Implement io.Reader

[xoen]

simplejson.Json implements the io.Reader interface:

type Reader interface {
  Read(p []byte) (n int, err error)
}

Why?

By implementing this standard interface simplejson would play nice with the standard library and all the 3rd party packages that work with an io.Reader.

For example, it would allow to POST the JSON directly rather than being forced to Encode() and use bytes.NewReader():

// Currently
import ("bytes")
payloadBytes, _ := payloadJson.Encode()
req, _ := http.NewRequest("POST", "http://www.example.com", bytes.NewReader(payloadBytes))

// With io.Reader
req, _ := http.NewRequest("POST", "http://www.example.com", payloadJson)

Implementation

When starting to read the Json it encodes the data and save the bytes in the Reader struct.
This struct also keeps the index of the bytes read so far.
At every read the bytes are copied to the buffer argument and the index is increased.

(See bytes.Read() implementation)

The reader is reseted when Json.data changes

I'm far from a Go expert, so happy to receive feedback.

Tests

The test builds a first *simplejson, then a second one using NewFromReader(), this test would fail if *simplejson doesn't implement io.Reader.

Also, to test that the second JSON is equivalent with the original one (so Read() returns the correct bytes) I encode and compare them.