Holen IP-Paketdaten von ByteBuffer

Question

Ich versuche, die Quell-und Zieladresse aus einem Paket zu erhalten. Dies ist, wie ich das Paket lese:

private void debugPacket(ByteBuffer packet) 
{ 
    int buffer = packet.get(); 
    int version; 
    int headerlength; 
    version = buffer >> 4; 
    headerlength = buffer & 0x0F; 
    headerlength *= 4; 
    Log.d(TAG, "IP Version:"+version); 
    Log.d(TAG, "Header Length:"+headerlength); 

    String status = ""; 
    status += "Header Length:"+headerlength; 

    buffer = packet.get();  //DSCP + EN 
    buffer = packet.getChar(); //Total Length 

    Log.d(TAG, "Total Length:"+buffer); 

    buffer = packet.getChar(); //Identification 
    buffer = packet.getChar(); //Flags + Fragment Offset 
    buffer = packet.get();  //Time to Live 
    buffer = packet.get();  //Protocol 

    Log.d(TAG, "Protocol:"+buffer); 

    status += " Protocol:"+buffer; 

    buffer = packet.getChar(); //Header checksum 

    String sourceIP = ""; 
    buffer = packet.get(); //Source IP 1st Octet 
    sourceIP += ((int) buffer) & 0xFF; 
    sourceIP += "."; 

    buffer = packet.get(); //Source IP 2nd Octet 
    sourceIP += ((int) buffer) & 0xFF; 
    sourceIP += "."; 

    buffer = packet.get(); //Source IP 3rd Octet 
    sourceIP += ((int) buffer) & 0xFF; 
    sourceIP += "."; 

    buffer = packet.get(); //Source IP 4th Octet 
    sourceIP += ((int) buffer) & 0xFF; 

    Log.d(TAG, "Source IP:"+sourceIP); 

    status += " Source IP:"+sourceIP; 

    String destIP = ""; 
    buffer = packet.get(); //Destination IP 1st Octet 
    destIP += ((int) buffer) & 0xFF; 
    destIP += "."; 

    buffer = packet.get(); //Destination IP 2nd Octet 
    destIP += ((int) buffer) & 0xFF; 
    destIP += "."; 

    buffer = packet.get(); //Destination IP 3rd Octet 
    destIP += ((int) buffer) & 0xFF; 
    destIP += "."; 

    buffer = packet.get(); //Destination IP 4th Octet 
    destIP += ((int) buffer) & 0xFF; 

    Log.d(TAG, "Destination IP:" + destIP); 

    status += " Destination IP:"+destIP; 

    try { 
     InetAddress addr = InetAddress.getByName(destIP); 
     String host = addr.getHostName(); 
     Log.d(TAG, "Hostname:" + host); 
    } 
    catch (UnknownHostException e) { 
     Log.d(TAG,"Unknown host"); 
    } 
} 

Es funktioniert für die ersten paar Pakete in Ordnung, aber dann manchmal bekomme ich ein BufferUnderflowException an einem der packet.get() Linien. Wie kann ich das verhindern?

Answer 1

Ich kann nicht glauben, dass ich das früher nicht fing. Ich habe vergessen, packet.clear() nach debugPacket(packet) anzurufen.