| 1 | package maintenanceguard |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "encoding/json" |
| 6 | "errors" |
| 7 | "io" |
| 8 | "reflect" |
| 9 | "strings" |
| 10 | ) |
| 11 | |
| 12 | const MaxWireBytes = 16 << 10 |
| 13 | |
| 14 | var ErrInvalid = errors.New("maintenance guard: invalid record") |
| 15 | |
| 16 | // decode checks exact field names and duplicates before typed decoding. The |
| 17 | // expected schema bounds nesting; arbitrary JSON trees are never traversed. |
| 18 | func decode(raw []byte, dst any) error { |
| 19 | if len(raw) == 0 || len(raw) > MaxWireBytes { |
| 20 | return ErrInvalid |
| 21 | } |
| 22 | typ := reflect.TypeOf(dst) |
| 23 | if typ == nil || typ.Kind() != reflect.Pointer { |
| 24 | return ErrInvalid |
| 25 | } |
| 26 | dec := json.NewDecoder(bytes.NewReader(raw)) |
| 27 | dec.UseNumber() |
| 28 | if !jsonShape(dec, typ.Elem()) { |
| 29 | return ErrInvalid |
| 30 | } |
| 31 | if _, e := dec.Token(); e != io.EOF { |
| 32 | return ErrInvalid |
| 33 | } |
| 34 | if json.Unmarshal(raw, dst) != nil { |
| 35 | return ErrInvalid |
| 36 | } |
| 37 | return nil |
| 38 | } |
| 39 | func jsonShape(dec *json.Decoder, typ reflect.Type) bool { |
| 40 | for typ.Kind() == reflect.Pointer { |
| 41 | typ = typ.Elem() |
| 42 | } |
| 43 | token, e := dec.Token() |
| 44 | if e != nil || token == nil { |
| 45 | return false |
| 46 | } |
| 47 | if delim, ok := token.(json.Delim); ok { |
| 48 | switch delim { |
| 49 | case '{': |
| 50 | if typ.Kind() != reflect.Struct { |
| 51 | return false |
| 52 | } |
| 53 | fields := map[string]reflect.Type{} |
| 54 | for i := 0; i < typ.NumField(); i++ { |
| 55 | field := typ.Field(i) |
| 56 | name := strings.Split(field.Tag.Get("json"), ",")[0] |
| 57 | if name != "" && name != "-" { |
| 58 | fields[name] = field.Type |
| 59 | } |
| 60 | } |
| 61 | seen := map[string]bool{} |
| 62 | for dec.More() { |
| 63 | key, e := dec.Token() |
| 64 | if e != nil { |
| 65 | return false |
| 66 | } |
| 67 | name, ok := key.(string) |
| 68 | field, known := fields[name] |
| 69 | if !ok || !known || seen[name] { |
| 70 | return false |
| 71 | } |
| 72 | seen[name] = true |
| 73 | if !jsonShape(dec, field) { |
| 74 | return false |
| 75 | } |
| 76 | } |
| 77 | end, e := dec.Token() |
| 78 | return e == nil && end == json.Delim('}') |
| 79 | case '[': |
| 80 | if typ.Kind() != reflect.Slice { |
| 81 | return false |
| 82 | } |
| 83 | for dec.More() { |
| 84 | if !jsonShape(dec, typ.Elem()) { |
| 85 | return false |
| 86 | } |
| 87 | } |
| 88 | end, e := dec.Token() |
| 89 | return e == nil && end == json.Delim(']') |
| 90 | default: |
| 91 | return false |
| 92 | } |
| 93 | } |
| 94 | switch typ.Kind() { |
| 95 | case reflect.String: |
| 96 | _, ok := token.(string) |
| 97 | return ok |
| 98 | case reflect.Int, reflect.Int64: |
| 99 | _, ok := token.(json.Number) |
| 100 | return ok |
| 101 | case reflect.Bool: |
| 102 | _, ok := token.(bool) |
| 103 | return ok |
| 104 | } |
| 105 | return false |
| 106 | } |
| 107 | |
amadan