Process Proposal

ProcessProposal handles the validation of a proposal from PrepareProposal, which also includes a block header. Meaning, that after a block has been proposed the other validators have the right to vote on a block. The validator in the default implementation of PrepareProposal runs basic validity checks on each transaction.

Note, ProcessProposal MAY NOT be non-deterministic, i.e. it must be deterministic. This means if ProcessProposal panics or fails and we reject, all honest validator processes will prevote nil and the CometBFT round will proceed again until a valid proposal is proposed.

Here is the implementation of the default implementation:

package baseapp

import (
    
	"bytes"
    "fmt"
    "cosmossdk.io/math"
    "github.com/cockroachdb/errors"
	abci "github.com/cometbft/cometbft/abci/types"
	cmtcrypto "github.com/cometbft/cometbft/crypto"
	cryptoenc "github.com/cometbft/cometbft/crypto/encoding"
	cmtprotocrypto "github.com/cometbft/cometbft/proto/tendermint/crypto"
	cmtproto "github.com/cometbft/cometbft/proto/tendermint/types"
	protoio "github.com/cosmos/gogoproto/io"
    "github.com/cosmos/gogoproto/proto"

	cryptotypes "github.com/cosmos/cosmos-sdk/crypto/types"
	sdk "github.com/cosmos/cosmos-sdk/types"
    "github.com/cosmos/cosmos-sdk/types/mempool"
)

/ VoteExtensionThreshold defines the total voting power % that must be
/ submitted in order for all vote extensions to be considered valid for a
/ given height.
var VoteExtensionThreshold = math.LegacyNewDecWithPrec(667, 3)

type (
	/ Validator defines the interface contract require for verifying vote extension
	/ signatures. Typically, this will be implemented by the x/staking module,
	/ which has knowledge of the CometBFT public key.
	Validator interface {
    CmtConsPublicKey() (cmtprotocrypto.PublicKey, error)

BondedTokens()

math.Int
}

	/ ValidatorStore defines the interface contract require for verifying vote
	/ extension signatures. Typically, this will be implemented by the x/staking
	/ module, which has knowledge of the CometBFT public key.
	ValidatorStore interface {
    GetValidatorByConsAddr(sdk.Context, cryptotypes.Address) (Validator, error)

TotalBondedTokens(ctx sdk.Context)

math.Int
}
)

/ ValidateVoteExtensions defines a helper function for verifying vote extension
/ signatures that may be passed or manually injected into a block proposal from
/ a proposer in ProcessProposal. It returns an error if any signature is invalid
/ or if unexpected vote extensions and/or signatures are found or less than 2/3
/ power is received.
func ValidateVoteExtensions(
	ctx sdk.Context,
	valStore ValidatorStore,
	currentHeight int64,
	chainID string,
	extCommit abci.ExtendedCommitInfo,
)

error {
    cp := ctx.ConsensusParams()
    extsEnabled := cp.Abci != nil && cp.Abci.VoteExtensionsEnableHeight > 0
    marshalDelimitedFn := func(msg proto.Message) ([]byte, error) {
    var buf bytes.Buffer
    if err := protoio.NewDelimitedWriter(&buf).WriteMsg(msg); err != nil {
    return nil, err
}

return buf.Bytes(), nil
}

var sumVP math.Int
    for _, vote := range extCommit.Votes {
    if !extsEnabled {
    if len(vote.VoteExtension) > 0 {
    return fmt.Errorf("vote extensions disabled; received non-empty vote extension at height %d", currentHeight)
}
    if len(vote.ExtensionSignature) > 0 {
    return fmt.Errorf("vote extensions disabled; received non-empty vote extension signature at height %d", currentHeight)
}

continue
}
    if len(vote.ExtensionSignature) == 0 {
    return fmt.Errorf("vote extensions enabled; received empty vote extension signature at height %d", currentHeight)
}
    valConsAddr := cmtcrypto.Address(vote.Validator.Address)

validator, err := valStore.GetValidatorByConsAddr(ctx, valConsAddr)
    if err != nil {
    return fmt.Errorf("failed to get validator %X: %w", valConsAddr, err)
}
    if validator == nil {
    return fmt.Errorf("validator %X not found", valConsAddr)
}

cmtPubKeyProto, err := validator.CmtConsPublicKey()
    if err != nil {
    return fmt.Errorf("failed to get validator %X public key: %w", valConsAddr, err)
}

