judge the environment variable PORT whether is valid

utils.go

@@ -11,6 +11,7 @@ import (
 	"path"
 	"reflect"
 	"runtime"
+	"strconv"
 	"strings"
 )
 
@@ -149,3 +150,10 @@ func resolveAddress(addr []string) string {
 		panic("too many parameters")
 	}
 }
+
+// Determine whether the PORT environment variable is valid。
+// If the PORT can be parsed to int(0-65535)，return true。
+func isValidPortEnvVar(portString string) bool {
+	_, err := strconv.ParseUint(portString, 10, 16)
+	return err == nil
+}

utils_test.go

@@ -137,3 +137,14 @@ func TestMarshalXMLforH(t *testing.T) {
 	e := h.MarshalXML(enc, x)
 	assert.Error(t, e)
 }
+
+func TestIsValidPortEnvVar(t *testing.T) {
+	assert.Equal(t, false, isValidPortEnvVar("abc"))
+	assert.Equal(t, false, isValidPortEnvVar("-1"))
+	assert.Equal(t, true, isValidPortEnvVar("1"))
+	assert.Equal(t, true, isValidPortEnvVar("1000"))
+	assert.Equal(t, true, isValidPortEnvVar("10000"))
+	assert.Equal(t, true, isValidPortEnvVar("65535"))
+	assert.Equal(t, false, isValidPortEnvVar("65536"))
+	assert.Equal(t, false, isValidPortEnvVar("655360"))
+}