REST call with String parameter with control characters

I am trying to design a RESTful service that takes a string (with control characters). Does something with that in the logic on the server, then returns a string, which may also have control characters.

Basically the string is a pharmacy claim in a delimited format that uses control characters for those delimiters. The logic on the server will pull the entire claim apart and process it.

I was thinking that a GET method could be uses but I'm used to sending content in JSON format and wondered what other normal RESTful ways there were to do this.