From 21ba6609efe09a7e27d62d2c29ff61bab88b970d Mon Sep 17 00:00:00 2001
From: Toby Lawrence <toby@nuclearfurnace.com>
Date: Mon, 15 Apr 2024 17:39:07 +0000
Subject: [PATCH] Add MsgHdrMut::control_len to get how much of control buffer
 was filled.

---
 src/lib.rs         | 9 +++++++++
 src/sys/unix.rs    | 5 +++++
 src/sys/windows.rs | 4 ++++
 3 files changed, 18 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 4f6bd789..89dce26e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -719,6 +719,15 @@ impl<'addr, 'bufs, 'control> MsgHdrMut<'addr, 'bufs, 'control> {
     pub fn flags(&self) -> RecvFlags {
         sys::msghdr_flags(&self.inner)
     }
+
+    /// Gets the length of the control buffer.
+    ///
+    /// Can be used to determine how much, if any, of the control buffer was filled by `recvmsg`.
+    ///
+    /// Corresponds to `msg_controllen` on Unix and `Control.len` on Windows.
+    pub fn control_len(&self) -> usize {
+        sys::msghdr_control_len(&self.inner)
+    }
 }
 
 #[cfg(not(target_os = "redox"))]
diff --git a/src/sys/unix.rs b/src/sys/unix.rs
index 562cd60f..90d3eb1a 100644
--- a/src/sys/unix.rs
+++ b/src/sys/unix.rs
@@ -738,6 +738,11 @@ pub(crate) fn msghdr_flags(msg: &msghdr) -> RecvFlags {
     RecvFlags(msg.msg_flags)
 }
 
+#[cfg(not(target_os = "redox"))]
+pub(crate) fn msghdr_control_len(msg: &msghdr) -> usize {
+    msg.msg_controllen as _
+}
+
 /// Unix only API.
 impl SockAddr {
     /// Constructs a `SockAddr` with the family `AF_VSOCK` and the provided CID/port.
diff --git a/src/sys/windows.rs b/src/sys/windows.rs
index 4c5d9879..11f2b7b0 100644
--- a/src/sys/windows.rs
+++ b/src/sys/windows.rs
@@ -215,6 +215,10 @@ pub(crate) fn msghdr_flags(msg: &msghdr) -> RecvFlags {
     RecvFlags(msg.dwFlags as c_int)
 }
 
+pub(crate) fn msghdr_control_len(msg: &msghdr) -> usize {
+    msg.Control.len as _
+}
+
 fn init() {
     static INIT: Once = Once::new();