481 lines
11 KiB
Go
481 lines
11 KiB
Go
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// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package json
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import (
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"bytes"
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"errors"
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"io"
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)
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// A Decoder reads and decodes JSON objects from an input stream.
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type Decoder struct {
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r io.Reader
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buf []byte
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d decodeState
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scanp int // start of unread data in buf
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scan scanner
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err error
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tokenState int
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tokenStack []int
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}
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// NewDecoder returns a new decoder that reads from r.
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//
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// The decoder introduces its own buffering and may
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// read data from r beyond the JSON values requested.
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func NewDecoder(r io.Reader) *Decoder {
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return &Decoder{r: r}
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}
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// UseNumber causes the Decoder to unmarshal a number into an interface{} as a
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// Number instead of as a float64.
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func (dec *Decoder) UseNumber() { dec.d.useNumber = true }
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// Decode reads the next JSON-encoded value from its
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// input and stores it in the value pointed to by v.
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//
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// See the documentation for Unmarshal for details about
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// the conversion of JSON into a Go value.
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func (dec *Decoder) Decode(v interface{}) error {
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if dec.err != nil {
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return dec.err
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}
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if err := dec.tokenPrepareForDecode(); err != nil {
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return err
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}
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if !dec.tokenValueAllowed() {
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return &SyntaxError{msg: "not at beginning of value"}
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}
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// Read whole value into buffer.
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n, err := dec.readValue()
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if err != nil {
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return err
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}
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dec.d.init(dec.buf[dec.scanp : dec.scanp+n])
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dec.scanp += n
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// Don't save err from unmarshal into dec.err:
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// the connection is still usable since we read a complete JSON
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// object from it before the error happened.
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err = dec.d.unmarshal(v)
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// fixup token streaming state
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dec.tokenValueEnd()
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return err
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}
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// Buffered returns a reader of the data remaining in the Decoder's
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// buffer. The reader is valid until the next call to Decode.
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func (dec *Decoder) Buffered() io.Reader {
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return bytes.NewReader(dec.buf[dec.scanp:])
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}
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// readValue reads a JSON value into dec.buf.
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// It returns the length of the encoding.
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func (dec *Decoder) readValue() (int, error) {
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dec.scan.reset()
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scanp := dec.scanp
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var err error
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Input:
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for {
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// Look in the buffer for a new value.
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for i, c := range dec.buf[scanp:] {
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dec.scan.bytes++
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v := dec.scan.step(&dec.scan, c)
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if v == scanEnd {
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scanp += i
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break Input
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}
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// scanEnd is delayed one byte.
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// We might block trying to get that byte from src,
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// so instead invent a space byte.
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if (v == scanEndObject || v == scanEndArray) && dec.scan.step(&dec.scan, ' ') == scanEnd {
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scanp += i + 1
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break Input
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}
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if v == scanError {
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dec.err = dec.scan.err
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return 0, dec.scan.err
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}
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}
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scanp = len(dec.buf)
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// Did the last read have an error?
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// Delayed until now to allow buffer scan.
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if err != nil {
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if err == io.EOF {
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if dec.scan.step(&dec.scan, ' ') == scanEnd {
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break Input
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}
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if nonSpace(dec.buf) {
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err = io.ErrUnexpectedEOF
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}
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}
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dec.err = err
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return 0, err
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}
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n := scanp - dec.scanp
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err = dec.refill()
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scanp = dec.scanp + n
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}
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return scanp - dec.scanp, nil
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}
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func (dec *Decoder) refill() error {
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// Make room to read more into the buffer.
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// First slide down data already consumed.
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if dec.scanp > 0 {
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n := copy(dec.buf, dec.buf[dec.scanp:])
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dec.buf = dec.buf[:n]
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dec.scanp = 0
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}
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// Grow buffer if not large enough.
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const minRead = 512
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if cap(dec.buf)-len(dec.buf) < minRead {
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newBuf := make([]byte, len(dec.buf), 2*cap(dec.buf)+minRead)
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copy(newBuf, dec.buf)
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dec.buf = newBuf
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}
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// Read. Delay error for next iteration (after scan).
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n, err := dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
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dec.buf = dec.buf[0 : len(dec.buf)+n]
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return err
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}
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func nonSpace(b []byte) bool {
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for _, c := range b {
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if !isSpace(c) {
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return true
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}
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}
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return false
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}
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// An Encoder writes JSON objects to an output stream.
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type Encoder struct {
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w io.Writer
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err error
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}
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// NewEncoder returns a new encoder that writes to w.
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func NewEncoder(w io.Writer) *Encoder {
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return &Encoder{w: w}
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}
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// Encode writes the JSON encoding of v to the stream,
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// followed by a newline character.
