feat: enable udpgw via tun2proxy CLI API — no fork needed (#271)

Uses tun2proxy_run_with_cli_args (the C API) via dlsym instead of
modifying the JNI run() signature. The upstream tun2proxy maintainer
recommended this path — the CLI API accepts --udpgw-server natively.

- Cargo.toml: enable udpgw feature, remove [patch.crates-io]
- MhrvVpnService.kt: build CLI args with --udpgw-server in full mode
- Native.kt + android_jni.rs: dlsym wrapper for the C API
- Tun2proxy.kt: reverted to upstream signature

No fork, no patch, no submodule.

Co-authored-by: yyoyoian-pixel <279225925+yyoyoian-pixel@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yyoyoian-pixel

Cargo.lock

@@ -100,12 +100,6 @@ tun2proxy = { version = "0.7", default-features = false, features = ["udpgw"] }
 # Used in mitm tests to sanity-check the cert extensions we emit.
 x509-parser = "0.16"
 
-# Temporary patch: adds udpgw_server parameter to the Android JNI run()
-# function. Upstream PR: https://github.com/tun2proxy/tun2proxy/pull/247
-# Remove this section once tun2proxy >= 0.8 ships with the change.
-[patch.crates-io]
-tun2proxy = { git = "https://github.com/yyoyoian-pixel/tun2proxy", branch = "feat/udpgw-jni-param" }
-
 [profile.release]
 panic = "abort"
 codegen-units = 1

Cargo.toml

@@ -59,7 +59,6 @@ object Tun2proxy {
         tunMtu: Char,
         verbosity: Int,
         dnsStrategy: Int,
-        udpgwServer: String,
     ): Int
 
     /** Signals the running `run()` to shut down. Idempotent. */

android/app/src/main/java/com/github/shadowsocks/bg/Tun2proxy.kt

@@ -259,21 +259,20 @@ class MhrvVpnService : VpnService() {
         //    the sole owner once it's running.
         val detachedFd = parcelFd.detachFd()
         tun2proxyRunning.set(true)
-        // In full mode, enable udpgw so UDP traffic (DNS, QUIC, …) is
-        // forwarded through the tunnel-node's native udpgw handler.
-        // 198.18.0.1:7300 is a magic address the tunnel-node intercepts.
-        val udpgwAddr = if (cfg.mode == Mode.FULL) "198.18.0.1:7300" else ""
+        // Use tun2proxy_run_with_cli_args C API via dlsym — gives full
+        // CLI flexibility including --udpgw-server, no fork needed.
+        val cliArgs = buildString {
+            append("tun2proxy")
+            append(" --proxy socks5://127.0.0.1:$socks5Port")
+            append(" --tun-fd $detachedFd")
+            append(" --dns virtual")
+            append(" --verbosity info")
+            append(" --close-fd-on-drop true")
+            if (cfg.mode == Mode.FULL) append(" --udpgw-server 198.18.0.1:7300")
+        }
         val worker = Thread({
             try {
-                val rc = Tun2proxy.run(
-                    "socks5://127.0.0.1:$socks5Port",
-                    detachedFd,
-                    /* closeFdOnDrop = */ true,
-                    MTU.toChar(),
-                    /* verbosity = info */ 3,
-                    /* dnsStrategy = virtual */ 0,
-                    udpgwAddr,
-                )
+                val rc = Native.runTun2proxy(cliArgs, MTU)
                 Log.i(TAG, "tun2proxy exited rc=$rc")
             } catch (t: Throwable) {
                 Log.e(TAG, "tun2proxy crashed: ${t.message}", t)

android/app/src/main/java/com/therealaleph/mhrv/MhrvVpnService.kt

@@ -95,4 +95,14 @@ object Native {
      * Cheap — just reads atomics. Safe to poll on a second-scale timer.
      */
     external fun statsJson(handle: Long): String
+
+    /**
+     * Start tun2proxy via its CLI args C API (`tun2proxy_run_with_cli_args`).
+     * Resolved at runtime via dlsym from libtun2proxy.so — no fork needed.
+     *
+     * @param cliArgs full CLI string, e.g. "tun2proxy --proxy socks5://... --tun-fd 42 --udpgw-server 198.18.0.1:7300"
+     * @param tunMtu TUN MTU (typically 1500)
+     * @return 0 on normal shutdown, negative on error. BLOCKS.
+     */
+    external fun runTun2proxy(cliArgs: String, tunMtu: Int): Int
 }

android/app/src/main/java/com/therealaleph/mhrv/Native.kt

@@ -482,3 +482,53 @@ pub extern "system" fn Java_com_therealaleph_mhrv_Native_statsJson<'a>(
     }));
     env.new_string(out).map(|s| s.into_raw()).unwrap_or(std::ptr::null_mut())
 }
+
+// ---------------------------------------------------------------------------
+// tun2proxy CLI API wrapper (dlsym — no fork or patch needed)
+// ---------------------------------------------------------------------------
+
+/// `Native.runTun2proxy(cliArgs, tunMtu)` -> int
+///
+/// Calls `tun2proxy_run_with_cli_args` from libtun2proxy.so via dlsym.
+/// This is the C API the tun2proxy maintainer recommends for callers that
+/// need full CLI flexibility (e.g. --udpgw-server). BLOCKS until shutdown.
+#[no_mangle]
+pub extern "system" fn Java_com_therealaleph_mhrv_Native_runTun2proxy<'a>(
+    mut env: JNIEnv<'a>,
+    _class: JClass,
+    cli_args: JString,
+    tun_mtu: jni::sys::jint,
+) -> jni::sys::jint {
+    safe(-1, AssertUnwindSafe(|| {
+        let args_str = jstring_to_string(&mut env, &cli_args);
+        tracing::info!("runTun2proxy: cli={}", args_str);
+
+        unsafe {
+            use std::ffi::{CStr, CString};
+
+            let lib = CString::new("libtun2proxy.so").unwrap();
+            let handle = libc::dlopen(lib.as_ptr(), libc::RTLD_NOW);
+            if handle.is_null() {
+                let err = CStr::from_ptr(libc::dlerror());
+                tracing::error!("dlopen libtun2proxy.so failed: {:?}", err);
+                return -10;
+            }
+
+            let sym = CString::new("tun2proxy_run_with_cli_args").unwrap();
+            let func = libc::dlsym(handle, sym.as_ptr());
+            if func.is_null() {
+                let err = CStr::from_ptr(libc::dlerror());
+                tracing::error!("dlsym tun2proxy_run_with_cli_args: {:?}", err);
+                libc::dlclose(handle);
+                return -11;
+            }
+
+            type RunFn = unsafe extern "C" fn(*const std::ffi::c_char, u16, bool) -> i32;
+            let run: RunFn = std::mem::transmute(func);
+            let c_args = CString::new(args_str).unwrap();
+            let rc = run(c_args.as_ptr(), tun_mtu as u16, false);
+            libc::dlclose(handle);
+            rc
+        }
+    }))
+}