Add support for the IP_SENDSRCADDR control message

This control message (actually just an alias for IP_RECVDSTADDR) sets
the IPv4 source address when used with sendmsg. It is available on
FreeBSD, NetBSD, OpenBSD, and DragonFlyBSD.

CHANGELOG.md

@@ -38,6 +38,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1772](https://github.com/nix-rust/nix/pull/1772))
 - Added IPV6_ORIGDSTADDR using Ipv6OrigDstAddr in setsockopt and recvmsg.
   (#[1772](https://github.com/nix-rust/nix/pull/1772))
+- Added `IP_SENDSRCADDR` using `Ipv4SendSrcAddr` in `sendmsg`.
+  (#[1776](https://github.com/nix-rust/nix/pull/1776))
 
 ### Changed
 

src/sys/socket/mod.rs

@@ -1117,6 +1117,17 @@ pub enum ControlMessage<'a> {
     #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
     Ipv6PacketInfo(&'a libc::in6_pktinfo),
 
+    /// Configure the IPv4 source address with `IP_SENDSRCADDR`.
+    #[cfg(any(
+        target_os = "netbsd",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "dragonfly",
+    ))]
+    #[cfg(feature = "net")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
+    Ipv4SendSrcAddr(&'a libc::in_addr),
+
     /// SO_RXQ_OVFL indicates that an unsigned 32 bit value
     /// ancilliary msg (cmsg) should be attached to recieved
     /// skbs indicating the number of packets dropped by the
@@ -1226,6 +1237,10 @@ impl<'a> ControlMessage<'a> {
                       target_os = "android", target_os = "ios",))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv6PacketInfo(info) => info as *const _ as *const u8,
+            #[cfg(any(target_os = "netbsd", target_os = "freebsd",
+                      target_os = "openbsd", target_os = "dragonfly"))]
+            #[cfg(feature = "net")]
+            ControlMessage::Ipv4SendSrcAddr(addr) => addr as *const _ as *const u8,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(drop_count) => {
                 drop_count as *const _ as *const u8
@@ -1285,6 +1300,10 @@ impl<'a> ControlMessage<'a> {
               target_os = "android", target_os = "ios",))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv6PacketInfo(info) => mem::size_of_val(info),
+            #[cfg(any(target_os = "netbsd", target_os = "freebsd",
+                      target_os = "openbsd", target_os = "dragonfly"))]
+            #[cfg(feature = "net")]
+            ControlMessage::Ipv4SendSrcAddr(addr) => mem::size_of_val(addr),
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(drop_count) => {
                 mem::size_of_val(drop_count)
@@ -1320,6 +1339,10 @@ impl<'a> ControlMessage<'a> {
               target_os = "android", target_os = "ios",))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv6PacketInfo(_) => libc::IPPROTO_IPV6,
+            #[cfg(any(target_os = "netbsd", target_os = "freebsd",
+                      target_os = "openbsd", target_os = "dragonfly"))]
+            #[cfg(feature = "net")]
+            ControlMessage::Ipv4SendSrcAddr(_) => libc::IPPROTO_IP,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(_) => libc::SOL_SOCKET,
             #[cfg(target_os = "linux")]
@@ -1362,6 +1385,10 @@ impl<'a> ControlMessage<'a> {
                       target_os = "android", target_os = "ios",))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv6PacketInfo(_) => libc::IPV6_PKTINFO,
+            #[cfg(any(target_os = "netbsd", target_os = "freebsd",
+                      target_os = "openbsd", target_os = "dragonfly"))]
+            #[cfg(feature = "net")]
+            ControlMessage::Ipv4SendSrcAddr(_) => libc::IP_SENDSRCADDR,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(_) => {
                 libc::SO_RXQ_OVFL

test/sys/test_socket.rs

@@ -1122,6 +1122,58 @@ pub fn test_sendmsg_ipv6packetinfo() {
     .expect("sendmsg");
 }
 
+// Verify that ControlMessage::Ipv4SendSrcAddr works for sendmsg. This
+// creates a UDP socket bound to all local interfaces (0.0.0.0). It then
+// sends message to itself at 127.0.0.1 while explicitly specifying
+// 127.0.0.1 as the source address through an Ipv4SendSrcAddr
+// (IP_SENDSRCADDR) control message.
+//
+// Note that binding to 0.0.0.0 is *required* on FreeBSD; sendmsg
+// returns EINVAL otherwise. (See FreeBSD's ip(4) man page.)
+#[cfg(any(
+    target_os = "netbsd",
+    target_os = "freebsd",
+    target_os = "openbsd",
+    target_os = "dragonfly",
+))]
+#[test]
+pub fn test_sendmsg_ipv4sendsrcaddr() {
+    use nix::sys::socket::{
+        bind, sendmsg, socket, AddressFamily, ControlMessage, MsgFlags,
+        SockFlag, SockType, SockaddrIn,
+    };
+    use std::io::IoSlice;
+
+    let sock = socket(
+        AddressFamily::Inet,
+        SockType::Datagram,
+        SockFlag::empty(),
+        None,
+    )
+    .expect("socket failed");
+
+    let unspec_sock_addr = SockaddrIn::new(0, 0, 0, 0, 0);
+    bind(sock, &unspec_sock_addr).expect("bind failed");
+    let bound_sock_addr: SockaddrIn = getsockname(sock).unwrap();
+    let localhost_sock_addr: SockaddrIn =
+        SockaddrIn::new(127, 0, 0, 1, bound_sock_addr.port());
+
+    let slice = [1u8, 2, 3, 4, 5, 6, 7, 8];
+    let iov = [IoSlice::new(&slice)];
+    let cmsg = [ControlMessage::Ipv4SendSrcAddr(
+        &localhost_sock_addr.as_ref().sin_addr,
+    )];
+
+    sendmsg(
+        sock,
+        &iov,
+        &cmsg,
+        MsgFlags::empty(),
+        Some(&localhost_sock_addr),
+    )
+    .expect("sendmsg");
+}
+
 /// Tests that passing multiple fds using a single `ControlMessage` works.
 // Disable the test on emulated platforms due to a bug in QEMU versions <
 // 2.12.0.  https://bugs.launchpad.net/qemu/+bug/1701808