diff --git a/protocol/packet/encoder.go b/protocol/packet/encoder.go
new file mode 100644
index 0000000..451d073
--- /dev/null
+++ b/protocol/packet/encoder.go
@@ -0,0 +1,51 @@
+//    Licensed under the Apache License, Version 2.0 (the "License");
+//    you may not use this file except in compliance with the License.
+//    You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+package packet
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+var getId = func() uint64 {
+	return uint64(time.Now().UnixNano() / 1000)
+}
+
+func Marshal(p *Packet) ([]byte, error) {
+	if p == nil {
+		return nil, fmt.Errorf("no packet")
+	}
+
+	if p.Type == "" {
+		return nil, fmt.Errorf("packet type not set")
+	}
+
+	body, err := json.Marshal(p.auxBody)
+	if err != nil {
+		return nil, fmt.Errorf("failed to encode body: %v", err)
+	}
+	id := p.Id
+	if id == 0 {
+		id = getId()
+	}
+	data, err := json.Marshal(Packet{
+		Id:   id,
+		Type: p.Type,
+		Body: body,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return append(data, '\n'), nil
+}
diff --git a/protocol/packet/encoder_test.go b/protocol/packet/encoder_test.go
new file mode 100644
index 0000000..5ee8615
--- /dev/null
+++ b/protocol/packet/encoder_test.go
@@ -0,0 +1,52 @@
+//    Licensed under the Apache License, Version 2.0 (the "License");
+//    you may not use this file except in compliance with the License.
+//    You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+package packet_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/bboozzoo/mconnect/protocol/packet"
+)
+
+func TestMarshal(t *testing.T) {
+	data, err := packet.Marshal(nil)
+	assert.Error(t, err)
+
+	data, err = packet.Marshal(&packet.Packet{})
+	assert.Error(t, err)
+
+	exp := `{"id":123,"type":"foo","body":null}` + "\n"
+	p := packet.New("foo", nil)
+	p.Id = 123
+	data, err = packet.Marshal(p)
+	assert.NoError(t, err)
+	assert.Equal(t, []byte(exp), data)
+
+	exp = `{"id":123,"type":"foo","body":{}}` + "\n"
+	p = packet.New("foo", map[int]int{})
+	p.Id = 123
+	data, err = packet.Marshal(p)
+	assert.NoError(t, err)
+	assert.Equal(t, []byte(exp), data)
+
+	restore := packet.MockGetId(func() uint64 {
+		return uint64(889911)
+	})
+	defer restore()
+
+	exp = `{"id":889911,"type":"foo","body":{}}` + "\n"
+	data, err = packet.Marshal(packet.New("foo", map[int]int{}))
+	assert.NoError(t, err)
+	assert.Equal(t, []byte(exp), data)
+}
diff --git a/protocol/packet/export_test.go b/protocol/packet/export_test.go
new file mode 100644
index 0000000..efe8662
--- /dev/null
+++ b/protocol/packet/export_test.go
@@ -0,0 +1,20 @@
+//    Licensed under the Apache License, Version 2.0 (the "License");
+//    you may not use this file except in compliance with the License.
+//    You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+package packet
+
+func MockGetId(newGetId func() uint64) (restore func()) {
+	old := getId
+	getId = newGetId
+	return func() {
+		getId = old
+	}
+}