email-dkim-utils/lib/verify.js

Email Utils - DKIM, compose with dkim, etc...

var DKIM = require('./dkim')

const isDKIM = v => /^(DKIM-Signature|X-Google-DKIM-Signature)/.test(v);

/**
 * Verify a message's signatures
 * @memberOf DKIM
 * @param {Buffer} message
 * @param {Function} callback
 * @throws {Error} If input is not a buffer
 */
function verify(message, callback) {

  if (!Buffer.isBuffer(message)) {
    throw new Error('Message must be a Buffer')
  }

  const existRN = message.toString().search('\r\n')
  if (existRN == -1) {
    message = Buffer.from(message.toString().replace(/\n/g, "\r\n"))
  }

  var boundary = message.indexOf('\r\n\r\n')
  if (boundary === -1) {
    return callback(new Error('No header boundary found'))
  }

  var header = message.toString('utf8', 0, boundary)
  var body = message.slice(boundary + 4)

  var results = []
  var signatures = []

  header.split(/\r\n(?=[^\x20\x09]|$)/g).forEach(function (h, i, headers) {
    // ISSUE: executing line below, may result in including a different 'DKIM-Signature' header
    // signatures.push( headers.slice( i ) )
    // FIX: after slicing, remove any included 'DKIM-Signature' header that differ from "oneHeader"
    if (isDKIM(h)) {
      // remove DKIM headers
      const sigHeaders = headers.filter(v => !isDKIM(v));
      // add one DKIM header
      sigHeaders.unshift(h);

      signatures.push(sigHeaders);
    }
  });

  function verifyNextSignature() {

    var headers = signatures.pop()
    if (headers == null) {
      return callback(null, results)
    }

    DKIM.verifySignature(body, headers, function (error, result) {
      if (error) return callback(error, results)
      results.push(result)
      verifyNextSignature()
    })

  }

  verifyNextSignature()
}

/**
 * Filter out signature headers other than the specified `signatureHeader`
 * @param {Array<String>} headers - list of headers to filter
 * @param {String} signatureHeader - signature header to keep
 * @return {Array<String>} filtered headers
 */
verify.filterSignatureHeaders = function filterSignatureHeaders(headers, signatureHeader) {
  return headers.filter(function (header) {
    return header === signatureHeader ||
      !/^(DKIM-Signature|X-Google-DKIM-Signature)/i.test(header)
  })
}

module.exports = verify