From 06ebca013c0ce3eaa7df5cd71d787ad4e96ac2fb Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Fri, 6 Jul 2018 02:57:17 +0200
Subject: [PATCH] Reduce duplication in `encode_into`

---
 src/sys/socket/mod.rs | 124 +++++++++++++++++++-----------------------
 1 file changed, 57 insertions(+), 67 deletions(-)

diff --git a/src/sys/socket/mod.rs b/src/sys/socket/mod.rs
index 741779b15c..7d62fea917 100644
--- a/src/sys/socket/mod.rs
+++ b/src/sys/socket/mod.rs
@@ -523,6 +523,7 @@ pub enum ControlMessage<'a> {
     /// nix::unistd::close(in_socket).unwrap();
     /// ```
     ScmTimestamp(&'a TimeVal),
+    /// Catch-all variant for unimplemented cmsg types.
     #[doc(hidden)]
     Unknown(UnknownCmsg<'a>),
 }
@@ -566,84 +567,73 @@ impl<'a> ControlMessage<'a> {
         }
     }
 
+    /// Returns the value to put into the `cmsg_type` field of the header.
+    fn type_(&self) -> libc::c_int {
+        match *self {
+            ControlMessage::ScmRights(_) => libc::SCM_RIGHTS,
+            ControlMessage::ScmCredentials(_) => libc::SCM_CREDENTIALS,
+            ControlMessage::ScmTimestamp(_) => libc::SCM_TIMESTAMP,
+            ControlMessage::Unknown(ref cmsg) => cmsg.0.cmsg_type,
+        }
+    }
+
     // Unsafe: start and end of buffer must be cmsg_align'd. Updates
     // the provided slice; panics if the buffer is too small.
     unsafe fn encode_into(&self, buf: &mut [u8]) {
-        match *self {
-            ControlMessage::ScmRights(fds) => {
-                let cmsg = cmsghdr {
-                    cmsg_len: self.len() as _,
-                    cmsg_level: libc::SOL_SOCKET,
-                    cmsg_type: libc::SCM_RIGHTS,
-                    ..mem::uninitialized()
-                };
-                let buf = copy_bytes(&cmsg, buf);
-
-                let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
-                    mem::size_of_val(&cmsg);
-                let buf = pad_bytes(padlen, buf);
-
-                let buf = copy_bytes(fds, buf);
-
-                let padlen = self.space() - self.len();
-                pad_bytes(padlen, buf);
-            },
-            ControlMessage::ScmCredentials(creds) => {
-                let cmsg = cmsghdr {
-                    cmsg_len: self.len() as _,
-                    cmsg_level: libc::SOL_SOCKET,
-                    cmsg_type: libc::SCM_CREDENTIALS,
-                    ..mem::uninitialized()
-                };
-                let buf = copy_bytes(&cmsg, buf);
-
-                let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
-                    mem::size_of_val(&cmsg);
-                let buf = pad_bytes(padlen, buf);
-
-                let buf = copy_bytes(creds, buf);
-
-                let padlen = self.space() - self.len();
-                pad_bytes(padlen, buf);
+        let final_buf = if let ControlMessage::Unknown(ref cmsg) = *self {
+            let &UnknownCmsg(orig_cmsg, bytes) = cmsg;
+
+            let buf = copy_bytes(orig_cmsg, buf);
+
+            let padlen = cmsg_align(mem::size_of_val(&orig_cmsg)) -
+                mem::size_of_val(&orig_cmsg);
+            let buf = pad_bytes(padlen, buf);
+
+            copy_bytes(bytes, buf)
+        } else {
+            let cmsg = cmsghdr {
+                cmsg_len: self.len() as _,
+                cmsg_level: libc::SOL_SOCKET,
+                cmsg_type: self.type_(),
+            };
+            let buf = copy_bytes(&cmsg, buf);
+
+            match *self {
+                ControlMessage::ScmRights(fds) => {
+                    let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
+                        mem::size_of_val(&cmsg);
+                    let buf = pad_bytes(padlen, buf);
+
+                    copy_bytes(fds, buf)
+                },
+                ControlMessage::ScmCredentials(creds) => {
+                    let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
+                        mem::size_of_val(&cmsg);
+                    let buf = pad_bytes(padlen, buf);
+
+                    copy_bytes(creds, buf)
+                }
+                ControlMessage::ScmTimestamp(t) => {
+                    let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
+                        mem::size_of_val(&cmsg);
+                    let buf = pad_bytes(padlen, buf);
+
+                    copy_bytes(t, buf)
+                },
+                ControlMessage::Unknown(_) => unreachable!(),
             }
-            ControlMessage::ScmTimestamp(t) => {
-                let cmsg = cmsghdr {
-                    cmsg_len: self.len() as _,
-                    cmsg_level: libc::SOL_SOCKET,
-                    cmsg_type: libc::SCM_TIMESTAMP,
-                    ..mem::uninitialized()
-                };
-                let buf = copy_bytes(&cmsg, buf);
-
-                let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
-                    mem::size_of_val(&cmsg);
-                let buf = pad_bytes(padlen, buf);
-
-                let buf = copy_bytes(t, buf);
-
-                let padlen = self.space() - self.len();
-                pad_bytes(padlen, buf);
-            },
-            ControlMessage::Unknown(UnknownCmsg(orig_cmsg, bytes)) => {
-                let buf = copy_bytes(orig_cmsg, buf);
-
-                let padlen = cmsg_align(mem::size_of_val(&orig_cmsg)) -
-                    mem::size_of_val(&orig_cmsg);
-                let buf = pad_bytes(padlen, buf);
-
-                let buf = copy_bytes(bytes, buf);
+        };
 
-                let padlen = self.space() - self.len();
-                pad_bytes(padlen, buf);
-            }
-        }
+        let padlen = self.space() - self.len();
+        pad_bytes(padlen, final_buf);
     }
 
     /// Decodes a `ControlMessage` from raw bytes.
     ///
     /// This is only safe to call if the data is correct for the message type
     /// specified in the header. Normally, the kernel ensures that this is the
-    /// case.
+    /// case. "Correct" in this case includes correct length, alignment and
+    /// actual content.
     unsafe fn decode_from(header: &'a cmsghdr, data: &'a [u8]) -> ControlMessage<'a> {
         match (header.cmsg_level, header.cmsg_type) {
             (libc::SOL_SOCKET, libc::SCM_RIGHTS) => {