Problem (and solution): ActiveMerchant and Ruby 1.8.4

I recently lost a few hours debugging a Ruby issue that I thought I'd
post in the hope of saving someone else the time.

Ruby 1.8.4's net/http library has a bug in the post method: the
content-type header is not set by default. This can cause
ActiveMerchant transactions to be rejected by the gateway for
mysterious reasons.

The clean fix, if your server allows you to do so, is to upgrade to
Ruby 1.8.5 or later.

Alternatively, at the start of the ssl_post method (in
ActiveMerchant's posts_data.rb file), add this line at the start of
the method:

  headers['content-type'] = 'application/x-www-form-urlencoded'

Michael Slater