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Merged
MrAlias merged 2 commits into from
Mar 5, 2026
Merged

largebuffers: Add cursor integer helpers #1476

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1d84127
Add cursor helpers
rafaelroquetto Mar 5, 2026
9457c4a
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rafaelroquetto Mar 5, 2026
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117 changes: 117 additions & 0 deletions pkg/internal/largebuf/large_buffer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -543,6 +543,123 @@ func (r *LargeBufferReader) Bytes() []byte {
return b
}

// ── Cursor-based scalar helpers ───────────────────────────────────────────────
//
// Each helper reads a fixed-width integer at the current cursor position and advances it.
// All delegate to ReadN: zero-copy within a chunk, scratch-backed across boundaries.

// ReadU8 reads a uint8 at the current cursor position.
func (r *LargeBufferReader) ReadU8() (uint8, error) {
b, err := r.ReadN(1)
if err != nil {
return 0, err
}

return b[0], nil
}

// ReadU16BE reads a big-endian uint16 at the current cursor position.
func (r *LargeBufferReader) ReadU16BE() (uint16, error) {
b, err := r.ReadN(2)
if err != nil {
return 0, err
}

return binary.BigEndian.Uint16(b), nil
}
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rafaelroquetto marked this conversation as resolved.

// ReadI16BE reads a big-endian int16 at the current cursor position.
func (r *LargeBufferReader) ReadI16BE() (int16, error) {
v, err := r.ReadU16BE()

return int16(v), err
}

// ReadU32BE reads a big-endian uint32 at the current cursor position.
func (r *LargeBufferReader) ReadU32BE() (uint32, error) {
b, err := r.ReadN(4)
if err != nil {
return 0, err
}

return binary.BigEndian.Uint32(b), nil
}

// ReadI32BE reads a big-endian int32 at the current cursor position.
func (r *LargeBufferReader) ReadI32BE() (int32, error) {
v, err := r.ReadU32BE()

return int32(v), err
}

// ReadU64BE reads a big-endian uint64 at the current cursor position.
func (r *LargeBufferReader) ReadU64BE() (uint64, error) {
b, err := r.ReadN(8)
if err != nil {
return 0, err
}

return binary.BigEndian.Uint64(b), nil
}

// ReadI64BE reads a big-endian int64 at the current cursor position.
func (r *LargeBufferReader) ReadI64BE() (int64, error) {
v, err := r.ReadU64BE()

return int64(v), err
}

// ReadU16LE reads a little-endian uint16 at the current cursor position.
func (r *LargeBufferReader) ReadU16LE() (uint16, error) {
b, err := r.ReadN(2)
if err != nil {
return 0, err
}

return binary.LittleEndian.Uint16(b), nil
}

// ReadI16LE reads a little-endian int16 at the current cursor position.
func (r *LargeBufferReader) ReadI16LE() (int16, error) {
v, err := r.ReadU16LE()

return int16(v), err
}

// ReadU32LE reads a little-endian uint32 at the current cursor position.
func (r *LargeBufferReader) ReadU32LE() (uint32, error) {
b, err := r.ReadN(4)
if err != nil {
return 0, err
}

return binary.LittleEndian.Uint32(b), nil
}

// ReadI32LE reads a little-endian int32 at the current cursor position.
func (r *LargeBufferReader) ReadI32LE() (int32, error) {
v, err := r.ReadU32LE()

return int32(v), err
}

// ReadU64LE reads a little-endian uint64 at the current cursor position.
func (r *LargeBufferReader) ReadU64LE() (uint64, error) {
b, err := r.ReadN(8)
if err != nil {
return 0, err
}

return binary.LittleEndian.Uint64(b), nil
}

// ReadI64LE reads a little-endian int64 at the current cursor position.
func (r *LargeBufferReader) ReadI64LE() (int64, error) {
v, err := r.ReadU64LE()

return int64(v), err
}

// copyN copies exactly len(dst) bytes from the current read position into dst, advancing the
// cursor. Assumes the caller has already verified that len(dst) <= r.Remaining().
func (r *LargeBufferReader) copyN(dst []byte) {
Expand Down
209 changes: 209 additions & 0 deletions pkg/internal/largebuf/large_buffer_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -974,6 +974,215 @@ func TestCursorUnchanged_byAbsoluteOffsetMethods(t *testing.T) {
assert.Equal(t, before, r.ReadOffset(), "U32LEAt must not move cursor")
}

// ── Cursor-based scalar helpers ───────────────────────────────────────────────

func TestReaderScalarBE_withinSingleChunk(t *testing.T) {
// Sequential layout: U8 | U16BE | U32BE | U64BE | I16BE | I32BE | I64BE
data := []byte{
0x42,
0x01, 0x02,
0x01, 0x02, 0x03, 0x04,
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x01, 0x02,
0x01, 0x02, 0x03, 0x04,
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
}
lb := NewLargeBufferFrom(data)
r := lb.NewReader()

u8, err := r.ReadU8()
require.NoError(t, err)
assert.Equal(t, uint8(0x42), u8)

u16, err := r.ReadU16BE()
require.NoError(t, err)
assert.Equal(t, uint16(0x0102), u16)

u32, err := r.ReadU32BE()
require.NoError(t, err)
assert.Equal(t, uint32(0x01020304), u32)

u64, err := r.ReadU64BE()
require.NoError(t, err)
assert.Equal(t, uint64(0x0102030405060708), u64)

i16, err := r.ReadI16BE()
require.NoError(t, err)
assert.Equal(t, int16(0x0102), i16)

i32, err := r.ReadI32BE()
require.NoError(t, err)
assert.Equal(t, int32(0x01020304), i32)

