Add validation against MaxMessageSize before send,receive Message

[plgd-dev]

Add validation against MaxMessageSize before send,receive Message

[arun1587]

Is this still open?

[jkralik]

Yes. Unless someone implement I will do it in this year.

[arun1587]

So we validate the size of request against peerMaxMessageSize in handlePairMsg() and size of response against s.srv.MaxMessageSize in WriteMsgWithContext() for the sessionTCP. right? .If so, I could create a PR for it.

[jkralik]

peerMaxMessageSize:

• must be check in blockWiseSession.WriteMsgWithContext, sessionTCP.WriteMsgWithContext
• is set via CSM message from peer and it's determine maximum message (header+payload) size that can be send to the peer. (whole message that is send via blockwise),
• for UDP it is not supported

s.srv.MaxMessageSize:

• must be check when server read message from TCP/UDP connection: server.serveUDP , server.serverTCPconnnection - (for tcp it is immediately after parse coap header)
• and it must be dynamically check in blockwise via blockWiseReceiver

[arun1587]

thanks for the clarification.
peerMaxMessageSize if not set in the CSM of peer defaults to 1152, right ?

(whole message that is send via blockwise)

I think the limit is for each block and not for whole message as explained in this section of RFC8323, no ?

[jkralik]

If peerMaxMessageSize is not, then peer doesn't limit a message.

You are right. It' s only limit each block.

Hm but i want to somehow limit whole message, because peer can exhaust memory of the server/client.

[jkralik]

MaxMessageSize was implemented by #42