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feat: improve null and bool decoding #18

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merged 4 commits into from
Jan 14, 2022
Merged

feat: improve null and bool decoding #18

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a9b7a05
feat: improve null decoding
tdakkota Jan 12, 2022
1082630
fix: return ErrUnexpectedEOF if ReadAtLeast return EOF
tdakkota Jan 14, 2022
971965f
feat: improve true/false reading
tdakkota Jan 14, 2022
cbdf6d5
chore: add bools.json and nulls.json
tdakkota Jan 14, 2022
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22 changes: 22 additions & 0 deletions dec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -246,6 +246,28 @@ func (d *Decoder) read() error {
return nil
}

func (d *Decoder) readAtLeast(min int) error {
if d.reader == nil {
d.head = d.tail
return io.ErrUnexpectedEOF
}

if need := min - len(d.buf); need > 0 {
d.buf = append(d.buf, make([]byte, need)...)
}
n, err := io.ReadAtLeast(d.reader, d.buf, min)
if err != nil {
if err == io.EOF && n == 0 {
return io.ErrUnexpectedEOF
}
return err
}

d.head = 0
d.tail = n
return nil
}

func (d *Decoder) unread() { d.head-- }

// limit maximum depth of nesting, as allowed by https://tools.ietf.org/html/rfc7159#section-9
Expand Down
96 changes: 54 additions & 42 deletions dec_skip.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,35 +2,72 @@ package jx

import (
"io"
"math/bits"

"github.com/go-faster/errors"
)

func (d *Decoder) readExact4(b *[4]byte) error {
if buf := d.buf[d.head:d.tail]; len(buf) >= len(b) {
d.head += copy(b[:], buf[:4])
return nil
}

n := copy(b[:], d.buf[d.head:d.tail])
if err := d.readAtLeast(len(b) - n); err != nil {
return err
}
d.head += copy(b[n:], d.buf[d.head:d.tail])
return nil
}

func findInvalidToken4(buf [4]byte, mask uint32) error {
c := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
idx := bits.TrailingZeros32(c^mask) / 8
return badToken(buf[idx])
}

// Null reads a json object as null and
// returns whether it's a null or not.
func (d *Decoder) Null() error {
if err := d.consume('n'); err != nil {
var buf [4]byte
if err := d.readExact4(&buf); err != nil {
return err
}
return d.skipThreeBytes('u', 'l', 'l') // null

if string(buf[:]) != "null" {
const encodedNull = 'n' | 'u'<<8 | 'l'<<16 | 'l'<<24
return findInvalidToken4(buf, encodedNull)
}
return nil
}

// Bool reads a json object as Bool
func (d *Decoder) Bool() (bool, error) {
c, err := d.next()
if err != nil {
var buf [4]byte
if err := d.readExact4(&buf); err != nil {
return false, err
}
switch c {
case 't':
if err := d.skipThreeBytes('r', 'u', 'e'); err != nil {

switch string(buf[:]) {
case "true":
return true, nil
case "fals":
if err := d.consume('e'); err != nil {
return false, err
}
return true, nil
case 'f':
return false, d.skipFourBytes('a', 'l', 's', 'e')
return false, nil
default:
return false, badToken(c)
switch c := buf[0]; c {
case 't':
const encodedTrue = 't' | 'r'<<8 | 'u'<<16 | 'e'<<24
return false, findInvalidToken4(buf, encodedTrue)
case 'f':
const encodedAlse = 'a' | 'l'<<8 | 's'<<16 | 'e'<<24
return false, findInvalidToken4(buf, encodedAlse)
default:
return false, badToken(c)
}
}
}

Expand All @@ -47,11 +84,12 @@ func (d *Decoder) Skip() error {
}
return nil
case 'n':
return d.skipThreeBytes('u', 'l', 'l') // null
case 't':
return d.skipThreeBytes('r', 'u', 'e') // true
case 'f':
return d.skipFourBytes('a', 'l', 's', 'e') // false
d.unread()
return d.Null()
case 't', 'f':
d.unread()
_, err := d.Bool()
return err
case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
d.unread()
return d.skipNumber()
Expand All @@ -70,32 +108,6 @@ func (d *Decoder) Skip() error {
}
}

func (d *Decoder) skipFourBytes(b1, b2, b3, b4 byte) error {
for _, b := range [...]byte{b1, b2, b3, b4} {
c, err := d.byte()
if err != nil {
return err
}
if c != b {
return badToken(c)
}
}
return nil
}

func (d *Decoder) skipThreeBytes(b1, b2, b3 byte) error {
for _, b := range [...]byte{b1, b2, b3} {
c, err := d.byte()
if err != nil {
return err
}
if c != b {
return badToken(c)
}
}
return nil
}

var (
skipNumberSet = [256]byte{
'0': 1,
Expand Down
22 changes: 22 additions & 0 deletions null_test.go
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -44,3 +44,25 @@ func Test_decode_null_skip(t *testing.T) {
t.FailNow()
}
}

func TestNullError(t *testing.T) {
a := require.New(t)
var (
b = [4]byte{'n', 'u', 'l', 'l'}
valid = b
)
for i := range b {
// Reset buffer.
b = valid
for c := byte(0); c < 255; c++ {
// Skip expected value.
if valid[i] == c {
continue
}
b[i] = c
var token badTokenErr
a.ErrorAs(DecodeBytes(b[:]).Null(), &token)
a.Equalf(c, token.Token, "%c != %c (%q)", c, token.Token, b)
}
}
}
103 changes: 103 additions & 0 deletions testdata/bools.json
View file
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Original file line number Diff line number Diff line change
@@ -0,0 +1,103 @@
[
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false,
true,
false
]

103 changes: 103 additions & 0 deletions testdata/nulls.json
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,103 @@
[
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null,
null
]