// Ed: Go fmt yourself!
}
+// This example uses a Decoder to decode a stream of distinct JSON values.
+func ExampleDecoder_Token() {
+ const jsonStream = `
+ {"Message": "Hello", "Array": [1, 2, 3], "Null": null, "Number": 1.234}
+ `
+ dec := json.NewDecoder(strings.NewReader(jsonStream))
+ for {
+ t, err := dec.Token()
+ if err == io.EOF {
+ break
+ }
+ if err != nil {
+ log.Fatal(err)
+ }
+ fmt.Printf("%T: %v", t, t)
+ if dec.More() {
+ fmt.Printf(" (more)")
+ }
+ fmt.Printf("\n")
+ }
+ // Output:
+ // json.Delim: { (more)
+ // string: Message (more)
+ // string: Hello (more)
+ // string: Array (more)
+ // json.Delim: [ (more)
+ // float64: 1 (more)
+ // float64: 2 (more)
+ // float64: 3
+ // json.Delim: ] (more)
+ // string: Null (more)
+ // <nil>: <nil> (more)
+ // string: Number (more)
+ // float64: 1.234
+ // json.Delim: }
+}
+
+// This example uses a Decoder to decode a streaming array of JSON objects.
+func ExampleDecoder_Decode_stream() {
+ const jsonStream = `
+ [
+ {"Name": "Ed", "Text": "Knock knock."},
+ {"Name": "Sam", "Text": "Who's there?"},
+ {"Name": "Ed", "Text": "Go fmt."},
+ {"Name": "Sam", "Text": "Go fmt who?"},
+ {"Name": "Ed", "Text": "Go fmt yourself!"}
+ ]
+ `
+ type Message struct {
+ Name, Text string
+ }
+ dec := json.NewDecoder(strings.NewReader(jsonStream))
+
+ // read open bracket
+ t, err := dec.Token()
+ if err != nil {
+ log.Fatal(err)
+ }
+ fmt.Printf("%T: %v\n", t, t)
+
+ var m Message
+ // while the array contains values
+ for dec.More() {
+
+ // decode an array value (Message)
+ err := dec.Decode(&m)
+ if err != nil {
+ log.Fatal(err)
+ }
+
+ fmt.Printf("%v: %v\n", m.Name, m.Text)
+ }
+
+ // read closing bracket
+ t, err = dec.Token()
+ if err != nil {
+ log.Fatal(err)
+ }
+ fmt.Printf("%T: %v\n", t, t)
+
+ // Output:
+ // json.Delim: [
+ // Ed: Knock knock.
+ // Sam: Who's there?
+ // Ed: Go fmt.
+ // Sam: Go fmt who?
+ // Ed: Go fmt yourself!
+ // json.Delim: ]
+
+}
+
// This example uses RawMessage to delay parsing part of a JSON message.
func ExampleRawMessage() {
type Color struct {
// A Decoder reads and decodes JSON objects from an input stream.
type Decoder struct {
- r io.Reader
- buf []byte
- d decodeState
- scan scanner
- err error
+ r io.Reader
+ buf []byte
+ d decodeState
+ scanp int // start of unread data in buf
+ scan scanner
+ err error
+
+ tokenState int
+ tokenStack []int
}
// NewDecoder returns a new decoder that reads from r.
return dec.err
}
+ if err := dec.tokenPrepareForDecode(); err != nil {
+ return err
+ }
+
+ if !dec.tokenValueAllowed() {
+ return &SyntaxError{msg: "not at beginning of value"}
+ }
+
+ // Read whole value into buffer.
n, err := dec.readValue()
if err != nil {
return err
}
+ dec.d.init(dec.buf[dec.scanp : dec.scanp+n])
+ dec.scanp += n
// 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]
+ // fixup token streaming state
+ dec.tokenValueEnd()
return err
}
// Buffered returns a reader of the data remaining in the Decoder's
// buffer. The reader is valid until the next call to Decode.
