panic: unknown uid 32 (protocol error)

[lupine]

I've just started using Mox in earnest (thanks the work on it!) and noticed this in the logs:

Aug 28 14:40:14 ur.gs mox[57874]: l=info m="imap command ioerror" err="unknown uid 32 (protocol error)" pkg=imapserver cmd="uid fetch" duration="338.651µs" cid=198f0b40cf6 delta=11m42.04356248s username=me@ur.gs
Aug 28 14:40:14 ur.gs mox[57874]: goroutine 1075 [running]:
Aug 28 14:40:14 ur.gs mox[57874]: runtime/debug.Stack()
Aug 28 14:40:14 ur.gs mox[57874]:         /usr/lib/go/src/runtime/debug/stack.go:26 +0x5e
Aug 28 14:40:14 ur.gs mox[57874]: runtime/debug.PrintStack()
Aug 28 14:40:14 ur.gs mox[57874]:         /usr/lib/go/src/runtime/debug/stack.go:18 +0x13
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).command.func1()
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:1239 +0xe67
Aug 28 14:40:14 ur.gs mox[57874]: panic({0x119c940?, 0xc000b3e0a0?})
Aug 28 14:40:14 ur.gs mox[57874]:         /usr/lib/go/src/runtime/panic.go:792 +0x132
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.xserverErrorf(...)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/error.go:36
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).xsequence(0x0?, 0x14d9e20?)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:1475 +0x114
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).xapplyChanges(0xc000c95500, 0xa5?, {0xc000846180?, 0x4769a5?, 0x10?}, 0x0?)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:1910 +0x1da5
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).xbwriteresultf(0xc000c95500, {0x1297d86, 0xd}, {0xc000c5f270, 0x2, 0x2})
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:688 +0xf8
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).ok(0xc000c95500, {0xc000c33680?, 0x0?}, {0xc000c33686, 0x9})
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:1740 +0x9c
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).cmdxFetch(0xc000c95500, 0x1, {0xc000c33680, 0x5}, {0xc000c33686, 0x9}, 0xc0010051a0)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/fetch.go:372 +0xc3f
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).cmdUIDFetch(0x1146fe0?, {0xc000c33680?, 0xc001281130?}, {0xc000c33686?, 0x4?}, 0xc000e120c0?)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:4588 +0x31
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.(*conn).command(0xc000c95500)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:1375 +0x409
Aug 28 14:40:14 ur.gs mox[57874]: github.com/mjl-/mox/imapserver.serve({0xc000818a91, 0x6}, 0x198f0b40cf6, 0xc0004bf0e0, {0x14dfaf0, 0xc0000baa38}, 0x1, 0x0, 0x0, 0x0, ...)
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:938 +0x16cf
Aug 28 14:40:14 ur.gs mox[57874]: created by github.com/mjl-/mox/imapserver.listen1.func1 in goroutine 185
Aug 28 14:40:14 ur.gs mox[57874]:         /home/lupine/dev/github.com/mjl-/mox/imapserver/server.go:445 +0x2ec
Aug 28 14:40:14 ur.gs mox[57874]: l=info m="connection closed" err="unknown uid 32 (protocol error)" pkg=imapserver cid=198f0b40cf6 delta="343.32µs" username=me@ur.gs

I think it was caused by looking around folders in K-9 Mail, but can't swear to it. I've migrated between server software today, so it's possible K-9 had cached old values for uids or something from Dovecot (as far as it's concerned, it was the same account and it was just making new connections). An unusual situation, but panicking on bad client requests seems undesirable?