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//
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// See the documentation for Marshal for details about the
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// conversion of Go values to JSON.
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func (enc *Encoder) Encode(v interface{}) error {
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if enc.err != nil {
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return enc.err
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}
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e := newEncodeState()
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err := e.marshal(v)
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if err != nil {
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return err
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}
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// Terminate each value with a newline.
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// This makes the output look a little nicer
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// when debugging, and some kind of space
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// is required if the encoded value was a number,
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// so that the reader knows there aren't more
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// digits coming.
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e.WriteByte('\n')
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if _, err = enc.w.Write(e.Bytes()); err != nil {
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enc.err = err
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}
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encodeStatePool.Put(e)
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return err
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}
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// RawMessage is a raw encoded JSON object.
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// It implements Marshaler and Unmarshaler and can
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// be used to delay JSON decoding or precompute a JSON encoding.
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type RawMessage []byte
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// MarshalJSON returns *m as the JSON encoding of m.
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func (m *RawMessage) MarshalJSON() ([]byte, error) {
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return *m, nil
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}
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// UnmarshalJSON sets *m to a copy of data.
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func (m *RawMessage) UnmarshalJSON(data []byte) error {
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if m == nil {
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return errors.New("json.RawMessage: UnmarshalJSON on nil pointer")
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}
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*m = append((*m)[0:0], data...)
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return nil
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}
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var _ Marshaler = (*RawMessage)(nil)
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var _ Unmarshaler = (*RawMessage)(nil)
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// A Token holds a value of one of these types:
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//
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// Delim, for the four JSON delimiters [ ] { }
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// bool, for JSON booleans
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// float64, for JSON numbers
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// Number, for JSON numbers
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// string, for JSON string literals
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// nil, for JSON null
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//
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type Token interface{}
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const (
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tokenTopValue = iota
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tokenArrayStart
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tokenArrayValue
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tokenArrayComma
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tokenObjectStart
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tokenObjectKey
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tokenObjectColon
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tokenObjectValue
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tokenObjectComma
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)
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// advance tokenstate from a separator state to a value state
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func (dec *Decoder) tokenPrepareForDecode() error {
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// Note: Not calling peek before switch, to avoid
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// putting peek into the standard Decode path.
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// peek is only called when using the Token API.
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switch dec.tokenState {
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case tokenArrayComma:
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c, err := dec.peek()
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if err != nil {
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return err
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}
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if c != ',' {
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return &SyntaxError{"expected comma after array element", 0}
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}
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dec.scanp++
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dec.tokenState = tokenArrayValue
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case tokenObjectColon:
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c, err := dec.peek()
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if err != nil {
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return err
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}
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if c != ':' {
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return &SyntaxError{"expected colon after object key", 0}
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}
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dec.scanp++
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dec.tokenState = tokenObjectValue
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}
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return nil
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}
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func (dec *Decoder) tokenValueAllowed() bool {
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switch dec.tokenState {
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case tokenTopValue, tokenArrayStart, tokenArrayValue, tokenObjectValue:
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return true
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}
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return false
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}
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func (dec *Decoder) tokenValueEnd() {
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switch dec.tokenState {
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case tokenArrayStart, tokenArrayValue:
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dec.tokenState = tokenArrayComma
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case tokenObjectValue:
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dec.tokenState = tokenObjectComma
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}
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}
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// A Delim is a JSON array or object delimiter, one of [ ] { or }.
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type Delim rune
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func (d Delim) String() string {
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return string(d)
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}
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// Token returns the next JSON token in the input stream.
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// At the end of the input stream, Token returns nil, io.EOF.
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//
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// Token guarantees that the delimiters [ ] { } it returns are
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// properly nested and matched: if Token encounters an unexpected
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// delimiter in the input, it will return an error.
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//
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// The input stream consists of basic JSON values—bool, string,
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// number, and null—along with delimiters [ ] { } of type Delim
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// to mark the start and end of arrays and objects.
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// Commas and colons are elided.