func (dec *Decoder) Buffered() io.Reader {
- return bytes.NewReader(dec.buf)
+ return bytes.NewReader(dec.buf[dec.scanp:])
}
// readValue reads a JSON value into dec.buf.
func (dec *Decoder) readValue() (int, error) {
dec.scan.reset()
- scanp := 0
+ scanp := dec.scanp
var err error
Input:
for {
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
- }
+ n := scanp - dec.scanp
+ err = dec.refill()
+ scanp = dec.scanp + n
+ }
+ return scanp - dec.scanp, nil
+}
+
+func (dec *Decoder) refill() error {
+ // Make room to read more into the buffer.
+ // First slide down data already consumed.
+ if dec.scanp > 0 {
+ n := copy(dec.buf, dec.buf[dec.scanp:])
+ dec.buf = dec.buf[:n]
+ dec.scanp = 0
+ }
- // 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]
+ // Grow buffer if not large enough.
+ 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
}
- return scanp, nil
+
+ // Read. Delay error for next iteration (after scan).
+ n, err := dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
+ dec.buf = dec.buf[0 : len(dec.buf)+n]
+
+ return err
}
func nonSpace(b []byte) bool {
var _ Marshaler = (*RawMessage)(nil)
var _ Unmarshaler = (*RawMessage)(nil)
+
+// A Token holds a value of one of these types:
+//
+// Delim, for the four JSON delimiters [ ] { }
+// bool, for JSON booleans
+// float64, for JSON numbers
+// Number, for JSON numbers
+// string, for JSON string literals
+// nil, for JSON null
+//
+type Token interface{}
+
+const (
+ tokenTopValue = iota
+ tokenArrayStart
+ tokenArrayValue
+ tokenArrayComma
+ tokenObjectStart
+ tokenObjectKey
+ tokenObjectColon
+ tokenObjectValue
+ tokenObjectComma
+)
+
+// advance tokenstate from a separator state to a value state
+func (dec *Decoder) tokenPrepareForDecode() error {
+ c, err := dec.peek()
+ if err != nil {
+ return err
+ }
+ switch dec.tokenState {
+ case tokenArrayComma:
+ if c != ',' {
+ return &SyntaxError{"expected comma after array element", 0}
+ }
+ dec.scanp++
+ dec.tokenState = tokenArrayValue
+ case tokenObjectColon:
+ if c != ':' {
+ return &SyntaxError{"expected colon after object key", 0}
+ }
+ dec.scanp++
+ dec.tokenState = tokenObjectValue
+ }
+ return nil
+}
+
+func (dec *Decoder) tokenValueAllowed() bool {
+ switch dec.tokenState {
+ case tokenTopValue, tokenArrayStart, tokenArrayValue, tokenObjectValue:
+ return true
+ }
+ return false
+}
+
+func (dec *Decoder) tokenValueEnd() {
+ switch dec.tokenState {
+ case tokenArrayStart, tokenArrayValue:
+ dec.tokenState = tokenArrayComma
+ case tokenObjectValue:
+ dec.tokenState = tokenObjectComma
+ }
+}
+
+// A Delim is a JSON array or object delimiter, one of [ ] { or }.
+type Delim rune
+
+func (d Delim) String() string {
+ return string(d)
+}
+
+// Token returns the next JSON token in the input stream.
+// At the end of the input stream, Token returns nil, io.EOF.
+//
+// Token guarantees that the delimiters [ ] { } it returns are
+// properly nested and matched: if Token encounters an unexpected
+// delimiter in the input, it will return an error.
+//
+// The input stream consists of basic JSON values—bool, string,
+// number, and null—along with delimiters [ ] { } of type Delim
+// to mark the start and end of arrays and objects.
+// Commas and colons are elided.
