Add MsgHdrMut type

To be used in recvmsg(2) calls.

Author: Thomasdezeeuw

src/lib.rs

@@ -636,3 +636,70 @@ impl<'name, 'bufs, 'control> fmt::Debug for MsgHdr<'name, 'bufs, 'control> {
         "MsgHdr".fmt(fmt)
     }
 }
+
+/// Configuration of a `recvmsg(2)` system call.
+///
+/// This wraps `msghdr` on Unix and `WSAMSG` on Windows. Also see [`MsgHdr`] for
+/// the variant used by `sendmsg(2)`.
+#[cfg(not(target_os = "redox"))]
+pub struct MsgHdrMut<'addr, 'bufs, 'control> {
+    inner: sys::msghdr,
+    #[allow(clippy::type_complexity)]
+    _lifetimes: PhantomData<(
+        &'addr mut SockAddr,
+        &'bufs mut MaybeUninitSlice<'bufs>,
+        &'control mut [u8],
+    )>,
+}
+
+#[cfg(not(target_os = "redox"))]
+impl<'addr, 'bufs, 'control> MsgHdrMut<'addr, 'bufs, 'control> {
+    /// Create a new `MsgHdrMut` with all empty/zero fields.
+    #[allow(clippy::new_without_default)]
+    pub fn new() -> MsgHdrMut<'addr, 'bufs, 'control> {
+        // SAFETY: all zero is valid for `msghdr` and `WSAMSG`.
+        MsgHdrMut {
+            inner: unsafe { mem::zeroed() },
+            _lifetimes: PhantomData,
+        }
+    }
+
+    /// Set the mutable address (name) of the message.
+    ///
+    /// Corresponds to setting `msg_name` and `msg_namelen` on Unix and `name`
+    /// and `namelen` on Windows.
+    pub fn with_addr(mut self, addr: &'addr mut SockAddr) -> Self {
+        sys::set_msghdr_name(&mut self.inner, addr);
+        self
+    }
+
+    /// Set the mutable buffer(s) of the message.
+    ///
+    /// Corresponds to setting `msg_iov` and `msg_iovlen` on Unix and `lpBuffers`
+    /// and `dwBufferCount` on Windows.
+    pub fn with_buffers(mut self, bufs: &'bufs mut [MaybeUninitSlice<'bufs>]) -> Self {
+        sys::set_msghdr_iov(&mut self.inner, bufs.as_mut_ptr().cast(), bufs.len());
+        self
+    }
+
+    /// Set the mutable control buffer of the message.
+    ///
+    /// Corresponds to setting `msg_control` and `msg_controllen` on Unix and
+    /// `Control` on Windows.
+    pub fn with_control(mut self, buf: &'control mut [MaybeUninit<u8>]) -> Self {
+        sys::set_msghdr_control(&mut self.inner, buf.as_mut_ptr().cast(), buf.len());
+        self
+    }
+
+    /// Returns the flags of the message.
+    pub fn flags(&self) -> RecvFlags {
+        sys::msghdr_flags(&self.inner)
+    }
+}
+
+#[cfg(not(target_os = "redox"))]
+impl<'name, 'bufs, 'control> fmt::Debug for MsgHdrMut<'name, 'bufs, 'control> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "MsgHdrMut".fmt(fmt)
+    }
+}

src/sys/unix.rs

@@ -669,6 +669,11 @@ pub(crate) fn set_msghdr_flags(msg: &mut msghdr, flags: libc::c_int) {
     msg.msg_flags = flags;
 }
 
+#[cfg(not(target_os = "redox"))]
+pub(crate) fn msghdr_flags(msg: &msghdr) -> RecvFlags {
+    RecvFlags(msg.msg_flags)
+}
+
 /// Unix only API.
 impl SockAddr {
     /// Constructs a `SockAddr` with the family `AF_VSOCK` and the provided CID/port.

src/sys/windows.rs

@@ -28,7 +28,7 @@ use windows_sys::Win32::Networking::WinSock::{
 };
 use windows_sys::Win32::System::Threading::INFINITE;
 
-use crate::{MsgHdr, RecvFlags, SockAddr, TcpKeepalive, Type};
+use crate::{MsgHdr, MsgHdrMut, RecvFlags, SockAddr, TcpKeepalive, Type};
 
 #[allow(non_camel_case_types)]
 pub(crate) type c_int = std::os::raw::c_int;
@@ -209,6 +209,10 @@ pub(crate) fn set_msghdr_flags(msg: &mut msghdr, flags: c_int) {
     msg.dwFlags = flags as u32;
 }
 
+pub(crate) fn msghdr_flags(msg: &msghdr) -> RecvFlags {
+    RecvFlags(msg.dwFlags as c_int)
+}
+
 fn init() {
     static INIT: Once = Once::new();