diff --git a/countrw/cr.go b/countrw/cr.go
deleted file mode 100644
index 817dd25..0000000
--- a/countrw/cr.go
+++ /dev/null
@@ -1,26 +0,0 @@
-package countrw
-
-import (
-	"io"
-	"sync/atomic"
-)
-
-type CountReader struct {
-	r io.Reader
-	c *uint64
-}
-
-func NewCountReader(r io.Reader) *CountReader {
-	return &CountReader{r: r, c: new(uint64)}
-}
-
-func (c *CountReader) Reset()        { atomic.StoreUint64(c.c, 0) }
-func (c *CountReader) Count() uint64 { return atomic.LoadUint64(c.c) }
-
-func (c *CountReader) Read(p []byte) (int, error) {
-	n, err := c.r.Read(p)
-	atomic.AddUint64(c.c, uint64(n))
-	return n, err
-}
-
-var _ io.Reader = (*CountReader)(nil)
diff --git a/iout/copy_range.go b/iout/copy_range.go
new file mode 100644
index 0000000..f4f1f04
--- /dev/null
+++ b/iout/copy_range.go
@@ -0,0 +1,23 @@
+package iout
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+func CopyRange(w io.Writer, r io.Reader, start, length int64) error {
+	if _, err := io.CopyN(io.Discard, r, start); err != nil && !errors.Is(err, io.EOF) {
+		return fmt.Errorf("discard %d: %w", start, err)
+	}
+	if length == 0 {
+		if _, err := io.Copy(w, r); err != nil && !errors.Is(err, io.EOF) {
+			return fmt.Errorf("direct copy: %w", err)
+		}
+		return nil
+	}
+	if _, err := io.CopyN(w, io.MultiReader(r, NewNullReader()), length); err != nil && !errors.Is(err, io.EOF) {
+		return fmt.Errorf("copy %d: %w", length, err)
+	}
+	return nil
+}
diff --git a/iout/copy_range_test.go b/iout/copy_range_test.go
new file mode 100644
index 0000000..b6a1867
--- /dev/null
+++ b/iout/copy_range_test.go
@@ -0,0 +1,42 @@
+package iout_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/matryer/is"
+	"go.senan.xyz/gonic/iout"
+)
+
+func TestCopyRange(t *testing.T) {
+	t.Parallel()
+	is := is.New(t)
+
+	realLength := 50
+	cr := func(start, length int64) []byte {
+		is.Helper()
+		var data []byte
+		for i := 0; i < realLength; i++ {
+			data = append(data, byte(i%10))
+		}
+		var buff bytes.Buffer
+		is.NoErr(iout.CopyRange(&buff, bytes.NewReader(data), start, length))
+		return buff.Bytes()
+	}
+
+	// range
+	is.Equal(len(cr(0, 50)), 50)
+	is.Equal(len(cr(10, 10)), 10)
+	is.Equal(cr(10, 10)[0], byte(0))
+	is.Equal(cr(10, 10)[5], byte(5))
+	is.Equal(cr(25, 35)[0], byte(5))
+	is.Equal(cr(25, 35)[5], byte(0))
+
+	// 0 padding
+	is.Equal(len(cr(0, 5000)), 5000)
+	is.Equal(cr(0, 5000)[50:], make([]byte, 5000-50))
+
+	// no bound
+	is.Equal(len(cr(0, 0)), 50)
+	is.Equal(len(cr(50, 0)), 0)
+}
diff --git a/countrw/cw.go b/iout/countrw.go
similarity index 51%
rename from countrw/cw.go
rename to iout/countrw.go
index 5d27d9c..35a9364 100644
--- a/countrw/cw.go
+++ b/iout/countrw.go
@@ -1,10 +1,30 @@
-package countrw
+package iout
 
 import (
 	"io"
 	"sync/atomic"
 )
 
+type CountReader struct {
+	r io.Reader
+	c *uint64
+}
+
+func NewCountReader(r io.Reader) *CountReader {
+	return &CountReader{r: r, c: new(uint64)}
+}
+
+func (c *CountReader) Reset()        { atomic.StoreUint64(c.c, 0) }
+func (c *CountReader) Count() uint64 { return atomic.LoadUint64(c.c) }
+
+func (c *CountReader) Read(p []byte) (int, error) {
+	n, err := c.r.Read(p)
+	atomic.AddUint64(c.c, uint64(n))
+	return n, err
+}
+
+var _ io.Reader = (*CountReader)(nil)
+
 type CountWriter struct {
 	r io.Writer
 	c *uint64
diff --git a/iout/null_reader.go b/iout/null_reader.go
new file mode 100644
index 0000000..d7477d6
--- /dev/null
+++ b/iout/null_reader.go
@@ -0,0 +1,18 @@
+package iout
+
+import "io"
+
+type nullReader struct{}
+
+func NewNullReader() io.Reader {
+	return &nullReader{}
+}
+
+func (*nullReader) Read(p []byte) (n int, err error) {
+	for b := range p {
+		p[b] = 0
+	}
+	return len(p), nil
+}
+
+var _ io.Reader = (*nullReader)(nil)
diff --git a/iout/tee_closer.go b/iout/tee_closer.go
new file mode 100644
index 0000000..92cfea6
--- /dev/null
+++ b/iout/tee_closer.go
@@ -0,0 +1,28 @@
+package iout
+
+import "io"
+
+type teeCloser struct {
+	r io.ReadCloser
+	w io.WriteCloser
+}
+
+func NewTeeCloser(r io.ReadCloser, w io.WriteCloser) io.ReadCloser {
+	return &teeCloser{r, w}
+}
+
+func (t *teeCloser) Read(p []byte) (int, error) {
+	n, err := t.r.Read(p)
+	if n > 0 {
+		if n, err := t.w.Write(p[:n]); err != nil {
+			return n, err
+		}
+	}
+	return n, err
+}
+
+func (t *teeCloser) Close() error {
+	t.r.Close()
+	t.w.Close()
+	return nil
+}