Methods

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Methods existing in ABCI

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Echo

• Request:
  • Message (string): A string to echo back
• Response:
  • Message (string): The input string
• Usage:
  • Echo a string to test an ABCI client/server implementation

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Flush

• Usage:
  • Signals that messages queued on the client should be flushed to the server. It is called periodically by the client implementation to ensure asynchronous requests are actually sent, and is called immediately to make a synchronous request, which returns when the Flush response comes back.

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Info

• Request:

  Name	Type	Description	Field Number
  version	string	The CometBFT software semantic version	1
  block_version	uint64	The CometBFT Block version	2
  p2p_version	uint64	The CometBFT P2P version	3
  abci_version	string	The CometBFT ABCI semantic version	4

• Response:

  Name	Type	Description	Field Number	Deterministic
  data	string	Some arbitrary information	1	N/A
  version	string	The application software semantic version	2	N/A
  app_version	uint64	The application version	3	N/A
  last_block_height	int64	Latest height for which the app persisted its state	4	N/A
  last_block_app_hash	bytes	Latest AppHash returned by FinalizeBlock	5	N/A

• Usage:
  • Return information about the application state.
  • Used to sync CometBFT with the application during a handshake that happens on startup or on recovery.
  • The returned app_version will be included in the Header of every block.
  • CometBFT expects last_block_app_hash and last_block_height to be updated and persisted during Commit.

Note: Semantic version is a reference to semantic versioning. Semantic versions in info will be displayed as X.X.x.

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InitChain

• Request:

  Name	Type	Description	Field Number
  time	google.protobuf.Timestamp	Genesis time	1
  chain_id	string	ID of the blockchain.	2
  consensus_params	ConsensusParams	Initial consensus-critical parameters.	3
  validators	repeated ValidatorUpdate	Initial genesis validators, sorted by voting power.	4
  app_state_bytes	bytes	Serialized initial application state. JSON bytes.	5
  initial_height	int64	Height of the initial block (typically 1).	6

• Response:

  Name	Type	Description	Field Number	Deterministic
  consensus_params	ConsensusParams	Initial consensus-critical parameters (optional)	1	Yes
  validators	repeated ValidatorUpdate	Initial validator set (optional).	2	Yes
  app_hash	bytes	Initial application hash.	3	Yes

• Usage:
  • Called once upon genesis.
  • If ResponseInitChain.Validators is empty, the initial validator set will be the RequestInitChain.Validators
  • If ResponseInitChain.Validators is not empty, it will be the initial validator set (regardless of what is in RequestInitChain.Validators).
  • This allows the app to decide if it wants to accept the initial validator set proposed by CometBFT (ie. in the genesis file), or if it wants to use a different one (perhaps computed based on some application specific information in the genesis file).
  • Both RequestInitChain.Validators and ResponseInitChain.Validators are ValidatorUpdate structs. So, technically, they both are updating the set of validators from the empty set.

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Query

• Request:

  Name	Type	Description	Field Number
  data	bytes	Request parameters for the application to interpret analogously to a URI query component. Can be used with or in lieu of path.	1
  path	string	A request path for the application to interpret analogously to a URI path component in e.g. routing. Can be used with or in lieu of data. Applications MUST interpret “/store” or any path starting with “/store/” as a query by key on the underlying store, in which case a key SHOULD be specified in data. Applications SHOULD allow queries over specific types like /accounts/... or /votes/....	2
  height	int64	The block height against which to query (default=0 returns data for the latest committed block). Note that this is the height of the block containing the application’s Merkle root hash, which represents the state as it was after committing the block at Height-1.	3
  prove	bool	Return Merkle proof with response if possible.	4

• Response:

  Name	Type	Description	Field Number	Deterministic
  code	uint32	Response code.	1	N/A
  log	string	The output of the application’s logger.	3	N/A
  info	string	Additional information.	4	N/A
  index	int64	The index of the key in the tree.	5	N/A
  key	bytes	The key of the matching data.	6	N/A
  value	bytes	The value of the matching data.	7	N/A
  proof_ops	ProofOps	Serialized proof for the value data, if requested, to be verified against the app_hash for the given Height.	8	N/A
  height	int64	The block height from which data was derived. Note that this is the height of the block containing the application’s Merkle root hash, which represents the state as it was after committing the block at Height-1	9	N/A
  codespace	string	Namespace for the code.	10	N/A

• Usage:
  • Query for data from the application at current or past height.
  • Optionally return Merkle proof.
  • Merkle proof includes self-describing type field to support many types of Merkle trees and encoding formats.

