[#1060] writecache: compress big object if needed

Small objects use `blobstor.Put`, so no changes are required.

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

pkg/local_object_storage/writecache/flush.go

@@ -125,11 +125,21 @@ func (c *cache) flushBigObjects() {
 					return nil
 				}
 
-				if _, err := c.blobstor.PutRaw(addr, data, true); err != nil {
+				c.mtx.Lock()
+				_, compress := c.compressFlags[sAddr]
+				c.mtx.Unlock()
+
+				if _, err := c.blobstor.PutRaw(addr, data, compress); err != nil {
 					c.log.Error("cant flush object to blobstor", zap.Error(err))
 					return nil
 				}
 
+				if compress {
+					c.mtx.Lock()
+					delete(c.compressFlags, sAddr)
+					c.mtx.Unlock()
+				}
+
 				// mark object as flushed
 				c.store.flushed.Add(sAddr, false)
 

pkg/local_object_storage/writecache/persist.go

@@ -99,6 +99,11 @@ func (c *cache) persistBigObject(objInfo objectInfo) {
 		err := c.fsTree.Put(objInfo.obj.Address(), objInfo.data)
 		if err == nil {
 			metaIndex = 1
+			if c.blobstor.NeedsCompression(objInfo.obj) {
+				c.mtx.Lock()
+				c.compressFlags[objInfo.addr] = struct{}{}
+				c.mtx.Unlock()
+			}
 			c.objCounters.IncFS()
 			storagelog.Write(c.log, storagelog.AddressField(objInfo.addr), storagelog.OpField("fstree PUT"))
 		}

pkg/local_object_storage/writecache/writecache.go

@@ -31,10 +31,14 @@ type Cache interface {
 type cache struct {
 	options
 
-	// mtx protects mem field, statistics and counters.
+	// mtx protects mem field, statistics, counters and compressFlags.
 	mtx sync.RWMutex
 	mem []objectInfo
 
+	// compressFlags maps address of a big object to boolean value indicating
+	// whether object should be compressed.
+	compressFlags map[string]struct{}
+
 	// curMemSize is the current size of all objects cached in memory.
 	curMemSize uint64
 
@@ -80,6 +84,7 @@ func New(opts ...Option) Cache {
 		closeCh:  make(chan struct{}),
 		evictCh:  make(chan []byte),
 
+		compressFlags: make(map[string]struct{}),
 		options: options{
 			log:             zap.NewNop(),
 			maxMemSize:      maxInMemorySizeBytes,