bash74 bash74 - 1 year ago 186
HTTP Question

Multipart forms from C# client

I am trying to fill a form in a php application from a C# client (Outlook addin). I used Fiddler to see the original request from within the php application and the form is transmitted as a multipart/form. Unfortunately .Net does not come with native support for this type of forms (WebClient has only a method for uploading a file).
Does anybody know a library or has some code to achieve this? I want to post different values and additionally (but only sometimes) a file.

Thanks for your help,

Answer Source

This is cut and pasted from some sample code I wrote, hopefully it should give the basics. It only supports File data and form-data at the moment.

public class PostData

    private List<PostDataParam> m_Params;

    public List<PostDataParam> Params
        get { return m_Params; }
        set { m_Params = value; }

    public PostData()
        m_Params = new List<PostDataParam>();

        // Add sample param
        m_Params.Add(new PostDataParam("email", "MyEmail", PostDataParamType.Field));

    /// <summary>
    /// Returns the parameters array formatted for multi-part/form data
    /// </summary>
    /// <returns></returns>
    public string GetPostData()
        // Get boundary, default is --AaB03x
        string boundary = ConfigurationManager.AppSettings["ContentBoundary"].ToString();

        StringBuilder sb = new StringBuilder();
        foreach (PostDataParam p in m_Params)

            if (p.Type == PostDataParamType.File)
                sb.AppendLine(string.Format("Content-Disposition: file; name=\"{0}\"; filename=\"{1}\"", p.Name, p.FileName));
                sb.AppendLine("Content-Type: text/plain");
                sb.AppendLine(string.Format("Content-Disposition: form-data; name=\"{0}\"", p.Name));


        return sb.ToString();           

public enum PostDataParamType

public class PostDataParam

    public PostDataParam(string name, string value, PostDataParamType type)
        Name = name;
        Value = value;
        Type = type;

    public string Name;
    public string FileName;
    public string Value;
    public PostDataParamType Type;

To send the data you then need to:

HttpWebRequest oRequest = null;
oRequest = (HttpWebRequest)HttpWebRequest.Create(oURL.URL);
oRequest.ContentType = "multipart/form-data";                       
oRequest.Method = "POST";
PostData pData = new PostData();

byte[] buffer = encoding.GetBytes(pData.GetPostData());

// Set content length of our data
oRequest.ContentLength = buffer.Length;

// Dump our buffered postdata to the stream, booyah
oStream = oRequest.GetRequestStream();
oStream.Write(buffer, 0, buffer.Length);

// get the response
oResponse = (HttpWebResponse)oRequest.GetResponse();

Hope thats clear, i've cut and pasted from a few sources to get that tidier.

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