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CheckTx

• Request:

  Name	Type	Description	Field Number
  tx	bytes	The request transaction bytes	1
  type	CheckTxType	One of CheckTx_New or CheckTx_Recheck. CheckTx_New is the default and means that a full check of the tranasaction is required. CheckTx_Recheck types are used when the mempool is initiating a normal recheck of a transaction.	2

• Response:

  Name	Type	Description	Field Number	Deterministic
  code	uint32	Response code.	1	N/A
  data	bytes	Result bytes, if any.	2	N/A
  log	string	The output of the application’s logger.	3	N/A
  info	string	Additional information.	4	N/A
  gas_wanted	int64	Amount of gas requested for transaction.	5	N/A
  gas_used	int64	Amount of gas consumed by transaction.	6	N/A
  events	repeated Event	Type & Key-Value events for indexing transactions (e.g. by account).	7	N/A
  codespace	string	Namespace for the code.	8	N/A

• Usage:
  • Technically optional - not involved in processing blocks.
  • Guardian of the mempool: every node runs CheckTx before letting a transaction into its local mempool.
  • The transaction may come from an external user or another node
  • CheckTx validates the transaction against the current state of the application, for example, checking signatures and account balances, but does not apply any of the state changes described in the transaction.
  • Transactions where ResponseCheckTx.Code != 0 will be rejected - they will not be broadcast to other nodes or included in a proposal block. CometBFT attributes no other value to the response code.

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Commit

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Parameters and Types

• Request: Commit signals the application to persist application state. It takes no parameters.
• Response:

  Name	Type	Description	Field Number	Deterministic
  retain_height	int64	Blocks below this height may be removed. Defaults to 0 (retain all).	3	No

• Usage:
  • Signal the Application to persist the application state. Application is expected to persist its state at the end of this call, before calling ResponseCommit.
  • Use ResponseCommit.retain_height with caution! If all nodes in the network remove historical blocks then this data is permanently lost, and no new nodes will be able to join the network and bootstrap, unless state sync is enabled on the chain. Historical blocks may also be required for other purposes, e.g. auditing, replay of non-persisted heights, light client verification, and so on.

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ListSnapshots

• Request: Empty request asking the application for a list of snapshots.
• Response:

  Name	Type	Description	Field Number	Deterministic
  snapshots	repeated Snapshot	List of local state snapshots.	1	N/A

• Usage:
  • Used during state sync to discover available snapshots on peers.
  • See Snapshot data type for details.

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LoadSnapshotChunk

• Request:

  Name	Type	Description	Field Number
  height	uint64	The height of the snapshot the chunk belongs to.	1
  format	uint32	The application-specific format of the snapshot the chunk belongs to.	2
  chunk	uint32	The chunk index, starting from 0 for the initial chunk.	3

• Response:

  Name	Type	Description	Field Number	Deterministic
  chunk	bytes	The binary chunk contents, in an arbitrary format. Chunk messages cannot be larger than 16 MB including metadata, so 10 MB is a good starting point.	1	N/A

• Usage:
  • Used during state sync to retrieve snapshot chunks from peers.

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OfferSnapshot

• Request:

  Name	Type	Description	Field Number
  snapshot	Snapshot	The snapshot offered for restoration.	1
  app_hash	bytes	The light client-verified app hash for this height, from the blockchain.	2

• Response:

  Name	Type	Description	Field Number	Deterministic
  result	Result	The result of the snapshot offer.	1	N/A

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Result

  enum Result {
    UNKNOWN       = 0;  // Unknown result, abort all snapshot restoration
    ACCEPT        = 1;  // Snapshot is accepted, start applying chunks.
    ABORT         = 2;  // Abort snapshot restoration, and don't try any other snapshots.
    REJECT        = 3;  // Reject this specific snapshot, try others.
    REJECT_FORMAT = 4;  // Reject all snapshots with this `format`, try others.
    REJECT_SENDER = 5;  // Reject all snapshots from all senders of this snapshot, try others.
  }

• Usage:
  • OfferSnapshot is called when bootstrapping a node using state sync. The application may accept or reject snapshots as appropriate. Upon accepting, CometBFT will retrieve and apply snapshot chunks via ApplySnapshotChunk. The application may also choose to reject a snapshot in the chunk response, in which case it should be prepared to accept further OfferSnapshot calls.
  • Only AppHash can be trusted, as it has been verified by the light client. Any other data can be spoofed by adversaries, so applications should employ additional verification schemes to avoid denial-of-service attacks. The verified AppHash is automatically checked against the restored application at the end of snapshot restoration.
  • For more information, see the Snapshot data type or the state sync section.

