Panic on no supported client-requested "namedCurves"

[RyanGordon]

Your environment.

• Version: 1.5.0
• Browser: Node.JS @nodertc/dtls library
• Other Information:

panic: runtime error: index out of range

goroutine 266 [running]:
github.com/pion/dtls.serverHandshakeHandler.func1(0xc0000cc360, 0x52, 0x60, 0x1, 0xc0000c4050)
	/go/pkg/mod/github.com/pion/dtls@v1.5.0/server_handlers.go:38 +0x13cd
github.com/pion/dtls.serverHandshakeHandler(0xc0000ec500, 0x1c9eed8, 0xc0000ec500)
	/go/pkg/mod/github.com/pion/dtls@v1.5.0/server_handlers.go:163 +0x5af
github.com/pion/dtls.(*Conn).handleIncomingPacket(0xc0000ec500, 0xc000128000, 0x5f, 0x2000, 0x0, 0x0)
	/go/pkg/mod/github.com/pion/dtls@v1.5.0/conn.go:417 +0x4bc
github.com/pion/dtls.(*Conn).inboundLoop(0xc0000ec500)
	/go/pkg/mod/github.com/pion/dtls@v1.5.0/conn.go:360 +0x1bb
created by github.com/pion/dtls.createConn
	/go/pkg/mod/github.com/pion/dtls@v1.5.0/conn.go:170 +0x600

What did you do?

1. Started a pion/dtls listen server.
2. Using openssl 1.0.2s client:
   openssl s_client -dtls1_2 -connect 127.0.0.1:4444 -debug -cipher ECDHE-ECDSA-AES128-GCM-SHA256 -curves secp384r1

What did you expect?

Connection closes gracefully, rather than a panic

What happened?

The application panic'ed and crashed.

The offending line is here: 6dec1ec#diff-84f73d0d6a8b3cb71ba4ae9da4d57470R51

This assumes the client provides at least one supported Elliptic Curve, but in some cases the server may not support any of Elliptic Curve's that the client is requesting be used.

[Sean-Der]

Nice find!

You interested in fixing @RyanGordon? That would be an awesome first issue! If there is anything I can do to help please tell me.

If you don't have the time/aren't allowed I can grab instead!

[RyanGordon]

Yes, I will gladly put up a PR tomorrow