Add port checking functionality and tests

pkg/connection/port.go

@@ -0,0 +1,33 @@
+package connection
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+)
+
+// Check if the TCP port available on localhost
+func portAvailable(port int) bool {
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%v", port))
+
+	if err != nil {
+		if strings.Index(err.Error(), "connection refused") > 0 {
+			return true
+		}
+		return false
+	}
+
+	conn.Close()
+	return false
+}
+
+// Get available TCP port on localhost by trying available ports in a range
+func getAvailablePort(start int, limit int) (int, error) {
+	for i := start; i <= (start + limit); i++ {
+		if portAvailable(i) {
+			return i, nil
+		}
+	}
+	return -1, errors.New("No available port")
+}

pkg/connection/port_test.go

@@ -0,0 +1,65 @@
+package connection
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_portAvailable(t *testing.T) {
+	assert.Equal(t, true, portAvailable(8081))
+
+	serv, err := net.Listen("tcp", "127.0.0.1:8081")
+	if err != nil {
+		fmt.Println(os.Stderr, "Unable to start test tcp listener:", err)
+		t.Fail()
+		return
+	}
+	defer serv.Close()
+
+	go func() {
+		for {
+			conn, err := serv.Accept()
+			if err == nil {
+				conn.Close()
+			}
+		}
+	}()
+
+	assert.Equal(t, false, portAvailable(8081))
+	assert.Equal(t, true, portAvailable(8082))
+}
+
+func Test_getAvailablePort(t *testing.T) {
+	port, err := getAvailablePort(8081, 1)
+	assert.Equal(t, nil, err)
+	assert.Equal(t, 8081, port)
+
+	serv, err := net.Listen("tcp", "127.0.0.1:8081")
+	if err != nil {
+		fmt.Println(os.Stderr, "Unable to start test tcp listener:", err)
+		t.Fail()
+		return
+	}
+	defer serv.Close()
+
+	go func() {
+		for {
+			conn, err := serv.Accept()
+			if err == nil {
+				conn.Close()
+			}
+		}
+	}()
+
+	port, err = getAvailablePort(8081, 0)
+	assert.EqualError(t, err, "No available port")
+	assert.Equal(t, -1, port)
+
+	port, err = getAvailablePort(8081, 1)
+	assert.Equal(t, nil, err)
+	assert.Equal(t, 8082, port)
+}