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ApplySnapshotChunk

• Request:

  Name	Type	Description	Field Number
  index	uint32	The chunk index, starting from 0. CometBFT applies chunks sequentially.	1
  chunk	bytes	The binary chunk contents, as returned by LoadSnapshotChunk.	2
  sender	string	The P2P ID of the node who sent this chunk.	3

• Response:

  Name	Type	Description	Field Number	Deterministic
  result	Result (see below)	The result of applying this chunk.	1	N/A
  refetch_chunks	repeated uint32	Refetch and reapply the given chunks, regardless of result. Only the listed chunks will be refetched, and reapplied in sequential order.	2	N/A
  reject_senders	repeated string	Reject the given P2P senders, regardless of Result. Any chunks already applied will not be refetched unless explicitly requested, but queued chunks from these senders will be discarded, and new chunks or other snapshots rejected.	3	N/A

  enum Result {
    UNKNOWN         = 0;  // Unknown result, abort all snapshot restoration
    ACCEPT          = 1;  // The chunk was accepted.
    ABORT           = 2;  // Abort snapshot restoration, and don't try any other snapshots.
    RETRY           = 3;  // Reapply this chunk, combine with `RefetchChunks` and `RejectSenders` as appropriate.
    RETRY_SNAPSHOT  = 4;  // Restart this snapshot from `OfferSnapshot`, reusing chunks unless instructed otherwise.
    REJECT_SNAPSHOT = 5;  // Reject this snapshot, try a different one.
  }

• Usage:
  • The application can choose to refetch chunks and/or ban P2P peers as appropriate. CometBFT will not do this unless instructed by the application.
  • The application may want to verify each chunk, e.g. by attaching chunk hashes in Snapshot.Metadata and/or incrementally verifying contents against AppHash.
  • When all chunks have been accepted, CometBFT will make an ABCI Info call to verify that LastBlockAppHash and LastBlockHeight matches the expected values, and record the AppVersion in the node state. It then switches to block sync or consensus and joins the network.
  • If CometBFT is unable to retrieve the next chunk after some time (e.g. because no suitable peers are available), it will reject the snapshot and try a different one via OfferSnapshot. The application should be prepared to reset and accept it or abort as appropriate.

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New methods introduced in ABCI 2.0

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PrepareProposal

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Parameters and Types

• Request:

  Name	Type	Description	Field Number
  max_tx_bytes	int64	Currently configured maximum size in bytes taken by the modified transactions.	1
  txs	repeated bytes	Preliminary list of transactions that have been picked as part of the block to propose.	2
  local_last_commit	ExtendedCommitInfo	Info about the last commit, obtained locally from CometBFT’s data structures.	3
  misbehavior	repeated Misbehavior	List of information about validators that misbehaved.	4
  height	int64	The height of the block that will be proposed.	5
  time	google.protobuf.Timestamp	Timestamp of the block that that will be proposed.	6
  next_validators_hash	bytes	Merkle root of the next validator set.	7
  proposer_address	bytes	Address of the validator that is creating the proposal.	8

• Response:

  Name	Type	Description	Field Number	Deterministic
  txs	repeated bytes	Possibly modified list of transactions that have been picked as part of the proposed block.	2	No

• Usage:
  • RequestPrepareProposal’s parameters txs, misbehavior, height, time, next_validators_hash, and proposer_address are the same as in RequestProcessProposal and RequestFinalizeBlock.
  • RequestPrepareProposal.local_last_commit is a set of the precommit votes for the previous height, including the ones that led to the decision of the previous block, together with their corresponding vote extensions.
  • The height, time, and proposer_address values match the values from the header of the proposed block.
  • RequestPrepareProposal contains a preliminary set of transactions txs that CometBFT retrieved from the mempool, called raw proposal. The Application can modify this set and return a modified set of transactions via ResponsePrepareProposal.txs .
    • The Application can modify the raw proposal: it can reorder, remove or add transactions. Let tx be a transaction in txs (set of transactions within RequestPrepareProposal):
      • If the Application considers that tx should not be proposed in this block, e.g., there are other transactions with higher priority, then it should not include it in ResponsePrepareProposal.txs. However, this will not remove tx from the mempool.
      • If the Application wants to add a new transaction to the proposed block, then the Application includes it in ResponsePrepareProposal.txs. CometBFT will not add the transaction to the mempool.
    • The Application should be aware that removing and adding transactions may compromise traceability.

      Consider the following example: the Application transforms a client-submitted transaction t1 into a second transaction t2, i.e., the Application asks CometBFT to remove t1 from the block and add t2 to the block. If a client wants to eventually check what happened to t1, it will discover that t1 is not in a committed block (assuming a re-CheckTx evicted it from the mempool), getting the wrong idea that t1 did not make it into a block. Note that t2 will be in a committed block, but unless the Application tracks this information, no component will be aware of it. Thus, if the Application wants traceability, it is its responsibility’s to support it. For instance, the Application could attach to a transformed transaction a list with the hashes of the transactions it derives from.

