{"record":{"id":"ad57f7380edd6650","repo":"hyperledger/fabric","slug":"first-block-header-is-nil","errorCode":null,"errorMessage":"first block header is nil","messagePattern":"first block header is nil","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"orderer/common/follower/block_puller.go","lineNumber":157,"sourceCode":"\tverifier, err := creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)\n\tif err != nil {\n\t\treturn errors.WithMessage(err, \"failed to construct a block signature verifier from config envelope\")\n\t}\n\tcreator.blockSigVerifier = verifier\n\treturn nil\n}\n\n// VerifyBlockSequence verifies a sequence of blocks, using the internal block signature verifier. It also bootstraps\n// the block sig verifier form the genesis block if it does not exist, and skips verifying the genesis block.\nfunc (creator *BlockPullerCreator) VerifyBlockSequence(blocks []*common.Block, _ string) error {\n\tif len(blocks) == 0 {\n\t\treturn errors.New(\"buffer is empty\")\n\t}\n\tif blocks[0] == nil {\n\t\treturn errors.New(\"first block is nil\")\n\t}\n\tif blocks[0].Header == nil {\n\t\treturn errors.New(\"first block header is nil\")\n\t}\n\tif blocks[0].Header.Number == 0 {\n\t\tif creator.JoinBlock != nil && creator.JoinBlock.Header.Number == 0 {\n\t\t\t// If we have joined with a genesis block,\n\t\t\t// replace the genesis block we got from the network\n\t\t\t// with our own.\n\t\t\tblocks[0] = creator.JoinBlock\n\t\t}\n\t\tconfigEnv, err := deliverclient.ConfigFromBlock(blocks[0])\n\t\tif err != nil {\n\t\t\treturn errors.WithMessage(err, \"failed to extract config envelope from genesis block\")\n\t\t}\n\t\t// Bootstrap the verifier from the genesis block, as it will be used to verify\n\t\t// the subsequent blocks in the batch.\n\t\tcreator.blockSigVerifier, err = creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)\n\t\tif err != nil {\n\t\t\treturn errors.WithMessage(err, \"failed to construct a block signature verifier from genesis block\")\n\t\t}","sourceCodeStart":139,"sourceCodeEnd":175,"githubUrl":"https://github.com/hyperledger/fabric/blob/2736b63f8fd5932511d56fe68b7039d15977f7f6/orderer/common/follower/block_puller.go#L139-L175","documentation":"VerifyBlockSequence reads blocks[0].Header to get the block number and signature; a block with a nil header cannot be verified or sequenced, so the call fails immediately. Headers are required for signature verification and genesis handling.","triggerScenarios":"Calling VerifyBlockSequence where blocks[0] is non-nil but blocks[0].Header is nil — malformed block produced by puller/decoder, corrupted serialized block, or hand-constructed block without a header.","commonSituations":"Corruption during block transfer or storage; protobuf unmarshaling returning an empty block on failure without surfacing the error; unit tests building &common.Block{} without a Header.","solutions":["Fix the block producer to return errors instead of blocks with nil headers (check Unmarshal errors)","Validate block.Header before adding to the pull buffer; drop and re-pull corrupted blocks","Repair the local ledger if corruption is on-disk (re-pull blocks from an orderer or restore from snapshot)","In tests, always initialize &common.Block{Header: &common.BlockHeader{...}}"],"exampleFix":"// before\nblock := &common.Block{}\ncreator.VerifyBlockSequence([]*common.Block{block}, channelID)\n// after\nif block.Header == nil {\n    return errors.New(\"refusing to verify block with nil header\")\n}\ncreator.VerifyBlockSequence([]*common.Block{block}, channelID)","handlingStrategy":"type-guard","validationCode":"func hasHeader(b *common.Block) bool { return b != nil && b.Header != nil }\nif !hasHeader(blocks[0]) {\n    return errors.New(\"first block has no header; block is malformed\")\n}","typeGuard":"func isWellFormedBlock(b *common.Block) bool {\n    return b != nil && b.Header != nil && b.Data != nil\n}","tryCatchPattern":"if err := creator.VerifyBlockSequence(blocks, channelID); err != nil {\n    if err.Error() == \"first block header is nil\" {\n        return fmt.Errorf(\"malformed block received; re-pull from orderer\")\n    }\n    return err\n}","preventionTips":["Check protobuf Unmarshal errors instead of using partially decoded blocks","Validate Header presence before buffering pulled blocks","Re-pull from another orderer if a block arrives header-less (corruption signal)"],"tags":["blocks","malformed-data","verification"],"backgroundTag":"nil-block-header","analyzedSha":"2736b63f8fd5932511d56fe68b7039d15977f7f6","analyzedAt":"2026-09-04T08:52:36.465Z","contentChangedAt":"2026-09-04T08:52:36.465Z","schemaVersion":2},"datasetVersion":"2026-09-08T15:18:49.778Z"}