Add the --disable-get-blobs-v2 flag and fixes #16171 (#16155)

**What type of PR is this?**
Feature + Bugfix

**What does this PR do? Why is it needed?**
Starting at Fusaka, the beacon node can pull blobs with the
`engine_getBlobsV2` API from the execution layer.
This reduces by a lot the burden on the beacon node. However, the beacon
node should be able to work 100% correctly without this execution layer
help.

This PR introduces the `--disable-get-blobs-v2` flag to simulate a 0%
success rate of this engine API.

This PR also fixes:
- https://github.com/OffchainLabs/prysm/issues/16171

Please read commit by commit with commit messages.

**How to test it:**
For the `--disable-get-blobs-v2` part:

Run the beacon node with the `--disable-get-blobs-v2` flag in DEBUG
mode.
For every block with commitments, the following log should be displayed:
```
[2025-12-19 15:36:25.49] DEBUG sync: No data column sidecars constructed from the execution client ...
```

And the following log should **never** be displayed:
```
[2026-01-05 10:19:00.55] DEBUG sync: Constructed data column sidecars from the execution client count=...
```

For the #16171 part:
- No ERROR log showed in the linked issue should never be displayed.

**Acknowledgements**
- [x] I have read
[CONTRIBUTING.md](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md).
- [x] I have included a uniquely named [changelog fragment
file](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md#maintaining-changelogmd).
- [x] I have added a description with sufficient context for reviewers
to understand this PR.
- [x] I have tested that my changes work as expected and I added a
testing plan to the PR description (if applicable).

beacon-chain/execution/BUILD.bazel

@@ -40,6 +40,7 @@ go_library(
         "//beacon-chain/state/state-native:go_default_library",
         "//beacon-chain/state/stategen:go_default_library",
         "//beacon-chain/verification:go_default_library",
+        "//cmd/beacon-chain/flags:go_default_library",
         "//config/fieldparams:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/blocks:go_default_library",

beacon-chain/execution/engine_client.go

@@ -11,6 +11,7 @@ import (
 	"github.com/OffchainLabs/prysm/v7/beacon-chain/core/peerdas"
 	"github.com/OffchainLabs/prysm/v7/beacon-chain/execution/types"
 	"github.com/OffchainLabs/prysm/v7/beacon-chain/verification"
+	"github.com/OffchainLabs/prysm/v7/cmd/beacon-chain/flags"
 	fieldparams "github.com/OffchainLabs/prysm/v7/config/fieldparams"
 	"github.com/OffchainLabs/prysm/v7/config/params"
 	"github.com/OffchainLabs/prysm/v7/consensus-types/blocks"
@@ -538,6 +539,10 @@ func (s *Service) GetBlobsV2(ctx context.Context, versionedHashes []common.Hash)
 		return nil, errors.New(fmt.Sprintf("%s is not supported", GetBlobsV2))
 	}
 
+	if flags.Get().DisableGetBlobsV2 {
+		return []*pb.BlobAndProofV2{}, nil
+	}
+
 	result := make([]*pb.BlobAndProofV2, len(versionedHashes))
 	err := s.rpcClient.CallContext(ctx, &result, GetBlobsV2, versionedHashes)
 

beacon-chain/sync/subscriber_beacon_blocks.go

@@ -48,7 +48,14 @@ func (s *Service) beaconBlockSubscriber(ctx context.Context, msg proto.Message)
 		return errors.Wrap(err, "new ro block with root")
 	}
 