+func (dec *Decoder) Token() (Token, error) {
+ for {
+ c, err := dec.peek()
+ if err != nil {
+ return nil, err
+ }
+ switch c {
+ case '[':
+ if !dec.tokenValueAllowed() {
+ return dec.tokenError(c)
+ }
+ dec.scanp++
+ dec.tokenStack = append(dec.tokenStack, dec.tokenState)
+ dec.tokenState = tokenArrayStart
+ return Delim('['), nil
+
+ case ']':
+ if dec.tokenState != tokenArrayStart && dec.tokenState != tokenArrayComma {
+ return dec.tokenError(c)
+ }
+ dec.scanp++
+ dec.tokenState = dec.tokenStack[len(dec.tokenStack)-1]
+ dec.tokenStack = dec.tokenStack[:len(dec.tokenStack)-1]
+ dec.tokenValueEnd()
+ return Delim(']'), nil
+
+ case '{':
+ if !dec.tokenValueAllowed() {
+ return dec.tokenError(c)
+ }
+ dec.scanp++
+ dec.tokenStack = append(dec.tokenStack, dec.tokenState)
+ dec.tokenState = tokenObjectStart
+ return Delim('{'), nil
+
+ case '}':
+ if dec.tokenState != tokenObjectStart && dec.tokenState != tokenObjectComma {
+ return dec.tokenError(c)
+ }
+ dec.scanp++
+ dec.tokenState = dec.tokenStack[len(dec.tokenStack)-1]
+ dec.tokenStack = dec.tokenStack[:len(dec.tokenStack)-1]
+ dec.tokenValueEnd()
+ return Delim('}'), nil
+
+ case ':':
+ if dec.tokenState != tokenObjectColon {
+ return dec.tokenError(c)
+ }
+ dec.scanp++
+ dec.tokenState = tokenObjectValue
+ continue
+
+ case ',':
+ if dec.tokenState == tokenArrayComma {
+ dec.scanp++
+ dec.tokenState = tokenArrayValue
+ continue
+ }
+ if dec.tokenState == tokenObjectComma {
+ dec.scanp++
+ dec.tokenState = tokenObjectKey
+ continue
+ }
+ return dec.tokenError(c)
+
+ case '"':
+ if dec.tokenState == tokenObjectStart || dec.tokenState == tokenObjectKey {
+ var x string
+ old := dec.tokenState
+ dec.tokenState = tokenTopValue
+ err := dec.Decode(&x)
+ dec.tokenState = old
+ if err != nil {
+ clearOffset(err)
+ return nil, err
+ }
+ dec.tokenState = tokenObjectColon
+ return x, nil
+ }
+ fallthrough
+
+ default:
+ if !dec.tokenValueAllowed() {
+ return dec.tokenError(c)
+ }
+ var x interface{}
+ if err := dec.Decode(&x); err != nil {
+ clearOffset(err)
+ 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(int(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) {
+ for {
+ for i := dec.scanp; i < len(dec.buf); i++ {
+ c := dec.buf[i]
+ if isSpace(rune(c)) {
+ continue
+ }
+ dec.scanp = i
+ return c, nil
+ }
+ if err := dec.refill(); err != nil {
+ return 0, err
+ }
+ }
+}
+
+/*
+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 {
+ ...
