Methods - Cosmos Docs

Methods existing in ABCI

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

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.

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
data	string	Some arbitrary information	1
version	string	The application software semantic version	2
app_version	uint64	The application version	3
last_block_height	int64	Latest height for which the app persisted its state	4
last_block_app_hash	bytes	Latest AppHash returned by `Commit`	5

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.

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
consensus_params	ConsensusParams	Initial consensus-critical parameters (optional)	1
validators	repeated ValidatorUpdate	Initial validator set (optional).	2
app_hash	bytes	Initial application hash.	3

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.

Query

Request:

Name	Type	Description	Field Number
data	bytes	Raw query bytes. Can be used with or in lieu of Path.	1
path	string	Path field of the request URI. Can be used with or in lieu of `data`. Apps MUST interpret `/store` as a query by key on the underlying store. The key SHOULD be specified in the `data` field. Apps SHOULD allow queries over specific types like `/accounts/...` or `/votes/...`	2
height	int64	The block height for which you want the 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
code	uint32	Response code.	1
log	string	The output of the application’s logger. May be non-deterministic.	3
info	string	Additional information. May be non-deterministic.	4
index	int64	The index of the key in the tree.	5
key	bytes	The key of the matching data.	6
value	bytes	The value of the matching data.	7
proof_ops	ProofOps	Serialized proof for the value data, if requested, to be verified against the `app_hash` for the given Height.	8
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
codespace	string	Namespace for the `code`.	10

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.

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
code	uint32	Response code.	1
data	bytes	Result bytes, if any.	2
gas_wanted	int64	Amount of gas requested for transaction.	5
codespace	string	Namespace for the `code`.	8
sender	string	The transaction’s sender (e.g. the signer)	9
priority	int64	The transaction’s priority (for mempool ordering)	10

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.

BeginBlock

Request:

Name	Type	Description	Field Number
hash	bytes	The block’s hash. This can be derived from the block header.	1
header	Header	The block header.	2
last_commit_info	CommitInfo	Info about the last commit, including the round, and the list of validators and which ones signed the last block.	3
byzantine_validators	repeated Evidence	List of evidence of validators that acted maliciously.	4

Response:
Name Type Description Field Number
events repeated Event type & Key-Value events for indexing 1
Usage:
- Signals the beginning of a new block.
- Called prior to any DeliverTx method calls.
- The header contains the height, timestamp, and more - it exactly matches the CometBFT block header. We may seek to generalize this in the future.
- The CommitInfo and ByzantineValidators can be used to determine rewards and punishments for the validators.

Name	Type	Description	Field Number
events	repeated Event	type & Key-Value events for indexing	1

DeliverTx

Request:
Name Type Description Field Number
tx bytes The request transaction bytes. 1

Name	Type	Description	Field Number
tx	bytes	The request transaction bytes.	1

Response:

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

Usage:
- [Required] The core method of the application.
- DeliverTx is called once for each transaction in the block.
- When DeliverTx is called, the application must execute the transaction deterministically in full before returning control to CometBFT.
- Alternatively, the application can apply a candidate state corresponding to the same block previously executed via PrepareProposal or ProcessProposal any time between the calls to BeginBlock, the various calls to DeliverTx and EndBlock.
- ResponseDeliverTx.Code == 0 only if the transaction is fully valid.

EndBlock

Request:
Name Type Description Field Number
height int64 Height of the block just executed. 1

Name	Type	Description	Field Number
height	int64	Height of the block just executed.	1

Response:

Name	Type	Description	Field Number
validator_updates	repeated ValidatorUpdate	Changes to validator set (set voting power to 0 to remove).	1
consensus_param_updates	ConsensusParams	Changes to consensus-critical time, size, and other parameters.	2
events	repeated Event	Type & Key-Value events for indexing	3

Usage:
- Signals the end of a block.
- Called after all the transactions for the current block have been delivered, prior to the block’s Commit message.
- Optional validator_updates triggered by block H. These updates affect validation for blocks H+1, H+2, and H+3.
- Heights following a validator update are affected in the following way:
  - H+1: NextValidatorsHash includes the new validator_updates value.
  - H+2: The validator set change takes effect and ValidatorsHash is updated.
  - H+3: last_commit_info (BeginBlock) is changed to include the altered validator set and *_last_commit fields in PrepareProposal, ProcessProposal now include the altered validator set.
- 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 application spec entry on consensus parameters.
- validator_updates and consensus_param_updates may be empty. In this case, CometBFT will keep the current values.

