parser.rb

require 'active_support/all'

def parse_stream(stream)
  begin
    boundary = stream.readline.strip # Boundary is the first thing in the stream
    loop do
      fail 'Nothing in stream' unless boundary.present?

      header = {}
      stream.each_line do |line|
        break if line.blank?
        key, val = line.split(': ')
        header[key] = val&.strip
      end

      fail 'No Content Length' unless header.key?('Content-Length')
      fail 'No Content Type' unless header.key?('Content-Type')

      content_length = header['Content-Length'].to_i
      data = stream.read(content_length)

      yield header, data

      # Try to find the next boundary, ignoring blank lines
      (1..10).each do
        new_boundary = stream.readline.strip
        next unless new_boundary.present?
        if new_boundary != boundary
          fail "Bad boundary: #{new_boundary}, expected: #{boundary}"
        else
          break
        end
      end
    end
  rescue EOFError
    puts "End of stream, returning..."
    return
  ensure
    stream.close
  end
end

def parse_plate(plate)
  parsed = {}
  plate.each_line do |line|
    keys, val = line.split('=')
    keys = keys.split('.')
    val = val&.strip

    ctx = parsed
    keys[1...-1].each do |key| # Exclude initial 'Events[0].'
      ctx[key] = {} unless ctx.key?(key)
      ctx = ctx[key] # Update context for nested hashes
    end

    has_array = keys.last.split(/\[(\d)\]/)
    if has_array[1] # Deal with keys ending in [0] etc, e.g. BoundingBox[1]
      key = has_array[0]
      val = val.to_i.zero? ? val : val.to_i # Try to cast to int
      ctx[key] ? ctx[key] << val : ctx[key] = [val] # Create or append array
    else
      ctx[keys.last] = val
    end
  end

  parsed
end

stream = open('snap.cgi', 'r')
parse_stream(stream) do |header, data|
  content_type = header['Content-Type']
  unless %w[text/plain image/jpeg].include?(content_type)
    puts "Unknown content type: #{content_type}"
    next
  end

  if content_type == 'text/plain'
    p parse_text(data)
  elsif content_type == 'image/jpeg'
    puts "Skipping image"
  end
end