  • The Application MAY configure CometBFT to include a list of transactions in RequestPrepareProposal.txs whose total size in bytes exceeds RequestPrepareProposal.max_tx_bytes. If the Application sets ConsensusParams.Block.MaxBytes to -1, CometBFT will include all transactions currently in the mempool in RequestPrepareProposal.txs, which may not fit in RequestPrepareProposal.max_tx_bytes. Therefore, if the size of RequestPrepareProposal.txs is greater than RequestPrepareProposal.max_tx_bytes, the Application MUST remove transactions to ensure that the RequestPrepareProposal.max_tx_bytes limit is respected by those transactions returned in ResponsePrepareProposal.txs. This is specified in Requirement 2.
  • As a result of executing the prepared proposal, the Application may produce block events or transaction events. The Application must keep those events until a block is decided and then pass them on to CometBFT via ResponseFinalizeBlock.
  • CometBFT does NOT provide any additional validity checks (such as checking for duplicate transactions).
  • If CometBFT fails to validate the ResponsePrepareProposal, CometBFT will assume the Application is faulty and crash.
  • The implementation of PrepareProposal MAY be non-deterministic.

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When does CometBFT call “PrepareProposal” ?

1. CometBFT collects outstanding transactions from p’s mempool
   • the transactions will be collected in order of priority
   • p’s CometBFT creates a block header.
2. p’s CometBFT calls RequestPrepareProposal with the newly generated block, the local commit of the previous height (with vote extensions), and any outstanding evidence of misbehavior. The call is synchronous: CometBFT’s execution will block until the Application returns from the call.
3. The Application uses the information received (transactions, commit info, misbehavior, time) to (potentially) modify the proposal.
   • the Application MAY fully execute the block and produce a candidate state (immediate execution)
   • the Application can manipulate transactions:
     • leave transactions untouched
     • add new transactions (not present initially) to the proposal
     • remove transactions from the proposal (but not from the mempool thus effectively delaying them) - the Application does not include the transaction in ResponsePrepareProposal.txs.
     • modify transactions (e.g. aggregate them). As explained above, this compromises client traceability, unless it is implemented at the Application level.
     • reorder transactions - the Application reorders transactions in the list
   • the Application MAY use the vote extensions in the commit info to modify the proposal, in which case it is suggested that extensions be validated in the same maner as done in VerifyVoteExtension, since extensions of votes included in the commit info after the minimum of +2/3 had been reached are not verified.
4. The Application includes the transaction list (whether modified or not) in the return parameters (see the rules in section Usage), and returns from the call.
5. p uses the (possibly) modified block as p’s proposal in round r, height h.

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ProcessProposal

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Parameters and Types

• Request:

  Name	Type	Description	Field Number
  txs	repeated bytes	List of transactions of the proposed block.	1
  proposed_last_commit	CommitInfo	Info about the last commit, obtained from the information in the proposed block.	2
  misbehavior	repeated Misbehavior	List of information about validators that misbehaved.	3
  hash	bytes	The hash of the proposed block.	4
  height	int64	The height of the proposed block.	5
  time	google.protobuf.Timestamp	Timestamp of the proposed block.	6
  next_validators_hash	bytes	Merkle root of the next validator set.	7
  proposer_address	bytes	Address of the validator that created the proposal.	8

• Response:

  Name	Type	Description	Field Number	Deterministic
  status	ProposalStatus	enum that signals if the application finds the proposal valid.	1	Yes

• Usage:
  • Contains all information on the proposed block needed to fully execute it.
    • The Application may fully execute the block as though it was handling RequestFinalizeBlock.
    • However, any resulting state changes must be kept as candidate state, and the Application should be ready to discard it in case another block is decided.
  • RequestProcessProposal is also called at the proposer of a round. Normally the call to RequestProcessProposal occurs right after the call to RequestPrepareProposal and RequestProcessProposal matches the block produced based on ResponsePrepareProposal (i.e., RequestPrepareProposal.txs equals RequestProcessProposal.txs). However, no such guarantee is made since, in the presence of failures, RequestProcessProposal may match ResponsePrepareProposal from an earlier invocation or ProcessProposal may not be invoked at all.
  • The height and time values match the values from the header of the proposed block.
  • If ResponseProcessProposal.status is REJECT, consensus assumes the proposal received is not valid.
  • The Application MAY fully execute the block (immediate execution)
  • The implementation of ProcessProposal MUST be deterministic. Moreover, the value of ResponseProcessProposal.status MUST exclusively depend on the parameters passed in the call to RequestProcessProposal, and the last committed Application state (see Requirements section).
  • Moreover, application implementors SHOULD always set ResponseProcessProposal.status to ACCEPT, unless they really know what the potential liveness implications of returning REJECT are.

