2 files changed, 44 insertions, 0 deletions
diff --git a/talpid-core/src/firewall/windows/mod.rs b/talpid-core/src/firewall/windows/mod.rs
index 01c6dd4c53..64fe32191f 100644
--- a/talpid-core/src/firewall/windows/mod.rs
+++ b/talpid-core/src/firewall/windows/mod.rs
@@ -15,6 +15,7 @@ use self::widestring::WideCString;
 mod ffi;
 mod dns;
 mod system_state;
+mod route;
 
 use self::dns::WinDns;
 
diff --git a/talpid-core/src/firewall/windows/route.rs b/talpid-core/src/firewall/windows/route.rs
new file mode 100644
index 0000000000..c66dfbfabd
--- /dev/null
+++ b/talpid-core/src/firewall/windows/route.rs
@@ -0,0 +1,43 @@
+use super::ffi;
+use super::widestring::WideCString;
+use libc;
+use std::ptr;
+
+error_chain!{
+    errors{
+        /// Failure to set metrics of network interfaces
+        MetricApplication{
+            description("Failed to set the metrics for a network interface")
+        }
+    }
+}
+
+// Returns true if metrics were changed, false otherwise
+pub fn ensure_top_metric_for_interface(interface_alias: &str) -> Result<bool> {
+    let interface_alias_ws =
+        WideCString::new(interface_alias.encode_utf16().collect::<Vec<_>>()).unwrap();
+    match unsafe {
+        WinRoute_EnsureTopMetric(
+            interface_alias_ws.as_wide_c_str().as_ptr(),
+            Some(ffi::error_sink),
+            ptr::null_mut(),
+        )
+    } {
+        0 => Ok(false),
+        1 => Ok(true),
+        -1 => Err(Error::from(ErrorKind::MetricApplication)),
+        _ => {
+            error!("Unexpected return code from WinRoute_EnsureTopMetric");
+            Err(Error::from(ErrorKind::MetricApplication))
+        }
+    }
+}
+
+extern "system" {
+    #[link_name(WinRoute_EnsureTopMetric)]
+    pub fn WinRoute_EnsureTopMetric(
+        tunnel_interface_alias: *const libc::wchar_t,
+        sink: Option<ffi::ErrorSink>,
+        sink_context: *mut libc::c_void,
+    ) -> i32;
+}