`panic: lost connection to pod` after forwarding is closed

[kormachevt]

Hi !
I have the following question/issue: go panics panic: lost connection to pod even after port-forwards were closed.

github.com/anthhub/forwarder v1.1.0

Here is simplified code I use. The main function actually is executed in Go routine (it is some e2e tests running in k8s)

package main

import (
	"context"
	"fmt"
	"time"

	"github.com/anthhub/forwarder"
)

func PortForward(options []*forwarder.Option, config string) (*forwarder.Result, error) {
	ret, err := forwarder.WithForwarders(context.Background(), options, config)
	if err != nil {
		fmt.Printf("Error occurred while configuring port-forwarding with config (%s) and options %v", config, &options)
		ret.Close()
		return nil, err
	}

	ports, err := ret.Ready()
	if err != nil {
		fmt.Printf("Errror occurred while waiting for port-forwarding to be ready with config (%s) and options %v", config, options)
		ret.Close()
		return nil, err
	}
	fmt.Printf("Port-forwarding established with ports: %+v\n", ports)
	fmt.Printf("Make sure to close forwarding via Close()")

	return ret, nil
}

func main() {
	const httpsPort int = 443
	const certRenewalTimeoutSeconds = 120
	localPortForwardPort := 26842
	kubeConfig := "~/.kube/config"
	type test struct {
		Namespace  string
		Source     string
		RemotePort int
	}
	tests := []test{
		{
			Namespace:  "default",
			Source:     "svc/my-service-1",
			RemotePort: 8000,
		},
		{
			Namespace:  "default",
			Source:     "svc/my-service-2",
			RemotePort: 8443,
		},
	}

	for _, test := range tests {
		var portForward *forwarder.Result
		portForwardOptions := []*forwarder.Option{
			{
				LocalPort:  localPortForwardPort,
				RemotePort: test.RemotePort,
				Source:     test.Source,
				Namespace:  test.Namespace,
			},
		}

		portForward, err := PortForward(portForwardOptions, kubeConfig)
		if err != nil {
			fmt.Println(err)
		}
		portForwardOpenedAt := time.Now().Unix()
		fmt.Printf("Portforward opened to %d at %d", localPortForwardPort, portForwardOpenedAt)

		close := func(rst *forwarder.Result, port int, timestamp int64) {
			fmt.Printf("Closing portforward %v on port %d opened at %d", rst, port, timestamp)
			rst.Close()
		}
		defer close(portForward, localPortForwardPort, portForwardOpenedAt)
		// do some tests here, this code returns some value
		localPortForwardPort++
		fmt.Printf("Port incremented. Next port-forwarding will be opened at %d. They all will be closed on return from this func", localPortForwardPort)
	}

}

It all works great, in logs after this particular test is concluded I see

2024/06/19 10:30:42 Closing portforward &{0x1041d7c30 0x1041d7ab0 0x1041d79c0} on port 26843 opened at 1718782197
2024/06/19 10:30:42 Closing portforward &{0x1041d7c30 0x1041d7ab0 0x1041d79c0} on port 26842 opened at 1718782153

However down the road, long after all ports were supposedly closed, in the next tests Go panics with

panic: lost connection to pod
goroutine 3903 [running]:
github.com/anthhub/forwarder.portForwardAPod.func1()
	/vendor/github.com/anthhub/forwarder/forwarder.go:164 +0x2d
created by github.com/anthhub/forwarder.portForwardAPod in goroutine 3902
	/vendor/github.com/anthhub/forwarder/forwarder.go:162 +0x419

In my initial implementation I was calling Close() on each iteration manually (not through defer), but on the second iteration port from the first one was still in use somehow, so I resorted to use separate port in each iteration. Now I tried with defer and ports are closed on return (as they should) , but still this issue persists.

Any thoughts will be appreciated.

[kormachevt]

I've added some logs to my vendored package version and observed, that only the first call to "Close()" is handled.
Looks like module level var once sync.Once prevents subsequent calls, even though new port-forward instances are created (and they all run successfully).

As a workaround I've moved it to to the top of forwarders func, then all my port-forward were successfully closed on defer.

This is probably just a hack, but works for me for now.

[aslafy-z]

This fix looks fine to me. There should be one call to close by forwarders call.