cmtPubKey, err := cryptoenc.PubKeyFromProto(cmtPubKeyProto)
    if err != nil {
    return fmt.Errorf("failed to convert validator %X public key: %w", valConsAddr, err)
}
    cve := cmtproto.CanonicalVoteExtension{
    Extension: vote.VoteExtension,
    Height:    currentHeight - 1, / the vote extension was signed in the previous height
			Round:     int64(extCommit.Round),
    ChainId:   chainID,
}

extSignBytes, err := marshalDelimitedFn(&cve)
    if err != nil {
    return fmt.Errorf("failed to encode CanonicalVoteExtension: %w", err)
}
    if !cmtPubKey.VerifySignature(extSignBytes, vote.ExtensionSignature) {
    return fmt.Errorf("failed to verify validator %X vote extension signature", valConsAddr)
}

sumVP = sumVP.Add(validator.BondedTokens())
}

	/ Ensure we have at least 2/3 voting power that submitted valid vote
	/ extensions.
    totalVP := valStore.TotalBondedTokens(ctx)
    percentSubmitted := math.LegacyNewDecFromInt(sumVP).Quo(math.LegacyNewDecFromInt(totalVP))
    if percentSubmitted.LT(VoteExtensionThreshold) {
    return fmt.Errorf("insufficient cumulative voting power received to verify vote extensions; got: %s, expected: >=%s", percentSubmitted, VoteExtensionThreshold)
}

return nil
}

type (
	/ ProposalTxVerifier defines the interface that is implemented by BaseApp,
	/ that any custom ABCI PrepareProposal and ProcessProposal handler can use
	/ to verify a transaction.
	ProposalTxVerifier interface {
    PrepareProposalVerifyTx(tx sdk.Tx) ([]byte, error)

ProcessProposalVerifyTx(txBz []byte) (sdk.Tx, error)
}

	/ DefaultProposalHandler defines the default ABCI PrepareProposal and
	/ ProcessProposal handlers.
	DefaultProposalHandler struct {
    mempool    mempool.Mempool
		txVerifier ProposalTxVerifier
}
)

func NewDefaultProposalHandler(mp mempool.Mempool, txVerifier ProposalTxVerifier)

DefaultProposalHandler {
    return DefaultProposalHandler{
    mempool:    mp,
		txVerifier: txVerifier,
}
}

/ PrepareProposalHandler returns the default implementation for processing an
/ ABCI proposal. The application's mempool is enumerated and all valid
/ transactions are added to the proposal. Transactions are valid if they:
/
/ 1)

Successfully encode to bytes.
/ 2)

Are valid (i.e. pass runTx, AnteHandler only).
/
/ Enumeration is halted once RequestPrepareProposal.MaxBytes of transactions is
/ reached or the mempool is exhausted.
/
/ Note:
/
/ - Step (2)

is identical to the validation step performed in
/ DefaultProcessProposal. It is very important that the same validation logic
/ is used in both steps, and applications must ensure that this is the case in
/ non-default handlers.
/
/ - If no mempool is set or if the mempool is a no-op mempool, the transactions
/ requested from CometBFT will simply be returned, which, by default, are in
/ FIFO order.
func (h DefaultProposalHandler)

PrepareProposalHandler()

sdk.PrepareProposalHandler {
    return func(ctx sdk.Context, req *abci.RequestPrepareProposal) (*abci.ResponsePrepareProposal, error) {
		/ If the mempool is nil or NoOp we simply return the transactions
		/ requested from CometBFT, which, by default, should be in FIFO order.
		_, isNoOp := h.mempool.(mempool.NoOpMempool)
    if h.mempool == nil || isNoOp {
    return &abci.ResponsePrepareProposal{
    Txs: req.Txs
}, nil
}

var (
			selectedTxs  [][]byte
			totalTxBytes int64
		)
    iterator := h.mempool.Select(ctx, req.Txs)
    for iterator != nil {
    memTx := iterator.Tx()

			/ NOTE: Since transaction verification was already executed in CheckTx,
			/ which calls mempool.Insert, in theory everything in the pool should be
			/ valid. But some mempool implementations may insert invalid txs, so we
			/ check again.
			bz, err := h.txVerifier.PrepareProposalVerifyTx(memTx)
    if err != nil {
    err := h.mempool.Remove(memTx)
    if err != nil && !errors.Is(err, mempool.ErrTxNotFound) {
    panic(err)
}
	
