labelprint/app.rb

# /usr/bin/env ruby
require 'sinatra'
require "sinatra/reloader"
require 'tmpdir'
require 'net/http'

set :protection, :except => :frame_options
set :environment, :production
set :bind, "::"
set :port, 80

if !File.exist?('config.json') || !File.readable?('config.json')
  raise RuntimeException, 'Could not read config.json'
end

# Direct libusb bulk transfer (bypassing the kernel usblp driver, matching how
# brother_ql_web addresses its printers) times out on this Pi 3B's USB
# controller -- back to the kernel driver via a stable udev symlink instead.
PRINTER_DEVICE = '/dev/usb/lp_datamax' # see /etc/udev/rules.d/99-datamax.rules
PRINTER_DPI = 203 # DatamaxONeil E4204B Mark III native head resolution
PRINTER_DARKNESS = 8 # lower than factory default to stop thermal dot-gain from fusing barcode bars
TEST_LABEL_PDF = File.join(File.dirname(__FILE__), 'test-label.pdf')

BROTHER_PRINTERS = {
  'ql560'  => { port: 8560, label: 'Brother QL-560' },
  'ql700'  => { port: 8700, label: 'Brother QL-700' },
  'ql1100' => { port: 9100, label: 'Brother QL-1100' }
}.freeze

configure do
  enable :static
  set :session_secret, File.read(File.join(File.dirname(__FILE__), '.session_secret')).strip
  enable :sessions

  set :views, File.join(File.dirname(__FILE__), 'views')
  set :public_folder, File.join(File.dirname(__FILE__), 'public')
  set :files, File.join(settings.public_folder, 'files')
  set :unallowed_paths, ['.', '..']
end

configure :production do
  enable :reloader
end

helpers do
  def flash(message = '', level)
    case level
    when "success"
      session[:alert_success] = message
    when "danger"
      session[:alert_danger]  = message
    when "warning"
      session[:alert_warning] = message
    end
  end

  # Renders a PDF to ZPL ^GFA graphic labels at the printer's native DPI,
  # bypassing CUPS/Gutenprint's raster pipeline which blurs text and 1px-shifts
  # output compared to native ZPL rendering.
  def pdf_to_zpl(pdf_path, dpi: PRINTER_DPI)
    Dir.mktmpdir do |dir|
      pattern = File.join(dir, 'page-%03d.pbm')
      ok = system('gs', '-q', '-dNOPAUSE', '-dBATCH', '-dSAFER',
                  '-sDEVICE=pbmraw', "-r#{dpi}",
                  '-dTextAlphaBits=4', '-dGraphicsAlphaBits=4',
                  "-sOutputFile=#{pattern}", pdf_path)
      raise 'ghostscript rendering failed' unless ok

      Dir.glob(File.join(dir, 'page-*.pbm')).sort.map { |f| pbm_to_zpl_label(f) }.join
    end
  end

  def pbm_to_zpl_label(pbm_path)
    bytes = File.binread(pbm_path)
    header = /\AP4\s+(?:#[^\n]*\n\s*)*(\d+)\s+(\d+)\s/.match(bytes)
    raise "unreadable PBM header in #{pbm_path}" unless header

    width, height = header[1].to_i, header[2].to_i
    bytes_per_row = (width + 7) / 8
    total_bytes = bytes_per_row * height
    body = bytes.byteslice(header.end(0), total_bytes)
    hexdata = body.unpack1('H*').upcase

    "^XA\n^MD#{PRINTER_DARKNESS}\n^PW#{width}\n^LL#{height}\n^FO0,0^GFA,#{total_bytes},#{total_bytes},#{bytes_per_row},#{hexdata}\n^XZ\n"
  end

  def print_to_datamax(data)
    File.open(PRINTER_DEVICE, 'wb') { |f| f.write(data) }
  end

  # Transparently reverse-proxies the current request to one of the
  # brother_ql_web instances, so all three printers (web UI and API alike)
  # are reachable through this single sinatra port instead of their own
  # dedicated ports.
  def proxy_to_brother(port, prefix, path)
    uri = URI("http://127.0.0.1:#{port}#{path}")
    uri.query = request.query_string unless request.query_string.empty?

    proxied = Net::HTTP.const_get(request.request_method.capitalize).new(uri)
    request.env.each do |key, value|
      next unless key.start_with?('HTTP_') && key != 'HTTP_HOST'

      header = key.sub(/^HTTP_/, '').split('_').map(&:capitalize).join('-')
      proxied[header] = value
    end
    proxied['Content-Type'] = request.content_type if request.content_type
    proxied['X-Forwarded-Prefix'] = prefix
    proxied['X-Forwarded-Host'] = request.host
    proxied.body = request.body.read unless request.request_method == 'GET'

    res = Net::HTTP.start(uri.host, uri.port) { |http| http.request(proxied) }

    body = res.body || ''
    if res['Content-Type']&.include?('text/html')
      body = body.sub(/(<body[^>]*>)/i) { "#{Regexp.last_match(1)}\n#{erb(:_navbar, layout: false)}" }
    end

    headers = {}
    res.each_header do |key, value|
      next if %w[transfer-encoding connection content-length].include?(key.downcase)

      headers[key] = value
    end
    [res.code.to_i, headers, [body]]
  end
end

before do
  @alert_success = session.delete(:alert_success)
  @alert_danger  = session.delete(:alert_danger)
  @alert_warning = session.delete(:alert_warning)
end


get '/' do
  erb :index
end

get '/upload' do
  erb :upload
end

post '/upload' do
    if params[:file]

      tempfile = params[:file][:tempfile]
      filename = params[:file][:filename]
      filetype = File.extname filename
      filepath = File.join(settings.files, filename)

      File.open(filepath, 'wb') do |f|
        f.write tempfile.read
      end

      case filetype
      when ".pdf"
        begin
          zpl = pdf_to_zpl(filepath)
          print_to_datamax(zpl)
          flash "PDF: Upload successful (#{filename})", "success"
        rescue => e
          flash "PDF: Failed to print (#{e.message})", "danger"
        end
      when ".zpl"
        print_to_datamax(File.binread(filepath))
        flash "ZPL: Upload successful (#{filename})", "success"
      else
        flash "#{filetype} is not supported. Only .pdf and .zpl!", "false"
      end

      File.delete(filepath) if File.exist?(filepath)
    else
      flash 'You have to choose a file', "warning"
    end

    redirect '/upload'
end

post '/test-print' do
  begin
    zpl = pdf_to_zpl(TEST_LABEL_PDF)
    print_to_datamax(zpl)
    flash 'Test label sent to printer', 'success'
  rescue => e
    flash "Test print failed (#{e.message})", 'danger'
  end
  redirect '/upload'
end

get '/brother' do
  @printers = BROTHER_PRINTERS
  erb :brother_picker
end

%w[get post put delete].each do |verb|
  send(verb, '/brother/:printer/*') do
    printer = BROTHER_PRINTERS[params[:printer]]
    halt 404, 'unknown printer' unless printer

    proxy_to_brother(printer[:port], "/brother/#{params[:printer]}", '/' + params[:splat].first)
  end
end