Change:
<del> /* Copyright 2015 The Kubernetes Authors. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. */ package unstructured import ( "fmt" "reflect" "testing" "k8s.io/apimachinery/pkg/util/diff" "k8s.io/apimachinery/pkg/util/json" ) // Definte a number of test types. type A struct { A int    `json:"aa,omitempty"` B string `json:"ab,omitempty"` C bool   `json:"ac,omitempty"` } type B struct { A A                 `json:"ba"` B string            `json:"bb"` C map[string]string `json:"bc"` D []string          `json:"bd"` } type C struct { A []A `json:"ca"` B `json:",inline"` C string         `json:"cc"` D *int64         `json:"cd"` E map[string]int `json:"ce"` F []bool         `json:"cf"` G []int          `json:"cg"` H float32        `json:"ch"` I []interface{}  `json:"ci"` } type D struct { A []interface{} `json:"da"` } type E struct { A interface{} `json:"ea"` } type F struct { A string            `json:"fa"` B map[string]string `json:"fb"` C []A               `json:"fc"` D int               `json:"fd"` E float32           `json:"fe"` F []string          `json:"ff"` G []int             `json:"fg"` H []bool            `json:"fh"` I []float32         `json:"fi"` } type G struct { Custom Custom `json:"custom"` } type Custom struct { data []byte } func (c Custom) MarshalJSON() ([]byte, error) { return c.data, nil } func doRoundTrip(t *testing.T, item interface{}) { data, err := json.Marshal(item) if err != nil { t.Errorf("Error when marshaling object: %v", err) return } unstr := make(map[string]interface{}) err = json.Unmarshal(data, &unstr) if err != nil { t.Errorf("Error when unmarshaling to unstructured: %v", err) return } data, err = json.Marshal(unstr) if err != nil { t.Errorf("Error when marshaling unstructured: %v", err) return } unmarshalledObj := reflect.New(reflect.TypeOf(item).Elem()).Interface() err = json.Unmarshal(data, &unmarshalledObj) if err != nil { t.Errorf("Error when unmarshaling to object: %v", err) return } if !reflect.DeepEqual(item, unmarshalledObj) { t.Errorf("Object changed during JSON operations, diff: %v", diff.ObjectReflectDiff(item, unmarshalledObj)) return } newUnstr, err := DefaultConverter.ToUnstructured(item) if err != nil { t.Errorf("ToUnstructured failed: %v", err) return } newObj := reflect.New(reflect.TypeOf(item).Elem()).Interface() err = DefaultConverter.FromUnstructured(newUnstr, newObj) if err != nil { t.Errorf("FromUnstructured failed: %v", err) return } if !reflect.DeepEqual(item, newObj) { t.Errorf("Object changed, diff: %v", diff.ObjectReflectDiff(item, newObj)) } } func TestRoundTrip(t *testing.T) { intVal := int64(42) testCases := []struct { obj interface{} }{ { // This (among others) tests nil map, slice and pointer. obj: &C{ C: "ccc", }, }, { // This (among others) tests empty map and slice. obj: &C{ A: []A{}, C: "ccc", E: map[string]int{}, I: []interface{}{}, }, }, { obj: &C{ A: []A{ { A: 1, B: "11", C: true, }, { A: 2, B: "22", C: false, }, }, B: B{ A: A{ A: 3, B: "33", }, B: "bbb", C: map[string]string{ "k1": "v1", "k2": "v2", }, D: []string{"s1", "s2"}, }, C: "ccc", D: &intVal, E: map[string]int{ "k1": 1, "k2": 2, }, F: []bool{true, false, false}, G: []int{1, 2, 5}, H: 3.3, I: []interface{}{nil, nil, nil}, }, }, { // Test slice of interface{} with empty slices. obj: &D{ A: []interface{}{[]interface{}{}, []interface{}{}}, }, }, { // Test slice of interface{} with different values. obj: &D{ A: []interface{}{3.0, "3.0", nil}, }, }, } for i := range testCases { doRoundTrip(t, testCases[i].obj) if t.Failed() { break } } } // Verifies that: // 1) serialized json -> object // 2) serialized json -> map[string]interface{} -> object // produces the same object. func doUnrecognized(t *testing.T, jsonData string, item interface{}, expectedErr error) { unmarshalledObj := reflect.New(reflect.TypeOf(item).Elem()).Interface() err := json.Unmarshal([]byte(jsonData), &unmarshalledObj) if (err != nil) != (expectedErr != nil) { t.Errorf("Unexpected error when unmarshaling to object: %v, expected: %v", err, expectedErr) return } unstr := make(map[string]interface{}) err = json.Unmarshal([]byte(jsonData), &unstr) if err != nil { t.Errorf("Error when unmarshaling to unstructured: %v", err) return } newObj := reflect.New(reflect.TypeOf(item).Elem()).Interface() err = DefaultConverter.FromUnstructured(unstr, newObj) if (err != nil) != (expectedErr != nil) { t.Errorf("Unexpected error in FromUnstructured: %v, expected: %v", err, expectedErr) } if expectedErr == nil && !reflect.DeepEqual(unmarshalledObj, newObj) { t.Errorf("Object changed, diff: %v", diff.ObjectReflectDiff(unmarshalledObj, newObj)) } } func TestUnrecognized(t *testing.T) { testCases := []struct { data string obj  interface{} err  error }{ { data: "{"da":[3.0,"3.0",null]}", obj:  &D{}, }, { data: "{"ea":[3.0,"3.0",null]}", obj:  &E{}, }, { data: "{"ea":[null,null,null]}", obj:  &E{}, }, { data: "{"ea":[[],[null]]}", obj:  &E{}, }, { data: "{"ea":{"a":[],"b":null}}", obj:  &E{}, }, { data: "{"fa":"fa","fb":{"a":"a"}}", obj:  &F{}, }, { data: "{"fa":"fa","fb":{"a":null}}", obj:  &F{}, }, { data: "{"fc":[null]}", obj:  &F{}, }, { data: "{"fc":[{"aa":123,"ab":"bbb"}]}", obj:  &F{}, }, { // Only unknown fields data: "{"fx":[{"aa":123,"ab":"bbb"}],"fz":123}", obj:  &F{}, }, { data: "{"fc":[{"aa":"aaa","ab":"bbb"}]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type int"), }, { data: "{"fd":123,"fe":3.5}", obj:  &F{}, }, { data: "{"ff":["abc"],"fg":[123],"fh":[true,false]}", obj:  &F{}, }, { // Invalid string data data: "{"fa":123}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type string"), }, { // Invalid string data data: "{"fa":13.5}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type string"), }, { // Invalid string data data: "{"fa":true}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal bool into Go value of type string"), }, { // Invalid []string data data: "{"ff":123}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type []string"), }, { // Invalid []string data data: "{"ff":3.5}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type []string"), }, { // Invalid []string data data: "{"ff":[123,345]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type string"), }, { // Invalid []int data data: "{"fg":123}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type []int"), }, { // Invalid []int data data: "{"fg":"abc"}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type []int"), }, { // Invalid []int data data: "{"fg":["abc"]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type int"), }, { // Invalid []int data data: "{"fg":[3.5]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number 3.5 into Go value of type int"), }, { // Invalid []int data data: "{"fg":[true,false]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number 3.5 into Go value of type int"), }, { // Invalid []bool data data: "{"fh":123}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type []bool"), }, { // Invalid []bool data data: "{"fh":"abc"}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type []bool"), }, { // Invalid []bool data data: "{"fh":["abc"]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type bool"), }, { // Invalid []bool data data: "{"fh":[3.5]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type bool"), }, { // Invalid []bool data data: "{"fh":[123]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type bool"), }, { // Invalid []float data data: "{"fi":123}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal number into Go value of type []float32"), }, { // Invalid []float data data: "{"fi":"abc"}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type []float32"), }, { // Invalid []float data data: "{"fi":["abc"]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal string into Go value of type float32"), }, { // Invalid []float data data: "{"fi":[true]}", obj:  &F{}, err:  fmt.Errorf("json: cannot unmarshal bool into Go value of type float32"), }, } for i := range testCases { doUnrecognized(t, testCases[i].data, testCases[i].obj, testCases[i].err) if t.Failed() { break } } } func TestFloatIntConversion(t *testing.T) { unstr := map[string]interface{}{"fd": float64(3)} var obj F if err := DefaultConverter.FromUnstructured(unstr, &obj); err != nil { t.Errorf("Unexpected error in FromUnstructured: %v", err) } data, err := json.Marshal(unstr) if err != nil { t.Fatalf("Error when marshaling unstructured: %v", err) } var unmarshalled F if err := json.Unmarshal(data, &unmarshalled); err != nil { t.Fatalf("Error when unmarshaling to object: %v", err) } if !reflect.DeepEqual(obj, unmarshalled) { t.Errorf("Incorrect conversion, diff: %v", diff.ObjectReflectDiff(obj, unmarshalled)) } } func TestCustomToUnstructured(t *testing.T) { testcases := []struct { Data     string Expected interface{} }{ {Data: `null`, Expected: nil}, {Data: `true`, Expected: true}, {Data: `false`, Expected: false}, {Data: `[]`, Expected: []interface{}{}}, {Data: `[1]`, Expected: []interface{}{int64(1)}}, {Data: `{}`, Expected: map[string]interface{}{}}, {Data: `{"a":1}`, Expected: map[string]interface{}{"a": int64(1)}}, {Data: `0`, Expected: int64(0)}, {Data: `0.0`, Expected: float64(0)}, } for _, tc := range testcases { result, err := DefaultConverter.ToUnstructured(&G{Custom: Custom{data: []byte(tc.Data)}}) if err != nil { t.Errorf("%s: %v", tc.Data, err) continue } fieldResult := result["custom"] if !reflect.DeepEqual(fieldResult, tc.Expected) { t.Errorf("%s: expected %v, got %v", tc.Data, tc.Expected, fieldResult) // t.Log("expected", spew.Sdump(tc.Expected)) // t.Log("actual", spew.Sdump(fieldResult)) continue } } } </del>

Discussion:
Kubernetes version (use ): master. What happened: Unstructured converter from does not roundtrip . What you expected to happen: When I call on a which is backed by it should basically make a copy of the content (can be optimized btw using deep copy ) and not a json object with key. How to reproduce it (as minimally and precisely as possible): See the test in my branch Test output: Anything else we need to know: For some reason changed the argument types from to . I guess the intent is to make the converter a more generic tool. But based on the previous signature I assume I'm doing the right thing. Actually, my code works with and I don't know if the actual object behind the interface is an or not - I just pass it to the converter and it works for usual API types, but not for unstructured. Also it would be useful to have a more type-safe version of the converter (i.e. the previous signature) that just delegates to a lower-level converter that does not care about types.
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Looked into this issue just now. It is caused by the pointer vs non-pointer receiver of the method - similar to . In detail: is passed as to when it calls passing as . if passed value implements (has method ) does not implement this interface, does. Because on it . So perhaps the fix is to do the dereferencing inside of the ? Or maybe the same way as - check if the value is addressable, get a pointer to the value and then see if it matches the interface (I dunno if it will work that way)? In any case, the check whether a value implements the interface should be done on both the value itself () and the pointer to the value (; if the value is addressable) to cover both valid cases. This is what stdlib package does. Right now it is broken - it dereferences the pointer and then checks if the thing implements the interface. Does it make sense?

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does this helps? Look like we need to do MarshalJSON on non-pointers for it to work. I didn't get into the details but if that is the case then making Unstructured's MarshalJSON() receiver, a object instead of pointer should fix your problem, right?
Only if we don't fix the actual cause of the bug which I described above. From the stack overflow question that is mentioned in the link you provided: This code is buggy - to work it should be passing into and into . Yes, json package tries to take the address of the passed (so a pointer receiver should satisfy the interface check) but it cannot take an address of a function argument ( will return false). So, pointer receiver will be invoked if either is a field in a struct (so that an address can be taken via reflection) and a struct is passed (either by value or via a pointer) to / OR is passed. Please take a look at - both issues have the same cause.
I'm happy to take a stab at it and submit a PR but I don't want to spend my time if it is not going to get merged - if we could merge first to make sure people who can approve/lgtm are happy with the approach taken. I strongly believe it is the right thing to do - that is how standard library does it and, well, it is just logical and makes sense :)