diff options
| author |  David Benjamin <davidben@mit.edu> | 2013-07-14 13:23:11 -0400 |
|---|---|---|
| committer |  Karl Ramm <kcr@1ts.org> | 2013-08-08 00:24:58 -0400 |
| commit | b9ec2cdc23b77fd86b69ba884c5513f3f71cf025 (patch) | |
| tree | c032cb5663a00ead030dec9e48ddb790a328dd7b /lib | |
| parent | 4ebc7e98991e3aea45e950fa5485ddf3157d39bb (diff) | |
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.
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/ZSubs.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/lib/ZSubs.c b/lib/ZSubs.c index a3d0b78..e0d39ee 100644 --- a/lib/ZSubs.c +++ b/lib/ZSubs.c @@ -85,8 +85,11 @@ ZSubscriptions(register ZSubscription_t *sublist, char **list; char *recip; int hdrlen; - int size_avail = Z_MAXPKTLEN-Z_FRAGFUDGE; /* space avail for data, - adjusted below */ + /* Space available for data, adjusted below. Take off Z_FRAGFUDGE twice. + The first is to account for Z_SendFragmentedNotice's space. The second + to account for hdrlen not being constant. Zcode escapes bytes 0x00 and + 0xFF, so some bytes are encoded as two bytes. */ + int size_avail = Z_MAXPKTLEN-Z_FRAGFUDGE-Z_FRAGFUDGE; int size, start, numok; /* nitems = 0 means cancel all subscriptions; still need to allocate a */ |