ManageIQ/binary_struct

Supporting bit decoding and encoding

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#14 opened on Mar 5, 2020

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enhancementgood first issuehelp wantedpinnedsize/m

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Description

I'd like to specify the following:

BinaryStruct.decode([
  'L', :some_num,
  'b', :flag1,
  'b', :flag2,
  'b', :flag3,
  'L', :another_num,
])

Given that, I'd expect BinaryStruct.decode to extract a number, then on the next byte extract the first 3 bits as booleans stored in :flag1, :flag2, :flag3, then move ahead to the next byte and extract another number.

I'd probably be happy with having to align my definition to byte boundaries, so perhaps...

BinaryStruct.decode([
  'L', :some_num,
  'b', :flag1,
  'b', :flag2,
  'b', :flag3,
  'b5', :unused, # ideally optional
  'L', :another_num,
])

I would expect encode and size to handle similar structures.

Implementation wise, the 'b' identifier reads 1 bit then skips to the next byte, So, when building the decode string it will have to be aware of successive bits and then pack those into a b8.

Contributor guide

Research direction
Study how Ruby's Array#pack and String#unpack handle bit directives ('b' and 'B'). Determine how BinaryStruct currently builds format strings for bytes and extend to accumulate consecutive 'b' fields into a single byte pack. For encoding, reverse the process: extract bits from booleans and pack into a byte. For size, calculate based on number of bits and byte alignment.
Tech stack
ruby
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RubyBinary data handling (Array#pack, String#unpack)
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60