"panic: connection already exists" when running example client

[stevenmcdonald]

I'm seeing a panic when I run the example client in cmd/client:

❯ ./client -t "https://mdev.scm.codes:443/{target_host}/{target_port}/" https://ietf.org
2025/01/21 12:18:12 dialed connection: [::]:52959 <-> 104.16.44.99:443
2025/01/21 12:18:12 connection doesn't allow setting of receive buffer size. Not a *net.UDPConn?. See https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes for details.
2025/01/21 12:18:12 dialed connection: [::]:52959 <-> 104.16.44.99:443
panic: connection already exists

goroutine 65 [running]:
github.com/quic-go/quic-go.(*connMultiplexer).AddConn(0x14000140300, {0x101400e10?, 0x1400030a300?})
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/multiplexer.go:59 +0x194
github.com/quic-go/quic-go.(*Transport).init.func1()
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/transport.go:266 +0x3b0
sync.(*Once).doSlow(0x14000325d28?, 0x100a3c1fc?)
	/usr/local/go/src/sync/once.go:76 +0xf8
sync.(*Once).Do(...)
	/usr/local/go/src/sync/once.go:67
github.com/quic-go/quic-go.(*Transport).init(0x14000344100, 0x0?)
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/transport.go:225 +0x50
github.com/quic-go/quic-go.(*Transport).dial(0x14000344100, {0x100e46ae0, 0x1400032c190}, {0x100e44cc0, 0x14000308690}, {0x0, 0x0}, 0x14000312540, 0x1400034c2d0, 0x1)
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/transport.go:212 +0x70
github.com/quic-go/quic-go.(*Transport).DialEarly(...)
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/transport.go:204
github.com/quic-go/quic-go.DialEarly({0x100e46ae0, 0x1400032c190}, {0x100e48780?, 0x1400030a300?}, {0x100e44cc0, 0x14000308690}, 0x14000312540, 0x1400034c2d0)
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/client.go:95 +0xf8
main.main.func1({0x100e46ae0, 0x1400032c190}, {0x140000677a8?, 0x100cdae9c?}, 0x14000312540, 0x1400015a3f0)
	/Users/scm/code/masque-go/cmd/client/main.go:61 +0x240
github.com/quic-go/quic-go/http3.(*Transport).dial(0x1400015a240, {0x100e46ae0, 0x1400032c190}, {0x1400031e1f0, 0x10})
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/http3/transport.go:324 +0x220
github.com/quic-go/quic-go/http3.(*Transport).getClient.func1()
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/http3/transport.go:261 +0x78
created by github.com/quic-go/quic-go/http3.(*Transport).getClient in goroutine 1
	/Users/scm/go/pkg/mod/github.com/quic-go/[email protected]/http3/transport.go:258 +0x268

The MASQUE proxy, mdev.scm.codes is a VM running h2o as the server. Is there some more info I can provide? Am I doing something wrong? Thanks for any help you can provide

[marten-seemann]

How do you set up your code? This is worrying as well:

2025/01/21 12:18:12 connection doesn't allow setting of receive buffer size. Not a *net.UDPConn?. See https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes for details.