JSONStream provides helper functions to enable true JSON streaming capabilities.

How to get:

go get github.com/tada/jsonstream

Sample usage

Since jsonstream uses the github.com/tada/catch module, all error handling is baked into the support functions. If any error is encountered, it will result in a panic that is recovered in the top level functions Marshal and Unmarshal. Code using the support functions, like in the example below, is compact since no error propagation is needed.

package tst

import (
  "encoding/json"
  "io"
  "time"

  "github.com/tada/catch/pio"
  "github.com/tada/jsonstream"
)

type ts struct {
  v time.Duration
}

// MarshalJSON is from the json.Marshaller interface
func (t *ts) MarshalJSON() ([]byte, error) {
  // Dispatch to the helper function
  return jsonstream.Marshal(t)
}

// UnmarshalJSON is from the json.Marshaller interface
func (t *ts) UnmarshalJSON(bs []byte) error {
  // Dispatch to the helper function
  return jsonstream.Unmarshal(t, bs)
}

// MarshalToJSON encode as json and stream result to the writer
func (t *ts) MarshalToJSON(w io.Writer) {
  pio.WriteByte('{', w)
  jsonstream.WriteString("v", w)
  pio.WriteByte(':', w)
  pio.WriteInt(int64(t.v/time.Millisecond), w)
  pio.WriteByte('}', w)
}

// UnmarshalToJSON decodes using the given decoder
func (t *ts) UnmarshalFromJSON(js jsonstream.Decoder, firstToken json.Token) {
  jsonstream.AssertDelim(firstToken, '{')
  for {
    s, ok := js.ReadStringOrEnd('}')
    if !ok {
      break
    }
    if s == "v" {
      t.v = time.Duration(js.ReadInt()) * time.Millisecond
    }
  }
}