feat: init

.gitignore

@@ -13,3 +13,4 @@
 
 # Dependency directories (remove the comment below to include it)
 # vendor/
+output/

block.go

@@ -0,0 +1,78 @@
+package tapewriter
+
+import (
+	"io"
+	"os"
+	"sync"
+	"syscall"
+)
+
+var (
+	_ = io.WriteCloser(new(BlockWriter))
+)
+
+type BlockWriter struct {
+	target    uintptr
+	blockSize int
+	buffer    chan []byte
+	pool      sync.Pool
+	closed    sync.WaitGroup
+
+	current []byte
+	off     int
+}
+
+func NewBlockWriter(tape *os.File, blockSize, bufferBlocks int) *BlockWriter {
+	w := &BlockWriter{
+		target:    tape.Fd(),
+		blockSize: blockSize,
+		buffer:    make(chan []byte, bufferBlocks),
+		current:   make([]byte, blockSize),
+		pool:      sync.Pool{New: func() interface{} { return make([]byte, blockSize) }},
+	}
+
+	w.closed.Add(1)
+	go w.loop()
+	return w
+}
+
+func (w *BlockWriter) Write(buf []byte) (int, error) {
+	var n, cn int
+	for len(buf) > 0 {
+		cn = copy(w.current, buf)
+		buf = buf[cn:]
+		w.off += cn
+		n += cn
+
+		if w.off >= w.blockSize {
+			w.buffer <- w.current
+			w.current = w.pool.Get().([]byte)
+		}
+	}
+
+	return n, nil
+}
+
+func (w *BlockWriter) Close() error {
+	w.buffer <- w.current[:w.off]
+	close(w.buffer)
+
+	w.closed.Wait()
+	return nil
+}
+
+func (w *BlockWriter) loop() {
+	defer w.closed.Done()
+
+	for {
+		buf, ok := <-w.buffer
+		if !ok {
+			break
+		}
+
+		_, err := syscall.Write(int(w.target), buf)
+		if err != nil {
+			panic(err)
+		}
+	}
+}