-	go s.processSidecarsFromExecutionFromBlock(ctx, roBlock)
+	go func() {
+		if err := s.processSidecarsFromExecutionFromBlock(ctx, roBlock); err != nil {
+			log.WithError(err).WithFields(logrus.Fields{
+				"root": fmt.Sprintf("%#x", root),
+				"slot": block.Slot(),
+			}).Error("Failed to process sidecars from execution from block")
+		}
+	}()
 
 	if err := s.cfg.chain.ReceiveBlock(ctx, signed, root, nil); err != nil {
 		if blockchain.IsInvalidBlock(err) {
@@ -69,28 +76,37 @@ func (s *Service) beaconBlockSubscriber(ctx context.Context, msg proto.Message)
 		}
 		return err
 	}
+
 	if err := s.processPendingAttsForBlock(ctx, root); err != nil {
 		return errors.Wrap(err, "process pending atts for block")
 	}
+
 	return nil
 }
 
 // processSidecarsFromExecutionFromBlock retrieves (if available) sidecars data from the execution client,
 // builds corresponding sidecars, save them to the storage, and broadcasts them over P2P if necessary.
-func (s *Service) processSidecarsFromExecutionFromBlock(ctx context.Context, roBlock blocks.ROBlock) {
+func (s *Service) processSidecarsFromExecutionFromBlock(ctx context.Context, roBlock blocks.ROBlock) error {
 	if roBlock.Version() >= version.Fulu {
 		if err := s.processDataColumnSidecarsFromExecution(ctx, peerdas.PopulateFromBlock(roBlock)); err != nil {
-			log.WithError(err).Error("Failed to process data column sidecars from execution")
-			return
+			// Do not log if the context was cancelled on purpose.
+			// (Still log other context errors such as deadlines exceeded).
+			if errors.Is(err, context.Canceled) {
+				return nil
+			}
+
+			return errors.Wrap(err, "process data column sidecars from execution")
 		}
 
-		return
+		return nil
 	}
 
 	if roBlock.Version() >= version.Deneb {
 		s.processBlobSidecarsFromExecution(ctx, roBlock)
-		return
+		return nil
 	}
+
+	return nil
 }
 
 // processBlobSidecarsFromExecution retrieves (if available) blob sidecars data from the execution client,
@@ -168,7 +184,6 @@ func (s *Service) processDataColumnSidecarsFromExecution(ctx context.Context, so
 	key := fmt.Sprintf("%#x", source.Root())
 	if _, err, _ := s.columnSidecarsExecSingleFlight.Do(key, func() (any, error) {
 		const delay = 250 * time.Millisecond
-		secondsPerHalfSlot := time.Duration(params.BeaconConfig().SecondsPerSlot/2) * time.Second
 
 		commitments, err := source.Commitments()
 		if err != nil {
@@ -186,9 +201,6 @@ func (s *Service) processDataColumnSidecarsFromExecution(ctx context.Context, so
 			return nil, errors.Wrap(err, "column indices to sample")
 		}
 
-		ctx, cancel := context.WithTimeout(ctx, secondsPerHalfSlot)
-		defer cancel()
-
 		log := log.WithFields(logrus.Fields{
 			"root":          fmt.Sprintf("%#x", source.Root()),
 			"slot":          source.Slot(),
@@ -209,6 +221,11 @@ func (s *Service) processDataColumnSidecarsFromExecution(ctx context.Context, so
 				return nil, nil
 			}
 
+			// Return if the context is done.
+			if ctx.Err() != nil {
+				return nil, ctx.Err()
+			}
+
 			if iteration == 0 {
 				dataColumnsRecoveredFromELAttempts.Inc()
 			}
@@ -220,20 +237,10 @@ func (s *Service) processDataColumnSidecarsFromExecution(ctx context.Context, so
 			}
 
 			// No sidecars are retrieved from the EL, retry later
-			constructedSidecarCount = uint64(len(constructedSidecars))
-			if constructedSidecarCount == 0 {
-				if ctx.Err() != nil {
-					return nil, ctx.Err()
-				}
-
-				time.Sleep(delay)
-				continue
-			}
-
-			dataColumnsRecoveredFromELTotal.Inc()
+			constructedCount := uint64(len(constructedSidecars))
 
