fd-listener.deno.ts

const libc = Deno.dlopen(
  "libc.so.6",
  {
    dup2: {
      parameters: ["i32", "i32"],
      result: "i32",
    },
    errno: {
      type: "i32",
    },
  },
);

function findUnixSocketPathInode(path: string) {
  const out = Deno.readTextFileSync("/proc/net/unix");

  const rg = new RegExp("([0-9]+) " + path);

  const match = out.match(rg);
  if (match === null) {
    return null;
  }

  return parseInt(match[1]);
}

function findProcessFileDescriptorByInode(pid: number, inode: number) {
  for (const entry of Deno.readDirSync(`/proc/${pid}/fd`)) {
    const stat = Deno.statSync(`/proc/${pid}/fd/${entry.name}`);
    if (stat.ino === inode) {
      return parseInt(entry.name);
    }
  }
  return null;
}

function hijackFileDescriptorAsUnixSocketListener(
  fd: number,
): Deno.UnixListener {
  const tmpDir = Deno.makeTempDirSync();
  const tmpFile = `${tmpDir}/tmp.sock`;

  try {
    const listener = Deno.listen({
      path: tmpFile,
      transport: "unix",
    });

    const socketInode = findUnixSocketPathInode(tmpFile);
    if (socketInode === null) {
      listener.close();
      throw new Error("could not find socket inode");
    }

    const socketFd = findProcessFileDescriptorByInode(Deno.pid, socketInode);
    if (socketFd === null) {
      listener.close();
      throw new Error("could not find socket file descriptor");
    }

    const ret = libc.symbols.dup2(fd, socketFd);
    if (ret === -1) {
      listener.close();
      throw new Error("dup2() errno: " + libc.symbols.errno);
    }

    if (ret !== socketFd) {
      listener.close();
      throw new Error("unexpected");
    }

    return listener;
  } finally {
    Deno.removeSync(tmpFile);
    Deno.removeSync(tmpDir);
  }
}