FusionAuth Email Validator

EmailValidator.java

/*
 * Copyright (c) 2021, Inversoft Inc., All Rights Reserved
 */
package com.inversoft.validator;

/**
 * @author Daniel DeGroff
 */
public class EmailValidator {

  /**
   * Validation an email address.
   *
   * @param email the email address
   * @return true if the email is valid
   */
  public static boolean isValid(String email) {
    if (email == null) {
      return false;
    }

    boolean valid = false;
    // An email address has two parts, a local and a domain.
    String[] parts = email.split("@");
    if (parts.length == 2) {
      // Validate local
      char[] local = parts[0].toCharArray();
      valid = validateLocal(local);

      // Validate domain
      if (valid) {
        char[] domain = parts[1].toCharArray();
        valid = validateDomain(domain);
      }
    }
    return valid;
  }

  private static boolean validateDomain(char[] ca) {
    // Cannot begin with a dash.
    if (ca[0] == '-') {
      return false;
    }

    int alpha = -1;
    int dot = -1;

    for (int i = 0; i < ca.length; i++) {

      if (ca[i] == '.') {
        // A dot cannot be sequential
        if (i == dot + 1 || i == dot - 1) {
          return false;
        }

        dot = i;
      } else {
        // Allowed characters are [0-9A-Za-Z-]
        boolean isHyphen = ca[i] == 45;
        boolean isDigit = ca[i] >= 48 && ca[i] <= 57;
        boolean isAlpha = (ca[i] >= 65 && ca[i] <= 90) || (ca[i] >= 97 && ca[i] <= 122);

        if (!isHyphen && !isDigit && !isAlpha) {
          // If this is the first or last position and is a square bracket, don't fail yet.
          if (i == 0 && ca[i] == '[' || ((i == ca.length - 1) && ca[i] == ']')) {
            continue;
          }

          return false;
        }

        if (isAlpha) {
          alpha = i;
        }
      }
    }

    if (dot == -1) {
      return false;
    }

    // This is allowed if we think it is an IP address. This is a naive check, but it is likely close enough.
    // Email deliver-ability is still the only true test to see if it is valid.
    if (alpha == -1) {
      return ca[0] == '[' && ca[ca.length - 1] == ']';
    }

    return true;
  }

  private static boolean validateLocal(char[] ca) {
    // Cannot begin or end with a '.'
    if (ca[0] == '.' || ca[ca.length - 1] == '.') {
      return false;
    }

    // Max local length of 64
    if (ca.length > 64) {
      return false;
    }

    int dot = -1;
    for (int i = 0; i < ca.length; i++) {
      if (ca[i] == '.') {
        // A dot cannot be sequential
        if (i == dot + 1 || i == dot - 1) {
          return false;
        }

        dot = i;
      }
    }

    return true;
  }
}