Add Socket::passcred/set_passcred for working with SO_PASSCRED.

Author: tobz

src/socket.rs

@@ -965,6 +965,37 @@ impl Socket {
         }
     }
 
+    /// Get value for the `SO_PASSCRED` option on this socket.
+    ///
+    /// For more information about this option, see [`set_passcred`].
+    ///
+    /// [`set_passcred`]: Socket::set_passcred
+    #[cfg(all(unix, target_os = "linux"))]
+    #[cfg_attr(docsrs, doc(cfg(all(unix, target_os = "linux"))))]
+    pub fn passcred(&self) -> io::Result<bool> {
+        unsafe {
+            getsockopt::<c_int>(self.as_raw(), sys::SOL_SOCKET, sys::SO_PASSCRED)
+                .map(|passcred| passcred != 0)
+        }
+    }
+
+    /// Set value for the `SO_PASSCRED` option on this socket.
+    ///
+    /// If this option is enabled, enables the receiving of the `SCM_CREDENTIALS`
+    /// control messages.
+    #[cfg(all(unix, target_os = "linux"))]
+    #[cfg_attr(docsrs, doc(cfg(all(unix, target_os = "linux"))))]
+    pub fn set_passcred(&self, passcred: bool) -> io::Result<()> {
+        unsafe {
+            setsockopt(
+                self.as_raw(),
+                sys::SOL_SOCKET,
+                sys::SO_PASSCRED,
+                passcred as c_int,
+            )
+        }
+    }
+
     /// Get value for the `SO_RCVBUF` option on this socket.
     ///
     /// For more information about this option, see [`set_recv_buffer_size`].

src/sys/unix.rs

@@ -179,6 +179,8 @@ pub(crate) use libc::{
     SO_BROADCAST, SO_ERROR, SO_KEEPALIVE, SO_RCVBUF, SO_RCVTIMEO, SO_REUSEADDR, SO_SNDBUF,
     SO_SNDTIMEO, SO_TYPE, TCP_NODELAY,
 };
+#[cfg(target_os = "linux")]
+pub(crate) use libc::SO_PASSCRED;
 #[cfg(not(any(
     target_os = "dragonfly",
     target_os = "haiku",