Get a list of macOS' in-use network ports.

sysctl_inet_ports_list_copy.swift

import Foundation;

/// Copy the list of in-use network ports — optionally filtering by the ports' state.
/// - Parameters:
///   - buffer: The buffer into which the port list will populate
///   - state: The port state by which to filter.
/// - Returns: Expect `KERN_SUCCESS` if the operation was successful.
@discardableResult
func sysctl_inet_ports_list_copy(_ buffer: UnsafeMutablePointer<[UInt16]>, _ state: Int32? = nil) -> kern_return_t {
    var kern_return: kern_return_t;
    
    // How big does the buffer need to be to acquire the information we're going to get?
    var mgmt_info_size = 0;
    kern_return = sysctlbyname("net.inet.tcp.pcblist", nil, &mgmt_info_size, nil, 0);
    guard kern_return == KERN_SUCCESS else {
        return kern_return;
    }

    // Create and fill that buffer.
    var sysctl_result_buf = [UInt8](repeating: 0, count: mgmt_info_size);
    kern_return = sysctlbyname("net.inet.tcp.pcblist", &sysctl_result_buf, &mgmt_info_size, nil, 0);
    guard kern_return == KERN_SUCCESS else {
        return kern_return;
    }

    // Loop through the structured buffer of PCBs and extract each port — optionally filtering by state.
    sysctl_result_buf.withUnsafeBytes({ ptr in
        var pcbAddr = ptr.baseAddress!;
        var pcbHeader = pcbAddr.bindMemory(to: xinpgen.self, capacity: 1);
        
        while Int(pcbHeader.pointee.xig_len) >= MemoryLayout<xinpgen>.size {
            let tcp_pcb = pcbHeader.withMemoryRebound(to: xtcpcb.self, capacity: 1, {
                $0.pointee
            });
            
            if state == nil || (state != nil && state! == tcp_pcb.xt_tp.t_state) {
                buffer.pointee.append(_OSSwapInt16(tcp_pcb.xt_inp.inp_lport));
            }
            
            pcbAddr += .init(pcbHeader.pointee.xig_len);
            pcbHeader = pcbAddr.bindMemory(to: xinpgen.self, capacity: 1);
        }
    })
    
    return kern_return;
}