Add WS ProxyPath option

[ido-gold-apolicy]

This is a PR to fix the issue described here: #859

[coveralls]

Coverage increased (+0.03%) to 83.92% when pulling 4f94f48 on draios:ws-proxy-path-option into 4b259ed on nats-io:main.

[kozlovic]

Thank you for the contribution. I would make some changes to the test.

[kozlovic]

Instead of commenting line by line, I feel it is easier to show you how I would like the test to look like. The main difference with yours is that we are going to check with a prefix "/" and without, and use a go channel to check that the proxy was invoked. (note that you don't need to run the NATS Server since the connection is actually not happening)

        const proxyPath = "proxy1"

	// Listen to a random port
	l, err := net.Listen("tcp", ":0")
	if err != nil {
		t.Fatalf("Error in listen: %v", err)
	}
	defer l.Close()

	proxyPort := l.Addr().(*net.TCPAddr).Port

	ch := make(chan struct{}, 1)
	proxySrv := &http.Server{
		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if r.URL.Path == "/"+proxyPath {
				ch <- struct{}{}
			}
		}),
	}
	defer proxySrv.Shutdown(context.Background())
	go proxySrv.Serve(l)

	for _, test := range []struct {
		name string
		path string
	}{
		{"without slash", proxyPath},
		{"with slash", "/" + proxyPath},
	} {
		t.Run(test.name, func(t *testing.T) {
			url := fmt.Sprintf("ws://127.0.0.1:%d", proxyPort)
			nc, err := Connect(url, ProxyPath(test.path))
			if err == nil {
				nc.Close()
				t.Fatal("Did not expect to connect")
			}
			select {
			case <-ch:
				// OK:
			case <-time.After(time.Second):
				t.Fatal("Proxy was not reached")
			}
		})
	}

[ido-gold-apolicy]

Thanks for your great feedback.
Done.

[kozlovic]

LGTM. Thank you for your contribution!