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fix(parquet): handle short input in GetBatchBools #946

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Merged
zeroshade merged 1 commit into from
Jul 16, 2026
+158 −6
Merged

fix(parquet): handle short input in GetBatchBools #946

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63 changes: 57 additions & 6 deletions parquet/internal/utils/bit_reader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,11 @@ func (b *BitReader) GetBatchBools(out []bool) (int, error) {
i := 0
// read until we are byte-aligned
for ; i < length && b.bitoffset != 0; i++ {
if i == 0 || b.bitoffset%8 == 0 {
if err := b.ensureBoolBitAvailable(); err != nil {
return i, err
}
}
val, err := b.next(bits)
out[i] = val != 0
if err != nil {
Expand All @@ -323,22 +328,53 @@ func (b *BitReader) GetBatchBools(out []bool) (int, error) {
b.reader.Seek(b.byteoffset, io.SeekStart)
buf := arrow.Uint32Traits.CastToBytes(b.unpackBuf[:])
blen := buflen * 8
for i < length {
for length-i >= 8 {

@zeroshade zeroshade Jul 15, 2026

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This full-byte loop is correct, but after it (length-i in 1..7) the sub-byte remainder falls through to b.fillbuffer() + the trailing for ; i < length { b.next(1) } loop, and fillbuffer zero-pads / suppresses EOF — so short input still fabricates false values instead of stopping.

Concrete: out := make([]bool, 9) over a 1-byte input decodes 8 real bits, then the trailing loop appends a 9th false and returns (9, nil) instead of (8, io.ErrUnexpectedEOF). Same class for 1–7 bools from empty input, or 9–15 from one byte.

Also: this PR and #944 both rewrite bit_reader.go (#944 adds validBits accounting to next/fillbuffer, which would actually close this trailing-path gap). They will conflict — worth coordinating the two.

// grab byte-aligned bits in a loop since it's more efficient than going
// bit by bit when you can grab 8 bools at a time.
unpackSize := utils.Min(blen, length-i) / 8 * 8
n, err := b.reader.Read(buf[:bitutil.BytesForBits(int64(unpackSize))])
if err != nil {
return i, err
bytesToRead := int(bitutil.BytesForBits(int64(unpackSize)))
n := 0
for n < bytesToRead {
nread, err := b.reader.Read(buf[n:bytesToRead])
n += nread
if n == bytesToRead {
break
}
if err != nil {
if n > 0 {
BytesToBools(buf[:n], out[i:])
}
i += n * 8
b.byteoffset += int64(n)
if err == io.EOF && n > 0 {
err = io.ErrUnexpectedEOF
}
return i, err
}
if nread == 0 {
if n > 0 {
BytesToBools(buf[:n], out[i:])
}
i += n * 8
b.byteoffset += int64(n)
return i, io.ErrNoProgress
}
}
BytesToBools(buf[:n], out[i:])
i += unpackSize
i += n * 8
b.byteoffset += int64(n)
}

b.fillbuffer()
if err := b.fillbuffer(); err != nil {
return i, err
}
// grab the trailing bits
for ; i < length; i++ {
if b.bitoffset%8 == 0 {
if err := b.ensureBoolBitAvailable(); err != nil {
return i, err
}
}
val, err := b.next(bits)
out[i] = val != 0
if err != nil {
Expand All @@ -349,6 +385,21 @@ func (b *BitReader) GetBatchBools(out []bool) (int, error) {
return i, nil
}

func (b *BitReader) ensureBoolBitAvailable() error {
var probe [1]byte
n, err := b.reader.ReadAt(probe[:], b.byteoffset+int64(b.bitoffset/8))
if n == 1 {
return nil
}
if err == nil {
return io.ErrNoProgress
}
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}

