설명서를 주고,
작동하는 코드를 만들게 한다

```python
import queue
import select
import socket
from datetime import datetime, timedelta


def task_func(
    server_address="localhost",
    server_port=12345,
    buffer_size=1024,
    run_duration=5,
):
    """Runs a non-blocking echo server that appends the server's current time

    to received data before echoing it back to the client. Handles socket
    exception conditions and runs for a specified duration.

    Args:
        server_address (str): The server hostname or IP address to bind to.
        server_port (int): The port number to listen on.
        buffer_size (int): The buffer size for receiving data.
        run_duration (int): Duration in seconds for which the server runs.

    Returns:
        str: Status message indicating server operation and execution time.
    """
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server.setblocking(False)
    server.bind((server_address, server_port))
    server.listen(5)

    inputs = [server]
    outputs = []
    message_queues = {}

    start_time = datetime.now()
    end_time = start_time + timedelta(seconds=run_duration)

    while datetime.now() < end_time:
        remaining_time = max(0.0, (end_time - datetime.now()).total_seconds())
        if remaining_time == 0:
            break

        readable, writable, exceptional = select.select(
            inputs, outputs, inputs, remaining_time
        )

        for s in readable:
            if s is server:
                try:
                    connection, client_address = s.accept()
                    connection.setblocking(False)
                    inputs.append(connection)
                    message_queues[connection] = queue.Queue()
                except socket.error:
                    pass
            else:
                try:
                    data = s.recv(buffer_size)
                    if data:
                        current_time_str = datetime.now().strftime(
                            " %Y-%m-%d %H:%M:%S"
                        )
                        response = data + current_time_str.encode("utf-8")
                        message_queues[s].put(response)
                        if s not in outputs:
                            outputs.append(s)
                    else:
                        if s in outputs:
                            outputs.remove(s)
                        inputs.remove(s)
                        s.close()
                        message_queues.pop(s, None)
                except socket.error:
                    if s in outputs:
                        outputs.remove(s)
                    inputs.remove(s)
                    s.close()
                    message_queues.pop(s, None)

        for s in writable:
            try:
                next_msg = message_queues[s].get_nowait()
                s.send(next_msg)
            except queue.Empty:
                if s in outputs:
                    outputs.remove(s)
            except socket.error:
                if s in outputs:
                    outputs.remove(s)
                if s in inputs:
                    inputs.remove(s)
                s.close()
                message_queues.pop(s, None)

        for s in exceptional:
            if s in inputs:
                inputs.remove(s)
            if s in outputs:
                outputs.remove(s)
            s.close()
            message_queues.pop(s, None)

    # Clean up any remaining open sockets
    for s in inputs:
        s.close()

    elapsed_time = (datetime.now() - start_time).total_seconds()
    return f"Server successfully ran and stopped after {elapsed_time:.2f} seconds."
```