bring back dlopen

Cargo.toml

@@ -14,6 +14,9 @@ license = "MIT"
 libc = "0.2"
 
 [target.'cfg(target_os = "android")'.dependencies]
+# DL Open
+dlopen = "0.1.8"
+once_cell = "1.17.1"
 # netlink
 netlink-packet-core = "0.5"
 netlink-packet-route = "0.15"

src/interface/android.rs

@@ -1,10 +1,49 @@
-use crate::interface::Interface;
+use once_cell::sync::OnceCell;
 
-pub fn unix_interfaces() -> Vec<Interface> {
+pub fn get_libc_ifaddrs() -> Option<(
-    netlink::unix_interfaces()
+    unsafe extern "C" fn(*mut *mut libc::ifaddrs) -> libc::c_int,
+    unsafe extern "C" fn(*mut libc::ifaddrs),
+)> {
+    match (get_getifaddrs(), get_freeifaddrs()) {
+        (Some(a), Some(b)) => Some((a, b)),
+        _ => None,
+    }
+}
+
+fn load_symbol<T>(sym: &'static str) -> Option<T> {
+    const LIB_NAME: &str = "libc.so";
+
+    println!("loading symbol: {} from {}", sym, LIB_NAME);
+    match dlopen::raw::Library::open(LIB_NAME) {
+        Ok(lib) => match unsafe { lib.symbol::<T>(sym) } {
+            Ok(val) => Some(val),
+            Err(err) => {
+                eprintln!("failed to load symbol {} from {}: {:?}", sym, LIB_NAME, err);
+                None
+            }
+        },
+        Err(err) => {
+            eprintln!("failed to load {}: {:?}", LIB_NAME, err);
+            None
+        }
+    }
+}
+
+fn get_getifaddrs() -> Option<unsafe extern "C" fn(*mut *mut libc::ifaddrs) -> libc::c_int> {
+    static INSTANCE: OnceCell<
+        Option<unsafe extern "C" fn(*mut *mut libc::ifaddrs) -> libc::c_int>,
+    > = OnceCell::new();
+
+    *INSTANCE.get_or_init(|| load_symbol("getifaddrs"))
+}
+
+fn get_freeifaddrs() -> Option<unsafe extern "C" fn(*mut libc::ifaddrs)> {
+    static INSTANCE: OnceCell<Option<unsafe extern "C" fn(*mut libc::ifaddrs)>> = OnceCell::new();
+
+    *INSTANCE.get_or_init(|| load_symbol("freeifaddrs"))
 }
 
-mod netlink {
+pub mod netlink {
     //! Netlink based getifaddrs.
     //!
     //! Based on the logic found in https://git.musl-libc.org/cgit/musl/tree/src/network/getifaddrs.c

src/interface/unix.rs

@@ -198,17 +198,29 @@ fn sockaddr_to_network_addr(sa: *const libc::sockaddr) -> (Option<MacAddr>, Opti
     }
 }
 
-
 #[cfg(target_os = "android")]
 pub fn unix_interfaces() -> Vec<Interface> {
-    super::android::unix_interfaces()
+    use super::android;
+
+    if let Some((getifaddrs, freeifaddrs)) = android::get_libc_ifaddrs() {
+        return unix_interfaces_inner(getifaddrs, freeifaddrs);
+    }
+
+    android::netlink::unix_interfaces()
 }
 
 #[cfg(not(target_os = "android"))]
 pub fn unix_interfaces() -> Vec<Interface> {
+    unix_interfaces_inner(libc::getifaddrs, libc::freeifaddrs)
+}
+
+fn unix_interfaces_inner(
+    getifaddrs: unsafe extern "C" fn(*mut *mut libc::ifaddrs) -> libc::c_int,
+    freeifaddrs: unsafe extern "C" fn(*mut libc::ifaddrs),
+) -> Vec<Interface> {
     let mut ifaces: Vec<Interface> = vec![];
     let mut addrs: MaybeUninit<*mut libc::ifaddrs> = MaybeUninit::uninit();
-    if unsafe { libc::getifaddrs(addrs.as_mut_ptr()) } != 0 {
+    if unsafe { getifaddrs(addrs.as_mut_ptr()) } != 0 {
         return ifaces;
     }
     let addrs = unsafe { addrs.assume_init() };
@@ -304,7 +316,7 @@ pub fn unix_interfaces() -> Vec<Interface> {
         addr = addr_ref.ifa_next;
     }
     unsafe {
-        libc::freeifaddrs(addrs);
+        freeifaddrs(addrs);
     }
     for iface in &mut ifaces {
         let name = CString::new(iface.name.as_bytes()).unwrap();