Verify DST.ADDR of "presets/ss-base"

[micooz]

+------+----------+----------+----------+
| ATYP | DST.ADDR | DST.PORT |   DATA   |
+------+----------+----------+----------+
|  1   | Variable |    2     | Variable |
+------+----------+----------+----------+

When use stream ciphers, original implementation lack of verification on DST.ADDR.

Only check ATYP(is one of [0x01, 0x03, 0x04]) can be lose integrity and become easy to sniff.

We can simply check if DST.ADDR is valid or not to avoid attacking to ATYP:

/**
 * verify hostname
 *
 * @param hostname
 * @returns {boolean}
 *
 * @reference
 *   http://stackoverflow.com/questions/1755144/how-to-validate-domain-name-in-php
 */
function isValidHostname(hostname) {
  // overall length check
  if (hostname.length < 1 || hostname.length > 253) {
    return false;
  }
  // valid chars check
  if (/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i.test(hostname) === false) {
    return false;
  }
  // length of each label
  if (/^[^.]{1,63}(\.[^.]{1,63})*$/.test(hostname) === false) {
    return false;
  }
  return true;
}