VCR and XMLRPC: Fixing the 'wrong size' error

Yesterday I had the perfect opportunity to hack a little bit with VCR, a very nice library that Andrei Ursan has recommended me several times.

In a nutshell, the library wraps requests to an external HTTP server and saves the responses in files in the yaml format, replaying them in consecutive calls (hence the name). This allows for perfect decoupling in tests, not only making them faster but more reliable, as they don’t depend on external factors anymore.

So I modified the project I was working on to add support for VCR, created the pull request and… broke the build as it was merged into master.

The specs failed in all Ruby 1.8.x interpreters (this includes REE, JRuby and Rubinius) with messages like the following:

Wrong size. Was 9764, should be 9662

I haven’t been able to trace the exact cause of problem, but at least I have been able to fix it. The solution is to record the HTTP requests using one of the Ruby 1.8.x versions. While the responses saved in 1.9.x don’t work with 1.8.x versions, the ones generated in 1.8.x are compatible with newer versions of Ruby.