Extract the data from certain "data:" URIs

URL+Data.swift

// known-good Xcode 8.2.1
extension URL
{
  /** 
   Returns the data from a URI with the "data:" scheme, which includes the optional "base64" annotation, and which has a mediatype that is encoded in ASCII. As described in https://tools.ietf.org/html/rfc2397.
   */
  var asData:Data?
  {
    guard
      let scheme = self.scheme, scheme == "data",
      let path = URLComponents(url: u, resolvingAgainstBaseURL: false)?.path,
      let regex = try? NSRegularExpression(pattern: "^.*;base64,", options: []),
      let firstMatch = regex.firstMatch(in: path, options: [], range: NSMakeRange(0, path.characters.count))
      else { return nil }
    let dataString = path.substring(from: path.index(path.startIndex, offsetBy: firstMatch.range.length))
    guard let data = Data(base64Encoded: dataString) else { return nil }
    return data
  }
}