[#1806] writecache: Allow to start flush manually

Allow user to initiate flushing objects from a writecache.
We need this in 2 cases:
1. During writecache storage schema update, it should be flushed with
   the old version of node and started clean with a new one.
2. During SSD replacement, to avoid data loss.

Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>

pkg/local_object_storage/writecache/flush_test.go

@@ -0,0 +1,135 @@
+package writecache
+
+import (
+	"path/filepath"
+	"testing"
+
+	objectCore "github.com/nspcc-dev/neofs-node/pkg/core/object"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/blobstor"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/blobstor/common"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/blobstor/fstree"
+	meta "github.com/nspcc-dev/neofs-node/pkg/local_object_storage/metabase"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard/mode"
+	checksumtest "github.com/nspcc-dev/neofs-sdk-go/checksum/test"
+	cidtest "github.com/nspcc-dev/neofs-sdk-go/container/id/test"
+	"github.com/nspcc-dev/neofs-sdk-go/object"
+	oid "github.com/nspcc-dev/neofs-sdk-go/object/id"
+	oidtest "github.com/nspcc-dev/neofs-sdk-go/object/id/test"
+	usertest "github.com/nspcc-dev/neofs-sdk-go/user/test"
+	versionSDK "github.com/nspcc-dev/neofs-sdk-go/version"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zaptest"
+)
+
+func TestFlush(t *testing.T) {
+	const (
+		objCount  = 4
+		smallSize = 256
+	)
+
+	dir := t.TempDir()
+	mb := meta.New(
+		meta.WithPath(filepath.Join(dir, "meta")),
+		meta.WithEpochState(dummyEpoch{}))
+	require.NoError(t, mb.Open(false))
+	require.NoError(t, mb.Init())
+
+	fsTree := fstree.New(fstree.WithPath(filepath.Join(dir, "blob")))
+	bs := blobstor.New(blobstor.WithStorages([]blobstor.SubStorage{
+		{Storage: fsTree},
+	}))
+	require.NoError(t, bs.Open(false))
+	require.NoError(t, bs.Init())
+
+	wc := New(
+		WithLogger(zaptest.NewLogger(t)),
+		WithPath(filepath.Join(dir, "writecache")),
+		WithSmallObjectSize(smallSize),
+		WithMetabase(mb),
+		WithBlobstor(bs))
+	require.NoError(t, wc.Open(false))
+	require.NoError(t, wc.Init())
+
+	// First set mode for metabase and blobstor to prevent background flushes.
+	require.NoError(t, mb.SetMode(mode.ReadOnly))
+	require.NoError(t, bs.SetMode(mode.ReadOnly))
+
+	type objectPair struct {
+		addr oid.Address
+		obj  *object.Object
+	}
+
+	objects := make([]objectPair, objCount)
+	for i := range objects {
+		obj := object.New()
+		ver := versionSDK.Current()
+
+		obj.SetID(oidtest.ID())
+		obj.SetOwnerID(usertest.ID())
+		obj.SetContainerID(cidtest.ID())
+		obj.SetType(object.TypeRegular)
+		obj.SetVersion(&ver)
+		obj.SetPayloadChecksum(checksumtest.Checksum())
+		obj.SetPayloadHomomorphicHash(checksumtest.Checksum())
+		obj.SetPayload(make([]byte, 1+(i%2)*smallSize))
+
+		addr := objectCore.AddressOf(obj)
+		data, err := obj.Marshal()
+		require.NoError(t, err)
+
+		var prm common.PutPrm
+		prm.Address = objectCore.AddressOf(obj)
+		prm.Object = obj
+		prm.RawData = data
+
+		_, err = wc.Put(prm)
+		require.NoError(t, err)
+
+		objects[i] = objectPair{addr: addr, obj: obj}
+	}
+
+	t.Run("must be read-only", func(t *testing.T) {
+		require.ErrorIs(t, wc.Flush(), errMustBeReadOnly)
+	})
+
+	require.NoError(t, wc.SetMode(mode.ReadOnly))
+	require.NoError(t, bs.SetMode(mode.ReadWrite))
+	require.NoError(t, mb.SetMode(mode.ReadWrite))
+
+	wc.(*cache).flushed.Add(objects[0].addr.EncodeToString(), true)
+	wc.(*cache).flushed.Add(objects[1].addr.EncodeToString(), false)
+
+	require.NoError(t, wc.Flush())
+
+	for i := 0; i < 2; i++ {
+		var mPrm meta.GetPrm
+		mPrm.SetAddress(objects[i].addr)
+		_, err := mb.Get(mPrm)
+		require.Error(t, err)
+
+		_, err = bs.Get(common.GetPrm{Address: objects[i].addr})
+		require.Error(t, err)
+	}
+
+	for i := 2; i < objCount; i++ {
+		var mPrm meta.StorageIDPrm
+		mPrm.SetAddress(objects[i].addr)
+
+		mRes, err := mb.StorageID(mPrm)
+		require.NoError(t, err)
+
+		var prm common.GetPrm
+		prm.Address = objects[i].addr
+		prm.StorageID = mRes.StorageID()
+
+		res, err := bs.Get(prm)
+		require.NoError(t, err)
+		require.Equal(t, objects[i].obj, res.Object)
+	}
+}
+
+type dummyEpoch struct{}
+
+func (dummyEpoch) CurrentEpoch() uint64 {
+	return 0
+}