Parsing a git tree

parsing_git_trees.rb

require 'zlib'

file = File.read(".git/objects/f2/e2c063fb85137b4fc3bef895ed9d6eed03df42")
# f2e2c063fb85137b4fc3bef895ed9d6eed03df42

buf = Zlib::Inflate.inflate(file)

header, body = buf.split("\0", 2)

puts header

headers = []

SPACE_BYTE = 32
NULL_BYTE = 0
OID_LENGTH = 20
found_space = false
found_null = false
oid = []
name = []
permissions = []
body.bytes.each do |byte|
  if !found_space
    if byte == SPACE_BYTE
      found_space = true

      next
    end

    permissions << byte
  elsif !found_null
    if byte == NULL_BYTE 
      found_null = true

      next
    end

    name << byte
  else
    if oid.length == OID_LENGTH
      headers << {
        oid:,
        name:,
        permissions:
      }

      found_space = false
      found_null = false
      oid = []
      name = []
      permissions = []

      permissions << byte
    else
      oid << byte
    end
  end
end

formatted_headers = headers.map do |header|
  {
    permissions: header[:permissions].pack("c*"),
    name: header[:name].pack("c*"),
    oid: header[:oid].pack("c*").unpack("H*").first
  }
end

pp formatted_headers

# [0, 32], [46, 32], [32, 34]
# 00  2E  20
#