Merge pull request #2193 from OffchainLabs/improve-errorlogging-blobr…

…eader

Improve error logging when blob client fails to read blobs from beacon-URL [NIT-2318]

util/headerreader/blob_client.go

@@ -17,6 +17,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/crypto/kzg4844"
+	"github.com/ethereum/go-ethereum/log"
 	"github.com/offchainlabs/nitro/arbutil"
 	"github.com/offchainlabs/nitro/util/blobs"
 	"github.com/offchainlabs/nitro/util/jsonapi"
@@ -133,7 +134,11 @@ func (b *BlobClient) GetBlobs(ctx context.Context, blockHash common.Hash, versio
 		return nil, errors.New("BlobClient hasn't been initialized")
 	}
 	slot := (header.Time - b.genesisTime) / b.secondsPerSlot
-	return b.blobSidecars(ctx, slot, versionedHashes)
+	blobs, err := b.blobSidecars(ctx, slot, versionedHashes)
+	if err != nil {
+		return nil, fmt.Errorf("error fetching blobs in %d l1 block: %w", header.Number, err)
+	}
+	return blobs, nil
 }
 
 type blobResponseItem struct {
@@ -147,14 +152,22 @@ type blobResponseItem struct {
 	KzgProof        hexutil.Bytes        `json:"kzg_proof"`
 }
 
+const trailingCharsOfResponse = 25
+
 func (b *BlobClient) blobSidecars(ctx context.Context, slot uint64, versionedHashes []common.Hash) ([]kzg4844.Blob, error) {
 	rawData, err := beaconRequest[json.RawMessage](b, ctx, fmt.Sprintf("/eth/v1/beacon/blob_sidecars/%d", slot))
 	if err != nil {
 		return nil, fmt.Errorf("error calling beacon client in blobSidecars: %w", err)
 	}
 	var response []blobResponseItem
 	if err := json.Unmarshal(rawData, &response); err != nil {
-		return nil, fmt.Errorf("error unmarshalling raw data into array of blobResponseItem in blobSidecars: %w", err)
+		rawDataStr := string(rawData)
+		log.Debug("response from beacon URL cannot be unmarshalled into array of blobResponseItem in blobSidecars", "slot", slot, "responseLength", len(rawDataStr), "response", rawDataStr)
+		if len(rawDataStr) > 100 {
+			return nil, fmt.Errorf("error unmarshalling response from beacon URL into array of blobResponseItem in blobSidecars: %w. Trailing %d characters of the response: %s", err, trailingCharsOfResponse, rawDataStr[len(rawDataStr)-trailingCharsOfResponse:])
+		} else {
+			return nil, fmt.Errorf("error unmarshalling response from beacon URL into array of blobResponseItem in blobSidecars: %w. Response: %s", err, rawDataStr)
+		}
 	}
 
 	if len(response) < len(versionedHashes) {