code: function streamResultsPromise (command, args, options, cb) {
      var output = ''
      var stderr = ''
      var child = spawn(command, args, options)
      child.stdout.setEncoding('utf8')
      child.stderr.setEncoding('utf8')
      child.stdout.on('data', stdoutHandler)
      child.stderr.on('data', stderrHandler)
      child.on('close', closeHandler)
  
      function stdoutHandler (data) {
        output += data
      }
  
      function stderrHandler (data) {
        stderr += data
      }
  
      function closeHandler (code) {
        if (code !== 0) {
          var ex = new Error('pdf-text-extract command failed: ' + stderr)
          throw ex
        }
        cb(output)
      }
    }
docs: Duplicated from function splitPages of streamResults