Commit

Request:
Name Type Description Field Number
Commit signals the application to persist application state. It takes no parameters.
Response:
Name Type Description Field Number
data bytes The Merkle root hash of the application state. 2
retain_height int64 Blocks below this height may be removed. Defaults to 0 (retain all). 3
Usage:
- Signal the application to persist the application state.
- Return an (optional) Merkle root hash of the application state
- ResponseCommit.Data is included as the Header.AppHash in the next block
  - It may 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 the execution calls (BeginBlock/DeliverTx/EndBlock methods) and the previous committed state.
- Later calls to Query can return proofs about the application state anchored in this Merkle root hash
- Use RetainHeight 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. Historical blocks may also be required for other purposes, e.g. auditing, replay of non-persisted heights, light client verification, and so on.

Name	Type	Description	Field Number
data	bytes	The Merkle root hash of the application state.	2
retain_height	int64	Blocks below this height may be removed. Defaults to `0` (retain all).	3

ListSnapshots

Request:
Name Type Description Field Number
Empty request asking the application for a list of snapshots.
Response:
Name Type Description Field Number
snapshots repeated Snapshot List of local state snapshots. 1
Usage:
- Used during state sync to discover available snapshots on peers.
- See Snapshot data type for details.

Name	Type	Description	Field Number
snapshots	repeated Snapshot	List of local state snapshots.	1

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
chunk bytes The binary chunk contents, in an arbitray format. Chunk messages cannot be larger than 16 MB including metadata, so 10 MB is a good starting point. 1
Usage:
- Used during state sync to retrieve snapshot chunks from peers.

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

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
result Result The result of the snapshot offer. 1

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

Name	Type	Description	Field Number
result	Result	The result of the snapshot offer.	1

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.

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
result	Result (see below)	The result of applying this chunk.	1
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
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

  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.

New methods introduced in ABCI 2.0

PrepareProposal

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
txs repeated bytes Possibly modified list of transactions that have been picked as part of the proposed block. 2
Usage:
- RequestPrepareProposal’s parameters txs, misbehavior, height, time, next_validators_hash, and proposer_address are the same as in RequestProcessProposal.
- RequestPrepareProposal.local_last_commit is a set of the precommit votes that allowed the decision of the previous block.
- Fields height, time, proposer_address, and next_validators_hash 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 evited 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 responsability to support it. For instance, the Application could attach to a transformed transaction a list with the hashes of the transactions it derives from.
- CometBFT MAY include a list of transactions in RequestPrepareProposal.txs whose total size in bytes exceeds 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 .
- 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. It will then forward the events to the BeginBlock-DeliverTx-EndBlock functions depending on where each event should be placed, thereby returning the events to CometBFT.
- 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 can be non-deterministic.

Name	Type	Description	Field Number
txs	repeated bytes	Possibly modified list of transactions that have been picked as part of the proposed block.	2

When does CometBFT call `PrepareProposal` ?

When a validator p enters consensus round r, height h, in which p is the proposer, and p’s validValue is nil:

CometBFT collects outstanding transactions from p’s mempool
- the transactions will be collected in order of priority
- p’s CometBFT creates a block header.
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.
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 includes the transaction list (whether modified or not) in the return parameters (see the rules in section Usage), and returns from the call.
p uses the (possibly) modified block as p’s proposal in round r, height h.

