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support callback api and early abort #14

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69 changes: 42 additions & 27 deletions decoder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,10 @@ import (
"unicode/utf16"
)

// Receiver defines the callback function to receive the emitted tokens,
// return true to continue parsing, false to stop.
type Receiver = func(*MetaValue) bool

// ValueType - defines the type of each JSON value
type ValueType int

Expand Down Expand Up @@ -73,7 +77,6 @@ type Decoder struct {

depth int
scratch *scratch
metaCh chan *MetaValue
err error

// follow line position to add context to errors
Expand All @@ -89,7 +92,6 @@ func NewDecoder(r io.Reader, emitDepth int) *Decoder {
scanner: newScanner(r),
emitDepth: emitDepth,
scratch: &scratch{data: make([]byte, 1024)},
metaCh: make(chan *MetaValue, 128),
}
if emitDepth < 0 {
d.emitDepth = 0
Expand Down Expand Up @@ -127,8 +129,15 @@ func (d *Decoder) Recursive() *Decoder {
// Stream begins decoding from the underlying reader and returns a
// streaming MetaValue channel for JSON values at the configured emitDepth.
func (d *Decoder) Stream() chan *MetaValue {
go d.decode()
return d.metaCh
metaCh := make(chan *MetaValue, 128)
go func() {
defer close(metaCh)
d.err = d.Decode(func(meta *MetaValue) bool {
metaCh <- meta
return true
})
}()
return metaCh
}

// Pos returns the number of bytes consumed from the underlying reader
Expand All @@ -138,32 +147,32 @@ func (d *Decoder) Pos() int { return int(d.pos) }
func (d *Decoder) Err() error { return d.err }

// Decode parses the JSON-encoded data and returns an interface value
func (d *Decoder) decode() {
defer close(d.metaCh)
func (d *Decoder) Decode(receiver Receiver) error {
d.skipSpaces()
for d.remaining() > 0 {
_, err := d.emitAny()
if err != nil {
d.err = err
break
if _, err := d.emitAny(receiver); err != nil {
return err
}
d.skipSpaces()
}
return nil
}

func (d *Decoder) emitAny() (interface{}, error) {
func (d *Decoder) emitAny(receiver Receiver) (interface{}, error) {
if d.pos >= atomic.LoadInt64(&d.end) {
return nil, d.mkError(ErrUnexpectedEOF)
}
offset := d.pos - 1
i, t, err := d.any()
i, t, err := d.any(receiver)
if d.willEmit() {
d.metaCh <- &MetaValue{
if !receiver(&MetaValue{
Offset: int(offset),
Length: int(d.pos - offset),
Depth: d.depth,
Value: i,
ValueType: t,
}) {
return nil, d.mkError(ErrCanceled)
}
}
return i, err
Expand All @@ -180,7 +189,7 @@ func (d *Decoder) willEmit() bool {

// any used to decode any valid JSON value, and returns an
// interface{} that holds the actual data
func (d *Decoder) any() (interface{}, ValueType, error) {
func (d *Decoder) any(receiver Receiver) (interface{}, ValueType, error) {
c := d.cur()

switch c {
Expand Down Expand Up @@ -224,15 +233,15 @@ func (d *Decoder) any() (interface{}, ValueType, error) {
}
return nil, Unknown, d.mkError(ErrSyntax, "in literal null")
case '[':
i, err := d.array()
i, err := d.array(receiver)
return i, Array, err
case '{':
var i interface{}
var err error
if d.objectAsKVS {
i, err = d.objectOrdered()
i, err = d.objectOrdered(receiver)
} else {
i, err = d.object()
i, err = d.object(receiver)
}
return i, Object, err
default:
Expand Down Expand Up @@ -415,7 +424,7 @@ func (d *Decoder) number() (float64, error) {
}

// array accept valid JSON array value
func (d *Decoder) array() ([]interface{}, error) {
func (d *Decoder) array(receiver Receiver) ([]interface{}, error) {
d.depth++

var (
Expand All @@ -431,7 +440,7 @@ func (d *Decoder) array() ([]interface{}, error) {
}

scan:
if v, err = d.emitAny(); err != nil {
if v, err = d.emitAny(receiver); err != nil {
goto out
}

