Android system tun

mobile/Cargo.toml

@@ -19,6 +19,9 @@ once_cell = "1.21.1"
 serde_json = "1.0"
 
 [target.'cfg(target_os = "android")'.dependencies]
+# Android consumers (VpnService.Builder hands in a pre-configured fd) use the
+# fd-handoff TUN path. This feature enables that path in mycelium.
+mycelium = { path = "../mycelium", features = ["vendored-openssl", "androidtunfd"] }
 tracing-android = "0.2.0"
 
 [target.'cfg(target_os = "ios")'.dependencies]

mycelium-tun/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 edition = "2024"
 license-file = "../LICENSE"
 
-[target.'cfg(target_os = "linux")'.dependencies]
+[target.'cfg(any(target_os = "linux", target_os = "android"))'.dependencies]
 tokio = { version = "1.52.3", default-features = false, features = ["net"] }
 nix = { version = "0.31.3", features = ["ioctl", "net"] }
 libc = "0.2"

mycelium-tun/src/lib.rs

@@ -1,13 +1,15 @@
 //! Platform-specific TUN device implementations.
 //!
-//! Currently only Linux is supported. On other platforms this crate is empty.
+//! Linux and Android share the same implementation (Android is Linux + bionic
+//! and exposes the same `/dev/net/tun` uAPI). On other platforms this crate
+//! is empty.
 
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 mod checksum;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 mod linux;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 mod offload;
 
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 pub use linux::{ReadHalf, Tun, WriteHalf};

mycelium/Cargo.toml

@@ -12,6 +12,11 @@ vendored-openssl = ["openssl/vendored"]
 mactunfd = [
   "tun/appstore",
 ] #mactunfd is a flag to specify that macos should provide tun FD instead of tun name
+# androidtunfd is the Android equivalent of mactunfd: when enabled the caller
+# (typically an app using Android's VpnService) provides a pre-configured TUN
+# file descriptor. Default Android builds (e.g. a `cargo ndk` system-service
+# build) open and manage the TUN device themselves via the shared Linux path.
+androidtunfd = []
 # Build a C ABI surface (cdylib + staticlib + generated header) on top of the
 # core node. Used by external daemons that wrap libmycelium without depending
 # on Rust as a build dependency.
@@ -97,6 +102,8 @@ wintun = "0.5.1"
 [target.'cfg(target_os = "android")'.dependencies]
 tun = { git = "https://github.com/LeeSmet/rust-tun", features = ["async"] }
 libc = "0.2.186"
+nix = { version = "0.31.3", features = ["socket"] }
+mycelium-tun = { path = "../mycelium-tun" }
 
 [target.'cfg(target_os = "ios")'.dependencies]
 tun = { git = "https://github.com/LeeSmet/rust-tun", features = ["async"] }