hick-compio 0.2.0

compio-native async mDNS driver (responder + querier + DNS-SD discovery), thread-per-core.
Documentation 
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//! Emits capability `cfg`s for the receive-side ancillary (cmsg) features
//! hick-compio uses, so the per-function `#[cfg]`s reference ONE central
//! availability matrix instead of hand-maintained `target_os` lists (which
//! repeatedly drifted out of sync with what `libc` actually defines).
//!
//! This matrix is kept identical to `hick-udp/build.rs` on purpose: both crates
//! decode the same cmsg families against the same `libc` constants, so sharing
//! one matrix (down to the emitted cfg names) keeps the two recv paths in step.
//!
//! Supported targets are capped by the `getifs` dependency (linux/android,
//! apple, freebsd/dragonfly, openbsd/netbsd, windows); illumos/solaris/fuchsia
//! and other Unixes are intentionally out of scope and get none of these cfgs.
//!
//! Capability → enabling libc constants (verified against libc 0.2):
//!   * has_ip_pktinfo IP_PKTINFO / IP_RECVPKTINFO (+ in_pktinfo parse)
//!   * has_ipv6_pktinfo IPV6_PKTINFO + IPV6_RECVPKTINFO
//!   * has_recv_hoplimit IP_RECVTTL + IPV6_HOPLIMIT + IPV6_RECVHOPLIMIT (§11)
//!   * has_recv_timestamp SO_TIMESTAMP[NS] + SCM_TIMESTAMP[NS]
//!   * recv_timestamp_ns the timestamp cmsg is nanosecond SO_TIMESTAMPNS
//!     (Linux/Android); otherwise it is microsecond SO_TIMESTAMP.

fn main() {
  println!("cargo:rerun-if-changed=build.rs");

  // Declare every cfg we may emit so the `unexpected_cfgs` lint (the crate
  // builds under `-D warnings`) recognises them whether or not they fire.
  for name in [
    "has_ip_pktinfo",
    "has_ipv6_pktinfo",
    "has_recv_hoplimit",
    "has_recv_timestamp",
    "recv_timestamp_ns",
  ] {
    println!("cargo::rustc-check-cfg=cfg({name})");
  }

  let os = std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
  let vendor = std::env::var("CARGO_CFG_TARGET_VENDOR").unwrap_or_default();

  // Target families (mirrors getifs' own grouping). `target_vendor = "apple"`
  // covers macos/ios/tvos/watchos/visionos uniformly.
  let apple = vendor == "apple";
  let linux_like = os == "linux" || os == "android";
  let freebsdlike = os == "freebsd" || os == "dragonfly";
  let netbsdlike = os == "openbsd" || os == "netbsd";

  // IPv4 PKTINFO: only Linux/Android/Apple, which share the 12-byte in_pktinfo
  // layout (ipi_ifindex / ipi_spec_dst / ipi_addr) that the v4 decoder reads.
  // The BSDs are excluded: FreeBSD/OpenBSD/DragonFly have no IP_PKTINFO at all,
  // and NetBSD's in_pktinfo is a DIFFERENT 8-byte layout (ipi_addr /
  // ipi_ifindex) the shared parser would misread as too-short. All of them
  // degrade to an unspecified local address + interface index 0, exactly as the
  // IPv4 path already does elsewhere.
  if linux_like || apple {
    println!("cargo::rustc-cfg=has_ip_pktinfo");
  }
  // IPv6 PKTINFO: every supported Unix defines both IPV6_PKTINFO and
  // IPV6_RECVPKTINFO.
  if linux_like || apple || freebsdlike || netbsdlike {
    println!("cargo::rustc-cfg=has_ipv6_pktinfo");
  }
  // RFC 6762 §11 TTL/Hop-Limit receive cmsg. Absent on netbsdlike
  // (OpenBSD/NetBSD don't define IP_RECVTTL/IPV6_HOPLIMIT/IPV6_RECVHOPLIMIT).
  if linux_like || apple || freebsdlike {
    println!("cargo::rustc-cfg=has_recv_hoplimit");
  }
  // Kernel receive-timestamp cmsg (all supported Unix).
  if linux_like || apple || freebsdlike || netbsdlike {
    println!("cargo::rustc-cfg=has_recv_timestamp");
  }
  // Linux/Android deliver nanosecond SO_TIMESTAMPNS; the BSDs/Apple deliver
  // microsecond SO_TIMESTAMP.
  if linux_like {
    println!("cargo::rustc-cfg=recv_timestamp_ns");
  }
}