 			// Boundary check.
-			if constructedSidecarCount != fieldparams.NumberOfColumns {
+			if constructedSidecarCount > 0 && constructedSidecarCount != fieldparams.NumberOfColumns {
 				return nil, errors.Errorf("reconstruct data column sidecars returned %d sidecars, expected %d - should never happen", constructedSidecarCount, fieldparams.NumberOfColumns)
 			}
 
@@ -242,14 +249,24 @@ func (s *Service) processDataColumnSidecarsFromExecution(ctx context.Context, so
 				return nil, errors.Wrap(err, "broadcast and receive unseen data column sidecars")
 			}
 
-			log.WithFields(logrus.Fields{
-				"count":   len(unseenIndices),
-				"indices": helpers.SortedPrettySliceFromMap(unseenIndices),
-			}).Debug("Constructed data column sidecars from the execution client")
+			if constructedCount > 0 {
+				dataColumnsRecoveredFromELTotal.Inc()
 
-			dataColumnSidecarsObtainedViaELCount.Observe(float64(len(unseenIndices)))
+				log.WithFields(logrus.Fields{
+					"root":          fmt.Sprintf("%#x", source.Root()),
+					"slot":          source.Slot(),
+					"proposerIndex": source.ProposerIndex(),
+					"iteration":     iteration,
+					"type":          source.Type(),
+					"count":         len(unseenIndices),
+					"indices":       helpers.SortedPrettySliceFromMap(unseenIndices),
+				}).Debug("Constructed data column sidecars from the execution client")
 
-			return nil, nil
+				return nil, nil
+			}
+
+			// Wait before retrying.
+			time.Sleep(delay)
 		}
 	}); err != nil {
 		return err
@@ -284,6 +301,11 @@ func (s *Service) broadcastAndReceiveUnseenDataColumnSidecars(
 		unseenIndices[sidecar.Index] = true
 	}
 
+	// Exit early if there are no nothing to broadcast or receive.
+	if len(unseenSidecars) == 0 {
+		return nil, nil
+	}
+
 	// Broadcast all the data column sidecars we reconstructed but did not see via gossip (non blocking).
 	if err := s.cfg.p2p.BroadcastDataColumnSidecars(ctx, unseenSidecars); err != nil {
 		return nil, errors.Wrap(err, "broadcast data column sidecars")

beacon-chain/sync/subscriber_beacon_blocks_test.go

@@ -194,7 +194,8 @@ func TestProcessSidecarsFromExecutionFromBlock(t *testing.T) {
 					},
 					seenBlobCache: lruwrpr.New(1),
 				}
-				s.processSidecarsFromExecutionFromBlock(t.Context(), roBlock)
+				err := s.processSidecarsFromExecutionFromBlock(t.Context(), roBlock)
+				require.NoError(t, err)
 				require.Equal(t, tt.expectedBlobCount, len(chainService.Blobs))
 			})
 		}
@@ -293,7 +294,8 @@ func TestProcessSidecarsFromExecutionFromBlock(t *testing.T) {
 				roBlock, err := blocks.NewROBlock(sb)
 				require.NoError(t, err)
 
-				s.processSidecarsFromExecutionFromBlock(t.Context(), roBlock)
+				err = s.processSidecarsFromExecutionFromBlock(t.Context(), roBlock)
+				require.NoError(t, err)
 				require.Equal(t, tt.expectedDataColumnCount, len(chainService.DataColumns))
 			})
 		}

beacon-chain/sync/subscriber_data_column_sidecar.go

@@ -25,12 +25,12 @@ func (s *Service) dataColumnSubscriber(ctx context.Context, msg proto.Message) e
 	}
 
 	if err := s.receiveDataColumnSidecar(ctx, sidecar); err != nil {
-		return errors.Wrap(err, "receive data column sidecar")
+		return wrapDataColumnError(sidecar, "receive data column sidecar", err)
 	}
 
