Parse each line of `key=value` pairs into an array of separate `key=value` pairs in Ruby

parser_from_scratch.rb

# frozen_string_literal: true

# Parse each line of key=value pairs into an array of separate key=value pairs.
# Some values will be in double quotes and contain white space,
# and some will not. All values with whitespace in them will be double quoted.
# No keys will be double quoted.

# annotated breakdown and explanation derived from
# https://stackoverflow.com/a/23613257, originally written by user
# https://stackoverflow.com/users/2195474/jbr in 2014
#   changes:
#     - use post-Ruby 2.3 "frozen string" conventions & idioms
#     - passes default rubocop scans

example_str = 'timestamp="Wed Jun 19 09:35:36 PDT 2019" message="test 10" id=10 field_1="test 10" field_6="test 1"'

def key_value_parser(str)
  # assume a default state of "unquoted"
  state = :unquoted

  # initialize a constructor
  result = ['']

  # walk the characters in the string, one by one
  str.chars do |char|
    # while the state is unquoted, iterate characters until we find whitespace
    case state
    when :unquoted
      case char
      when /\s/
        # whitespace has been encountered, initialize a new empty string
        # to begin appending characters to
        result << ''

      # if we encounter an opening double quote, change state to quoted and
      # then append the double quote to the string. We don't care about
      # preserving the double quote character itself.
      when '"'
        state = :quoted

      else
        # append the character to the end of the last value in our constructor.
        result[-1] = "#{result[-1]}#{char}"
      end

    # while state is quoted, all whitespace is treated as literal and appended
    # to the end of the last element in the array like any other character.
    when :quoted
      case char

      # a closing double quote has been encountered and our current value is
      # complete. initialize a new empty string to append the next iteration to
      # and reset state.
      when '"'
        result << ''
        state = :unquoted

      else
        # append the character to the end of the last value in our constructor.
        result[-1] = "#{result[-1]}#{char}"
      end
    end
  end

  # ensure that the empty string initialized when the last delimiter
  # was encountered is removed before the resulting array is returned.
  result.reject(&:empty?)
end

puts key_value_parser(example_str).inspect

When an interviewer asks you to parse a bunch of key=value log lines into something else and you frantically google "ruby parse key value pairs whitespace", I hope that this helps you out.