fleetd/bridged/src/main/java/dev/ltms/bridged/mcp/LsofPeerPidLookup.java

package dev.ltms.bridged.mcp;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.TimeUnit;

/**
 * {@link PeerPidLookup} via {@code lsof} (present on macOS and Linux). For a loopback TCP source
 * {@code port}, both the client and this daemon appear on that port — so we exclude our own PID
 * and take the other end, which is the calling process.
 */
public final class LsofPeerPidLookup implements PeerPidLookup {

    private static final Logger log = LoggerFactory.getLogger(LsofPeerPidLookup.class);

    private final long selfPid = ProcessHandle.current().pid();

    @Override
    public long pidForLocalPort(int port) {
        try {
            Process p = new ProcessBuilder("lsof", "-nP", "-FpP", "-iTCP:" + port)
                    .redirectErrorStream(true).start();
            long found = -1;
            try (BufferedReader r = new BufferedReader(
                    new InputStreamReader(p.getInputStream(), StandardCharsets.UTF_8))) {
                long current = -1;
                String line;
                // -Fp emits records: a 'p<pid>' line, then the ports/files under that pid.
                while ((line = r.readLine()) != null) {
                    if (line.startsWith("p")) {
                        current = parse(line.substring(1));
                    } else if (current > 0 && current != selfPid) {
                        found = current; // first process on this port that isn't us = the client
                    }
                }
            }
            if (!p.waitFor(2, TimeUnit.SECONDS)) {
                p.destroyForcibly();
            }
            return found;
        } catch (Exception e) {
            log.debug("lsof peer-pid lookup for port {} failed: {}", port, e.getMessage());
            return -1;
        }
    }

    private static long parse(String s) {
        try {
            return Long.parseLong(s.trim());
        } catch (NumberFormatException e) {
            return -1;
        }
    }
}