On Wed, Jan 18, 2017 at 04:24:39AM -0600, Elizabeth Myers wrote:
Hello,
I've noticed a lot of binary protocols require variable length bytestrings (with or without a null terminator), but it is not easy to unpack these in Python without first reading the desired length, or reading bytes until a null terminator is reached.
This sounds like a fairly straight-forward feature request for the struct module, which probably could go straight to the bug tracker. Unfortunately I can't *quite* work out what the feature request is :-) If you're asking for struct to support Pascal strings, with a single byte (0...255) for the length, it already does with format code "p". I was going to suggest P for "large" Pascal string, with the length given by *two* bytes rather than one (0...65535), but P is already in use. Are you proposing the "$" format code from netstruct? That would be interesting, as it would allow format codes: B$ standard Pascal string, like p I$ Pascal string with a two-byte length L$ Pascal string with a four-byte length 4294967295 bytes should be enough for anyone :-) Another common format is "ASCIIZ", or a one-byte Pascal string including a null terminator. People actually use this: http://stackoverflow.com/questions/11850950/unpacking-a-struct-ending-with-a... Which just leaves C-style null terminated strings. c/n/N are all already in use; I guess that C (for C-string) or S (for c-String) are possibilities. All of these seem like perfectly reasonable formats for the struct module to support. They're all in use. struct already supports variable-width formats. I think its just a matter of raising one or more feature requests, and then doing the work. I guess this is just my long-winded way of saying +1. -- Steve