add `isValidPORTEnvVar` function to judge the environment variable PORT whether is valid

utils.go

@@ -11,6 +11,7 @@ import (
 	"path"
 	"reflect"
 	"runtime"
+	"strconv"
 	"strings"
 )
 
@@ -138,10 +139,12 @@ func resolveAddress(addr []string) string {
 	switch len(addr) {
 	case 0:
 		if port := os.Getenv("PORT"); port != "" {
-			debugPrint("Environment variable PORT=\"%s\"", port)
-			return ":" + port
+			if isValidPORTEnvVar(port) {
+				debugPrint("Environment variable PORT=\"%s\"", port)
+				return ":" + port
+			}
 		}
-		debugPrint("Environment variable PORT is undefined. Using port :8080 by default")
+		debugPrint("Environment variable PORT is undefined or invalid. Using port :8080 by default")
 		return ":8080"
 	case 1:
 		return addr[0]
@@ -149,3 +152,10 @@ func resolveAddress(addr []string) string {
 		panic("too many parameters")
 	}
 }
+
+// Determine the PORT environment variable whether is valid。
+// If the PORT can be parsed to uint(0-65535)，return true。
+func isValidPORTEnvVar(portString string) bool {
+	_, err := strconv.ParseUint(portString, 10, 16)
+	return err == nil
+}

utils_test.go

@@ -137,3 +137,18 @@ func TestMarshalXMLforH(t *testing.T) {
 	e := h.MarshalXML(enc, x)
 	assert.Error(t, e)
 }
+
+func TestIsValidPPORTEnvVar(t *testing.T) {
+	assert.Equal(t, false, isValidPORTEnvVar("abc"))
+	assert.Equal(t, false, isValidPORTEnvVar("-1"))
+	assert.Equal(t, false, isValidPORTEnvVar("-100"))
+	assert.Equal(t, true, isValidPORTEnvVar("1"))
+	assert.Equal(t, true, isValidPORTEnvVar("1000"))
+	assert.Equal(t, true, isValidPORTEnvVar("10000"))
+	assert.Equal(t, false, isValidPORTEnvVar(" 10000"))
+	assert.Equal(t, false, isValidPORTEnvVar("10000 "))
+	assert.Equal(t, false, isValidPORTEnvVar("10000."))
+	assert.Equal(t, true, isValidPORTEnvVar("65535"))
+	assert.Equal(t, false, isValidPORTEnvVar("65536"))
+	assert.Equal(t, false, isValidPORTEnvVar("655360"))
+}