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// Copyright 2010 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 json
import (
"io"
"os"
)
// A Decoder reads and decodes JSON objects from an input stream.
type Decoder struct {
r io.Reader
buf []byte
d decodeState
scan scanner
err os.Error
}
// NewDecoder returns a new decoder that reads from r.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{r: r}
}
// Decode reads the next JSON-encoded value from the
// connection and stores it in the value pointed to by v.
//
// See the documentation for Unmarshal for details about
// the conversion of JSON into a Go value.
func (dec *Decoder) Decode(v interface{}) os.Error {
if dec.err != nil {
return dec.err
}
n, err := dec.readValue()
if err != nil {
return err
}
// Don't save err from unmarshal into dec.err:
// the connection is still usable since we read a complete JSON
// object from it before the error happened.
dec.d.init(dec.buf[0:n])
err = dec.d.unmarshal(v)
// Slide rest of data down.
rest := copy(dec.buf, dec.buf[n:])
dec.buf = dec.buf[0:rest]
return err
}
// readValue reads a JSON value into dec.buf.
// It returns the length of the encoding.
func (dec *Decoder) readValue() (int, os.Error) {
dec.scan.reset()
scanp := 0
var err os.Error
Input:
for {
// Look in the buffer for a new value.
for i, c := range dec.buf[scanp:] {
v := dec.scan.step(&dec.scan, int(c))
if v == scanEnd {
scanp += i
break Input
}
// scanEnd is delayed one byte.
// We might block trying to get that byte from src,
// so instead invent a space byte.
if v == scanEndObject && dec.scan.step(&dec.scan, ' ') == scanEnd {
scanp += i + 1
break Input
}
if v == scanError {
dec.err = dec.scan.err
return 0, dec.scan.err
}
}
scanp = len(dec.buf)
// Did the last read have an error?
// Delayed until now to allow buffer scan.
if err != nil {
if err == os.EOF {
if dec.scan.step(&dec.scan, ' ') == scanEnd {
break Input
}
if nonSpace(dec.buf) {
err = io.ErrUnexpectedEOF
}
}
dec.err = err
return 0, err
}
// Make room to read more into the buffer.
const minRead = 512
if cap(dec.buf)-len(dec.buf) < minRead {
newBuf := make([]byte, len(dec.buf), 2*cap(dec.buf)+minRead)
copy(newBuf, dec.buf)
dec.buf = newBuf
}
// Read. Delay error for next iteration (after scan).
var n int
n, err = dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
dec.buf = dec.buf[0 : len(dec.buf)+n]
}
return scanp, nil
}
func nonSpace(b []byte) bool {
for _, c := range b {
if !isSpace(int(c)) {
return true
}
}
return false
}
// An Encoder writes JSON objects to an output stream.
type Encoder struct {
w io.Writer
e encodeState
err os.Error
}
// NewEncoder returns a new encoder that writes to w.
func NewEncoder(w io.Writer) *Encoder {
return &Encoder{w: w}
}
// Encode writes the JSON encoding of v to the connection.
//
// See the documentation for Marshal for details about the
// conversion of Go values to JSON.
func (enc *Encoder) Encode(v interface{}) os.Error {
if enc.err != nil {
return enc.err
}
enc.e.Reset()
err := enc.e.marshal(v)
if err != nil {
return err
}
// Terminate each value with a newline.
// This makes the output look a little nicer
// when debugging, and some kind of space
// is required if the encoded value was a number,
// so that the reader knows there aren't more
// digits coming.
enc.e.WriteByte('\n')
if _, err = enc.w.Write(enc.e.Bytes()); err != nil {
enc.err = err
}
return err
}
// RawMessage is a raw encoded JSON object.
// It implements Marshaler and Unmarshaler and can
// be used to delay JSON decoding or precompute a JSON encoding.
type RawMessage []byte
// MarshalJSON returns *m as the JSON encoding of m.
func (m *RawMessage) MarshalJSON() ([]byte, os.Error) {
return *m, nil
}
// UnmarshalJSON sets *m to a copy of data.
func (m *RawMessage) UnmarshalJSON(data []byte) os.Error {
if m == nil {
return os.NewError("json.RawMessage: UnmarshalJSON on nil pointer")
}
*m = append((*m)[0:0], data...)
return nil
}
var _ Marshaler = (*RawMessage)(nil)
var _ Unmarshaler = (*RawMessage)(nil)
|
