hyperledger/fabric · error

first block is nil

Error message

first block is nil

What it means

VerifyBlockSequence requires the first block of the sequence to be non-nil because it bootstraps signature verification from blocks[0]. A nil element means the producer of the slice emitted a placeholder, which cannot be verified.

Source

Thrown at orderer/common/follower/block_puller.go:154

	if err != nil {
		return errors.WithMessage(err, "failed to extract config envelope from block")
	}
	verifier, err := creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)
	if err != nil {
		return errors.WithMessage(err, "failed to construct a block signature verifier from config envelope")
	}
	creator.blockSigVerifier = verifier
	return nil
}

// VerifyBlockSequence verifies a sequence of blocks, using the internal block signature verifier. It also bootstraps
// the block sig verifier form the genesis block if it does not exist, and skips verifying the genesis block.
func (creator *BlockPullerCreator) VerifyBlockSequence(blocks []*common.Block, _ string) error {
	if len(blocks) == 0 {
		return errors.New("buffer is empty")
	}
	if blocks[0] == nil {
		return errors.New("first block is nil")
	}
	if blocks[0].Header == nil {
		return errors.New("first block header is nil")
	}
	if blocks[0].Header.Number == 0 {
		if creator.JoinBlock != nil && creator.JoinBlock.Header.Number == 0 {
			// If we have joined with a genesis block,
			// replace the genesis block we got from the network
			// with our own.
			blocks[0] = creator.JoinBlock
		}
		configEnv, err := deliverclient.ConfigFromBlock(blocks[0])
		if err != nil {
			return errors.WithMessage(err, "failed to extract config envelope from genesis block")
		}
		// Bootstrap the verifier from the genesis block, as it will be used to verify
		// the subsequent blocks in the batch.
		creator.blockSigVerifier, err = creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)

View on GitHub (pinned to 2736b63f8f)

Solutions

1. Fix the producer (puller/buffer) to never append nil blocks; drop failed blocks and adjust the sequence
2. Filter nil entries out of the slice before calling VerifyBlockSequence
3. If pre-allocating, fill the slice with real blocks before verification

Example fix

// before
blocks := make([]*common.Block, len(pulled))
creator.VerifyBlockSequence(blocks, channelID)
// after
var blocks []*common.Block
for _, b := range pulled {
    if b != nil {
        blocks = append(blocks, b)
    }
}
creator.VerifyBlockSequence(blocks, channelID)

func isVerifiableSequence(blocks []*common.Block) bool {
    return len(blocks) > 0 && blocks[0] != nil
}
// guard before calling VerifyBlockSequence

func firstBlockPresent(blocks []*common.Block) bool {
    return len(blocks) > 0 && blocks[0] != nil && blocks[0].Header != nil
}

if err := creator.VerifyBlockSequence(blocks, channelID); err != nil {
    if err.Error() == "first block is nil" {
        return fmt.Errorf("pull buffer produced nil block; inspect puller/buffer implementation")
    }
    return err
}

When it happens

Trigger: Calling VerifyBlockSequence with a slice whose first element is nil — usually a puller or buffer that appends a nil on error instead of skipping, or manual construction of the slice in tests/tools.

Common situations: Custom block-buffer implementations between puller and verifier appending nil entries; gRPC decode failure leaving a nil slot; test harnesses pre-allocating make([]*common.Block, n) without filling elements.

Related errors

• buffer is empty
• first block header is nil
• no such policy
• No such policy
• nil policy field

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/19f4d37cc5ddc16e. Report an issue: GitHub.