Add zero-copy serialization APIs.

buffer.go

@@ -8,6 +8,7 @@ import "C"
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"math"
 	"runtime"
 	"unsafe"
@@ -94,6 +95,8 @@ func (b *Buffer) Type() (Datatype, error) {
 }
 
 // Serialize returns a copy of the bytes in the buffer.
+//
+// Deprecated: Use WriteTo instead for increased performance.
 func (b *Buffer) Serialize(serializationType SerializationType) ([]byte, error) {
 	bs, err := b.dataCopy()
 	if err != nil {
@@ -103,14 +106,60 @@ func (b *Buffer) Serialize(serializationType SerializationType) ([]byte, error)
 	case TILEDB_CAPNP:
 		// The entire byte array contains Cap'nP data. Don't bother it.
 	case TILEDB_JSON:
-		// The data is a null-terminated string. Strip off the terminator.
+		// The data might be a null-terminated string. Strip off the terminator.
 		bs = bytes.TrimSuffix(bs, []byte{0})
 	default:
 		return nil, fmt.Errorf("unsupported serialization type: %v", serializationType)
 	}
 	return bs, nil
 }
 
+// WriteTo writes the contents of a Buffer to an io.Writer.
+func (b *Buffer) WriteTo(w io.Writer) (int64, error) {
+	var cbuffer unsafe.Pointer
+	var csize C.uint64_t
+
+	ret := C.tiledb_buffer_get_data(b.context.tiledbContext, b.tiledbBuffer, &cbuffer, &csize)
+	if ret != C.TILEDB_OK {
+		return 0, fmt.Errorf("error getting tiledb buffer data: %w", b.context.LastError())
+	}
+
+	if cbuffer == nil || csize == 0 {
+		return 0, nil
+	}
+
+	remaining := int64(csize)
+
+	// Because io.Writer supports writing up to 2GB of data at a time, we have to use a loop
+	// for the bigger buffers.
+	for remaining > 0 {
+		// TODO: Use min on Go 1.21+
+		var writeSize int32
+		if remaining > math.MaxInt32 {
+			writeSize = math.MaxInt32
+		} else {
+			writeSize = int32(remaining)
+		}
+
+		// Construct a slice from the buffer's data without copying it.
+		// Keep the buffer alive during the write, to prevent the GC from
+		// collecting the memory while it's being used.
+		n, err := w.Write(unsafe.Slice((*byte)(cbuffer), writeSize))
+
+		cbuffer = unsafe.Pointer(uintptr(cbuffer) + uintptr(n))
+		remaining -= int64(n)
+
+		if err != nil {
+			return int64(csize) - remaining, fmt.Errorf("error writing buffer to writer: %w", err)
+		}
+	}
+
+	return int64(csize), nil
+}
+
+// Static assert that Buffer implements io.WriterTo.
+var _ io.WriterTo = (*Buffer)(nil)
+
 // SetBuffer sets the buffer to point at the given Go slice. The memory is now
 // Go-managed.
 func (b *Buffer) SetBuffer(buffer []byte) error {

buffer_list.go

@@ -7,6 +7,7 @@ package tiledb
 import "C"
 import (
 	"fmt"
+	"io"
 )
 
 // BufferList A list of TileDB BufferList objects
@@ -44,6 +45,36 @@ func (b *BufferList) Context() *Context {
 	return b.context
 }
 
+// WriteTo writes the contents of a BufferList to an io.Writer.
+func (b *BufferList) WriteTo(w io.Writer) (int64, error) {
+	nbuffs, err := b.NumBuffers()
+	if err != nil {
+		return 0, err
+	}
+
+	written := int64(0)
+
+	for i := uint(0); i < uint(nbuffs); i++ {
+		buff, err := b.GetBuffer(i)
+		if err != nil {
+			return 0, err
+		}
+		n, err := buff.WriteTo(w)
+		written += n
+
+		buff.Free()
+
+		if err != nil {
+			return written, err
+		}
+	}
+
+	return written, nil
+}
+
+// Static assert that BufferList implements io.WriterTo.
+var _ io.WriterTo = (*BufferList)(nil)
+
 // NumBuffers returns number of buffers in the list.
 func (b *BufferList) NumBuffers() (uint64, error) {
 	var numBuffers C.uint64_t
@@ -82,6 +113,8 @@ func (b *BufferList) TotalSize() (uint64, error) {
 }
 
 // Flatten copies and concatenates all buffers in the list into a new buffer.
+//
+// Deprecated: Use WriteTo instead for increased performance.
 func (b *BufferList) Flatten() (*Buffer, error) {
 	buffer := Buffer{context: b.context}
 	freeOnGC(&buffer)

buffer_test.go

@@ -95,3 +95,30 @@ func TestBufferSafety(t *testing.T) {
 	t.Log("post gc 2")
 	verify()
 }
+
+type ByteCounter struct {
+	BytesWritten int64
+}
+
+func (b *ByteCounter) Write(x []byte) (int, error) {
+	b.BytesWritten = b.BytesWritten + int64(len(x))
+	return len(x), nil
+}
+
+func TestWriteTo(t *testing.T) {
+	context, err := NewContext(nil)
+	require.NoError(t, err)
+	buffer, err := NewBuffer(context)
+	require.NoError(t, err)
+
+	testSizes := [5]int{0, 16, 256, 65536, 268435456}
+	for _, size := range testSizes {
+		err := buffer.SetBuffer(make([]byte, size))
+		require.NoError(t, err)
+
+		counter := &ByteCounter{BytesWritten: 0}
+		n, err := buffer.WriteTo(counter)
+		require.NoError(t, err)
+		assert.Equal(t, size, int(n))
+	}
+}