implement i2p_pex, peer exchange support for i2p torrents

CMakeLists.txt

@@ -131,6 +131,7 @@ set(libtorrent_extensions_include_files
 	smart_ban.hpp
 	ut_metadata.hpp
 	ut_pex.hpp
+	i2p_pex.hpp
 )
 
 set(libtorrent_aux_include_files
@@ -443,6 +444,7 @@ set(sources
 # -- extensions --
 	smart_ban.cpp
 	ut_pex.cpp
+	i2p_pex.cpp
 	ut_metadata.cpp
 )
 

ChangeLog

@@ -1,5 +1,6 @@
 2.1.0 not released
 
+	* implement i2p_pex, peer exchange support for i2p torrents
 	* deprecate torrent_alert::torrent_name()
 	* requires OpenSSL minimum version 1.1.0 with SNI support
 	* try harder to bind TCP and UDP sockets to the same port

Jamfile

@@ -920,6 +920,7 @@ SOURCES =
 
 # -- extensions --
 	ut_pex
+	i2p_pex
 	ut_metadata
 	smart_ban
 	;

Makefile

@@ -427,6 +427,7 @@ SOURCES = \
   upnp.cpp                        \
   ut_metadata.cpp                 \
   ut_pex.cpp                      \
+  i2p_pex.cpp                     \
   utf8.cpp                        \
   utp_socket_manager.cpp          \
   utp_stream.cpp                  \
@@ -702,6 +703,7 @@ HEADERS = \
   extensions/smart_ban.hpp          \
   extensions/ut_metadata.hpp        \
   extensions/ut_pex.hpp             \
+  extensions/i2p_pex.hpp            \
   \
   kademlia/announce_flags.hpp       \
   kademlia/dht_observer.hpp         \

include/libtorrent/aux_/bt_peer_connection.hpp

@@ -79,10 +79,12 @@ namespace libtorrent::aux {
 			// metadata_msg = 2,
 			upload_only_msg = 3,
 			holepunch_msg = 4,
-			// recommend_msg = 5,
-			// comment_msg = 6,
+			// i2p_pex_msg = 5,
 			dont_have_msg = 7,
 			share_mode_msg = 8
+
+			// recommend_msg = x,
+			// comment_msg = x,
 		};
 
 		~bt_peer_connection() override;

include/libtorrent/aux_/peer.hpp

@@ -44,6 +44,7 @@ namespace libtorrent::aux {
 	};
 
 #if TORRENT_USE_I2P
+	// TODO: it seems unnecessary to wrap this i2p address in a struct
 	struct i2p_peer_entry
 	{
 		sha256_hash destination;

include/libtorrent/aux_/session_impl.hpp

@@ -708,6 +708,7 @@ namespace aux {
 #endif
 
 #if TORRENT_USE_I2P
+			i2p_connection& i2p_conn() override { return m_i2p_conn; }
 			char const* i2p_session() const override { return m_i2p_conn.session_id(); }
 			std::string const& local_i2p_endpoint() const override { return m_i2p_conn.local_endpoint(); }
 

include/libtorrent/aux_/session_interface.hpp

@@ -190,6 +190,7 @@ namespace libtorrent::aux {
 		virtual proxy_settings proxy() const = 0;
 
 #if TORRENT_USE_I2P
+		virtual i2p_connection& i2p_conn() = 0;
 		virtual char const* i2p_session() const = 0;
 		virtual std::string const& local_i2p_endpoint() const = 0;
 #endif

include/libtorrent/aux_/torrent.hpp

@@ -921,8 +921,11 @@ namespace libtorrent::aux {
 		void completed();
 
 #if TORRENT_USE_I2P
-		void on_i2p_resolve(error_code const& ec, char const* dest);
+		void on_i2p_resolve(error_code const& ec, char const* dest, peer_source_flags_t const source);
+		void add_i2p_peer(sha256_hash const& dest, peer_source_flags_t source);
 		bool is_i2p() const { return m_i2p; }
+#else
+		bool is_i2p() const { return false; }
 #endif
 
 		// this is the asio callback that is called when a name

include/libtorrent/aux_/torrent_peer.hpp

@@ -219,6 +219,9 @@ namespace libtorrent::aux {
 		i2p_peer(i2p_peer&&) = default;
 		i2p_peer& operator=(i2p_peer&&) & = default;
 
+		// TODO: This destination should probably be kept in binary form (rather than
+		// base64). The peers should primarily be handled by their sha256 hash
+		// of the destination, that should be kept in here as well.
 		aux::string_ptr destination;
 	};
 #endif

include/libtorrent/extensions/i2p_pex.hpp

@@ -0,0 +1,37 @@
+/*
+
+Copyright (c) 2025, 2019-2021, Arvid Norberg
+All rights reserved.
+
+You may use, distribute and modify this code under the terms of the BSD license,
+see LICENSE file.
+*/
+
+#ifndef TORRENT_I2P_PEX_EXTENSION_HPP_INCLUDED
+#define TORRENT_I2P_PEX_EXTENSION_HPP_INCLUDED
+
+#ifndef TORRENT_DISABLE_EXTENSIONS
+#if TORRENT_USE_I2P
+
+#include "libtorrent/config.hpp"
+
+#include <memory>
+
+namespace libtorrent {
+
+	struct torrent_plugin;
+	struct torrent_handle;
+	struct client_data_t;
+
+	// The i2p_pex extension gossips i2p peer addresses, only on i2p torrents.
+	// The extension will not activate for non-i2p torrents.
+	//
+	// This can either be passed in the add_torrent_params::extensions field, or
+	// via torrent_handle::add_extension().
+	TORRENT_EXPORT std::shared_ptr<torrent_plugin> create_i2p_pex_plugin(torrent_handle const&, client_data_t);
+}
+
+#endif
+#endif // TORRENT_DISABLE_EXTENSIONS
+
+#endif // TORRENT_I2P_PEX_EXTENSION_HPP_INCLUDED

include/libtorrent/i2p_stream.hpp

@@ -454,7 +454,7 @@ struct i2p_stream : aux::proxy_base
 	state_t m_state;
 };
 
-class i2p_connection
+class TORRENT_EXTRA_EXPORT i2p_connection
 {
 public:
 	explicit i2p_connection(io_context& ios);

include/libtorrent/libtorrent.hpp

@@ -23,6 +23,7 @@
 #include "libtorrent/error.hpp"
 #include "libtorrent/error_code.hpp"
 #include "libtorrent/extensions.hpp"
+#include "libtorrent/extensions/i2p_pex.hpp"
 #include "libtorrent/extensions/smart_ban.hpp"
 #include "libtorrent/extensions/ut_metadata.hpp"
 #include "libtorrent/extensions/ut_pex.hpp"

include/libtorrent/torrent_info.hpp

@@ -456,6 +456,8 @@ TORRENT_VERSION_NAMESPACE_3
 		// or not it has a tracker whose URL domain name ends with ".i2p". i2p
 		// torrents disable the DHT and local peer discovery as well as talking
 		// to peers over anything other than the i2p network.
+		// This is not reliably set for torrents created via resume data or
+		// magnet links. Prefer using torrent::is_i2p() instead.
 		bool is_i2p() const { return bool(m_flags & i2p); }
 
 		// internal