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ifbridge

ifbridge is a macOS-only Rust crate for reading bridge member and forwarding database state via private bridge ioctls used by Apple's ifconfig.

Why

The standard way to inspect bridge state on macOS is to parse ifconfig text output. This is fragile, locale-dependent, and unnecessarily slow.

Under the hood, ifconfig itself talks to the kernel through SIOCGDRVSPEC / SIOCSDRVSPEC ioctls defined in xnu's bsd/net/if_bridgevar.h. This crate calls those ioctls directly and returns typed Rust structs.

API

// Enumerate all bridgeN interfaces on the system.
pub fn list_bridges() -> io::Result<Vec<String>>;

// List member interfaces of a bridge.
pub fn list_members(bridge: &str) -> io::Result<Vec<BridgeMember>>;

// List forwarding database (FDB) entries of a bridge.
pub fn list_fdb(bridge: &str) -> io::Result<Vec<BridgeEntry>>;

// Find which bridge has learned a given MAC address.
pub fn find_bridge_by_mac(target: MacAddr) -> io::Result<Option<String>>;

Example

fn main() -> std::io::Result<()> {
    for bridge in ifbridge::list_bridges()? {
        println!("{bridge}:");
        for m in ifbridge::list_members(&bridge)? {
            println!("  member {} flags={:?}", m.name, m.flags);
        }
        for e in ifbridge::list_fdb(&bridge)? {
            println!("  fdb {} on {} vlan={}", e.mac, e.member, e.vlan);
        }
    }
    Ok(())
}

Platform

macOS only (Apple Silicon and Intel). Attempting to compile on other platforms will produce a compile_error!.

Risk

This crate depends on xnu bridge private SPI (bsd/net/if_bridgevar.h). Apple does not guarantee ABI or API stability for these interfaces. A future macOS release may change struct layouts, ioctl semantics, or remove these interfaces entirely. Pin your macOS deployment target and test on each OS update.

License

MIT OR Apache-2.0