Hello,
we are using Protobuf to communicate between two devices via Ad-hoc WiFi.
One of the devices is running a Java application and the other a Python
application.
Here is an example of how we build our messages in python:
def serialize(self):
# create outer packet message
packetMessage = protoPackets_pb2.PacketMessage()
packetMessage.type = protoPackets_pb2.PacketMessage.ADVERT
packetMessage.transactionID = self.transactionID
# add advert-specific content
packetMessage.advertMessage.finalDestinationIP =
self.finalDestinationIP
packetMessage.advertMessage.ceil = self.ceil
packetMessage.advertMessage.deadline = self.deadline
packetMessage.advertMessage.fine = self.fine
packetMessage.advertMessage.initialBudget = self.initialBudget
return packetMessage.SerializeToString()
The problem we are having is the following:
1.We build an Object that we want to send to the Java Device on the python
device
2.We serialize it as above (with SerializeToString())
2.1 We checked that we can successfully deserialize it in python, just to
make sure that the error is not there
3. We send that over UDP to the Java device
4. The java device now receives the datagram packet and tries to parse the
byte array into something useful to build an object with:
public Packet buildPacket(byte[] rawdata, Inet4Address sourceIP) throws
InvalidProtocolBufferException {
PacketMessage packetMessage = PacketMessage.parseFrom(rawdata);
int type = packetMessage.getType().getNumber();
Packet packet = null;
try{
switch (type) {
case 0:
packet = new Advert(packetMessage);
packet.setSourceIP(sourceIP);
break;
case 1:
etc. etc. etc. more code.
4.1 You see that parseFrom(rawdata) is called, rawdata being the byte array
from the received datagram packet.
5. parseFrom causes an InvalidProtocolBufferException.
6. Upon closer inspection, we saw that the parser seems to be doing
alright, successfully assembling the packet message. However the message is
only a few bytes long, and after that the
parser just keeps reading the byte array(buffer, which is 128 byte long).
The byte array is filled with 0's. Upon reading a 0 the exception occurs.
7. We tried to work around it with a dirty hack, but obv. this is not a
good solution. in CodeInputStream.java, line 700 we changed the function
isAtEnd() to return true in case of a zero:
public boolean isAtEnd() throws IOException {
// EVIL HACK: ToDo: Change BACK!
return bufferPos == bufferSize && !refillBuffer(false) ||
buffer[bufferPos] == 0;
// return bufferPos == bufferSize && !refillBuffer(false);
}
8. This solves our problem for one type of message we have, but in another
type the byte array does not end with 0's but other numbers that are not
part of our packetMessage, so it reads them until it reaches a zero and
stores them in some unknownFields variable.
10. Obviously our solution is bad and we should have asked much sooner, but
we are out of ideas and hope that you can help us.
If I was unclear with anything please dont hesitate to ask for more info,
its late and I already typed this up once and deleted it by accident so Im
not sure how helpful my description is.
Cheers
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