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func (dec *Decoder) Token() (Token, error) {
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for {
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c, err := dec.peek()
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if err != nil {
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return nil, err
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}
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switch c {
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case '[':
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if !dec.tokenValueAllowed() {
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return dec.tokenError(c)
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}
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dec.scanp++
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dec.tokenStack = append(dec.tokenStack, dec.tokenState)
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dec.tokenState = tokenArrayStart
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return Delim('['), nil
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case ']':
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if dec.tokenState != tokenArrayStart && dec.tokenState != tokenArrayComma {
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return dec.tokenError(c)
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}
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dec.scanp++
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dec.tokenState = dec.tokenStack[len(dec.tokenStack)-1]
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dec.tokenStack = dec.tokenStack[:len(dec.tokenStack)-1]
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dec.tokenValueEnd()
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return Delim(']'), nil
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case '{':
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if !dec.tokenValueAllowed() {
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return dec.tokenError(c)
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}
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dec.scanp++
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dec.tokenStack = append(dec.tokenStack, dec.tokenState)
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dec.tokenState = tokenObjectStart
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return Delim('{'), nil
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case '}':
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if dec.tokenState != tokenObjectStart && dec.tokenState != tokenObjectComma {
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return dec.tokenError(c)
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}
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dec.scanp++
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dec.tokenState = dec.tokenStack[len(dec.tokenStack)-1]
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dec.tokenStack = dec.tokenStack[:len(dec.tokenStack)-1]
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dec.tokenValueEnd()
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return Delim('}'), nil
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case ':':
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if dec.tokenState != tokenObjectColon {
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return dec.tokenError(c)
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}
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dec.scanp++
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dec.tokenState = tokenObjectValue
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continue
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case ',':
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if dec.tokenState == tokenArrayComma {
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dec.scanp++
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dec.tokenState = tokenArrayValue
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continue
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}
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if dec.tokenState == tokenObjectComma {
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dec.scanp++
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dec.tokenState = tokenObjectKey
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continue
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}
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return dec.tokenError(c)
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case '"':
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if dec.tokenState == tokenObjectStart || dec.tokenState == tokenObjectKey {
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var x string
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old := dec.tokenState
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dec.tokenState = tokenTopValue
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err := dec.Decode(&x)
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dec.tokenState = old
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if err != nil {
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clearOffset(err)
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return nil, err
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}
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dec.tokenState = tokenObjectColon
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return x, nil
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}
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fallthrough
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default:
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if !dec.tokenValueAllowed() {
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return dec.tokenError(c)
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}
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var x interface{}
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if err := dec.Decode(&x); err != nil {
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clearOffset(err)
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|
|
return nil, err
|
||
|
|
}
|
||
|
|
return x, nil
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func clearOffset(err error) {
|
||
|
|
if s, ok := err.(*SyntaxError); ok {
|
||
|
|
s.Offset = 0
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func (dec *Decoder) tokenError(c byte) (Token, error) {
|
||
|
|
var context string
|
||
|
|
switch dec.tokenState {
|
||
|
|
case tokenTopValue:
|
||
|
|
context = " looking for beginning of value"
|
||
|
|
case tokenArrayStart, tokenArrayValue, tokenObjectValue:
|
||
|
|
context = " looking for beginning of value"
|
||
|
|
case tokenArrayComma:
|
||
|
|
context = " after array element"
|
||
|
|
case tokenObjectKey:
|
||
|
|
context = " looking for beginning of object key string"
|
||
|
|
case tokenObjectColon:
|
||
|
|
context = " after object key"
|
||
|
|
case tokenObjectComma:
|
||
|
|
context = " after object key:value pair"
|
||
|
|
}
|
||
|
|
return nil, &SyntaxError{"invalid character " + quoteChar(c) + " " + context, 0}
|
||
|
|
}
|
||
|
|
|
||
|
|
// More reports whether there is another element in the
|
||
|
|
// current array or object being parsed.
|
||
|
|
func (dec *Decoder) More() bool {
|
||
|
|
c, err := dec.peek()
|
||
|
|
return err == nil && c != ']' && c != '}'
|
||
|
|
}
|
||
|
|
|
||
|
|
func (dec *Decoder) peek() (byte, error) {
|
||
|
|
var err error
|
||
|
|
for {
|
||
|
|
for i := dec.scanp; i < len(dec.buf); i++ {
|
||
|
|
c := dec.buf[i]
|
||
|
|
if isSpace(c) {
|
||
|
|
continue
|
||
|
|
}
|
||
|
|
dec.scanp = i
|
||
|
|
return c, nil
|
||
|
|
}
|
||
|
|
// buffer has been scanned, now report any error
|
||
|
|
if err != nil {
|
||
|
|
return 0, err
|
||
|
|
}
|
||
|
|
err = dec.refill()
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
TODO
|
||
|
|
|
||
|
|
// EncodeToken writes the given JSON token to the stream.
|
||
|
|
// It returns an error if the delimiters [ ] { } are not properly used.
|
||
|
|
//
|
||
|
|
// EncodeToken does not call Flush, because usually it is part of
|
||
|
|
// a larger operation such as Encode, and those will call Flush when finished.
|
||
|
|
// Callers that create an Encoder and then invoke EncodeToken directly,
|
||
|
|
// without using Encode, need to call Flush when finished to ensure that
|
||
|
|
// the JSON is written to the underlying writer.
|
||
|
|
func (e *Encoder) EncodeToken(t Token) error {
|
||
|
|
...
|
||
|
|
}
|
||
|
|
|
||
|
|
*/
|