feat: Faster UDP/IO on Apple platforms

WIP

quinn-udp/Cargo.toml

@@ -29,6 +29,9 @@ tracing = { workspace = true, optional = true }
 once_cell = { workspace = true }
 windows-sys = { workspace = true }
 
+[target.'cfg(any(target_os = "macos", target_os = "ios"))'.build-dependencies]
+bindgen = "0.70.1"
+
 [dev-dependencies]
 criterion = "0.5"
 

quinn-udp/build.rs

@@ -0,0 +1,22 @@
+#![cfg(any(target_os = "macos", target_os = "ios"))]
+
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    // Generate the bindings for Apple's private `recvmsg_x` from
+    // https://github.com/apple-oss-distributions/xnu/blob/main/bsd/sys/socket.h.
+    let bindings = bindgen::Builder::default()
+        .clang_arg("-DPRIVATE=1")
+        .allowlist_function("recvmsg_x") // TODO: sendmsg_x
+        .no_copy("iovec") // msghdr_x
+        .header("src/bindings/socket.h")
+        .generate()
+        .expect("Unable to generate bindings");
+
+    // Write the bindings to the $OUT_DIR/bindings.rs file.
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("bindings.rs"))
+        .expect("Couldn't write bindings!");
+}