测试的代码)

byte[] data; // data goes here.

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Credentials = userNetworkCredentials;
request.Method = "PUT";
request.ContentType = "application/octet-stream";
request.ContentLength = data.Length;
Stream stream = request.GetRequestStream();
stream.Write(data,0,data.Length);
stream.Close();
response = (HttpWebResponse)request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
temp = reader.ReadToEnd();
reader.Close();

查看MyToolkit库:

var request = new HttpPostRequest("http://www.server.com");
request.Data.Add("name", "value"); // POST data
request.Files.Add(new HttpPostFile("name", "file.jpg", "path/to/file.jpg")); 

await Http.PostAsync(request, OnRequestFinished);

http://mytoolkit.codeplex.com/wikipage?title=Http

采取以上和修改它接受一些头值，和多个文件

    NameValueCollection headers = new NameValueCollection();
        headers.Add("Cookie", "name=value;");
        headers.Add("Referer", "http://google.com");
    NameValueCollection nvc = new NameValueCollection();
        nvc.Add("name", "value");

    HttpUploadFile(url, new string[] { "c:\\file1.txt", "c:\\file2.jpg" }, new string[] { "file", "image" }, new string[] { "application/octet-stream", "image/jpeg" }, nvc, headers);

public static void HttpUploadFile(string url, string[] file, string[] paramName, string[] contentType, NameValueCollection nvc, NameValueCollection headerItems)
{
    //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);

    foreach (string key in headerItems.Keys)
    {
        if (key == "Referer")
        {
            wr.Referer = headerItems[key];
        }
        else
        {
            wr.Headers.Add(key, headerItems[key]);
        }
    }

    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 = "";

    for(int i =0; i<file.Count();i++)
    {
        header = string.Format(headerTemplate, paramName[i], System.IO.Path.GetFileName(file[i]), contentType[i]);
        byte[] headerbytes = System.Text.Encoding.UTF8.GetBytes(header);
        rs.Write(headerbytes, 0, headerbytes.Length);

        FileStream fileStream = new FileStream(file[i], 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();
        rs.Write(boundarybytes, 0, boundarybytes.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);
            wresp.Close();
            wresp = null;
    }
    finally
    {
        wr = null;
    }
}

我写了一个类使用WebClient方式做多部分的表单上传。

http://ferozedaud.blogspot.com/2010/03/multipart-form-upload-helper.html

/// 
/// MimePart
/// Abstract class for all MimeParts
/// 

abstract class MimePart
{
    public string Name { get; set; }

    public abstract string ContentDisposition { get; }

    public abstract string ContentType { get; }

    public abstract void CopyTo(Stream stream);

    public String Boundary
    {
        get;
        set;
    }
}

class NameValuePart : MimePart
{
    private NameValueCollection nameValues;

    public NameValuePart(NameValueCollection nameValues)
    {
        this.nameValues = nameValues;
    }

    public override void CopyTo(Stream stream)
    {
        string boundary = this.Boundary;
        StringBuilder sb = new StringBuilder();

        foreach (object element in this.nameValues.Keys)
        {
            sb.AppendFormat("--{0}", boundary);
            sb.Append("\r\n");
            sb.AppendFormat("Content-Disposition: form-data; name=\"{0}\";", element);
            sb.Append("\r\n");
            sb.Append("\r\n");
            sb.Append(this.nameValues[element.ToString()]);

            sb.Append("\r\n");

        }

        sb.AppendFormat("--{0}", boundary);
        sb.Append("\r\n");

        //Trace.WriteLine(sb.ToString());
        byte [] data = Encoding.ASCII.GetBytes(sb.ToString());
        stream.Write(data, 0, data.Length);
    }

    public override string ContentDisposition
    {
        get { return "form-data"; }
    }

    public override string ContentType
    {
        get { return String.Empty; }
    }
} 

class FilePart : MimePart

{

    private Stream input;

    private String contentType;



    public FilePart(Stream input, String name, String contentType)

    {

        this.input = input;

        this.contentType = contentType;

        this.Name = name;

    }



    public override void CopyTo(Stream stream)

    {

        StringBuilder sb = new StringBuilder();

        sb.AppendFormat("Content-Disposition: {0}", this.ContentDisposition);

        if (this.Name != null)

            sb.Append("; ").AppendFormat("name=\"{0}\"", this.Name);

        if (this.FileName != null)

            sb.Append("; ").AppendFormat("filename=\"{0}\"", this.FileName);

        sb.Append("\r\n");

        sb.AppendFormat(this.ContentType);

        sb.Append("\r\n");

        sb.Append("\r\n");



    // serialize the header data.

    byte[] buffer = Encoding.ASCII.GetBytes(sb.ToString());

    stream.Write(buffer, 0, buffer.Length);



    // send the stream.

    byte[] readBuffer = new byte[1024];

    int read = input.Read(readBuffer, 0, readBuffer.Length);

    while (read > 0)

    {

        stream.Write(readBuffer, 0, read);

        read = input.Read(readBuffer, 0, readBuffer.Length);

    }



    // write the terminating boundary

    sb.Length = 0;

    sb.Append("\r\n");

    sb.AppendFormat("--{0}", this.Boundary);

    sb.Append("\r\n");

    buffer = Encoding.ASCII.GetBytes(sb.ToString());

    stream.Write(buffer, 0, buffer.Length);



