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// 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
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