csexp: S-expressions over the network

Canonical s-expressions (csexp) are a way to format s-expressions into data packets suitable for transmission over a network.

1 Overview

Consider the following expression:

'(bag "Inventory" (content cookie caramel aligator))

To get a canonical s-exp, it must first be changed into a tree of bytestrings:

(list #"bag" #"\"Inventory\"" (list #"content" #"cookie" #"caramel" #"aligator"))

Which can then be transmitted as:

#"(3:bag11:\"Inventory\"(7:content6:cookie7:caramel8:aligator))"

Spaces are removed and all strings are suffixed by their size and a colon : separator. This makes it easy to read the expression in a stream, and gives a unique (canonical) way of writing a given s-expression.

2 Hinted csexp

Canonical s-expressions can have an optional "hint", which is a bytestring attached to the front of a csexp atom, inside square brackets:

#"(6:animal(4:name[13:charset=utf-8]7:The Cat)(5:noise4:meow))"

Here the hint is attached to the atom The Cat and has the value charset=utf-8.

When parsing a csexp, hints are rendered by default as hinted structures.

3 Reference

If hinting is 'if-present, it generates a hinted instance every time a hint is found.
If hinting is 'always, it generates hinted instances for each atom, with #f as the default hint value.
If hinting is 'never, it ignores any hint and just returns bytestrings.