Checkjson

Check that a JSON object's keys correspond to a struct's exported members or JSON tags.

ANNOUNCEMENTS

2025.08.10 - checkjson package is no longer actively supported. 2021.08.18 - Merge in handling of checkjson:"norecurse" struct member tag. 2018.03.14 - Add ExistingJSONKeys() 2018.02.16 - Add test example of using go v1.10 (*Decoder)DisallowUnknownFields() 2017.02.13 - Handle "-" and "omitempty" JSON tags in struct definitions. 2017.02.08 - UnknownJSONKeys lists all JSON object keys that won't be decoded. 2016.11.18 - MissingJSONKeys lists all struct members that won't be set by JSON object.

USAGE

https://godoc.org/github.com/clbanning/checkjson

Example:

data := `
{
   "elem1":"a simple element",
   "elem2": {
      "subelem":"something more complex", 
      "notes":"take a look at this" }
   "elem4":"extraneous" 
}`

type sub struct {
   Subelem string `json:"subelem,omitempty"`
   Another string `json:"another"`
}
type elem struct {
   Elem1 string `json:"elem1"`
   Elem2 sub    `json:"elem2"`
   Elem3 bool   `json:"elem3"`
}

e := new(elem)
result, _ := MissingJSONKeys([]byte(data), e)
// result: [elem2.another elem3]

result, _ = UnknownJSONKeys([]byte(data), e)
// result: [elem2.notes elem4]
// NOTE: using the stdlib json.Decoder with (*Decoder)DisallowUnknownFields() set
//       will error on the first unknown key; it does not return a slice of all
//       unknown keys - see: unknownfieldserr_test.go.

LIMITATION

This package does not support recursive struct definitions.

MOTIVATION

I make extensive use of JSON configuration files. Sometimes the files are large or complex and JSON keys can be prone to typos or case errors. The "encoding/json" decoder just ignores JSON keys that do not correspond to struct member names/tags; this can result in unexpected initialization errors or the failure to override defaults. The checkjson.Validate() function identifies JSON object keys that cannot be decoded to a member of the struct using the "encoding/json" package.

RELATED

There is a similar package for validating XML tags against structs in https://github.com/clbanning/checkxml.