email-dkim/lib/process-header.js

DomainKeys Identified Mail (DKIM)

/**
 * Canonicalize the message header according to
 * methods defined in RFC[6376]
 * @memberOf DKIM
 * @param {Array<String>} headers - Each header is formatted as `<field>: <value>`
 * @param {Array} signHeaders
 * @param {String} method - (simple|relaxed)
 * @return {String}
 * @throws {Error} If canonicalization method is unsupported
 * @example
 * DKIM.processHeader( [ 'A: X', 'B : Y\t\r\n\tZ  '], [ 'A' ], 'relaxed' )
 */
function processHeader(headers, signHeaders, method) {

  if (typeof signHeaders === 'string') {
    method = signHeaders
    signHeaders = null
  }

  method = method || 'simple'

  if (method !== 'simple' && method !== 'relaxed') {
    throw new Error('Canonicalization method "' + method + '" not supported')
  }

  if (signHeaders != null) {

    // Clone this array so that newely added headers don't show up outsite this "processHeader" function
    // See https://tools.ietf.org/html/rfc5322#section-3.6
    signHeaders = signHeaders.slice()
    signHeaders.push('DKIM-Signature')
    signHeaders.push('X-Google-DKIM-Signature')

    signHeaders = signHeaders.map(function (header) {
      return header.toLowerCase()
    })

    // Remove duplicates
    // signHeaders = signHeaders.reduce((ac, val) => [...ac, ...ac.includes(val) ? [] : [val]], [])
    signHeaders = signHeaders.reduce(function (ac, val) {
      if (ac.indexOf(val) < 0) {
        ac.push(val)
      }
      return ac;
    }, [])

    // Sort elements of headers array using the "signHeaders" order
    var indexedHeaders = headers.map(function (header) {
      var key = header.slice(0, header.indexOf(':')).trim().toLowerCase()
      var idx = signHeaders.indexOf(key)
      return { idx, header }
    })

    headers = indexedHeaders
      .filter(function (h) { return h.idx > -1 })
      .sort(function (h1, h2) { return h1.idx - h2.idx })
      .map(function (h) { return h.header })

    // headers = headers.filter( function( header ) {
    //   var key = header.slice( 0, header.indexOf( ':' ) ).trim().toLowerCase()
    //   return signHeaders.indexOf( key ) !== -1
    // })
  }

  if (method === 'simple') {
    return headers.map((line, il) => {

      var colon = line.indexOf(':')
      var key = line.slice(0, colon).toLowerCase()

      if (/^(dkim-signature|x-google-dkim-signature)/i.test(key)) line = line.replace(/b=[^;]+;?/, 'b=')


      return line
    }).join('\r\n')
  }

  // TODO: Something's not right here...
  // relaxed signatures still don't verify
  if (method === 'relaxed') {
    return headers.map(function (line) {

      var colon = line.indexOf(':')
      var value = line.slice(colon)

      // Convert all header field names to lowercase
      var key = line.slice(0, colon).toLowerCase()

      // Unfold all header field continuation lines
      value = value.replace(/\r\n(?=[\x20\x09])/g, '')
      // Convert all sequences of one or more WSP characters to a single SP
      value = value.replace(/[\x20\x09]+/g, ' ')
      // Devare all WSP characters at the end of each unfolded header field
      value = value.replace(/[\x20\x09]+$/g, '')

      // Remove signature value for "dkim-signature" header
      if (/^(dkim-signature|x-google-dkim-signature)/i.test(key)) {
        value = value.replace(/ b=([^;]*)/, ' b=')
      }

      if (key === 'x-google-dkim-signature') {
        key = key.replace('x-google-dkim-signature', 'dkim-signature')
      }

      // Remove any WSP characters remaining before and after the colon
      return (key + value).replace(/[\x20\x09]*[:][\x20\x09]*/, ':')

    }).join('\r\n')
  }

}

module.exports = processHeader