Note that, if p has a non-nil validValue in round r, height h, the consensus algorithm will use it as proposal and will not call RequestPrepareProposal.

ProcessProposal

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
status ProposalStatus enum that signals if the application finds the proposal valid. 1
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 the calls to BeginBlock-DeliverTx-EndBlock.
  - 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.

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

When does CometBFT call `ProcessProposal` ?

When a node p enters consensus round r, height h, in which q is the proposer (possibly p = q):

p sets up timer ProposeTimeout.
If p is the proposer, p executes steps 1-6 in PrepareProposal.
Upon reception of Proposal message (which contains the header) for round r, height h from q, p verifies the block header.
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.
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.

Data Types existing in ABCI

Most of the data structures used in ABCI are shared common data structures. In certain cases, ABCI uses different data structures which are documented here:

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 in RequestBeginBlock as part of VoteInfo
- Does not include PubKey to avoid sending potentially large quantum pubkeys over the ABCI

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

ValidatorUpdate

Fields:
Name Type Description Field Number
pub_key Public Key Public key of the validator 1
power int64 Voting power of the validator 2
Usage:
- Validator identified by PubKey
- Used to tell CometBFT to update the validator set

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

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

Name	Field Number
UNKNOWN	0
DUPLICATE_VOTE	1
LIGHT_CLIENT_ATTACK	2

ConsensusParams

Fields:

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

ProofOps

Fields:

Name	Type	Description	Field Number
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

ProofOp

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

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

Snapshot

Fields:

Name	Type	Description	Field Number
height	uint64	The height at which the snapshot was taken (after commit).	1
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
chunks	uint32	The number of chunks in the snapshot. Must be at least 1 (even if empty).	3
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
metadata	bytes	Arbitrary application metadata, for example chunk hashes or other verification data.	5

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++

VoteInfo

Fields:
Name Type Description Field Number
validator Validator The validator that sent the vote. 1
signed_last_block bool Indicates whether or not the validator signed the last block. 2
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
signed_last_block	bool	Indicates whether or not the validator signed the last block.	2
vote_extension	bytes	Reserved for future use.	3

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 is reserved for future use when vote extensions are added. Currently, this field is always set to nil.

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

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

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.

CometBFT Spec

​Methods existing in ABCI

​Echo

​Flush

​Info

​InitChain

​Query

​CheckTx

​BeginBlock

​DeliverTx

​EndBlock

​Commit

​ListSnapshots

​LoadSnapshotChunk

​OfferSnapshot

​Result

​ApplySnapshotChunk

​New methods introduced in ABCI 2.0

​PrepareProposal

​Parameters and Types

​When does CometBFT call PrepareProposal ?

​ProcessProposal

​Parameters and Types

​When does CometBFT call ProcessProposal ?

​Data Types existing in ABCI

​Validator

​ValidatorUpdate

​Misbehavior

​MisbehaviorType

​ConsensusParams

​ProofOps

​ProofOp

​Snapshot

​Data types introduced or modified in ABCI++

​VoteInfo

​ExtendedVoteInfo

​CommitInfo

​ExtendedCommitInfo

​ProposalStatus

Methods existing in ABCI

Echo

Flush

Info

InitChain

Query

CheckTx

BeginBlock

DeliverTx

EndBlock

Commit

ListSnapshots

LoadSnapshotChunk

OfferSnapshot

Result

ApplySnapshotChunk

New methods introduced in ABCI 2.0

PrepareProposal

Parameters and Types

When does CometBFT call `PrepareProposal` ?

ProcessProposal

Parameters and Types

When does CometBFT call `ProcessProposal` ?

Data Types existing in ABCI

Validator

ValidatorUpdate

Misbehavior

MisbehaviorType

ConsensusParams

ProofOps

ProofOp

Snapshot

Data types introduced or modified in ABCI++

VoteInfo

ExtendedVoteInfo

CommitInfo

ExtendedCommitInfo

ProposalStatus