In Ruby, especially while writing low-level protocols, you may have encountered
String#unpack(). If you’ve ever experimented with them, they may seem mysterious; they take a cryptic string as a parameter (maybe something like
w*) and seem to return gibberish (or, conversely, convert gibberish into something humans can understand). I’m not going to go into tons of detail, nor am I going to cover every format that these methods accept, but I’ll cover a few that I’ve used.
What led me to writing this post was actually some recent experimenting that I’ve been doing with Crystal. I’m trying my hand at writing a simple BER parser/encoder as a part of my journey to writing an LDAP library for Crystal. The lack of an LDAP library is honestly the biggest reason I haven’t used Crystal for more things. Since BER is a binary method of encoding, the Ruby LDAP BER code uses a ton of
String#unpack(). Unfortunately, Crystal doesn’t have analogous methods for its
Array class or
String struct so I’ve had to write my own.
Here, I’ll describe a few of the formats supported by
#pack and write some compatible examples in Crystal.