If the naming doesn’t follow what Rails is looking for, just do a require ‘header.rb’ in whatever controller / model you want to use said library in. Rails already adds lib/ to the load path, so you don’t have to worry about finding the correct path.
That all looks fine, what does the code that uses this look like?
Hmm, everything looks good.
I’d say try SmsChat::MsrpURI.new…
and as a sanity check, are you restarting your server for each change to this library? Only classes that are auto-loaded by Rails (e.g. not yours) are reloaded with each request.