[net] Move ConnectionType to its own file

2 files changed, 108 insertions, 0 deletions

diff --git a/src/node/connection_types.cpp b/src/node/connection_types.cpp
new file mode 100644
index 0000000000..904f4371aa
--- /dev/null
+++ b/src/node/connection_types.cpp
@@ -0,0 +1,26 @@
+// 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.
+
+#include <node/connection_types.h>
+#include <cassert>
+
+std::string ConnectionTypeAsString(ConnectionType conn_type)
+{
+    switch (conn_type) {
+    case ConnectionType::INBOUND:
+        return "inbound";
+    case ConnectionType::MANUAL:
+        return "manual";
+    case ConnectionType::FEELER:
+        return "feeler";
+    case ConnectionType::OUTBOUND_FULL_RELAY:
+        return "outbound-full-relay";
+    case ConnectionType::BLOCK_RELAY:
+        return "block-relay-only";
+    case ConnectionType::ADDR_FETCH:
+        return "addr-fetch";
+    } // no default case, so the compiler can warn about missing cases
+
+    assert(false);
+}
diff --git a/src/node/connection_types.h b/src/node/connection_types.h
new file mode 100644
index 0000000000..5e1abcace6
--- /dev/null
+++ b/src/node/connection_types.h
@@ -0,0 +1,82 @@
+// 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