}

else {
    txSize := int64(len(bz))
    if totalTxBytes += txSize; totalTxBytes <= req.MaxTxBytes {
    selectedTxs = append(selectedTxs, bz)
}

else {
					/ We've reached capacity per req.MaxTxBytes so we cannot select any
					/ more transactions.
					break
}
	
}

iterator = iterator.Next()
}

return &abci.ResponsePrepareProposal{
    Txs: selectedTxs
}, nil
}
}

/ ProcessProposalHandler returns the default implementation for processing an
/ ABCI proposal. Every transaction in the proposal must pass 2 conditions:
/
/ 1. The transaction bytes must decode to a valid transaction.
/ 2. The transaction must be valid (i.e. pass runTx, AnteHandler only)
/
/ If any transaction fails to pass either condition, the proposal is rejected.
/ Note that step (2)

is identical to the validation step performed in
/ DefaultPrepareProposal. It is very important that the same validation logic
/ is used in both steps, and applications must ensure that this is the case in
/ non-default handlers.
func (h DefaultProposalHandler)

ProcessProposalHandler()

sdk.ProcessProposalHandler {
	/ If the mempool is nil or NoOp we simply return ACCEPT,
	/ because PrepareProposal may have included txs that could fail verification.
	_, isNoOp := h.mempool.(mempool.NoOpMempool)
    if h.mempool == nil || isNoOp {
    return NoOpProcessProposal()
}

return func(ctx sdk.Context, req *abci.RequestProcessProposal) (*abci.ResponseProcessProposal, error) {
    for _, txBytes := range req.Txs {
			_, err := h.txVerifier.ProcessProposalVerifyTx(txBytes)
    if err != nil {
    return &abci.ResponseProcessProposal{
    Status: abci.ResponseProcessProposal_REJECT
}, nil
}
	
}

return &abci.ResponseProcessProposal{
    Status: abci.ResponseProcessProposal_ACCEPT
}, nil
}
}

/ NoOpPrepareProposal defines a no-op PrepareProposal handler. It will always
/ return the transactions sent by the client's request.
func NoOpPrepareProposal()

sdk.PrepareProposalHandler {
    return func(_ sdk.Context, req *abci.RequestPrepareProposal) (*abci.ResponsePrepareProposal, error) {
    return &abci.ResponsePrepareProposal{
    Txs: req.Txs
}, nil
}
}

/ NoOpProcessProposal defines a no-op ProcessProposal Handler. It will always
/ return ACCEPT.
func NoOpProcessProposal()

sdk.ProcessProposalHandler {
    return func(_ sdk.Context, _ *abci.RequestProcessProposal) (*abci.ResponseProcessProposal, error) {
    return &abci.ResponseProcessProposal{
    Status: abci.ResponseProcessProposal_ACCEPT
}, nil
}
}

/ NoOpExtendVote defines a no-op ExtendVote handler. It will always return an
/ empty byte slice as the vote extension.
func NoOpExtendVote()

sdk.ExtendVoteHandler {
    return func(_ sdk.Context, _ *abci.RequestExtendVote) (*abci.ResponseExtendVote, error) {
    return &abci.ResponseExtendVote{
    VoteExtension: []byte{
}}, nil
}
}

/ NoOpVerifyVoteExtensionHandler defines a no-op VerifyVoteExtension handler. It
/ will always return an ACCEPT status with no error.
func NoOpVerifyVoteExtensionHandler()

sdk.VerifyVoteExtensionHandler {
    return func(_ sdk.Context, _ *abci.RequestVerifyVoteExtension) (*abci.ResponseVerifyVoteExtension, error) {
    return &abci.ResponseVerifyVoteExtension{
    Status: abci.ResponseVerifyVoteExtension_ACCEPT
}, nil
}
}

Like PrepareProposal this implementation is the default and can be modified by the application developer in app.go. If you decide to implement your own ProcessProposal handler, you must be sure to ensure that the transactions provided in the proposal DO NOT exceed the maximum block gas and maxtxbytes (if set).

processOpt := func(app *baseapp.BaseApp) {
    abciPropHandler := baseapp.NewDefaultProposalHandler(mempool, app)

app.SetProcessProposal(abciPropHandler.ProcessProposalHandler())
}

baseAppOptions = append(baseAppOptions, processOpt)