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When does CometBFT call “ProcessProposal” ?

1. p sets up timer ProposeTimeout.
2. If p is the proposer, p executes steps 1-6 in PrepareProposal.
3. Upon reception of Proposal message (which contains the header) for round r, height h from q, p verifies the block header.
4. Upon reception of Proposal message, along with all the block parts, for round r, height h from q, p follows the validators’ algorithm to check whether it should prevote for the proposed block, or nil.
5. If the validators’ consensus algorithm indicates p should prevote non-nil:
   1. CometBFT calls RequestProcessProposal with the block. The call is synchronous.
   2. The Application checks/processes the proposed block, which is read-only, and returns ACCEPT or REJECT in the ResponseProcessProposal.status field.
      • The Application, depending on its needs, may call ResponseProcessProposal
        • either after it has completely processed the block (immediate execution),
        • or after doing some basic checks, and process the block asynchronously. In this case the Application will not be able to reject the block, or force prevote/precommit nil afterwards.
        • or immediately, returning ACCEPT, if p is not a validator and the Application does not want non-validating nodes to handle ProcessProposal
   3. If p is a validator and the returned value is
      • ACCEPT: p prevotes on this proposal for round r, height h.
      • REJECT: p prevotes nil.

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ExtendVote

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Parameters and Types

• Request:

  Name	Type	Description	Field Number
  hash	bytes	The header hash of the proposed block that the vote extension is to refer to.	1
  height	int64	Height of the proposed block (for sanity check).	2
  time	google.protobuf.Timestamp	Timestamp of the proposed block (that the extension is to refer to).	3
  txs	repeated bytes	List of transactions of the block that the extension is to refer to.	4
  proposed_last_commit	CommitInfo	Info about the last proposed block’s last commit.	5
  misbehavior	repeated Misbehavior	List of information about validators that misbehaved contained in the proposed block.	6
  next_validators_hash	bytes	Merkle root of the next validator set contained in the proposed block.	7
  proposer_address	bytes	Address of the validator that created the proposal.	8

• Response:

  Name	Type	Description	Field Number	Deterministic
  vote_extension	bytes	Information signed by by CometBFT. Can have 0 length.	1	No

• Usage:
  • ResponseExtendVote.vote_extension is application-generated information that will be signed by CometBFT and attached to the Precommit message.
  • The Application may choose to use an empty vote extension (0 length).
  • The contents of RequestExtendVote correspond to the proposed block on which the consensus algorithm will send the Precommit message.
  • ResponseExtendVote.vote_extension will only be attached to a non-nil Precommit message. If the consensus algorithm is to precommit nil, it will not call RequestExtendVote.
  • The Application logic that creates the extension can be non-deterministic.

​

When does CometBFT call ExtendVote?

• the Proposal message v for round r, height h, along with all the block parts, from q,
• Prevote messages from 2f + 1 validators’ voting power for round r, height h, prevoting for the same block id(v),

1. p sets lockedValue and validValue to v, and sets lockedRound and validRound to r
2. p’s CometBFT calls RequestExtendVote with v (RequestExtendVote). The call is synchronous.
3. The Application returns an array of bytes, ResponseExtendVote.extension, which is not interpreted by the consensus algorithm.
4. p sets ResponseExtendVote.extension as the value of the extension field of type CanonicalVoteExtension, populates the other fields in CanonicalVoteExtension, and signs the populated data structure.
5. p constructs and signs the CanonicalVote structure.
6. p constructs the Precommit message (i.e. Vote structure) using CanonicalVoteExtension and CanonicalVote.
7. p broadcasts the Precommit message.

​

VerifyVoteExtension

​

Parameters and Types

• Request:

  Name	Type	Description	Field Number
  hash	bytes	The hash of the proposed block that the vote extension refers to.	1
  validator_address	bytes	Address of the validator that signed the extension.	2
  height	int64	Height of the block (for sanity check).	3
  vote_extension	bytes	Application-specific information signed by CometBFT. Can have 0 length.	4

• Response:

  Name	Type	Description	Field Number	Deterministic
  status	VerifyStatus	enum signaling if the application accepts the vote extension	1	Yes

• Usage:
  • RequestVerifyVoteExtension.vote_extension can be an empty byte array. The Application’s interpretation of it should be that the Application running at the process that sent the vote chose not to extend it. CometBFT will always call RequestVerifyVoteExtension, even for 0 length vote extensions.
  • RequestVerifyVoteExtension is not called for precommit votes sent by the local process.
  • RequestVerifyVoteExtension.hash refers to a proposed block. There is not guarantee that this proposed block has previously been exposed to the Application via ProcessProposal.
  • If ResponseVerifyVoteExtension.status is REJECT, the consensus algorithm will reject the whole received vote. See the Requirements section to understand the potential liveness implications of this.
  • The implementation of VerifyVoteExtension MUST be deterministic. Moreover, the value of ResponseVerifyVoteExtension.status MUST exclusively depend on the parameters passed in the call to RequestVerifyVoteExtension, and the last committed Application state (see Requirements section).
  • Moreover, application implementers SHOULD always set ResponseVerifyVoteExtension.status to ACCEPT, unless they really know what the potential liveness implications of returning REJECT are.

