commandline curl POST gives zero content length

Question

I'm using commandline curl to do a POST via a proxy but my form data is vanishing to zero content length. Any ideas what I'm doing wrong?

Here's my command line (uses a public test form so others can try it):

curl -v --proxy-ntlm --proxy proxyserver:proxyport --proxy-user : -d "fname=a&lname=b" http://www.snee.com/xml/crud/posttest.cgi

-v = verbose
next few arguments get us through the proxy using windows authentication
-d = should do a post with the given arguments

However, both the response and the verbose print out suggest the form content is vanishing. The curl prints "Content-Length: 0" and the returned html has both arguments missing and a content length of 0.

The bug doesn't seem to be in the proxy server as curl admits it is sending a content length of 0. Does anyone know a solution to this problem? Has anyone else seen it?

Update: this person appears to have the same bug, but no solution suggested, apart from not using ntlm which I have to

Update 2: This definitely only happens with NTLM authentication, I've tried an alternative authentication method which works. Also, using -F instead of -d (for binary form data) fails in the same way.

Update 3 (workaround): I've had a bit of discussion on the curl-users list about this. A workaround was provided which is to use --proxy-anyauth instead of --proxy-ntlm. I'm still investigating the problem but this workarounf works for me.

Answer 1

NTLM is a challenge-response protocol. When you indicate that you're going to use NTLM, a client will first send a request without the body (to avoid wasting the bandwidth of sending the body only to have it rejected by the HTTP/401 challenge from the server). Only once the Challenge/Response protocol is complete will the body actually be posted.

This causes a number of problems in cases where the client expects NTLM but the proxy or server has no idea (and thus acts on the 0-byte POST, never challenging the client).