Util to test if all ptr fields are nil

pkg/util/util.go

@@ -20,6 +20,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"reflect"
 	"regexp"
 	"runtime"
 	"strconv"
@@ -149,3 +150,28 @@ func ApplyOomScoreAdj(value int) error {
 
 	return nil
 }
+
+// Tests whether all pointer fields in a struct are nil.  This is useful when,
+// for example, an API struct is handled by plugins which need to distinguish
+// "no plugin accepted this spec" from "this spec is empty".
+//
+// This function is only valid for structs and pointers to structs.  Any other
+// type will cause a panic.  Passing a typed nil pointer will return true.
+func AllPtrFieldsNil(obj interface{}) bool {
+	v := reflect.ValueOf(obj)
+	if !v.IsValid() {
+		panic(fmt.Sprintf("reflect.ValueOf() produced a non-valid Value for %#v", obj))
+	}
+	if v.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			return true
+		}
+		v = v.Elem()
+	}
+	for i := 0; i < v.NumField(); i++ {
+		if v.Field(i).Kind() == reflect.Ptr && !v.Field(i).IsNil() {
+			return false
+		}
+	}
+	return true
+}

pkg/util/util_test.go

@@ -218,3 +218,48 @@ func TestCompileRegex(t *testing.T) {
 		t.Errorf("Wrong regex returned: '%v': %v", uncompiledRegexes[1], regexes[1])
 	}
 }
+
+func TestAllPtrFieldsNil(t *testing.T) {
+	testCases := []struct {
+		obj      interface{}
+		expected bool
+	}{
+		{struct{}{}, true},
+		{struct{ Foo int }{12345}, true},
+		{&struct{ Foo int }{12345}, true},
+		{struct{ Foo *int }{nil}, true},
+		{&struct{ Foo *int }{nil}, true},
+		{struct {
+			Foo int
+			Bar *int
+		}{12345, nil}, true},
+		{&struct {
+			Foo int
+			Bar *int
+		}{12345, nil}, true},
+		{struct {
+			Foo *int
+			Bar *int
+		}{nil, nil}, true},
+		{&struct {
+			Foo *int
+			Bar *int
+		}{nil, nil}, true},
+		{struct{ Foo *int }{new(int)}, false},
+		{&struct{ Foo *int }{new(int)}, false},
+		{struct {
+			Foo *int
+			Bar *int
+		}{nil, new(int)}, false},
+		{&struct {
+			Foo *int
+			Bar *int
+		}{nil, new(int)}, false},
+		{(*struct{})(nil), true},
+	}
+	for i, tc := range testCases {
+		if AllPtrFieldsNil(tc.obj) != tc.expected {
+			t.Errorf("case[%d]: expected %t, got %t", i, tc.expected, !tc.expected)
+		}
+	}
+}