refactor(sync): add snapshot writer

source/dnode/vnode/src/vnd/vnodeSync.c

@@ -469,11 +469,24 @@ static int32_t vnodeSnapshotDoRead(struct SSyncFSM *pFsm, void *pReader, void **
   return code;
 }
 
-static int32_t vnodeSnapshotStartWrite(struct SSyncFSM *pFsm, void *pParam, void **ppWriter) { return 0; }
+static int32_t vnodeSnapshotStartWrite(struct SSyncFSM *pFsm, void *pParam, void **ppWriter) {
+  SVnode         *pVnode = pFsm->data;
+  SSnapshotParam *pSnapshotParam = pParam;
+  int32_t code = vnodeSnapWriterOpen(pVnode, pSnapshotParam->start, pSnapshotParam->end, (SVSnapWriter **)ppWriter);
+  return code;
+}
 
-static int32_t vnodeSnapshotStopWrite(struct SSyncFSM *pFsm, void *pWriter, bool isApply) { return 0; }
+static int32_t vnodeSnapshotStopWrite(struct SSyncFSM *pFsm, void *pWriter, bool isApply) {
+  SVnode *pVnode = pFsm->data;
+  int32_t code = vnodeSnapWriterClose(pWriter, isApply);
+  return code;
+}
 
-static int32_t vnodeSnapshotDoWrite(struct SSyncFSM *pFsm, void *pWriter, void *pBuf, int32_t len) { return 0; }
+static int32_t vnodeSnapshotDoWrite(struct SSyncFSM *pFsm, void *pWriter, void *pBuf, int32_t len) {
+  SVnode *pVnode = pFsm->data;
+  int32_t code = vnodeSnapWrite(pWriter, pBuf, len);
+  return code;
+}
 
 static SSyncFSM *vnodeSyncMakeFsm(SVnode *pVnode) {
   SSyncFSM *pFsm = taosMemoryCalloc(1, sizeof(SSyncFSM));