fix: add validation for EC shard counts from VolumeInfo

- Validate DataShards/ParityShards are positive and within MaxShardCount
- Prevent zero or invalid values that could cause divide-by-zero
- Fallback to defaults if validation fails, with warning log
- VolumeEcShardsGenerate now preserves existing EC config when regenerating
- Critical safety fix for corrupted or legacy .vif files

weed/server/volume_grpc_erasure_coding.go

@@ -50,9 +50,23 @@ func (vs *VolumeServer) VolumeEcShardsGenerate(ctx context.Context, req *volume_
 		return nil, fmt.Errorf("existing collection:%v unexpected input: %v", v.Collection, req.Collection)
 	}
 
-	// Create EC context (Phase 1: always uses default 10+4)
+	// Create EC context - prefer existing .vif config if present (for regeneration scenarios)
 	ecCtx := erasure_coding.NewDefaultECContext(req.Collection, needle.VolumeId(req.VolumeId))
-	glog.V(0).Infof("Using EC context for volume %d: %s", req.VolumeId, ecCtx.String())
+	if volumeInfo, _, found, _ := volume_info.MaybeLoadVolumeInfo(baseFileName + ".vif"); found && volumeInfo.EcShardConfig != nil {
+		ds := int(volumeInfo.EcShardConfig.DataShards)
+		ps := int(volumeInfo.EcShardConfig.ParityShards)
+		
+		// Validate and use existing EC config
+		if ds > 0 && ps > 0 && ds+ps <= erasure_coding.MaxShardCount {
+			ecCtx.DataShards = ds
+			ecCtx.ParityShards = ps
+			glog.V(0).Infof("Using existing EC config for volume %d: %s", req.VolumeId, ecCtx.String())
+		} else {
+			glog.Warningf("Invalid EC config in .vif for volume %d (data=%d, parity=%d), using defaults", req.VolumeId, ds, ps)
+		}
+	} else {
+		glog.V(0).Infof("Using default EC config for volume %d: %s", req.VolumeId, ecCtx.String())
+	}
 
 	shouldCleanup := true
 	defer func() {

weed/storage/erasure_coding/ec_volume.go

@@ -77,13 +77,22 @@ func NewEcVolume(diskType types.DiskType, dir string, dirIdx string, collection
 		
 		// Initialize EC context from .vif if present; fallback to defaults
 		if volumeInfo.EcShardConfig != nil {
+			ds := int(volumeInfo.EcShardConfig.DataShards)
+			ps := int(volumeInfo.EcShardConfig.ParityShards)
+			
+			// Validate shard counts to prevent zero or invalid values
+			if ds <= 0 || ps <= 0 || ds+ps > MaxShardCount {
+				glog.Warningf("Invalid EC config in VolumeInfo for volume %d (data=%d, parity=%d), using defaults", vid, ds, ps)
+				ev.ECContext = NewDefaultECContext(collection, vid)
+			} else {
 				ev.ECContext = &ECContext{
 					Collection:   collection,
 					VolumeId:     vid,
-				DataShards:   int(volumeInfo.EcShardConfig.DataShards),
-				ParityShards: int(volumeInfo.EcShardConfig.ParityShards),
+					DataShards:   ds,
+					ParityShards: ps,
 				}
 				glog.V(1).Infof("Loaded EC config from VolumeInfo for volume %d: %s", vid, ev.ECContext.String())
+			}
 		} else {
 			ev.ECContext = NewDefaultECContext(collection, vid)
 		}