Add fudge factor in subscription sharding

Header lengths are not constant-size because Zcode escapes bytes 0xFF and 0x00
into two bytes. If we end up filling up close to all the space we have and
Z_SendFragmentedNotice then computes a header length larger than ours by
enough, the message gets fragmented.

Getting it fragmented is especially unfortunate because only the first of a
fragmented notice ever has a SERVACK survive. (They all get SERVACKs, but
libzephyr kindly drops all but the first on the floor.)

This isn't a watertight fix; we may get really really unlucky and blow up 13
bytes in the authenticator and checksum. But that's not likely, and a proper
fix would involve either computing based on the maximum possible authenticator
size (wasteful and hard to bound tightly) or changing to protocol to use a less
inappropriate encoding.

0 files changed, 0 insertions, 0 deletions