Question

I am developing an application which needs to use a web service.

Web service is running on the remote server and it accepts POST request and returns a JSON data

Here is the sample to consume service using “curl”

curl -F "api_key=ABCDEFGHIJKL" -F "query=@json_string.json" "http://serv/api/v4/song/identify"

An HTTP POST request with Content-Type “multipart/form-data” where all parameters are in the post body and the query is in the “query” parameter of the post “files”

So how could I implement client to consume the service in .NET

Answer 1

You could use a WCF REST service and parse the multipart/form-data.

---

UPDATE:

Sorry, I misread your question. You were looking for how to write the client. In a blog post of mine I suggested a sample class that allows to upload multiple files to a multipart/form-data enabled service along with parameters. It goes like this:

public class UploadFile
{
    public UploadFile()
    {
        ContentType = "application/octet-stream";
    }
    public string Name { get; set; }
    public string Filename { get; set; }
    public string ContentType { get; set; }
    public Stream Stream { get; set; }
}

and then a method to do the job:

public byte[] UploadFiles(string address, IEnumerable<UploadFile> files, NameValueCollection values)
{
    var request = WebRequest.Create(address);
    request.Method = "POST";
    var boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x", NumberFormatInfo.InvariantInfo);
    request.ContentType = "multipart/form-data; boundary=" + boundary;
    boundary = "--" + boundary;

    using (var requestStream = request.GetRequestStream())
    {
        // Write the values
        foreach (string name in values.Keys)
        {
            var buffer = Encoding.ASCII.GetBytes(boundary + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.ASCII.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"{1}{1}", name, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(values[name] + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
        }

        // Write the files
        foreach (var file in files)
        {
            var buffer = Encoding.ASCII.GetBytes(boundary + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"{2}", file.Name, file.Filename, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.ASCII.GetBytes(string.Format("Content-Type: {0}{1}{1}", file.ContentType, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            file.Stream.CopyTo(requestStream);
            buffer = Encoding.ASCII.GetBytes(Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
        }

        var boundaryBuffer = Encoding.ASCII.GetBytes(boundary + "--");
        requestStream.Write(boundaryBuffer, 0, boundaryBuffer.Length);
    }

    using (var response = request.GetResponse())
    using (var responseStream = response.GetResponseStream())
    using (var stream = new MemoryStream())
    {
        responseStream.CopyTo(stream);
        return stream.ToArray();
    }
}

and finally the client:

using (var stream1 = File.Open("test.txt", FileMode.Open))
using (var stream2 = File.Open("test.xml", FileMode.Open))
using (var stream3 = File.Open("test.pdf", FileMode.Open))
{
    var files = new[] 
    {
        new UploadFile
        {
            Name = "file",
            Filename = "test.txt",
            ContentType = "text/plain",
            Stream = stream1
        },
        new UploadFile
        {
            Name = "file",
            Filename = "test.xml",
            ContentType = "text/xml",
            Stream = stream2
        },
        new UploadFile
        {
            Name = "file",
            Filename = "test.pdf",
            ContentType = "application/pdf",
            Stream = stream3
        }
    };

    var values = new NameValueCollection
    {
        { "key1", "value1" },
        { "key2", "value2" },
        { "key3", "value3" },
    };

    byte[] result = UploadFiles("http://localhost:1234/upload", files, values);
    // TODO: process the result
}