[bug report] connection close by client when connect peer via proxy running locallly

[wen-long]

background

I always run a proxy in local to forward traffic, along with bittorrent. but if I set proxy address 127.0.0.1 in bittorrent(like qB), connection always be disconnected by qB, I tcpdump-ed and confirmd. thus I review code and found a bug below.

bug explain

m_remote would be proxy ip if connect peer via proxy, no wonder connection are closed.

workaround

I set proxy ip as LAN ip and it goes well.

how to fix

I think just delete these line is ok. I'm not sure if self_connection avoidance is necessary

https://github.com/arvidn/libtorrent/blob/6d64ac1dadb17df1c5719eb66179ac47e95eba12/src/peer_connection.cpp#L6335-L6339

disclaimer

Although I tested on my mac but I'didnt read too much code of libtorrent so maybe my misunderstanding.

[arvidn]

yes, this would break things if it looks like every peer is coming from localhost. are you using SOCKS5?

[wen-long]

yes, this would break things if it looks like every peer is coming from localhost. are you using SOCKS5?

http and socks5 both are effected, in my test.

[wen-long]

I have to update this, the above report is not right

I tried to debug, but I dont know how to output log of libtorrent in qBittorrent. I modify code in start of func disconnect

    void peer_connection::disconnect(error_code const& ec
        , operation_t const op, disconnect_severity_t const error)
    {
        std::ofstream outfile;
        outfile.open("/path/to/qblog.txt", std::ios_base::app); // append instead of overwrite
        outfile << operation_name(op);
        outfile.close();

and the log contains connect repeatly

and I remeber I had set Network Interface to a NIC(like en0 on mac)

thus I think below line cause the disconnection

https://github.com/arvidn/libtorrent/blob/75136d31a3e563284e84bfb80c8cf2310f5640d6/src/peer_connection.cpp#L6288-L6303

I change Network Interface to Any interface then http&socks5 proxy addredd 127.0.0.1 works fine.

[wen-long]

set Network Interface to lo0 means disconnect from network. maybe It's a ambiguity due to word usage. If qB setting key is literally outgoing_interfaces, I wont change the value

[arvidn]

I would expect that setting to correspond to listen_interfaces setting. But if you only talk to a proxy over loopback, it seems reasonable to set that to lo0 or loopback