(*Transport.)close: nil pointer dereference of handlerMap

[kelmenhorst]

Hi,
I noticed that in some cases, (*Transport.)close causes a nil pointer dereference due to (Transport.)handlerMap being uninitialized.

Minimal example to reproduce when using DialEarly:

addr, _ := net.ResolveUDPAddr("udp", "google.com:443")
conn, _ := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 0, Zone: ""})
var invalidVersion quic.VersionNumber = 0x3      // <-- there is no v3, so validateConfig will fail
qconf := &quic.Config{
	Versions: []quic.VersionNumber{
		invalidVersion,
	},
}
quic.DialEarly(context.Background(), conn, addr, <*tls.Config>, qconf)

I get the following output:

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x30 pc=0x837680]

goroutine 18 [running]:
testing.tRunner.func1.2({0xa96480, 0xffe130})
	/usr/local/go/src/testing/testing.go:1526 +0x24e
testing.tRunner.func1()
	/usr/local/go/src/testing/testing.go:1529 +0x39f
panic({0xa96480, 0xffe130})
	/usr/local/go/src/runtime/panic.go:884 +0x213
github.com/quic-go/quic-go.(*Transport).close(0xc0003c41c0, {0xc6d140, 0xc0003943d0})
	/home/kelmenhorst/go/pkg/mod/github.com/quic-go/quic-go@v0.35.1/transport.go:270 +0x100
github.com/quic-go/quic-go.(*Transport).Close(0xc0003c41c0)
	/home/kelmenhorst/go/pkg/mod/github.com/quic-go/quic-go@v0.35.1/transport.go:232 +0x6b
github.com/quic-go/quic-go.DialEarly({0xc73a70, 0xc00003e0b8}, {0xc76620?, 0xc0003960a0?}, {0xc71358, 0xc000392a80}, 0xc0003c0300, 0x55cff4?)
	/home/kelmenhorst/go/pkg/mod/github.com/quic-go/quic-go@v0.35.1/client.go:97 +0x190

Am I missing something here?
If not, I suggest to add a check in (*Transport.)close before trying to close the t.handlerMap.

Edit: Similarly (*Transport.)Close assumes t.conn and t.listening to be initialized which is not always the case (again referring to the example code above).

[marten-seemann]

Sounds reasonable. Want to submit a patch?