Netstrings is a specification for length-prefixed and delimited byte strings, useful mostly as a low-level building block for network protocols. With swift-netsring you can parse incoming data from a socket or some other stream by wrapping the stream in a simple closure that reads bytes synchronously. Or you can feed it an array of bytes.
You can find examples in the repo in the README, in a Swift playground and in tests. There's also API documentation (a big thank you to Jesse Squires for an excellent guide for setting up docs on GitHub pages for a Swift project.)