zengcity

    public init(payload: NSData) {
        let vl = UnsafePointer<UInt8>(payload.bytes).memory
        version = IPVersion(rawValue: vl >> 4)!
        IPHeaderLength = Int(vl & 0x0F) * 4
        let p = UnsafePointer<UInt8>(payload.bytes.advancedBy(9)).memory
        proto = TransportType(rawValue: p)!
        self.payload = NSMutableData(data: payload)
    }