path: root/include/hotstuff/consensus.h

#ifndef _HOTSTUFF_CONSENSUS_H
#define _HOTSTUFF_CONSENSUS_H

#include <cassert>
#include <set>
#include <unordered_map>

#include "hotstuff/promise.hpp"
#include "hotstuff/type.h"
#include "hotstuff/entity.h"
#include "hotstuff/crypto.h"

namespace hotstuff {

struct Proposal;
struct Vote;
struct Finality;

/** Abstraction for HotStuff protocol state machine (without network implementation). */
class HotStuffCore {
    block_t b0;                                  /** the genesis block */
    /* === state variables === */
    /** block containing the QC for the highest block having one */
    block_t bqc;
    block_t bexec;                            /**< last executed block */
    uint32_t vheight;          /**< height of the block last voted for */
    /* === auxilliary variables === */
    privkey_bt priv_key;            /**< private key for signing votes */
    std::set<block_t, BlockHeightCmp> tails;   /**< set of tail blocks */
    ReplicaConfig config;                   /**< replica configuration */
    /* === async event queues === */
    std::unordered_map<block_t, promise_t> qc_waiting;
    promise_t propose_waiting;
    promise_t receive_proposal_waiting;

    block_t get_delivered_blk(const uint256_t &blk_hash);
    void sanity_check_delivered(const block_t &blk);
    void check_commit(const block_t &_bqc);
    bool update(const uint256_t &bqc_hash);
    void on_qc_finish(const block_t &blk);
    void on_propose_(const block_t &blk);
    void on_receive_proposal_(const Proposal &prop);

    protected:
    ReplicaID id;                  /**< identity of the replica itself */

    public:
    BoxObj<EntityStorage> storage;

    HotStuffCore(ReplicaID id, privkey_bt &&priv_key);
    virtual ~HotStuffCore() {
        b0->qc_ref = nullptr;
    }

    /* Inputs of the state machine triggered by external events, should called
     * by the class user, with proper invariants. */

    /** Call to initialize the protocol, should be called once before all other
     * functions. */
    void on_init(uint32_t nfaulty) { config.nmajority = 2 * nfaulty + 1; }

    /* TODO: better name for "delivery" ? */
    /** Call to inform the state machine that a block is ready to be handled.
     * A block is only delivered if itself is fetched, the block for the
     * contained qc is fetched and all parents are delivered. The user should
     * always ensure this invariant. The invalid blocks will be dropped by this
     * function.
     * @return true if valid */
    bool on_deliver_blk(const block_t &blk);

    /** Call upon the delivery of a proposal message.
     * The block mentioned in the message should be already delivered. */
    void on_receive_proposal(const Proposal &prop);

    /** Call upon the delivery of a vote message.
     * The block mentioned in the message should be already delivered. */
    void on_receive_vote(const Vote &vote);

    /** Call to submit new commands to be decided (executed). "Parents" must
     * contain at least one block, and the first block is the actual parent,
     * while the others are uncles/aunts */
    void on_propose(const std::vector<command_t> &cmds,
                    const std::vector<block_t> &parents,
                    bytearray_t &&extra = bytearray_t());

    /* Functions required to construct concrete instances for abstract classes.
     * */

    /* Outputs of the state machine triggering external events.  The virtual
     * functions should be implemented by the user to specify the behavior upon
     * the events. */
    protected:
    /** Called by HotStuffCore upon the decision being made for cmd. */
    virtual void do_decide(Finality &&fin) = 0;
    /** Called by HotStuffCore upon broadcasting a new proposal.
     * The user should send the proposal message to all replicas except for
     * itself. */
    virtual void do_broadcast_proposal(const Proposal &prop) = 0;
    /** Called upon sending out a new vote to the next proposer.  The user
     * should send the vote message to a *good* proposer to have good liveness,
     * while safety is always guaranteed by HotStuffCore. */
    virtual void do_vote(ReplicaID last_proposer, const Vote &vote) = 0;

    /* The user plugs in the detailed instances for those
     * polymorphic data types. */
    public:
    /** Create a partial certificate that proves the vote for a block. */
    virtual part_cert_bt create_part_cert(const PrivKey &priv_key, const uint256_t &blk_hash) = 0;
    /** Create a partial certificate from its seralized form. */
    virtual part_cert_bt parse_part_cert(DataStream &s) = 0;
    /** Create a quorum certificate that proves 2f+1 votes for a block. */
    virtual quorum_cert_bt create_quorum_cert(const uint256_t &blk_hash) = 0;
    /** Create a quorum certificate from its serialized form. */
    virtual quorum_cert_bt parse_quorum_cert(DataStream &s) = 0;
    /** Create a command object from its serialized form. */
    virtual command_t parse_cmd(DataStream &s) = 0;

    public:
    /** Add a replica to the current configuration. This should only be called
     * before running HotStuffCore protocol. */
    void add_replica(ReplicaID rid, const NetAddr &addr, pubkey_bt &&pub_key);
    /** Try to prune blocks lower than last committed height - staleness. */
    void prune(uint32_t staleness);

    /* PaceMaker can use these functions to monitor the core protocol state
     * transition */
    /** Get a promise resolved when the block gets a QC. */
    promise_t async_qc_finish(const block_t &blk);
    /** Get a promise resolved when a new block is proposed. */
    promise_t async_wait_propose();
    /** Get a promise resolved when a new proposal is received. */
    promise_t async_wait_receive_proposal();

    /* Other useful functions */
    block_t get_genesis() { return b0; }
    const ReplicaConfig &get_config() { return config; }
    ReplicaID get_id() const { return id; }
    const std::set<block_t, BlockHeightCmp> get_tails() const { return tails; }
    operator std::string () const;
};

/** Abstraction for proposal messages. */
struct Proposal: public Serializable {
    ReplicaID proposer;
    /** hash for the block containing the highest QC */
    uint256_t bqc_hash;
    /** block being proposed */
    block_t blk;

    /** handle of the core object to allow polymorphism. The user should use
     * a pointer to the object of the class derived from HotStuffCore */
    HotStuffCore *hsc;

    Proposal(): blk(nullptr), hsc(nullptr) {}
    Proposal(ReplicaID proposer,
            const uint256_t &bqc_hash,
            block_t &blk,
            HotStuffCore *hsc):
        proposer(proposer),
        bqc_hash(bqc_hash),
        blk(blk), hsc(hsc) {}

    void serialize(DataStream &s) const override {
        s << proposer
          << bqc_hash
          << *blk;
    }

    void unserialize(DataStream &s) override {
        assert(hsc != nullptr);
        s >> proposer
          >> bqc_hash;
        Block _blk;
        _blk.unserialize(s, hsc);
        blk =