// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gensupport
import (
"encoding/json"
"fmt"
"reflect"
"strings"
)
// MarshalJSON returns a JSON encoding of schema containing only selected fields.
// A field is selected if any of the following is true:
// * it has a non-empty value
// * its field name is present in forceSendFields and it is not a nil pointer or nil interface
// * its field name is present in nullFields.
// The JSON key for each selected field is taken from the field's json: struct tag.
func MarshalJSON(schema interface{}, forceSendFields, nullFields []string) ([]byte, error) {
if len(forceSendFields) == 0 && len(nullFields) == 0 {
return json.Marshal(schema)
}
mustInclude := make(map[string]bool)
for _, f := range forceSendFields {
mustInclude[f] = true
}
useNull := make(map[string]bool)
useNullMaps := make(map[string]map[string]bool)
for _, nf := range nullFields {
parts := strings.SplitN(nf, ".", 2)
field := parts[0]
if len(parts) == 1 {
useNull[field] = true
} else {
if useNullMaps[field] == nil {
useNullMaps[field] = map[string]bool{}
}
useNullMaps[field][parts[1]] = true
}
}
dataMap, err := schemaToMap(schema, mustInclude, useNull, useNullMaps)
if err != nil {
return nil, err
}
return json.Marshal(dataMap)
}
func schemaToMap(schema interface{}, mustInclude, useNull map[string]bool, useNullMaps map[string]map[string]bool) (map[string]interface{}, error) {
m := make(map[string]interface{})
s := reflect.ValueOf(schema)
st := s.Type()
for i := 0; i < s.NumField(); i++ {
jsonTag := st.Field(i).Tag.Get("json")
if jsonTag == "" {
continue
}
tag, err := parseJSONTag(jsonTag)
if err != nil {
return nil, err
}
if tag.ignore {
continue
}
v := s.Field(i)
f := st.Field(i)
if useNull[f.Name] {
if !isEmptyValue(v) {
return nil, fmt.Errorf("field %q in NullFields has non-empty value", f.Name)
}
m[tag.apiName] = nil
continue
}
if !includeField(v, f, mustInclude) {
continue
}
// If map fields are explicitly set to null, use a map[string]interface{}.
if f.Type.Kind() == reflect.Map && useNullMaps[f.Name] != nil {
ms, ok := v.Interface().(map[string]string)
if !ok {
return nil, fmt.Errorf("field %q has keys in NullFields but is not a map[string]string", f.Name)
}
mi := map[string]interface{}{}
for k, v := range ms {
mi[k] = v
}
for k := range useNullMaps[f.Name] {
mi[k] = nil
}
m[tag.apiName] = mi
continue
}
// nil maps are treated as empty maps.
if f.Type.Kind() == reflect.Map && v.IsNil() {
m[tag.apiName] = map[string]string{}
continue
}
// nil slices are treated as empty slices.
if f.Type.Kind() == reflect.Slice && v.IsNil() {
m[tag.apiName] = []bool{}
continue
}
if tag.stringFormat {
m[tag.apiName] = formatAsString(v, f.Type.Kind())
} else {
m[tag.apiName] = v.Interface()
}
}
return m, nil
}
// formatAsString returns a string representation of v, dereferencing it first if possible.
func formatAsString(v reflect.Value, kind reflect.Kind) string {
if kind == reflect.Ptr && !v.IsNil() {
v = v.Elem()
}
return fmt.Sprintf("%v", v.Interface())
}
// jsonTag represents a restricted version of the struct tag format used by encoding/json.
// It is used to describe the JSON encoding of fields in a Schema struct.
type jsonTag struct {
apiName string
stringFormat bool
ignore bool
}
// parseJSONTag parses a restricted version of the struct tag format used by encoding/json.
// The format of the tag must match that generated by the Schema.writeSchemaStruct method
// in the api generator.
func parseJSONTag(val string) (jsonTag, error) {
if val == "-" {
return jsonTag{ignore: true}, nil
}
var tag jsonTag
i := strings.Index(val, ",")
if i == -1 || val[:i] == "" {
return tag, fmt.Errorf("malformed json tag: %s", val)
}
tag = jsonTag{
apiName: val[:i],
}
switch val[i+1:] {
case "omitempty":
case "omitempty,string":
tag.stringFormat = true
default:
return tag, fmt.Errorf("malformed json tag: %s", val)
}
return tag, nil
}
// Reports whether the struct field "f" with value "v" should be included in JSON output.
func includeField(v reflect.Value, f reflect.StructField, mustInclude map[string]bool) bool {
// The regular JSON encoding of a nil pointer is "null", which means "delete this field".
// Therefore, we could enable field deletion by honoring pointer fields' presence in the mustInclude set.
// However, many fields are not pointers, so there would be no way to delete these fields.
// Rather than partially supporting field deletion, we ignore mustInclude for nil pointer fields.
// Deletion will be handled by a separate mechanism.
if f.Type.Kind() == reflect.Ptr && v.IsNil() {
return false
}
// The "any" type is represented as an interface{}. If this interface
// is nil, there is no reasonable representation to send. We ignore
// these fields, for the same reasons as given above for pointers.
if f.Type.Kind() == reflect.Interface && v.IsNil() {
return false
}
return mustInclude[f.Name] || !isEmptyValue(v)
}
// isEmptyValue reports whether v is the empty value for its type. This
// implementation is based on that of the encoding/json package, but its
// correctness does not depend on it being identical. What's important is that
// this function return false in situations where v should not be sent as part
// of a PATCH operation.
func isEmptyValue(v reflect.Value) bool {
switch v.Kind() {
case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
return v.Len() == 0
case reflect.Bool:
return !v.Bool()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return v.Int() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
case reflect.Interface, reflect.Ptr:
return v.IsNil()
}
return false
}