}

 public override string ContentDisposition
 {
      get { return "file"; }
 }



 public override string ContentType
 {
    get { 
       return String.Format("content-type: {0}", this.contentType); 
     }
 }

 public String FileName { get; set; }

}

    /// 
    /// Helper class that encapsulates all file uploads
    /// in a mime part.
    /// 

    class FilesCollection : MimePart
    {
        private List files;

        public FilesCollection()
        {
            this.files = new List();
            this.Boundary = MultipartHelper.GetBoundary();
        }

        public int Count
        {
            get { return this.files.Count; }
        }

        public override string ContentDisposition
        {
            get
            {
                return String.Format("form-data; name=\"{0}\"", this.Name);
            }
        }

        public override string ContentType
        {
            get { return String.Format("multipart/mixed; boundary={0}", this.Boundary); }
        }

        public override void CopyTo(Stream stream)
        {
            // serialize the headers
            StringBuilder sb = new StringBuilder(128);
            sb.Append("Content-Disposition: ").Append(this.ContentDisposition).Append("\r\n");
            sb.Append("Content-Type: ").Append(this.ContentType).Append("\r\n");
            sb.Append("\r\n");
            sb.AppendFormat("--{0}", this.Boundary).Append("\r\n");

            byte[] headerBytes = Encoding.ASCII.GetBytes(sb.ToString());
            stream.Write(headerBytes, 0, headerBytes.Length);
            foreach (FilePart part in files)
            {
                part.Boundary = this.Boundary;
                part.CopyTo(stream);
            }
        }

        public void Add(FilePart part)
        {
            this.files.Add(part);
        }
    }

/// 
/// Helper class to aid in uploading multipart
/// entities to HTTP web endpoints.
/// 

class MultipartHelper
{
    private static Random random = new Random(Environment.TickCount);

    private List formData = new List();
    private FilesCollection files = null;
    private MemoryStream bufferStream = new MemoryStream();
    private string boundary;

    public String Boundary { get { return boundary; } }

    public static String GetBoundary()
    {
        return Environment.TickCount.ToString("X");
    }

    public MultipartHelper()
    {
        this.boundary = MultipartHelper.GetBoundary();
    }

    public void Add(NameValuePart part)
    {
        this.formData.Add(part);
        part.Boundary = boundary;
    }

    public void Add(FilePart part)
    {
        if (files == null)
        {
            files = new FilesCollection();
        }
        this.files.Add(part);
    }

    public void Upload(WebClient client, string address, string method)
    {
        // set header
        client.Headers.Add(HttpRequestHeader.ContentType, "multipart/form-data; boundary=" + this.boundary);
        Trace.WriteLine("Content-Type: multipart/form-data; boundary=" + this.boundary + "\r\n");

        // first, serialize the form data
        foreach (NameValuePart part in this.formData)
        {
            part.CopyTo(bufferStream);
        }

        // serialize the files.
        this.files.CopyTo(bufferStream);

        if (this.files.Count > 0)
        {
            // add the terminating boundary.
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("--{0}", this.Boundary).Append("\r\n");
            byte [] buffer = Encoding.ASCII.GetBytes(sb.ToString());
            bufferStream.Write(buffer, 0, buffer.Length);
        }

        bufferStream.Seek(0, SeekOrigin.Begin);

        Trace.WriteLine(Encoding.ASCII.GetString(bufferStream.ToArray()));
        byte [] response = client.UploadData(address, method, bufferStream.ToArray());
        Trace.WriteLine("----- RESPONSE ------");
        Trace.WriteLine(Encoding.ASCII.GetString(response));
    }

    /// 
    /// Helper class that encapsulates all file uploads
    /// in a mime part.
    /// 

    class FilesCollection : MimePart
    {
        private List files;

        public FilesCollection()
        {
            this.files = new List();
            this.Boundary = MultipartHelper.GetBoundary();
        }

        public int Count
        {
            get { return this.files.Count; }
        }

        public override string ContentDisposition
        {
            get
            {
                return String.Format("form-data; name=\"{0}\"", this.Name);
            }
        }

        public override string ContentType
        {
            get { return String.Format("multipart/mixed; boundary={0}", this.Boundary); }
        }

        public override void CopyTo(Stream stream)
        {
            // serialize the headers
            StringBuilder sb = new StringBuilder(128);
            sb.Append("Content-Disposition: ").Append(this.ContentDisposition).Append("\r\n");
            sb.Append("Content-Type: ").Append(this.ContentType).Append("\r\n");
            sb.Append("\r\n");
            sb.AppendFormat("--{0}", this.Boundary).Append("\r\n");

            byte[] headerBytes = Encoding.ASCII.GetBytes(sb.ToString());
            stream.Write(headerBytes, 0, headerBytes.Length);
            foreach (FilePart part in files)
            {
                part.Boundary = this.Boundary;
                part.CopyTo(stream);
            }
        }

        public void Add(FilePart part)
        {
            this.files.Add(part);
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        Trace.Listeners.Add(new ConsoleTraceListener());
        try
        {
            using (StreamWriter sw = new StreamWriter("testfile.txt", false))
            {
                sw.Write("Hello there!");
            }

            using (Stream iniStream = File.OpenRead(@"c:\platform.ini"))
            using (Stream fileStream = File.OpenRead("testfile.txt"))
            using (WebClient client = new WebClient())
            {
                MultipartHelper helper = new MultipartHelper();

                NameValueCollection props = new NameValueCollection();
                props.Add("fname", "john");
                props.Add("id", "acme");
                helper.Add(new NameValuePart(props));

                FilePart filepart = new FilePart(fileStream, "pics1", "text/plain");
                filepart.FileName = "1.jpg";
                helper.Add(filepart);

                FilePart ini = new FilePart(iniStream, "pics2", "text/plain");
                ini.FileName = "inifile.ini";
                helper.Add(ini);

                helper.Upload(client, "http://localhost/form.aspx", "POST");
            }
        }
        catch (Exception e)
        {
            Trace.WriteLine(e);
        }
    }
}

这将适用于所有版本的. net框架。