binary.js

/**
 * binary.js - binary data helper routines.
 *
 * 2010, Michel Beloshitsky
 *
 * Licensed under the terms of MIT license. See COPYING file in the
 * root of distribution.
 */

/**
 * Basic idea of this format functions borrowed from "binary format"
 * routine of tcl standart library. But abbreviations now did not match.
 *
 * This implementation of binary routines is not full; it's tuned for
 * tokyo tyrant connector.
 *
 * Abbreviations:
 *
 * b - byte (octet).
 * i - 32-bit big-endian integer
 * S - string (sequence of chars).
 *
 * In read function "S" means pascal string. In mean that at first
 * read length (N) from 32-integer. After that N bytes read into string.
 *
 * Example:
 *
 * > require('./binary').format('bbIIS', 1, 2, 4, 5, 'test')
 *
 * produces:
 *
 * > 0x01 0x02 0x00 0x00  0x00 0x04 0x00 0x00
 * > 0x00 0x05 0x74 0x65  0x73 0x74
 *
 * > require('./binary').read(formatString, binaryStringToParse)
 *
 * acts vice versa.
 */

exports.format = function () {

   var out = '', args = arguments, format = args[0].split(''), argi = 1

   format.map(function (spec) {
      switch (spec) {
      case 'b': out += String.fromCharCode(args[argi])
         break
      case 'i':
         var iv = args[argi], i=4, ov = []
         while (i--) {
            ov.push(String.fromCharCode(iv & 0xFF))
            iv >>= 8
         }
         out+=ov.reverse().join('')
         break
      case 's': out += args[argi]
         break
      default:
         throw 'Binary format syntax error'
      }
      argi++
   })
   return out
}

exports.read = function rd (fmtStr, reader, cb) {
   var out = [], spec = fmtStr.split('')

   function next(specCh) {
      if (!specCh)
         return cb(null, out)

      switch (specCh) {
      case 'b':
         reader.read(1, function (err, str) {
            out.push(str.charCodeAt(0));
            next(spec.shift())
         })
         break
      case 'i':
         reader.read(4, function (err, str) {
            var j = -1, v = 0
            while (++j < 4) {
               v += (str.charCodeAt(j) & 0xFF) << (8 * (3 - j))
            }
            out.push(v)
            next(spec.shift())
         })
         break
      case 'S':
         rd('i', reader, function (err, len) {
            reader.read(len[0], function (err, data) {
               out.push(data)
               next(spec.shift())
            })
         })
         break
      }
   }

   next(spec.shift())
}