application.rs

//! ABCI application interface.

#[cfg(feature = "echo-app")]
pub mod echo;
#[cfg(feature = "kvstore-app")]
pub mod kvstore;

use tendermint_proto::v0_38::abci::{
    request::Value, response, response_process_proposal, response_verify_vote_extension, Request,
    RequestApplySnapshotChunk, RequestCheckTx, RequestEcho, RequestExtendVote,
    RequestFinalizeBlock, RequestInfo, RequestInitChain, RequestLoadSnapshotChunk,
    RequestOfferSnapshot, RequestPrepareProposal, RequestProcessProposal, RequestQuery,
    RequestVerifyVoteExtension, Response, ResponseApplySnapshotChunk, ResponseCheckTx,
    ResponseCommit, ResponseEcho, ResponseExtendVote, ResponseFinalizeBlock, ResponseFlush,
    ResponseInfo, ResponseInitChain, ResponseListSnapshots, ResponseLoadSnapshotChunk,
    ResponseOfferSnapshot, ResponsePrepareProposal, ResponseProcessProposal, ResponseQuery,
    ResponseVerifyVoteExtension,
};

/// An ABCI application.
///
/// Applications are `Send` + `Clone` + `'static` because they are cloned for
/// each incoming connection to the ABCI [`Server`]. It is up to the
/// application developer to manage shared state between these clones of their
/// application.
///
/// [`Server`]: crate::Server
pub trait Application: Send + Clone + 'static {
    /// Echo back the same message as provided in the request.
    fn echo(&self, request: RequestEcho) -> ResponseEcho {
        ResponseEcho {
            message: request.message,
        }
    }

    /// Provide information about the ABCI application.
    fn info(&self, _request: RequestInfo) -> ResponseInfo {
        Default::default()
    }

    /// Called once upon genesis.
    fn init_chain(&self, _request: RequestInitChain) -> ResponseInitChain {
        Default::default()
    }

    /// Query the application for data at the current or past height.
    fn query(&self, _request: RequestQuery) -> ResponseQuery {
        Default::default()
    }

    /// Check the given transaction before putting it into the local mempool.
    fn check_tx(&self, _request: RequestCheckTx) -> ResponseCheckTx {
        Default::default()
    }

    /// Signals that messages queued on the client should be flushed to the server.
    fn flush(&self) -> ResponseFlush {
        ResponseFlush {}
    }

    /// Commit the current state at the current height.
    fn commit(&self) -> ResponseCommit {
        Default::default()
    }

    /// Used during state sync to discover available snapshots on peers.
    fn list_snapshots(&self) -> ResponseListSnapshots {
        Default::default()
    }

    /// Called when bootstrapping the node using state sync.
    fn offer_snapshot(&self, _request: RequestOfferSnapshot) -> ResponseOfferSnapshot {
        Default::default()
    }

    /// Used during state sync to retrieve chunks of snapshots from peers.
    fn load_snapshot_chunk(&self, _request: RequestLoadSnapshotChunk) -> ResponseLoadSnapshotChunk {
        Default::default()
    }

    /// Apply the given snapshot chunk to the application's state.
    fn apply_snapshot_chunk(
        &self,
        _request: RequestApplySnapshotChunk,
    ) -> ResponseApplySnapshotChunk {
        Default::default()
    }

    /// A stage where the application can modify the list of transactions
    /// in the preliminary proposal.
    ///
    /// The default implementation implements the required behavior in a
    /// very naive way, removing transactions off the end of the list
    /// until the limit on the total size of the transaction is met as
    /// specified in the `max_tx_bytes` field of the request, or there are
    /// no more transactions. It's up to the application to implement
    /// more elaborate removal strategies.
    ///
    /// This method is introduced in ABCI++.
    fn prepare_proposal(&self, request: RequestPrepareProposal) -> ResponsePrepareProposal {
        // Per the ABCI++ spec: 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.
        let RequestPrepareProposal {
            mut txs,
            max_tx_bytes,
            ..
        } = request;
        let max_tx_bytes: usize = max_tx_bytes.try_into().unwrap_or(0);
        let mut total_tx_bytes: usize = txs
            .iter()
            .map(|tx| tx.len())
            .fold(0, |acc, len| acc.saturating_add(len));
        while total_tx_bytes > max_tx_bytes {
            if let Some(tx) = txs.pop() {
                total_tx_bytes = total_tx_bytes.saturating_sub(tx.len());
            } else {
                break;
            }
        }
        ResponsePrepareProposal { txs }
    }

    /// A stage where the application can accept or reject the proposed block.
    ///
    /// The default implementation returns the status value of `ACCEPT`.
    ///
    /// This method is introduced in ABCI++.
    fn process_proposal(&self, _request: RequestProcessProposal) -> ResponseProcessProposal {
        ResponseProcessProposal {
            status: response_process_proposal::ProposalStatus::Accept as i32,
        }
    }

    fn extend_vote(&self, _request: RequestExtendVote) -> ResponseExtendVote {
        Default::default()
    }

    fn verify_vote_extension(
        &self,
        _request: RequestVerifyVoteExtension,
    ) -> ResponseVerifyVoteExtension {
        ResponseVerifyVoteExtension {
            status: response_verify_vote_extension::VerifyStatus::Accept as i32,
        }
    }

    fn finalize_block(&self, _request: RequestFinalizeBlock) -> ResponseFinalizeBlock {
        Default::default()
    }
}

/// Provides a mechanism for the [`Server`] to execute incoming requests while
/// expecting the correct response types.
pub trait RequestDispatcher {
    /// Executes the relevant application method based on the type of the
    /// request, and produces the corresponding response.
    fn handle(&self, request: Request) -> Response;
}

// Implement `RequestDispatcher` for all `Application`s.
impl<A: Application> RequestDispatcher for A {
    fn handle(&self, request: Request) -> Response {
        tracing::debug!("Incoming request: {:?}", request);
        Response {
            value: Some(match request.value.unwrap() {
                Value::Echo(req) => response::Value::Echo(self.echo(req)),
                Value::Flush(_) => response::Value::Flush(self.flush()),
                Value::Info(req) => response::Value::Info(self.info(req)),
                Value::InitChain(req) => response::Value::InitChain(self.init_chain(req)),
                Value::Query(req) => response::Value::Query(self.query(req)),
                Value::CheckTx(req) => response::Value::CheckTx(self.check_tx(req)),
                Value::Commit(_) => response::Value::Commit(self.commit()),
                Value::ListSnapshots(_) => response::Value::ListSnapshots(self.list_snapshots()),
                Value::OfferSnapshot(req) => {
                    response::Value::OfferSnapshot(self.offer_snapshot(req))
                },
                Value::LoadSnapshotChunk(req) => {
                    response::Value::LoadSnapshotChunk(self.load_snapshot_chunk(req))
                },
                Value::ApplySnapshotChunk(req) => {
                    response::Value::ApplySnapshotChunk(self.apply_snapshot_chunk(req))
                },
                Value::PrepareProposal(req) => {
                    response::Value::PrepareProposal(self.prepare_proposal(req))
                },
                Value::ProcessProposal(req) => {
                    response::Value::ProcessProposal(self.process_proposal(req))
                },
                Value::ExtendVote(req) => response::Value::ExtendVote(self.extend_vote(req)),
                Value::VerifyVoteExtension(req) => {
                    response::Value::VerifyVoteExtension(self.verify_vote_extension(req))
                },
                Value::FinalizeBlock(req) => {
                    response::Value::FinalizeBlock(self.finalize_block(req))
                },
            }),
        }
    }
}