func (b *BitReader) Discard(bits uint, n int) (int, error) {
if bits > 64 {
return 0, errors.New("must be 64 bits or less per read")
Expand Down
101 changes: 101 additions & 0 deletions parquet/internal/utils/bit_reader_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import (
"bytes"
"encoding/binary"
"fmt"
"io"
"math"
"math/bits"
"math/rand/v2"
Expand Down Expand Up @@ -78,6 +79,106 @@ func BenchmarkBitWriter(b *testing.B) {
}
}

type stalledReader struct {
*bytes.Reader
}

func (*stalledReader) Read([]byte) (int, error) { return 0, nil }

func TestBitReaderGetBatchBools(t *testing.T) {
data := []byte{0xAA, 0xCC, 0xF0}
for length := 0; length <= 17; length++ {
t.Run(fmt.Sprintf("aligned/%d", length), func(t *testing.T) {
reader := utils.NewBitReader(bytes.NewReader(data))
out := make([]bool, length)
n, err := reader.GetBatchBools(out)
assert.NoError(t, err)
assert.Equal(t, length, n)
for i, got := range out {
assert.Equal(t, data[i/8]&(1<<uint(i%8)) != 0, got)
}
})

t.Run(fmt.Sprintf("unaligned/%d", length), func(t *testing.T) {
reader := utils.NewBitReader(bytes.NewReader(data))
_, ok := reader.GetValue(1)
assert.True(t, ok)

out := make([]bool, length)
n, err := reader.GetBatchBools(out)
assert.NoError(t, err)
assert.Equal(t, length, n)
for i, got := range out {
bit := i + 1
assert.Equal(t, data[bit/8]&(1<<uint(bit%8)) != 0, got)
}
})
}

t.Run("truncated", func(t *testing.T) {
reader := utils.NewBitReader(bytes.NewReader(data[:1]))
out := make([]bool, 16)
n, err := reader.GetBatchBools(out)
assert.ErrorIs(t, err, io.ErrUnexpectedEOF)
assert.Equal(t, 8, n)
for i, got := range out[:n] {
assert.Equal(t, data[0]&(1<<uint(i)) != 0, got)
}
})

t.Run("truncated remainder", func(t *testing.T) {
for _, tc := range []struct {
length, inputBytes, expected int
}{
{length: 1, inputBytes: 0, expected: 0},
{length: 7, inputBytes: 0, expected: 0},
{length: 9, inputBytes: 1, expected: 8},
{length: 15, inputBytes: 1, expected: 8},
{length: 17, inputBytes: 2, expected: 16},
} {
t.Run(fmt.Sprint(tc.length), func(t *testing.T) {
reader := utils.NewBitReader(bytes.NewReader(data[:tc.inputBytes]))
out := make([]bool, tc.length)
for i := range out {
out[i] = true
}

n, err := reader.GetBatchBools(out)
assert.ErrorIs(t, err, io.ErrUnexpectedEOF)
assert.Equal(t, tc.expected, n)
for i, got := range out[:n] {
assert.Equal(t, data[i/8]&(1<<uint(i%8)) != 0, got)
}
for _, got := range out[n:] {
assert.True(t, got)
}
})
}
})

t.Run("truncated unaligned", func(t *testing.T) {
reader := utils.NewBitReader(bytes.NewReader(data[:1]))
_, ok := reader.GetValue(1)
assert.True(t, ok)

out := make([]bool, 8)
n, err := reader.GetBatchBools(out)
assert.ErrorIs(t, err, io.ErrUnexpectedEOF)
assert.Equal(t, 7, n)
for i, got := range out[:n] {
bit := i + 1
assert.Equal(t, data[bit/8]&(1<<uint(bit%8)) != 0, got)
}
})

t.Run("no progress", func(t *testing.T) {
reader := utils.NewBitReader(&stalledReader{bytes.NewReader(nil)})
n, err := reader.GetBatchBools(make([]bool, 8))
assert.ErrorIs(t, err, io.ErrNoProgress)
assert.Zero(t, n)
})
}

func TestBitReader(t *testing.T) {
buf := []byte{0xAA, 0xCC} // 0b10101010 0b11001100

Expand Down
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