isURL function

bool isURL(String? str, { List<String?> protocols = const ['http', 'https', 'ftp'], bool requireTld = true, bool requireProtocol = false, bool allowUnderscore = false, List<String> hostWhitelist = const [], List<String> hostBlacklist = const [], })

check if the string str is a URL

• protocols sets the list of allowed protocols
• requireTld sets if TLD is required
• requireProtocol is a bool that sets if protocol is required for validation
• allowUnderscore sets if underscores are allowed
• hostWhitelist sets the list of allowed hosts
• hostBlacklist sets the list of disallowed hosts

Implementation

bool isURL(String? str,
    {List<String?> protocols = const ['http', 'https', 'ftp'],
    bool requireTld = true,
    bool requireProtocol = false,
    bool allowUnderscore = false,
    List<String> hostWhitelist = const [],
    List<String> hostBlacklist = const []}) {
  if (str == null ||
      str.length == 0 ||
      str.length > 2083 ||
      str.startsWith('mailto:')) {
    return false;
  }

  var protocol,
      user,
      auth,
      host,
      hostname,
      port,
      port_str,
      path,
      query,
      hash,
      split;

  // check protocol
  split = str.split('://');
  if (split.length > 1) {
    protocol = shift(split);
    if (protocols.indexOf(protocol) == -1) {
      return false;
    }
  } else if (requireProtocol == true) {
    return false;
  }
  str = split.join('://');

  // check hash
  split = str!.split('#');
  str = shift(split);
  hash = split.join('#');
  if (hash != null && hash != "" && new RegExp(r'\s').hasMatch(hash)) {
    return false;
  }

  // check query params
  split = str!.split('?');
  str = shift(split);
  query = split.join('?');
  if (query != null && query != "" && new RegExp(r'\s').hasMatch(query)) {
    return false;
  }

  // check path
  split = str!.split('/');
  str = shift(split);
  path = split.join('/');
  if (path != null && path != "" && new RegExp(r'\s').hasMatch(path)) {
    return false;
  }

  // check auth type urls
  split = str!.split('@');
  if (split.length > 1) {
    auth = shift(split);
    if (auth.indexOf(':') >= 0) {
      auth = auth.split(':');
      user = shift(auth);
      if (!new RegExp(r'^\S+$').hasMatch(user)) {
        return false;
      }
      if (!new RegExp(r'^\S*$').hasMatch(user)) {
        return false;
      }
    }
  }

  // check hostname
  hostname = split.join('@');
  split = hostname.split(':');
  host = shift(split);
  if (split.length > 0) {
    port_str = split.join(':');
    try {
      port = int.parse(port_str, radix: 10);
    } catch (e) {
      return false;
    }
    if (!new RegExp(r'^[0-9]+$').hasMatch(port_str) ||
        port <= 0 ||
        port > 65535) {
      return false;
    }
  }

  if (!isIP(host) &&
      !isFQDN(host,
          requireTld: requireTld, allowUnderscores: allowUnderscore) &&
      host != 'localhost') {
    return false;
  }

  if (hostWhitelist.isNotEmpty && !hostWhitelist.contains(host)) {
    return false;
  }

  if (hostBlacklist.isNotEmpty && hostBlacklist.contains(host)) {
    return false;
  }

  return true;
}