i64, err := r.ReadI64BE()
require.NoError(t, err)
assert.Equal(t, int64(0x0102030405060708), i64)

assert.Equal(t, 0, r.Remaining())
}

func TestReaderScalarBE_crossChunkBoundary(t *testing.T) {
lb := NewLargeBuffer()
lb.AppendChunk([]byte{0x01, 0x02})
lb.AppendChunk([]byte{0x03, 0x04, 0x05, 0x06, 0x07, 0x08})

r := lb.NewReader()

u32, err := r.ReadU32BE()
require.NoError(t, err)
assert.Equal(t, uint32(0x01020304), u32)

r.Reset()
u64, err := r.ReadU64BE()
require.NoError(t, err)
assert.Equal(t, uint64(0x0102030405060708), u64)
}

func TestReaderScalarBE_signedNegativeValues(t *testing.T) {
lb := NewLargeBufferFrom(bytes.Repeat([]byte{0xFF}, 14)) // 2+4+8 bytes
r := lb.NewReader()

i16, err := r.ReadI16BE()
require.NoError(t, err)
assert.Equal(t, int16(-1), i16)

i32, err := r.ReadI32BE()
require.NoError(t, err)
assert.Equal(t, int32(-1), i32)

i64, err := r.ReadI64BE()
require.NoError(t, err)
assert.Equal(t, int64(-1), i64)
}

func TestReaderScalarLE_withinSingleChunk(t *testing.T) {
// Sequential layout: U16LE | U32LE | U64LE | I16LE | I32LE | I64LE
data := []byte{
0x02, 0x01,
0x04, 0x03, 0x02, 0x01,
0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01,
0x02, 0x01,
0x04, 0x03, 0x02, 0x01,
0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01,
}
lb := NewLargeBufferFrom(data)
r := lb.NewReader()

u16, err := r.ReadU16LE()
require.NoError(t, err)
assert.Equal(t, uint16(0x0102), u16)

u32, err := r.ReadU32LE()
require.NoError(t, err)
assert.Equal(t, uint32(0x01020304), u32)

u64, err := r.ReadU64LE()
require.NoError(t, err)
assert.Equal(t, uint64(0x0102030405060708), u64)

i16, err := r.ReadI16LE()
require.NoError(t, err)
assert.Equal(t, int16(0x0102), i16)

i32, err := r.ReadI32LE()
require.NoError(t, err)
assert.Equal(t, int32(0x01020304), i32)

i64, err := r.ReadI64LE()
require.NoError(t, err)
assert.Equal(t, int64(0x0102030405060708), i64)

assert.Equal(t, 0, r.Remaining())
}

func TestReaderScalarLE_crossChunkBoundary(t *testing.T) {
lb := NewLargeBuffer()
lb.AppendChunk([]byte{0x04, 0x03})
lb.AppendChunk([]byte{0x02, 0x01, 0x08, 0x07, 0x06, 0x05})

r := lb.NewReader()

u32, err := r.ReadU32LE()
require.NoError(t, err)
assert.Equal(t, uint32(0x01020304), u32)

r.Reset()
u64, err := r.ReadU64LE()
require.NoError(t, err)
assert.Equal(t, uint64(0x0506070801020304), u64)
}

func TestReaderScalarLE_signedNegativeValues(t *testing.T) {
lb := NewLargeBufferFrom(bytes.Repeat([]byte{0xFF}, 14)) // 2+4+8 bytes
r := lb.NewReader()

i16, err := r.ReadI16LE()
require.NoError(t, err)
assert.Equal(t, int16(-1), i16)

i32, err := r.ReadI32LE()
require.NoError(t, err)
assert.Equal(t, int32(-1), i32)

i64, err := r.ReadI64LE()
require.NoError(t, err)
assert.Equal(t, int64(-1), i64)
}

func TestReaderScalar_advancesCursor(t *testing.T) {
lb := NewLargeBufferFrom(bytes.Repeat([]byte{0x00}, 16))
r := lb.NewReader()

assert.Equal(t, 16, r.Remaining())
_, err := r.ReadU8()
require.NoError(t, err)
assert.Equal(t, 15, r.Remaining())
_, err = r.ReadU16BE()
require.NoError(t, err)
assert.Equal(t, 13, r.Remaining())
_, err = r.ReadU32BE()
require.NoError(t, err)
assert.Equal(t, 9, r.Remaining())
_, err = r.ReadU64BE()
require.NoError(t, err)
assert.Equal(t, 1, r.Remaining())
}

func TestReaderScalar_tooShort_returnsError(t *testing.T) {
lb := NewLargeBufferFrom([]byte{0x01, 0x02})
r := lb.NewReader()

_, _ = r.ReadU16BE() // consume all bytes

_, err := r.ReadU8()
require.Error(t, err)

r.Reset()
_, _ = r.ReadU8()
_, err = r.ReadU16BE() // only 1 byte left
require.Error(t, err)
}

func TestReaderScalar_zeroAllocs(t *testing.T) {
lb := NewLargeBufferFrom(bytes.Repeat([]byte{0x01}, 64))
r := lb.NewReader()
// lastErr is declared outside the closure so require.NoError can be called
// after AllocsPerRun as calling it inside the closure would itself allocate.
var lastErr error

allocs := testing.AllocsPerRun(1000, func() {
r.Reset()
for r.Remaining() >= 4 {
if _, lastErr = r.ReadU32BE(); lastErr != nil {
break
}
}
})

require.NoError(t, lastErr)
assert.Zero(t, allocs, "cursor scalar reads within a single chunk must be zero-alloc")
}

// ── Zero-alloc verification for hot path ─────────────────────────────────────

func TestReadN_singleChunk_zeroAllocsWithBinaryDecode(t *testing.T) {
Expand Down