Validate port-forwards by attempting to bind to port

[briandealwis]

Skaffold's port-forwarding now attempts a GET on forwarded-ports to verify that the port-forward was successful, but this breaks JVM debugging (non-HTTP based) and causes spurious log messages. (It also introduces latency when dealing with remote clusters.)

This patch changes the port-forwarding validation check to attempt to bind to the port instead, which is expected to fail.

$ cd examples/jib; ../../cmd/skaffold/skaffold debug --port-forward
...
Forwarding container web-586567d484-j6st9/web to local port 5006.
Port Forwarding pod/web-586567d484-j6st9 5005 -> 5006
[web-586567d484-j6st9 web] Debugger failed to attach: handshake failed - received >GET / HTTP/1.1< - expected >JDWP-Handshake<
[web-586567d484-j6st9 web] Debugger failed to attach: handshake failed - received >GET / HTTP/1.1< - expected >JDWP-Handshake<
[...repeated...]

[priyawadhwa]

Looks like a linting error

Gofmt errors in files:
./pkg/skaffold/kubernetes/portforward/kubectl_forwarder.go
diff -u ./pkg/skaffold/kubernetes/portforward/kubectl_forwarder.go.orig ./pkg/skaffold/kubernetes/portforward/kubectl_forwarder.go
--- ./pkg/skaffold/kubernetes/portforward/kubectl_forwarder.go.orig	2019-06-26 14:26:36.391552089 +0000
+++ ./pkg/skaffold/kubernetes/portforward/kubectl_forwarder.go	2019-06-26 14:26:36.391552089 +0000
@@ -63,7 +63,7 @@
 	// creating a listening port should not succeed
 	if ln, err := net.Listen("tcp", fmt.Sprintf("%s:%d", util.Loopback, port)); err == nil {
 		ln.Close()
-		return errors.New("port-forward failed") 
+		return errors.New("port-forward failed")
 	}
 	return nil
 }
FAILED hack/gofmt.sh

[codecov]

Codecov Report

Merging #2345 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

Impacted Files	Coverage Δ
...affold/kubernetes/portforward/kubectl_forwarder.go	0% <0%> (ø)	⬆️