List open file descriptors for a process using LibProc's `proc_pidinfo` and `PROC_PIDLISTFDS`.

proc_pidlistfds.swift

import Darwin

struct ProcFileDescriptorInfo {
    let fd: Int32
    let path: String
}

func getFileDescriptors(pid: pid_t) -> [ProcFileDescriptorInfo] {
    let bufferSize = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, nil, 0)
    
    if bufferSize < 0 {
        print("Error: Failed to get file descriptors")
        return []
    }
    
    let stride = MemoryLayout<proc_fdinfo>.stride

    let allFDs = Array<proc_fdinfo>(
        unsafeUninitializedCapacity: Int(bufferSize) / stride
    ) { buffer, initializedCount in
        let initialzedByteCount = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, buffer.baseAddress!, bufferSize)
        assert(Int(initialzedByteCount).isMultiple(of: stride))
        initializedCount = Int(initialzedByteCount) / stride
        print("count: \(initializedCount) / \(Int(bufferSize) / stride) entries")
        print("size: \(initialzedByteCount) / \(bufferSize) bytes")
    }
    
    return allFDs.compactMap { fdinfo -> ProcFileDescriptorInfo? in
        let fd = fdinfo.proc_fd
        let type = fdinfo.proc_fdtype
        
        switch Int32(type) {
        case PROX_FDTYPE_VNODE:
            var vnodeInfo = vnode_fdinfowithpath()
            let vnodeInfoSize = UInt32(MemoryLayout<vnode_fdinfowithpath>.size)
            let ret = proc_pidfdinfo(pid, fd, PROC_PIDFDVNODEPATHINFO, &vnodeInfo, Int32(vnodeInfoSize))
            
            if ret <= 0 {
                print("Error: Failed to retrieve vnode info for file descriptor \(fd) of PID \(pid)")
                return nil
            }
            
            let path = withUnsafeBytes(of: &vnodeInfo.pvip.vip_path) { rawPtr in
                let ptr = rawPtr.baseAddress!.assumingMemoryBound(to: CChar.self)
                return String(cString: ptr)
            }
            
            return ProcFileDescriptorInfo(fd: fd, path: path)
            
        case PROX_FDTYPE_ATALK:
            print("apple talk"); return nil
        case PROX_FDTYPE_SOCKET:
            print("socket"); return nil
        case PROX_FDTYPE_PSHM:
            print("pshm"); return nil
        case PROX_FDTYPE_PSEM:
            print("psem"); return nil
        case PROX_FDTYPE_KQUEUE:
            print("kqueue"); return nil
        case PROX_FDTYPE_PIPE:
            print("pipe"); return nil
        case PROX_FDTYPE_FSEVENTS:
            print("fsevents"); return nil
        case PROX_FDTYPE_NETPOLICY:
            print("netpolicy"); return nil
        case PROX_FDTYPE_CHANNEL:
            print("channel"); return nil
        case PROX_FDTYPE_NEXUS:
            print("nexus"); return nil
        default:
            print("unkonwn \(type)"); return nil
        }
    }
}

for info in getFileDescriptors(pid: 1597) {
    print(info.fd, info.path)
}