​

When does CometBFT call VerifyVoteExtension?

1. If the Precommit message does not contain a vote extension with a valid signature, p discards the Precommit message as invalid.
   • a 0-length vote extension is valid as long as its accompanying signature is also valid.
2. Else, p’s CometBFT calls RequestVerifyVoteExtension.
3. The Application returns ACCEPT or REJECT via ResponseVerifyVoteExtension.status.
4. If the Application returns
   • ACCEPT, p will keep the received vote, together with its corresponding vote extension in its internal data structures. It will be used to populate the ExtendedCommitInfo structure in calls to RequestPrepareProposal, in rounds of height h + 1 where p is the proposer.
   • REJECT, p will deem the Precommit message invalid and discard it.

​

FinalizeBlock

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Parameters and Types

• Request:

  Name	Type	Description	Field Number
  txs	repeated bytes	List of transactions committed as part of the block.	1
  decided_last_commit	CommitInfo	Info about the last commit, obtained from the block that was just decided.	2
  misbehavior	repeated Misbehavior	List of information about validators that misbehaved.	3
  hash	bytes	The block’s hash.	4
  height	int64	The height of the finalized block.	5
  time	google.protobuf.Timestamp	Timestamp of the finalized block.	6
  next_validators_hash	bytes	Merkle root of the next validator set.	7
  proposer_address	bytes	Address of the validator that created the proposal.	8

• Response:

  Name	Type	Description	Field Number	Deterministic
  events	repeated Event	Type & Key-Value events for indexing	1	No
  tx_results	repeated ExecTxResult	List of structures containing the data resulting from executing the transactions	2	Yes
  validator_updates	repeated ValidatorUpdate	Changes to validator set (set voting power to 0 to remove).	3	Yes
  consensus_param_updates	ConsensusParams	Changes to gas, size, and other consensus-related parameters.	4	Yes
  app_hash	bytes	The Merkle root hash of the application state.	5	Yes

• Usage:
  • Contains the fields of the newly decided block.
  • This method is equivalent to the call sequence BeginBlock, [DeliverTx], and EndBlock in ABCI 1.0.
  • The height and time values match the values from the header of the proposed block.
  • The Application can use RequestFinalizeBlock.decided_last_commit and RequestFinalizeBlock.misbehavior to determine rewards and punishments for the validators.
  • The Application executes the transactions in RequestFinalizeBlock.txs deterministically, according to the rules set up by the Application, before returning control to CometBFT. Alternatively, it can apply the candidate state corresponding to the same block previously executed via PrepareProposal or ProcessProposal.
  • ResponseFinalizeBlock.tx_results[i].Code == 0 only if the i-th transaction is fully valid.
  • The Application must provide values for ResponseFinalizeBlock.app_hash, ResponseFinalizeBlock.tx_results, ResponseFinalizeBlock.validator_updates, and ResponseFinalizeBlock.consensus_param_updates as a result of executing the block.
    • The values for ResponseFinalizeBlock.validator_updates, or ResponseFinalizeBlock.consensus_param_updates may be empty. In this case, CometBFT will keep the current values.
    • ResponseFinalizeBlock.validator_updates, triggered by block H, affect validation for blocks H+1, H+2, and H+3. Heights following a validator update are affected in the following way:
      • Height H+1: NextValidatorsHash includes the new validator_updates value.
      • Height H+2: The validator set change takes effect and ValidatorsHash is updated.
      • Height H+3: *_last_commit fields in PrepareProposal, ProcessProposal, and FinalizeBlock now include the altered validator set.
    • ResponseFinalizeBlock.consensus_param_updates returned for block H apply to the consensus params for block H+1. For more information on the consensus parameters, see the consensus parameters section.
  • ResponseFinalizeBlock.app_hash contains an (optional) Merkle root hash of the application state.
  • ResponseFinalizeBlock.app_hash is included as the Header.AppHash in the next block.
    • ResponseFinalizeBlock.app_hash may also be empty or hard-coded, but MUST be deterministic - it must not be a function of anything that did not come from the parameters of RequestFinalizeBlock and the previous committed state.
  • Later calls to Query can return proofs about the application state anchored in this Merkle root hash.
  • The implementation of FinalizeBlock MUST be deterministic, since it is making the Application’s state evolve in the context of state machine replication.
  • Currently, CometBFT will fill up all fields in RequestFinalizeBlock, even if they were already passed on to the Application via RequestPrepareProposal or RequestProcessProposal.
  • When calling FinalizeBlock with a block, the consensus algorithm run by CometBFT guarantees that at least one non-byzantine validator has run ProcessProposal on that block.