Expand All @@ -456,7 +465,7 @@ out:
}

// object accept valid JSON array value
func (d *Decoder) object() (map[string]interface{}, error) {
func (d *Decoder) object(receiver Receiver) (map[string]interface{}, error) {
d.depth++

var (
Expand Down Expand Up @@ -500,20 +509,23 @@ scan:
// read value
d.skipSpaces()
if d.emitKV {
if v, t, err = d.any(); err != nil {
if v, t, err = d.any(receiver); err != nil {
break
}
if d.willEmit() {
d.metaCh <- &MetaValue{
if !receiver(&MetaValue{
Offset: int(offset),
Length: int(d.pos - offset),
Depth: d.depth,
Value: KV{k, v},
ValueType: t,
}) {
err = d.mkError(ErrCanceled)
break
}
}
} else {
if v, err = d.emitAny(); err != nil {
if v, err = d.emitAny(receiver); err != nil {
break
}
}
Expand Down Expand Up @@ -541,7 +553,7 @@ out:
}

// object (ordered) accept valid JSON array value
func (d *Decoder) objectOrdered() (KVS, error) {
func (d *Decoder) objectOrdered(receiver Receiver) (KVS, error) {
d.depth++

var (
Expand Down Expand Up @@ -585,20 +597,23 @@ scan:
// read value
d.skipSpaces()
if d.emitKV {
if v, t, err = d.any(); err != nil {
if v, t, err = d.any(receiver); err != nil {
break
}
if d.willEmit() {
d.metaCh <- &MetaValue{
if !receiver(&MetaValue{
Offset: int(offset),
Length: int(d.pos - offset),
Depth: d.depth,
Value: KV{k, v},
ValueType: t,
}) {
err = d.mkError(ErrCanceled)
break
}
}
} else {
if v, err = d.emitAny(); err != nil {
if v, err = d.emitAny(receiver); err != nil {
break
}
}
Expand Down
39 changes: 39 additions & 0 deletions decoder_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ package jstream

import (
"bytes"
"strings"
"testing"
)

Expand Down Expand Up @@ -235,3 +236,41 @@ func TestDecoderReaderFailure(t *testing.T) {
t.Fatalf("missing expected underlying reader error")
}
}

func TestDecoderCallback(t *testing.T) {
var result []*MetaValue
body := `{ "bio": "bada bing bada boom", "id": 1, "name": "Charles" }
{ "bio": "bada bing bada boom", "id": 2, "name": "Charles" }
{ "bio": "bada bing bada boom", "id": 3, "name": "Charles" }
{ "bio": "bada bing bada boom", "id": 4, "name": "Charles" }
{ "bio": "bada bing bada boom", "id": 5, "name": "Charles" }
`

// receive all
result = result[:0]
decoder := NewDecoder(mkReader(body), 0)
decoder.Decode(func(meta *MetaValue) bool {
result = append(result, meta)
return true
})
// assert result
if len(result) != 5 {
t.Fatalf("expected 5 items, got %d", len(result))
}

// receive 2
result = result[:0]
decoder = NewDecoder(mkReader(body), 0)
err := decoder.Decode(func(meta *MetaValue) bool {
result = append(result, meta)
return len(result) < 2
})
// assert result
if len(result) != 2 {
t.Fatalf("expected 2 items, got %d", len(result))
}
// assert cancel error
if err == nil || !strings.Contains(err.Error(), "operation canceled") {
t.Fatalf("expected cancel error, got %s", err)
}
}
1 change: 1 addition & 0 deletions errors.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import (
var (
ErrSyntax = DecoderError{msg: "invalid character"}
ErrUnexpectedEOF = DecoderError{msg: "unexpected end of JSON input"}
ErrCanceled = DecoderError{msg: "operation canceled"}
)

type errPos [2]int // line number, byte offset where error occurred
Expand Down