How do I use cookies with RCurl?

Question

I am trying to write an R package that accesses some data via a REST API. The API, however, doesn't use http authentication, but rather relies on cookies to keep credentials with the session.

Essentially, I'd like to replace the following two lines from a bash script with two R functions: One to perform the login, and store the session cookie, and the second to GET the data.

curl -X POST -c cookies.txt -d"username=xxx&password=yyy" http://api.my.url/login
curl         -b cookies.txt                               http://api.my.url/data

I'm clearly not understanding how RCurl works with curl options. My script as it stands has:

library(RCurl)
curl <- getCurlHandle()
curlSetOpt(cookiejar='cookies.txt', curl=curl)
postForm("http://api.my.url/login", username='xxx', password='yyy', curl=curl)
getURL('http://api.my.url/data", curl=curl)

The final getURL() fails with a "Not logged in." message from the server, and after the postForm() no cookies.txt file exists.

Answer 1

My bad. Neal Richter pointed out to me http://www.omegahat.org/RCurl/RCurlJSS.pdf - which better explains the difference between cookiefile and cookiejar. The sample script in the question actually does work. But it only writes the file to disk when it is no longer being used.