Split messages

[corrados]

Large Jamulus protocol messages may hit a limit where UDP packets are blocked by some fragmentation issues (see #255). Recently, when a lot of clients are connected to the server, we do not only see this UDP blocking issue for the server list but also at normal operation of Jamulus (i.e. the procol mechanism gets stuck), see #547.

Since the protocol stack in Jamulus is a very critical part regarding stability and security:

@softins Since you are the wireshark/protocol expert, could you please review the code to make sure it works correctly, does not break compatibility and does not crash.

@atsampson I saw that you have done a lot of stability/fuzzing testing for the Issue #314. Since with this new code a lot of the protocol mechanism is changed, I may have introduced new security issues. Could you please review the code and/or test the new code with your fuzzing tools to make sure it still is stable and secure?

[pljones]

I can't see anything seriously wrong structurally. I can't comment on performance aspects just from looking at the code, though.

[softins]

Sure, happy to have a look, but it will be on Friday.

[corrados]

I can't see anything seriously wrong structurally. I can't comment on performance aspects just from looking at the code, though.

Thank you for your review.

[softins]

It looks ok to me so far. I have compiled both server and client on local machines from the branch split_messages, with the split threshold reduced to 100 bytes so I can observe the split protocol without needing too many clients.

I have updated my Wireshark dissector at https://github.com/softins/jamulus-wireshark to display the new messages and the split container fields. I have yet to implement re-assembly of the split packet data parts into a virtual packet for display.

[softins]

Maybe you also need to implement a CLM_REQ_SERVER_LIST_SPLIT, which a newer client could use instead of CLM_REQ_SERVER_LIST, to allow the server to split a CLM_CONN_CLIENTS_LIST in the same way? Although in that case, you might need a CLM_SPECIAL_SPLIT_MESSAGE container that doesn't need an ack response.

[corrados]

split threshold reduced to 100 bytes so I can observe the split protocol without needing too many clients.

You can also simply use a long Chat text message. This will force the message split as well.

CLM_REQ_SERVER_LIST_SPLIT

Yes, something similar will be the next step. But first things first. Let's for now fix the problems with multiple clients.

[corrados]

I have run this code on the Central server for days now and it seems to be stable. So I will merge this pull request to master now. You can still put your reviews here and I will consider them on the master branch.

[atsampson]

Could you please review the code and/or test the new code with your fuzzing tools to make sure it still is stable and secure?

I've had a look through these changes, and they look OK to me so far. I'll try and add support for these to my fuzzing branch when I get a chance.