relation-get with invalid relation name panics agent

[Stuart Bishop]

In debug-hooks, I typed 'relation-get - db' instead of 'relation-get - db/0', and crashed the agent.

panic: "db" is not a valid unit name

goroutine 2613 [running]:
runtime.panic(0xc1d0e0, 0xc2101fda30)
 /usr/lib/go/src/pkg/runtime/panic.c:266 +0xb6
github.com/juju/names.NewUnitTag(0xc2102adcc8, 0x2, 0xc2101fda10, 0xc)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/names/unit.go:30 +0x28f
github.com/juju/juju/state/api/uniter.(*RelationUnit).ReadSettings(0xc210114300, 0xc2102adcc8, 0x2, 0x2, 0x118f6c0, ...)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/juju/state/api/uniter/relationunit.go:138 +0x42
github.com/juju/juju/worker/uniter.(*ContextRelation).ReadSettings(0xc210113d80, 0xc2102adcc8, 0x2, 0xc210113d80, 0x0, ...)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/juju/worker/uniter/context.go:433 +0xdc
github.com/juju/juju/worker/uniter/jujuc.(*RelationGetCommand).Run(0xc2101a5870, 0xc2101a58c0, 0xc2101a58c0, 0x0)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/juju/worker/uniter/jujuc/relation-get.go:90 +0x2d2
github.com/juju/cmd.Main(0x7fa7bd5c2008, 0xc2101a5870, 0xc2101a58c0, 0xc210216f80, 0x2, ...)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/cmd/cmd.go:247 +0x283
github.com/juju/juju/worker/uniter/jujuc.(*Jujuc).Main(0xc21038b700, 0xc210207180, 0x34, 0xc210201c60, 0x2c, ...)
 /build/buildd/juju-core-1.20.6/src/github.com/juju/juju/worker/uniter/jujuc/server.go:104 +0x5fd
reflect.Value.call(0xd4f6a0, 0xd84430, 0x130, 0xf31990, 0x4, ...)
 /usr/lib/go/src/pkg/reflect/value.go:474 +0xe0b
reflect.Value.Call(0xd4f6a0, 0xd84430, 0x130, 0x7fa7b83d6ee8, 0x3, ...)
 /usr/lib/go/src/pkg/reflect/value.go:345 +0x9d
net/rpc.(*service).call(0xc2102afcc0, 0xc2102afc80, 0xc2102ad8a8, 0xc2101ac000, 0xc21021f880, ...)
 /usr/lib/go/src/pkg/net/rpc/server.go:381 +0x159
created by net/rpc.(*Server).ServeCodec
 /usr/lib/go/src/pkg/net/rpc/server.go:452 +0x3bb

[Stuart Bishop (stub)]

Full panic at http://pastebin.ubuntu.com/8231715/ in case it is needed. Flagged CRITICAL per jam's opinion.

[John A Meinel (jameinel)]

I'm targetting 1.20 since Stub said that is what he was using.
Essentially, bad input to the system (typo in a relation-get request) should not be able to crash the API server.

[John A Meinel (jameinel)]

The comment from Dave Cheney was that the code should be using ParseUnitTag rather than NewUnitTag, I haven't dug into the code at all.

[Ian Booth (wallyworld)]

1.20.7 is in the process of being released so moving to 1.20.8 milestone

[Dave Cheney (dave-cheney)]

https://github.com/juju/juju/pull/677