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turncat: Swiss-army-knife testing tool for STUNner

turncat is a STUN/TURN client to open a connection through a TURN server to an arbitrary remote address/port. The main use is to open a local tunnel endpoint to any service running inside a Kubernetes cluster via STUNner. This is very similar in functionality to kubectl port-forward, but it uses STUN/TURN to enter the cluster. This is much faster than the TCP connection used by kubectl.

Installation

Install the turncat binary using the standard Go toolchain and add it to $PATH.

go install github.com/l7mp/stunner/cmd/turncat@latest

You can also enforce a specific OS, CPU architecture, and STUNner version like below:

GOOS=windows GOARCH=amd64 go install github.com/l7mp/stunner/cmd/[email protected]

Building from source is as easy as it usually gets with Go:

cd stunner
go build -o turncat cmd/turncat/main.go

Usage

Listen to client connections on the UDP listener 127.0.0.1:5000 and tunnel the received packets through the TURN server located at 192.0.2.1:3478 to the UDP listener located at 192.0.2.2:53. Use the static STUN/TURN credential mechanism to authenticate with the TURN server and set the user/passwd to test/test:

./turncat --log=all:INFO,turncat:DEBUG udp://127.0.0.1:5000 turn://test:[email protected]:3478 \
    udp://192.0.2.2:53

TLS/DTLS should also work. Below --insecure allows turncat to accept self-signed TLS certificates and --verbose is equivalent to setting all loggers to DEBUG mode (-l all:DEBUG).

./turncat --verbose --insecure udp://127.0.0.1:5000 \
    turn://test:[email protected]:3478?transport=tls udp://192.0.2.2:53

Alternatively, you can specify the special TURN server meta-URI k8s://stunner/udp-gateway:udp-listener to let turncat parse the running STUNner configuration from the active Kubernetes cluster. The URI directs turncat to read the config of the STUNner Gateway called udp-gateway in the stunner namespace and connect to the TURN listener named udp-listener. The CLI flag - instructs turncat to listen on the standard input: anything you type in the terminal will be sent via STUNner to the peer udp://10.0.0.1:9001 (after you press Enter). The CLI flag -v will enable verbose logging.

./turncat -v - k8s://stunner/udp-gateway:udp-listener udp://10.0.0.1:9001

Note that the standard kubectl command line flags are available. For instance, the below will use the context prod-europe from the kubeconfig file kube-prod.conf:

./turncat --kubeconfig=kube-prod.conf --context prod-europe -v - k8s://... udp://...

License

Copyright 2021-2023 by its authors. Some rights reserved. See AUTHORS.

MIT License - see LICENSE for full text.

Acknowledgments

Initial code adopted from pion/stun and pion/turn.