support Android per-app routing scenarios (#245)

README.md

@@ -21,7 +21,36 @@ A tunnel interface for HTTP and SOCKS proxies on Linux, Android, macOS, iOS and
 - SOCKS5 UDP support
 - Native support for proxying DNS over TCP
 - UdpGW (UDP gateway) support for UDP over TCP, see the [wiki](https://github.com/tun2proxy/tun2proxy/wiki/UDP-gateway-feature) for more information
+- Session info embedding for per-app routing on Android (see below)
 
+## Session Info for Per-App Routing (Android)
+
+To enable per-app traffic routing on Android 10+, you can embed session information (protocol, source IP, source port) in the SOCKS5 username field. This allows your proxy server to call `getConnectionOwnerUid()` to identify which app initiated the connection.
+
+To enable this feature, append `+info` to your username:
+
+```bash
+# Without session info (normal mode)
+tun2proxy --proxy "socks5://user:[email protected]:1080"
+
+# With session info
+tun2proxy --proxy "socks5://user+info:[email protected]:1080"
+```
+
+The proxy server will receive the username in the format:
+```
+original_username|protocol|src_ip|src_port
+```
+
+`|` is a literal field delimiter in this format. The client does not escape `|` characters in
+`original_username`, so when using `+info`, the original username must not contain `|` (including
+a `|` introduced via percent-encoding in the proxy URL), otherwise the value becomes ambiguous for
+server-side parsers.
+
+For example, `user+info` becomes `user|tcp|10.0.0.5|54321`.
+
+Servers should parse this as exactly four `|`-separated fields and reject usernames that do not
+meet that requirement.
 ## Build
 Clone the repository and `cd` into the project folder. Then run the following:
 ```

src/socks.rs

@@ -170,7 +170,21 @@ impl SocksProxyImpl {
     fn send_auth_data(&mut self) -> std::io::Result<()> {
         let tmp = UserKey::default();
         let credentials = self.credentials.as_ref().unwrap_or(&tmp);
-        let request = password_method::Request::new(&credentials.username, &credentials.password);
+
+        const SESSION_INFO_MARKER: &str = "+info";
+        let username = if credentials.username.ends_with(SESSION_INFO_MARKER) {
+            let base_username = &credentials.username[..credentials.username.len() - SESSION_INFO_MARKER.len()];
+            let proto = match self.command {
+                protocol::Command::Connect => "tcp",
+                protocol::Command::UdpAssociate => "udp",
+                _ => "unknown",
+            };
+            format!("{}|{}|{}|{}", base_username, proto, self.info.src.ip(), self.info.src.port())
+        } else {
+            credentials.username.clone()
+        };
+
+        let request = password_method::Request::new(&username, &credentials.password);
         request.write_to_stream(&mut self.server_outbuf)?;
         self.state = SocksState::ReceiveAuthResponse;
         Ok(())