// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_NODE_CONNECTION_TYPES_H
#define BITCOIN_NODE_CONNECTION_TYPES_H

#include <string>

/** Different types of connections to a peer. This enum encapsulates the
 * information we have available at the time of opening or accepting the
 * connection. Aside from INBOUND, all types are initiated by us.
 *
 * If adding or removing types, please update CONNECTION_TYPE_DOC in
 * src/rpc/net.cpp and src/qt/rpcconsole.cpp, as well as the descriptions in
 * src/qt/guiutil.cpp and src/bitcoin-cli.cpp::NetinfoRequestHandler. */
enum class ConnectionType {
    /**
     * Inbound connections are those initiated by a peer. This is the only
     * property we know at the time of connection, until P2P messages are
     * exchanged.
     */
    INBOUND,

    /**
     * These are the default connections that we use to connect with the
     * network. There is no restriction on what is relayed; by default we relay
     * blocks, addresses & transactions. We automatically attempt to open
     * MAX_OUTBOUND_FULL_RELAY_CONNECTIONS using addresses from our AddrMan.
     */
    OUTBOUND_FULL_RELAY,


    /**
     * We open manual connections to addresses that users explicitly requested
     * via the addnode RPC or the -addnode/-connect configuration options. Even if a
     * manual connection is misbehaving, we do not automatically disconnect or
     * add it to our discouragement filter.
     */
    MANUAL,

    /**
     * Feeler connections are short-lived connections made to check that a node
     * is alive. They can be useful for:
     * - test-before-evict: if one of the peers is considered for eviction from
     *   our AddrMan because another peer is mapped to the same slot in the tried table,
     *   evict only if this longer-known peer is offline.
     * - move node addresses from New to Tried table, so that we have more
     *   connectable addresses in our AddrMan.
     * Note that in the literature ("Eclipse Attacks on Bitcoin’s Peer-to-Peer Network")
     * only the latter feature is referred to as "feeler connections",
     * although in our codebase feeler connections encompass test-before-evict as well.
     * We make these connections approximately every FEELER_INTERVAL:
     * first we resolve previously found collisions if they exist (test-before-evict),
     * otherwise we connect to a node from the new table.
     */
    FEELER,

    /**
     * We use block-relay-only connections to help prevent against partition
     * attacks. By not relaying transactions or addresses, these connections
     * are harder to detect by a third party, thus helping obfuscate the
     * network topology. We automatically attempt to open
     * MAX_BLOCK_RELAY_ONLY_ANCHORS using addresses from our anchors.dat. Then
     * addresses from our AddrMan if MAX_BLOCK_RELAY_ONLY_CONNECTIONS
     * isn't reached yet.
     */
    BLOCK_RELAY,

    /**
     * AddrFetch connections are short lived connections used to solicit
     * addresses from peers. These are initiated to addresses submitted via the
     * -seednode command line argument, or under certain conditions when the
     * AddrMan is empty.
     */
    ADDR_FETCH,
};

/** Convert ConnectionType enum to a string value */
std::string ConnectionTypeAsString(ConnectionType conn_type);

#endif // BITCOIN_NODE_CONNECTION_TYPES_H
