Merge branch '9-add-helpers-to-get-free-tcp-port-and-wait-for-listener' into 'master'

Resolve "add helpers to get free tcp port and wait for listener"

Closes #9

See merge request slon/shad-go-private!7

tools/testtool/freeport.go

@@ -0,0 +1,62 @@
+package testtool
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+	"time"
+)
+
+// GetFreePort returns free local tcp port.
+func GetFreePort() (string, error) {
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	if err != nil {
+		return "", err
+	}
+
+	l, err := net.ListenTCP("tcp", addr)
+	if err != nil {
+		return "", err
+	}
+	defer func() { _ = l.Close() }()
+
+	p := l.Addr().(*net.TCPAddr).Port
+
+	return strconv.Itoa(p), nil
+}
+
+type logger interface {
+	Logf(format string, args ...interface{})
+}
+
+// WaitForPort tries to connect to given local port with constant backoff.
+//
+// Returns error if port is not ready after timeout.
+func WaitForPort(l logger, timeout time.Duration, port string) error {
+	stopTimer := time.NewTimer(timeout)
+	defer stopTimer.Stop()
+
+	t := time.NewTicker(time.Millisecond * 100)
+	defer t.Stop()
+
+	for {
+		select {
+		case <-stopTimer.C:
+			return fmt.Errorf("no server started listening on port %s after timeout %s", port, timeout)
+		case <-t.C:
+			if err := portIsReady(port); err != nil {
+				l.Logf("waiting for port: %s\n", err)
+				break
+			}
+			return nil
+		}
+	}
+}
+
+func portIsReady(port string) error {
+	conn, err := net.Dial("tcp", net.JoinHostPort("localhost", port))
+	if err != nil {
+		return err
+	}
+	return conn.Close()
+}

tools/testtool/freeport_test.go

@@ -0,0 +1,39 @@
+package testtool
+
+import (
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetFreePort(t *testing.T) {
+	p, err := GetFreePort()
+	require.NoError(t, err)
+	require.NotEmpty(t, p)
+}
+
+func TestWaitForPort(t *testing.T) {
+	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	defer s.Close()
+
+	u, err := url.Parse(s.URL)
+	require.Nil(t, err)
+	_, port, err := net.SplitHostPort(u.Host)
+	require.Nil(t, err)
+
+	require.NoError(t, WaitForPort(t, time.Second, port))
+}
+
+func TestWaitForPort_timeout(t *testing.T) {
+	p, err := GetFreePort()
+	require.NoError(t, err)
+
+	err = WaitForPort(t, time.Second, p)
+	require.Error(t, err)
+	t.Log(err.Error())
+}