Enabling proxy for trackers prevents incoming TCP connections from peers

[grechnik]

My usecase is similar to #4904 : I setup proxy to connect to trackers while using direct connections with peers. In this configuration after #4904 is solved, UDP traffic is fine; however, any incoming TCP connection is accepted but immediately closed by the library.

It seems that the fix in #4909 leaves out a check in session_impl::on_accept_connection:

libtorrent/src/session_impl.cpp

Line 2698 in 985fc00

if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none)

At the very least, I think it should be synchronized with session_impl::reopen_listen_sockets

libtorrent/src/session_impl.cpp

Lines 1952 to 1953 in 985fc00

	if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none
	&& m_settings.get_bool(settings_pack::proxy_peer_connections))

More generally, I'm not sure whether the check in on_accept_connection makes sense at all: if we don't want to deal with the connection, we shouldn't be even listening on the port. Removing the check seems to fix the problem for me.

libtorrent version (or branch): 1.2.12.0, built in qBittorrent v4.3.3

platform/architecture: Windows 10 Build 19042.804, 64-bit

[arvidn]

I think you're right. The case where you don't proxy connection is not taken into account in that check.

I imagine this would fix it:

diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index 892d9b895..7b3ecf553 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -2646,7 +2646,8 @@ namespace {
 
                // don't accept any connections from our local sockets if we're using a
                // proxy
-               if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none)
+               if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none
+                       && m_settings.get_bool(settings_pack::proxy_peer_connections))
                        return;
 
                auto listen = std::find_if(m_listen_sockets.begin(), m_listen_sockets.end()
@@ -5509,7 +5510,8 @@ namespace {
                        return std::uint16_t(sock->tcp_external_port());
                }
 
-               if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none)
+               if (m_settings.get_int(settings_pack::proxy_type) != settings_pack::none
+                       && m_settings.get_bool(settings_pack::proxy_peer_connections))
                        return 0;
 
                for (auto const& s : m_listen_sockets)

[arvidn]

could you test this patch? #6002

[grechnik]

I have tested the patch, it fixes the issue.