fix: error on different frag lens

relay.go

@@ -0,0 +1,72 @@
+package terasu
+
+import (
+	"io"
+	"sync"
+)
+
+type relay struct {
+	mu  sync.Mutex
+	buf chan []byte
+	rem []byte
+}
+
+func newrelay() relay {
+	return relay{buf: make(chan []byte, 64)}
+}
+
+// Read ...
+func (r *relay) Read(p []byte) (n int, err error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	switch {
+	case len(p) == 0:
+		return
+	case len(p) <= len(r.rem):
+		n = copy(p, r.rem)
+		r.rem = r.rem[n:]
+		if len(r.rem) == 0 {
+			r.rem = nil
+		}
+		return
+	case len(r.rem) > 0:
+		n = copy(p, r.rem)
+		r.rem = nil
+		fallthrough
+	default:
+		for n < len(p) {
+			buf := <-r.buf
+			if len(buf) == 0 {
+				err = io.EOF
+				return
+			}
+			switch {
+			case len(buf) >= len(p)-n:
+				cnt := copy(p[n:], buf)
+				n += cnt
+				r.rem = buf[cnt:]
+				if len(r.rem) == 0 {
+					r.rem = nil
+				}
+				return
+			default:
+				n += copy(p[n:], buf)
+			}
+		}
+	}
+	panic("unexpected")
+}
+
+// Write ...
+func (r *relay) Write(p []byte) (n int, err error) {
+	buf := make([]byte, len(p))
+	n = copy(buf, p)
+	r.buf <- p
+	return
+}
+
+// Close ...
+func (r *relay) Close() error {
+	close(r.buf)
+	return nil
+}