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Marshaler (WIP)

Unmarshal and Marshal generators for Go. For use in Bud.

Example

Given the following struct:

type Input struct {
  B string
  C int
  D float64
  E bool
  F map[string]string
  G []int
  H *string
}

This library will generate an UnmarshalJSON function that can take arbitrary JSON and produce Input:

func UnmarshalJSON(json []byte, in *Input) error {
  // Generated code
}

Then usage would look something like this:

func ReadBody(r io.ReadCloser) (*Input, error) {
  json, err := io.ReadAll(r)
  if err != nil {
    return nil, err
  }
  in := new(Input)
  if err := UnmarshalJSON(json, in); err != nil {
    return nil, err
  }
  return in, nil
}

TODO

This package is still very much WIP. There's a lot more work to do:

  • Unmarshal nested structs
  • Get tests running from a temporary directory
  • Unmarshal referenced types
  • Support the json tag
  • Support Valid() error that gets called while Unmarshaling
  • Pull in tests from other libraries
  • Encode nil maps and nil structs as empty objects
  • Fallback to json.{Decode,Encode} (?)
  • Bundle into Bud
  • Add MarshalJSON support using the writer
  • Re-organize the package structure to allow more marshalers (e.g. form)

If you have the itch, I'd very much appreciate your help! I plan to work on this here and there over the next couple months. Your PRs would speed up this timeline significantly.

Why?

  • Nice speed improvement over the reflection-based alternatives.
  • Validate while you're unmarshaling.
  • Nil maps and structs can be changed to empty objects.
  • Code can be re-used for other formats like URL-encoded form data or protobufs.

Development

git clone https://github.com/livebud/marshaler
cd marshaler
go mod tidy
go test ./...

Prior Art

  • megajson: Simple, easy-to-understand code. Uses static analysis instead of build-time reflection. No longer in development. No built-in validation. No nested structure support.
  • ffjson: More features. No updates since 2019. Recent issues unanswered. No built-in validation. Build-time reflection doesn't jibe well with Bud.
  • go-codec: Actively maintained. More features. Probably a better choice for the time being. No built-in validation. Build-time reflection doesn't jibe well with Bud.

Thanks

The scanner and writer were originally written by Ben Johnson in megajson.

License

MIT