response partial content in node.js

partial.coffee

#
# blob : Object from MongoDB
#
# blob.body: Buffer
# blob.size: length of buffer, substitute for blob.body.length
# blob.type: MIME (Eg. audio/x-wav)
#
# req : Object from http
# res : Object from http
# _ : Object from underscore
#

if blob
  range = req.headers.range
  unless range
    res.writeHead 200,
      'Content-Type': blob.type
    res.end blob.body
  else
    [ini, end] = _.map range.replace(/bytes=/, '').split('-'), (n) -> parseInt n, 10
    total = blob.size
    chunk = end - ini + 1
    #console.log "#{ini}-#{end}/#{total} #{chunk}".cyan
    res.writeHead 206,
      'Content-Type': blob.type
      'Content-Length': chunk
      'Content-Range': "bytes #{ini}-#{end}/#{total}"
      'Accept-Ranges': 'bytes'
    res.end blob.body
else
  res.writeHead 404
  res.end()