Feat: Include a warning in Preferences => Proxy configuration

[ngosang]

A significant portion of aMule's connections and traffic is leaked if a proxy is configured; please include a warning or a message to that effect and recommend using a VPN if privacy is a concern.

https://amule-org.github.io/docs/manual/configuration/proxy#what-amule-routes-through-the-proxy

[got3nks]

Looked through the code paths and the concern reduces to one real gap plus one that's by-design:

HTTP requests through SOCKS proxies — real gap, blocked on wxWidgets 3.3. Startup HTTP downloads (IP filter, GeoIP, server list, nodes.dat, anti-leech) go through wxWebRequest / wxWebProxy, which on wx 3.2/3.3 supports HTTP-type proxies only. SOCKS4 / SOCKS4a / SOCKS5 are silently bypassed — the code already calls this out in HTTPDownload.cpp:170 ("wx 3.3's wxWebProxy is HTTP-only. A libcurl backend would be required if SOCKS support mattered — that is out of scope for this fix"). A clean fix means either waiting for wx 3.3 to ship in popular distros and gain SOCKS support, or adding libcurl as a dependency — the latter was previously declined, so we're effectively waiting on distro adoption.

Listen socket / incoming TCP — not actually a leak. If a user is HighID they've already explicitly forwarded their incoming port at the router level, so they know peers will reach them at their public IP — no proxy protocol (SOCKS, HTTP) supports proxying incoming connections (that'd need a TURN-like reverse tunnel). LowID users have no incoming traffic at all. So the privacy boundary at the listen socket is set by the user's own port-forwarding decision and is already visible to them.

[got3nks]

Should have added this for completeness — what is covered by the proxy today:

Proxy type	TCP (ed2k server, peer-to-peer, Kad TCP)	UDP (Kad, ed2k UDP, eMule extended UDP)
HTTP	✓ via CONNECT	✗ — silently dropped
SOCKS4	✓	✗
SOCKS4a	✓	✗
SOCKS5	✓	✓ via UDP_ASSOCIATE

So on SOCKS5 both the TCP and UDP halves of ed2k / Kad route through the proxy. On HTTP / SOCKS4 / SOCKS4a, only the TCP half is proxied — UDP is not leaked, but it's also not delivered (the proxy stack at Proxy.cpp:1280-1282 has no fall-through to a direct send), which means Kad lookups, eMule extended UDP queue rating, and ed2k UDP server probes effectively don't work under those proxy types.