​

When does CometBFT call FinalizeBlock?

• the Proposal message with block v for a round r, along with all its block parts, from q, which is the proposer of round r, height h,
• Precommit messages from 2f + 1 validators’ voting power for round r, height h, precommitting the same block id(v),

1. p persists v as the decision for height h.
2. p’s CometBFT calls RequestFinalizeBlock with v’s data. The call is synchronous.
3. p’s Application executes block v.
4. p’s Application calculates and returns the AppHash, along with a list containing the outputs of each of the transactions executed.
5. p’s CometBFT hashes all the transaction outputs and stores it in ResultHash.
6. p’s CometBFT persists the transaction outputs, AppHash, and ResultsHash.
7. p’s CometBFT locks the mempool — no calls to CheckTx on new transactions.
8. p’s CometBFT calls RequestCommit to instruct the Application to persist its state.
9. p’s CometBFT, optionally, re-checks all outstanding transactions in the mempool against the newly persisted Application state.
10. p’s CometBFT unlocks the mempool — newly received transactions can now be checked.
11. p starts consensus for height h+1, round 0

​

Data Types existing in ABCI

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Validator

• Fields:

  Name	Type	Description	Field Number
  address	bytes	Address of validator	1
  power	int64	Voting power of the validator	3

• Usage:
  • Validator identified by address
  • Used as part of VoteInfo within CommitInfo (used in ProcessProposal and FinalizeBlock), and ExtendedCommitInfo (used in PrepareProposal).
  • Does not include PubKey to avoid sending potentially large quantum pubkeys over the ABCI

​

ValidatorUpdate

• Fields:

  Name	Type	Description	Field Number	Deterministic
  pub_key	Public Key	Public key of the validator	1	Yes
  power	int64	Voting power of the validator	2	Yes

• Usage:
  • Validator identified by PubKey
  • Used to tell CometBFT to update the validator set

​

Misbehavior

• Fields:

  Name	Type	Description	Field Number
  type	MisbehaviorType	Type of the misbehavior. An enum of possible misbehaviors.	1
  validator	Validator	The offending validator	2
  height	int64	Height when the offense occurred	3
  time	google.protobuf.Timestamp	Timestamp of the block that was committed at height height	4
  total_voting_power	int64	Total voting power of the validator set at height height	5

​

MisbehaviorType

• Fields MisbehaviorType is an enum with the listed fields:

  Name	Field Number
  UNKNOWN	0
  DUPLICATE_VOTE	1
  LIGHT_CLIENT_ATTACK	2

​

ConsensusParams

• Fields:

  Name	Type	Description	Field Number	Deterministic
  block	BlockParams	Parameters limiting the size of a block and time between consecutive blocks.	1	Yes
  evidence	EvidenceParams	Parameters limiting the validity of evidence of byzantine behaviour.	2	Yes
  validator	ValidatorParams	Parameters limiting the types of public keys validators can use.	3	Yes
  version	VersionsParams	The ABCI application version.	4	Yes

​

ProofOps

• Fields:

  Name	Type	Description	Field Number	Deterministic
  ops	repeated ProofOp	List of chained Merkle proofs, of possibly different types. The Merkle root of one op is the value being proven in the next op. The Merkle root of the final op should equal the ultimate root hash being verified against..	1	N/A

​

ProofOp

• Fields:

  Name	Type	Description	Field Number	Deterministic
  type	string	Type of Merkle proof and how it’s encoded.	1	N/A
  key	bytes	Key in the Merkle tree that this proof is for.	2	N/A
  data	bytes	Encoded Merkle proof for the key.	3	N/A

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Snapshot

• Fields:

  Name	Type	Description	Field Number	Deterministic
  height	uint64	The height at which the snapshot was taken (after commit).	1	N/A
  format	uint32	An application-specific snapshot format, allowing applications to version their snapshot data format and make backwards-incompatible changes. CometBFT does not interpret this.	2	N/A
  chunks	uint32	The number of chunks in the snapshot. Must be at least 1 (even if empty).	3	N/A
  hash	bytes	An arbitrary snapshot hash. Must be equal only for identical snapshots across nodes. CometBFT does not interpret the hash, it only compares them.	4	N/A
  metadata	bytes	Arbitrary application metadata, for example chunk hashes or other verification data.	5	N/A

• Usage:
  • Used for state sync snapshots, see the state sync section for details.
  • A snapshot is considered identical across nodes only if all fields are equal (including Metadata). Chunks may be retrieved from all nodes that have the same snapshot.
  • When sent across the network, a snapshot message can be at most 4 MB.