+}
+
+*/
import (
"bytes"
+ "io"
"io/ioutil"
"net"
"reflect"
}
}
}
+
+type tokenStreamCase struct {
+ json string
+ expTokens []interface{}
+}
+
+type decodeThis struct {
+ v interface{}
+}
+
+var tokenStreamCases []tokenStreamCase = []tokenStreamCase{
+ // streaming token cases
+ {json: `10`, expTokens: []interface{}{float64(10)}},
+ {json: ` [10] `, expTokens: []interface{}{
+ Delim('['), float64(10), Delim(']')}},
+ {json: ` [false,10,"b"] `, expTokens: []interface{}{
+ Delim('['), false, float64(10), "b", Delim(']')}},
+ {json: `{ "a": 1 }`, expTokens: []interface{}{
+ Delim('{'), "a", float64(1), Delim('}')}},
+ {json: `{"a": 1, "b":"3"}`, expTokens: []interface{}{
+ Delim('{'), "a", float64(1), "b", "3", Delim('}')}},
+ {json: ` [{"a": 1},{"a": 2}] `, expTokens: []interface{}{
+ Delim('['),
+ Delim('{'), "a", float64(1), Delim('}'),
+ Delim('{'), "a", float64(2), Delim('}'),
+ Delim(']')}},
+ {json: `{"obj": {"a": 1}}`, expTokens: []interface{}{
+ Delim('{'), "obj", Delim('{'), "a", float64(1), Delim('}'),
+ Delim('}')}},
+ {json: `{"obj": [{"a": 1}]}`, expTokens: []interface{}{
+ Delim('{'), "obj", Delim('['),
+ Delim('{'), "a", float64(1), Delim('}'),
+ Delim(']'), Delim('}')}},
+
+ // streaming tokens with intermittent Decode()
+ {json: `{ "a": 1 }`, expTokens: []interface{}{
+ Delim('{'), "a",
+ decodeThis{float64(1)},
+ Delim('}')}},
+ {json: ` [ { "a" : 1 } ] `, expTokens: []interface{}{
+ Delim('['),
+ decodeThis{map[string]interface{}{"a": float64(1)}},
+ Delim(']')}},
+ {json: ` [{"a": 1},{"a": 2}] `, expTokens: []interface{}{
+ Delim('['),
+ decodeThis{map[string]interface{}{"a": float64(1)}},
+ decodeThis{map[string]interface{}{"a": float64(2)}},
+ Delim(']')}},
+ {json: `{ "obj" : [ { "a" : 1 } ] }`, expTokens: []interface{}{
+ Delim('{'), "obj", Delim('['),
+ decodeThis{map[string]interface{}{"a": float64(1)}},
+ Delim(']'), Delim('}')}},
+
+ {json: `{"obj": {"a": 1}}`, expTokens: []interface{}{
+ Delim('{'), "obj",
+ decodeThis{map[string]interface{}{"a": float64(1)}},
+ Delim('}')}},
+ {json: `{"obj": [{"a": 1}]}`, expTokens: []interface{}{
+ Delim('{'), "obj",
+ decodeThis{[]interface{}{
+ map[string]interface{}{"a": float64(1)},
+ }},
+ Delim('}')}},
+ {json: ` [{"a": 1} {"a": 2}] `, expTokens: []interface{}{
+ Delim('['),
+ decodeThis{map[string]interface{}{"a": float64(1)}},
+ decodeThis{&SyntaxError{"expected comma after array element", 0}},
+ }},
+ {json: `{ "a" 1 }`, expTokens: []interface{}{
+ Delim('{'), "a",
+ decodeThis{&SyntaxError{"expected colon after object key", 0}},
+ }},
+}
+
+func TestDecodeInStream(t *testing.T) {
+
+ for ci, tcase := range tokenStreamCases {
+
+ dec := NewDecoder(strings.NewReader(tcase.json))
+ for i, etk := range tcase.expTokens {
+
+ var tk interface{}
+ var err error
+
+ if dt, ok := etk.(decodeThis); ok {
+ etk = dt.v
+ err = dec.Decode(&tk)
+ } else {
+ tk, err = dec.Token()
+ }
+ if experr, ok := etk.(error); ok {
+ if err == nil || err.Error() != experr.Error() {
+ t.Errorf("case %v: Expected error %v in %q, but was %v", ci, experr, tcase.json, err)
+ }
+ break
+ } else if err == io.EOF {
+ t.Errorf("case %v: Unexpected EOF in %q", ci, tcase.json)
+ break
+ } else if err != nil {
+ t.Errorf("case %v: Unexpected error '%v' in %q", ci, err, tcase.json)
+ break
+ }
+ if !reflect.DeepEqual(tk, etk) {
+ t.Errorf(`case %v: %q @ %v expected %T(%v) was %T(%v)`, ci, tcase.json, i, etk, etk, tk, tk)
+ break
+ }
+ }
+ }
+
+}