WebRequest POST with both file and parameters

Question

I'm trying to upload a file and a send along a few parameters to my site using .NET / C#. Having read a few tutorials that do either a few parameters or a file, I've tried, unsuccessfully, to combine them. Here is how I try doing it:

WebRequest req = WebRequest.Create(baseURL + "upload");
req.Credentials = new NetworkCredential(username, password);
String boundary = "B0unD-Ary";
req.ContentType = "multipart/form-data; boundary=" + boundary;
req.Method = "POST";
((HttpWebRequest)req).UserAgent = "UploadTester v0.1";

string postData = "--" + boundary + "\nContent-Disposition: form-data\n";
postData += "myId=123&someFk=456";
postData += "\n--" + boundary + "\nContent-Disposition: form-data; name=\"file\" filename=\"upload.pdf\" Content-Type: application/pdf\n\n";
byte[] byteArray = Encoding.UTF8.GetBytes(postData);

byte[] filedata = null;
using (BinaryReader reader = new BinaryReader(File.OpenRead("myfile.pdf")))
    filedata = reader.ReadBytes((int)reader.BaseStream.Length);

req.ContentLength = byteArray.Length + filedata.Length;
req.GetRequestStream().Write(byteArray, 0, byteArray.Length);
req.GetRequestStream().Write(filedata, 0, filedata.Length);

WebResponse response = req.GetResponse();
Stream data = response.GetResponseStream();
StreamReader sReader = new StreamReader(data);
String sResponse = sReader.ReadToEnd();
response.Close();

When I execute it, I get a 500 exception, saying "Header section has more than 10240 bnytes (maybe it is not properly terminated)" and Wireshark informs me that the request sent was a malformed package, where the MIME multipart was malformed.

There are probably several issues here, so please let me know all the problems you can spot

Update: to separate MIME from C#/.NET, I've spawned a thread here: https://stackoverflow.com/questions/1880002/error-in-mime-packet-for-http-post

Update 2: So the backend indeed has issues with the content-length, saying that the amount of bytes available for reading is smaller than the stated content-length. BUT! If I reduce the content-length in req.ContentLength accordingly, I don't have a buffer size large enough for sending the data. Any suggestions?

Update 3: Actually, it looks like the header has a too large size compared to how much data it contains

Answer 1

The problem is that you're missing a '\n'. The following line:

string postData = "--" + boundary + "\nContent-Disposition: form-data\n";

should be:

string postData = "--" + boundary + "\nContent-Disposition: form-data\n\n";

And this line:

postData += "\n--" + boundary + "\nContent-Disposition: form-data; name=\"file\" filename=\"upload.pdf\" Content-Type: application/pdf\n\n"

is missing a '\n' before 'Content-Type'. It should be:

postData += "\n--" + boundary + "\nContent-Disposition: form-data; name=\"file\" filename=\"upload.pdf\"\nContent-Type: application/pdf\n\n"