Add storage backend interface (#1072)

* pkg: add storage package

Which contains storage.Backend interface to initial support for multiple
backend storage.

* pkg/storage: add inmemory storage

* internal/databroker: use storage.Backend interface

Instead of implementing multiple databroker server implementation for
each kind of storage backend, we use only one databroker server
implementation, which is supported multiple storage backends, which
satisfy storage.Backend interface.

pkg/storage/inmemory/inmemory_test.go

@@ -0,0 +1,62 @@
+package inmemory
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/types/known/anypb"
+)
+
+func TestDB(t *testing.T) {
+	ctx := context.Background()
+	db := NewDB("example", 2)
+	t.Run("get missing record", func(t *testing.T) {
+		assert.Nil(t, db.Get(ctx, "abcd"))
+	})
+	t.Run("get record", func(t *testing.T) {
+		data := new(anypb.Any)
+		assert.NoError(t, db.Put(ctx, "abcd", data))
+		record := db.Get(ctx, "abcd")
+		if assert.NotNil(t, record) {
+			assert.NotNil(t, record.CreatedAt)
+			assert.Equal(t, data, record.Data)
+			assert.Nil(t, record.DeletedAt)
+			assert.Equal(t, "abcd", record.Id)
+			assert.NotNil(t, record.ModifiedAt)
+			assert.Equal(t, "example", record.Type)
+			assert.Equal(t, "000000000001", record.Version)
+		}
+	})
+	t.Run("delete record", func(t *testing.T) {
+		assert.NoError(t, db.Delete(ctx, "abcd"))
+		record := db.Get(ctx, "abcd")
+		if assert.NotNil(t, record) {
+			assert.NotNil(t, record.DeletedAt)
+		}
+	})
+	t.Run("clear deleted", func(t *testing.T) {
+		db.ClearDeleted(ctx, time.Now().Add(time.Second))
+		assert.Nil(t, db.Get(ctx, "abcd"))
+	})
+	t.Run("keep remaining", func(t *testing.T) {
+		data := new(anypb.Any)
+		assert.NoError(t, db.Put(ctx, "abcd", data))
+		assert.NoError(t, db.Delete(ctx, "abcd"))
+		db.ClearDeleted(ctx, time.Now().Add(-10*time.Second))
+		assert.NotNil(t, db.Get(ctx, "abcd"))
+		db.ClearDeleted(ctx, time.Now().Add(time.Second))
+	})
+	t.Run("list", func(t *testing.T) {
+		for i := 0; i < 10; i++ {
+			data := new(anypb.Any)
+			assert.NoError(t, db.Put(ctx, fmt.Sprintf("%02d", i), data))
+		}
+
+		assert.Len(t, db.List(ctx, ""), 10)
+		assert.Len(t, db.List(ctx, "00000000000A"), 4)
+		assert.Len(t, db.List(ctx, "00000000000F"), 0)
+	})
+}