 	wg.Go(func() error {
 		if err := s.processDataColumnSidecarsFromReconstruction(ctx, sidecar); err != nil {
-			return errors.Wrap(err, "process data column sidecars from reconstruction")
+			return wrapDataColumnError(sidecar, "process data column sidecars from reconstruction", err)
 		}
 
 		return nil
@@ -38,7 +38,13 @@ func (s *Service) dataColumnSubscriber(ctx context.Context, msg proto.Message) e
 
 	wg.Go(func() error {
 		if err := s.processDataColumnSidecarsFromExecution(ctx, peerdas.PopulateFromSidecar(sidecar)); err != nil {
-			return errors.Wrap(err, "process data column sidecars from execution")
+			if errors.Is(err, context.Canceled) {
+				// Do not log if the context was cancelled on purpose.
+				// (Still log other context errors such as deadlines exceeded).
+				return nil
+			}
+
+			return wrapDataColumnError(sidecar, "process data column sidecars from execution", err)
 		}
 
 		return nil
@@ -110,3 +116,7 @@ func (s *Service) allDataColumnSubnets(_ primitives.Slot) map[uint64]bool {
 
 	return allSubnets
 }
+
+func wrapDataColumnError(sidecar blocks.VerifiedRODataColumn, message string, err error) error {
+	return fmt.Errorf("%s - slot %d, root %s: %w", message, sidecar.SignedBlockHeader.Header.Slot, fmt.Sprintf("%#x", sidecar.BlockRoot()), err)
+}

changelog/manu_disable_get_blobs_v2.md

@@ -0,0 +1,2 @@
+### Added
+- `--disable-get-blobs-v2` flag.

cmd/beacon-chain/flags/base.go

@@ -356,4 +356,9 @@ var (
 		Usage: "A comma-separated list of exponents (of 2) in decreasing order, defining the state diff hierarchy levels. The last exponent must be greater than or equal to 5.",
 		Value: cli.NewIntSlice(21, 18, 16, 13, 11, 9, 5),
 	}
+	// DisableGetBlobsV2 disables the engine_getBlobsV2 usage.
+	DisableGetBlobsV2 = &cli.BoolFlag{
+		Name:  "disable-get-blobs-v2",
+		Usage: "Disables the engine_getBlobsV2 usage.",
+	}
 )

cmd/beacon-chain/flags/config.go

@@ -17,6 +17,7 @@ type GlobalFlags struct {
 	SubscribeToAllSubnets           bool
 	Supernode                       bool
 	SemiSupernode                   bool
+	DisableGetBlobsV2               bool
 	MinimumSyncPeers                int
 	MinimumPeersPerSubnet           int
 	MaxConcurrentDials              int
@@ -72,6 +73,11 @@ func ConfigureGlobalFlags(ctx *cli.Context) error {
 		cfg.SemiSupernode = true
 	}
 
+	if ctx.Bool(DisableGetBlobsV2.Name) {
+		log.Warning("Disabling `engine_getBlobsV2` API")
+		cfg.DisableGetBlobsV2 = true
+	}
+
 	// State-diff-exponents
 	cfg.StateDiffExponents = ctx.IntSlice(StateDiffExponents.Name)
 	if features.Get().EnableStateDiff {

cmd/beacon-chain/main.go

@@ -148,6 +148,7 @@ var appFlags = []cli.Flag{
 	flags.SlasherDirFlag,
 	flags.SlasherFlag,
 	flags.JwtId,
+	flags.DisableGetBlobsV2,
 	storage.BlobStoragePathFlag,
 	storage.DataColumnStoragePathFlag,
 	storage.BlobStorageLayout,

cmd/beacon-chain/usage.go

@@ -169,6 +169,7 @@ var appHelpFlagGroups = []flagGroup{
 			flags.ExecutionJWTSecretFlag,
 			flags.JwtId,
 			flags.InteropMockEth1DataVotesFlag,
+			flags.DisableGetBlobsV2,
 		},
 	},
 	{ // Flags relevant to configuring beacon chain monitoring.