refactor(quinn-udp): extract decode_cmsg helper

quinn-udp/src/unix.rs

@@ -719,17 +719,42 @@ fn decode_recv(
     len: usize,
 ) -> io::Result<RecvMeta> {
     let name = unsafe { name.assume_init() };
-    let mut ecn_bits = 0;
-    let mut dst_ip = None;
-    let mut interface_index = None;
-    #[allow(unused_mut)] // only mutable on Linux
-    let mut stride = len;
+    let mut ctrl = ControlMetadata {
+        ecn_bits: 0,
+        dst_ip: None,
+        interface_index: None,
+        stride: len,
+    };
 
     let cmsg_iter = unsafe { cmsg::Iter::new(hdr) };
     for cmsg in cmsg_iter {
+        ctrl.decode(cmsg);
+    }
+
+    Ok(RecvMeta {
+        len,
+        stride: ctrl.stride,
+        addr: decode_socket_addr(&name)?,
+        ecn: EcnCodepoint::from_bits(ctrl.ecn_bits),
+        dst_ip: ctrl.dst_ip,
+        interface_index: ctrl.interface_index,
+    })
+}
+
+/// Metadata decoded from control messages
+struct ControlMetadata {
+    ecn_bits: u8,
+    dst_ip: Option<IpAddr>,
+    interface_index: Option<u32>,
+    stride: usize,
+}
+
+impl ControlMetadata {
+    /// Decodes a control message and updates the metadata state
+    fn decode(&mut self, cmsg: &libc::cmsghdr) {
         match (cmsg.cmsg_level, cmsg.cmsg_type) {
             (libc::IPPROTO_IP, libc::IP_TOS) => unsafe {
-                ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
+                self.ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
             },
             // FreeBSD uses IP_RECVTOS here, and we can be liberal because cmsgs are opt-in.
             #[cfg(not(any(
@@ -739,7 +764,7 @@ fn decode_recv(
                 solarish
             )))]
             (libc::IPPROTO_IP, libc::IP_RECVTOS) => unsafe {
-                ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
+                self.ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
             },
             (libc::IPPROTO_IPV6, libc::IPV6_TCLASS) => unsafe {
                 // Temporary hack around broken macos ABI. Remove once upstream fixes it.
@@ -748,73 +773,65 @@ fn decode_recv(
                 if cfg!(apple)
                     && cmsg.cmsg_len as usize == libc::CMSG_LEN(mem::size_of::<u8>() as _) as usize
                 {
-                    ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
+                    self.ecn_bits = cmsg::decode::<u8, libc::cmsghdr>(cmsg);
                 } else {
-                    ecn_bits = cmsg::decode::<libc::c_int, libc::cmsghdr>(cmsg) as u8;
+                    self.ecn_bits = cmsg::decode::<libc::c_int, libc::cmsghdr>(cmsg) as u8;
                 }
             },
             #[cfg(any(target_os = "linux", target_os = "android"))]
             (libc::IPPROTO_IP, libc::IP_PKTINFO) => {
                 let pktinfo = unsafe { cmsg::decode::<libc::in_pktinfo, libc::cmsghdr>(cmsg) };
-                dst_ip = Some(IpAddr::V4(Ipv4Addr::from(
+                self.dst_ip = Some(IpAddr::V4(Ipv4Addr::from(
                     pktinfo.ipi_addr.s_addr.to_ne_bytes(),
                 )));
-                interface_index = Some(pktinfo.ipi_ifindex as u32);
+                self.interface_index = Some(pktinfo.ipi_ifindex as u32);
             }
             #[cfg(any(bsd, apple))]
             (libc::IPPROTO_IP, libc::IP_RECVDSTADDR) => {
                 let in_addr = unsafe { cmsg::decode::<libc::in_addr, libc::cmsghdr>(cmsg) };
-                dst_ip = Some(IpAddr::V4(Ipv4Addr::from(in_addr.s_addr.to_ne_bytes())));
+                self.dst_ip = Some(IpAddr::V4(Ipv4Addr::from(in_addr.s_addr.to_ne_bytes())));
             }
             (libc::IPPROTO_IPV6, libc::IPV6_PKTINFO) => {
                 let pktinfo = unsafe { cmsg::decode::<libc::in6_pktinfo, libc::cmsghdr>(cmsg) };
-                dst_ip = Some(IpAddr::V6(Ipv6Addr::from(pktinfo.ipi6_addr.s6_addr)));
-                interface_index = Some(pktinfo.ipi6_ifindex as u32);
+                self.dst_ip = Some(IpAddr::V6(Ipv6Addr::from(pktinfo.ipi6_addr.s6_addr)));
+                self.interface_index = Some(pktinfo.ipi6_ifindex as u32);
             }
             #[cfg(any(target_os = "linux", target_os = "android"))]
             (libc::SOL_UDP, gro::UDP_GRO) => unsafe {
-                stride = cmsg::decode::<libc::c_int, libc::cmsghdr>(cmsg) as usize;
+                self.stride = cmsg::decode::<libc::c_int, libc::cmsghdr>(cmsg) as usize;
             },
             _ => {}
         }
     }
+}
 
-    let addr = match libc::c_int::from(name.ss_family) {
+/// Decodes a `sockaddr_storage` into a `SocketAddr`
+fn decode_socket_addr(name: &libc::sockaddr_storage) -> io::Result<SocketAddr> {
+    match libc::c_int::from(name.ss_family) {
         libc::AF_INET => {
             // Safety: if the ss_family field is AF_INET then storage must be a sockaddr_in.
             let addr: &libc::sockaddr_in =
-                unsafe { &*(&name as *const _ as *const libc::sockaddr_in) };
-            SocketAddr::V4(SocketAddrV4::new(
+                unsafe { &*(name as *const _ as *const libc::sockaddr_in) };
+            Ok(SocketAddr::V4(SocketAddrV4::new(
                 Ipv4Addr::from(addr.sin_addr.s_addr.to_ne_bytes()),
                 u16::from_be(addr.sin_port),
-            ))
+            )))
         }
         libc::AF_INET6 => {
             // Safety: if the ss_family field is AF_INET6 then storage must be a sockaddr_in6.
             let addr: &libc::sockaddr_in6 =
-                unsafe { &*(&name as *const _ as *const libc::sockaddr_in6) };
-            SocketAddr::V6(SocketAddrV6::new(
+                unsafe { &*(name as *const _ as *const libc::sockaddr_in6) };
+            Ok(SocketAddr::V6(SocketAddrV6::new(
                 Ipv6Addr::from(addr.sin6_addr.s6_addr),
                 u16::from_be(addr.sin6_port),
                 addr.sin6_flowinfo,
                 addr.sin6_scope_id,
-            ))
-        }
-        f => {
-            return Err(io::Error::other(format!(
-                "expected AF_INET or AF_INET6, got {f} in decode_recv"
-            )));
+            )))
         }
-    };
-
-    Ok(RecvMeta {
-        len,
-        stride,
-        addr,
-        ecn: EcnCodepoint::from_bits(ecn_bits),
-        dst_ip,
-        interface_index,
-    })
+        f => Err(io::Error::other(format!(
+            "expected AF_INET or AF_INET6, got {f}"
+        ))),
+    }
 }
 
 #[cfg(not(apple_slow))]