​

Data types introduced or modified in ABCI++

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VoteInfo

• Fields:

  Name	Type	Description	Field Number
  validator	Validator	The validator that sent the vote.	1
  block_id_flag	BlockIDFlag	Indicates whether the validator voted the last block, nil, or its vote was not received.	3

• Usage:
  • Indicates whether a validator signed the last block, allowing for rewards based on validator availability.
  • This information is typically extracted from a proposed or decided block.

​

ExtendedVoteInfo

• Fields:

  Name	Type	Description	Field Number
  validator	Validator	The validator that sent the vote.	1
  vote_extension	bytes	Non-deterministic extension provided by the sending validator’s Application.	3
  extension_signature	bytes	Signature of the vote extension produced by the sending validator and verified by CometBFT.	4
  block_id_flag	BlockIDFlag	Indicates whether the validator voted the last block, nil, or its vote was not received.	5

• Usage:
  • Indicates whether a validator signed the last block, allowing for rewards based on validator availability.
  • This information is extracted from CometBFT’s data structures in the local process.
  • vote_extension contains the sending validator’s vote extension, whose signature was verified by CometBFT. It can be empty.
  • extension_signature is the signature of the vote extension, which was verified verified by CometBFT. This way, we expose the signature to the application for further processing or verification.

​

CommitInfo

• Fields:

  Name	Type	Description	Field Number
  round	int32	Commit round. Reflects the round at which the block proposer decided in the previous height.	1
  votes	repeated VoteInfo	List of validators’ addresses in the last validator set with their voting information.	2

• Notes
  • The VoteInfo in votes are ordered by the voting power of the validators (descending order, highest to lowest voting power).
  • CometBFT guarantees the votes ordering through its logic to update the validator set in which, in the end, the validators are sorted (descending) by their voting power.
  • The ordering is also persisted when a validator set is saved in the store.
  • The validator set is loaded from the store when building the CommitInfo, ensuring order is maintained from the persisted validator set.

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ExtendedCommitInfo

• Fields:

  Name	Type	Description	Field Number
  round	int32	Commit round. Reflects the round at which the block proposer decided in the previous height.	1
  votes	repeated ExtendedVoteInfo	List of validators’ addresses in the last validator set with their voting information, including vote extensions.	2

• Notes
  • The ExtendedVoteInfo in votes are ordered by the voting power of the validators (descending order, highest to lowest voting power).
  • CometBFT guarantees the votes ordering through its logic to update the validator set in which, in the end, the validators are sorted (descending) by their voting power.
  • The ordering is also persisted when a validator set is saved in the store.
  • The validator set is loaded from the store when building the ExtendedCommitInfo, ensuring order is maintained from the persisted validator set.

​

ExecTxResult

• Fields:

  Name	Type	Description	Field Number	Deterministic
  code	uint32	Response code.	1	Yes
  data	bytes	Result bytes, if any.	2	Yes
  log	string	The output of the application’s logger.	3	No
  info	string	Additional information.	4	No
  gas_wanted	int64	Amount of gas requested for transaction.	5	Yes
  gas_used	int64	Amount of gas consumed by transaction.	6	Yes
  events	repeated Event	Type & Key-Value events for indexing transactions (e.g. by account).	7	No
  codespace	string	Namespace for the code.	8	Yes

​

ProposalStatus

enum ProposalStatus {
  UNKNOWN = 0; // Unknown status. Returning this from the application is always an error.
  ACCEPT  = 1; // Status that signals that the application finds the proposal valid.
  REJECT  = 2; // Status that signals that the application finds the proposal invalid.
}

• Usage:
  • Used within the ProcessProposal response.
    • If Status is UNKNOWN, a problem happened in the Application. CometBFT will assume the application is faulty and crash.
    • If Status is ACCEPT, the consensus algorithm accepts the proposal and will issue a Prevote message for it.
    • If Status is REJECT, the consensus algorithm rejects the proposal and will issue a Prevote for nil instead.

​

VerifyStatus

enum VerifyStatus {
  UNKNOWN = 0; // Unknown status. Returning this from the application is always an error.
  ACCEPT  = 1; // Status that signals that the application finds the vote extension valid.
  REJECT  = 2; // Status that signals that the application finds the vote extension invalid.
}

• Usage:
  • Used within the VerifyVoteExtension response.
    • If Status is UNKNOWN, a problem happened in the Application. CometBFT will assume the application is faulty and crash.
    • If Status is ACCEPT, the consensus algorithm will accept the vote as valid.
    • If Status is REJECT, the consensus algorithm will reject the vote as invalid.