diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 0b443f3..dfa61d3 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -19,7 +19,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v4
       with:
-        go-version: '1.20'
+        go-version-file: 'go.mod'
 
     - name: Build
       run: go build -v ./...
diff --git a/chunkfile.go b/chunkfile.go
index 1117095..d883481 100644
--- a/chunkfile.go
+++ b/chunkfile.go
@@ -2,24 +2,27 @@ package external
 
 import (
 	"bufio"
-	"encoding/json"
 	"errors"
 	"io"
 	"iter"
 	"os"
 	"slices"
+
+	"github.com/ajiyoshi-vg/external/codec"
 )
 
 type ChunkFile[T any] struct {
 	data    []T
 	tmpFile *string
 	length  int
+	codec   codec.Codec[T]
 }
 
 func NewChunkFile[T any](data []T) *ChunkFile[T] {
 	return &ChunkFile[T]{
 		data:   data,
 		length: len(data),
+		codec:  codec.JSON[T]{},
 	}
 }
 
@@ -52,13 +55,7 @@ func (x *ChunkFile[T]) Store() error {
 func (x *ChunkFile[T]) store(w io.WriteCloser) error {
 	buf := bufio.NewWriter(w)
 	defer buf.Flush()
-	enc := json.NewEncoder(buf)
-	for _, v := range x.data {
-		if err := enc.Encode(v); err != nil {
-			return err
-		}
-	}
-	return nil
+	return x.codec.Encode(slices.Values(x.data), buf)
 }
 
 func (x *ChunkFile[T]) Restore() (iter.Seq[T], error) {
@@ -69,21 +66,5 @@ func (x *ChunkFile[T]) Restore() (iter.Seq[T], error) {
 	if err != nil {
 		return nil, err
 	}
-	return x.restore(tempFile), nil
-}
-
-func (x *ChunkFile[T]) restore(r io.ReadCloser) iter.Seq[T] {
-	dec := json.NewDecoder(bufio.NewReader(r))
-	return func(yield func(T) bool) {
-		defer r.Close()
-		for dec.More() {
-			var v T
-			if err := dec.Decode(&v); err != nil {
-				return
-			}
-			if !yield(v) {
-				return
-			}
-		}
-	}
+	return x.codec.Decode(tempFile), nil
 }
diff --git a/codec/codec.go b/codec/codec.go
new file mode 100644
index 0000000..1c14fd8
--- /dev/null
+++ b/codec/codec.go
@@ -0,0 +1,11 @@
+package codec
+
+import (
+	"io"
+	"iter"
+)
+
+type Codec[T any] interface {
+	Encode(seq iter.Seq[T], w io.Writer) error
+	Decode(r io.ReadCloser) iter.Seq[T]
+}
diff --git a/codec/json.go b/codec/json.go
new file mode 100644
index 0000000..43785d7
--- /dev/null
+++ b/codec/json.go
@@ -0,0 +1,39 @@
+package codec
+
+import (
+	"encoding/json"
+	"io"
+	"iter"
+	"log"
+)
+
+type JSON[T any] struct{}
+
+var _ Codec[int] = (*JSON[int])(nil)
+
+func (JSON[T]) Encode(seq iter.Seq[T], w io.Writer) error {
+	enc := json.NewEncoder(w)
+	for x := range seq {
+		if err := enc.Encode(x); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (JSON[T]) Decode(r io.ReadCloser) iter.Seq[T] {
+	dec := json.NewDecoder(r)
+	return func(yield func(T) bool) {
+		defer r.Close()
+		for dec.More() {
+			var x T
+			if err := dec.Decode(&x); err != nil {
+				log.Printf("decode failed: %v", err)
+				return
+			}
+			if !yield(x) {
+				return
+			}
+		}
+	}
+}
diff --git a/codec/json_test.go b/codec/json_test.go
new file mode 100644
index 0000000..9d07fc8
--- /dev/null
+++ b/codec/json_test.go
@@ -0,0 +1,36 @@
+package codec
+
+import (
+	"bytes"
+	"io"
+	"slices"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestJSON(t *testing.T) {
+	cases := map[string]struct {
+		input  []int
+		expect []int
+	}{
+		"normal": {
+			input:  []int{1, 2, 3},
+			expect: []int{1, 2, 3},
+		},
+	}
+
+	for title, c := range cases {
+		t.Run(title, func(t *testing.T) {
+			codec := &JSON[int]{}
+			seq := slices.Values(c.input)
+			var b bytes.Buffer
+			err := codec.Encode(seq, &b)
+			assert.NoError(t, err)
+
+			r := io.NopCloser(&b)
+			actual := slices.Collect(codec.Decode(r))
+			assert.Equal(t, c.expect, actual)
+		})
+	}
+}