Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/uds_cred.rs

@@ -0,0 +1,26 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+#![cfg(all(unix, not(target_os = "dragonfly")))]
+
+use tokio::net::UnixStream;
+
+use libc::getegid;
+use libc::geteuid;
+
+#[tokio::test]
+#[cfg_attr(
+    target_os = "netbsd",
+    ignore = "NetBSD does not support getpeereid() for sockets created by socketpair()"
+)]
+async fn test_socket_pair() {
+    let (a, b) = UnixStream::pair().unwrap();
+    let cred_a = a.peer_cred().unwrap();
+    let cred_b = b.peer_cred().unwrap();
+    assert_eq!(cred_a, cred_b);
+
+    let uid = unsafe { geteuid() };
+    let gid = unsafe { getegid() };
+
+    assert_eq!(cred_a.uid(), uid);
+    assert_eq!(cred_a.gid(), gid);
+}