Add IP_DONTFRAG and IPV6_DONTFRAG SockOpts

IP_DONTFRAG: iOS, macOS
IPV6_DONTFRAG: android, iOS, linux and macOS

Test: `cargo test --test test dontfrag_opts`

Some CI tests running ENOPROTOOPT are disabled.

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Added `Ipv6DontFrag` for android, iOS, linux and macOS.
+- Added `IpDontFrag` for iOS, macOS.
+  (#[1692](https://github.com/nix-rust/nix/pull/1692))
 - Added fine-grained features flags.  Most Nix functionality can now be
   conditionally enabled.  By default, all features are enabled.
   (#[1611](https://github.com/nix-rust/nix/pull/1611))

src/sys/socket/sockopt.rs

@@ -615,6 +615,19 @@ sockopt_impl!(
 sockopt_impl!(
     /// Set the unicast hop limit for the socket.
     Ipv6Ttl, Both, libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS, libc::c_int);
+#[cfg(any(target_os = "ios", target_os = "macos"))]
+sockopt_impl!(
+    /// Set "don't fragment packet" flag on the IP packet.
+    IpDontFrag, Both, libc::IPPROTO_IP, libc::IP_DONTFRAG, bool);
+#[cfg(any(
+    target_os = "android",
+    target_os = "ios",
+    target_os = "linux",
+    target_os = "macos",
+))]
+sockopt_impl!(
+    /// Set "don't fragment packet" flag on the IPv6 packet.
+    Ipv6DontFrag, Both, libc::IPPROTO_IPV6, libc::IPV6_DONTFRAG, bool);
 
 #[allow(missing_docs)]
 // Not documented by Linux!

test/sys/test_sockopt.rs

@@ -196,3 +196,41 @@ fn test_ttl_opts() {
     setsockopt(fd6, sockopt::Ipv6Ttl, &1)
         .expect("setting ipv6ttl on an inet6 socket should succeed");
 }
+
+#[test]
+#[cfg(any(target_os = "ios", target_os = "macos"))]
+fn test_dontfrag_opts() {
+    let fd4 = socket(AddressFamily::Inet, SockType::Stream, SockFlag::empty(), SockProtocol::Tcp).unwrap();
+    setsockopt(fd4, sockopt::IpDontFrag, &true)
+        .expect("setting IP_DONTFRAG on an inet stream socket should succeed");
+    setsockopt(fd4, sockopt::IpDontFrag, &false)
+        .expect("unsetting IP_DONTFRAG on an inet stream socket should succeed");
+    let fd4d = socket(AddressFamily::Inet, SockType::Datagram, SockFlag::empty(), None).unwrap();
+    setsockopt(fd4d, sockopt::IpDontFrag, &true)
+        .expect("setting IP_DONTFRAG on an inet datagram socket should succeed");
+    setsockopt(fd4d, sockopt::IpDontFrag, &false)
+        .expect("unsetting IP_DONTFRAG on an inet datagram socket should succeed");
+}
+
+#[test]
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    any(
+        target_os = "android",
+        target_os = "ios",
+        target_os = "linux",
+        target_os = "macos",
+    )
+))]
+fn test_v6dontfrag_opts() {
+    let fd6 = socket(AddressFamily::Inet6, SockType::Stream, SockFlag::empty(), SockProtocol::Tcp).unwrap();
+    setsockopt(fd6, sockopt::Ipv6DontFrag, &true)
+        .expect("setting IPV6_DONTFRAG on an inet6 stream socket should succeed");
+    setsockopt(fd6, sockopt::Ipv6DontFrag, &false)
+        .expect("unsetting IPV6_DONTFRAG on an inet6 stream socket should succeed");
+    let fd6d = socket(AddressFamily::Inet6, SockType::Datagram, SockFlag::empty(), None).unwrap();
+    setsockopt(fd6d, sockopt::Ipv6DontFrag, &true)
+        .expect("setting IPV6_DONTFRAG on an inet6 datagram socket should succeed");
+    setsockopt(fd6d, sockopt::Ipv6DontFrag, &false)
+        .expect("unsetting IPV6_DONTFRAG on an inet6 datagram socket should succeed");
+}