用python实现ftp服务器

要实现一个 FTP 服务器，可以使用 Python 标准库中的 `ftplib` 和 `socket` 模块。以下是一个简单的实现：

import os
import socket
from ftplib import FTP

HOST = 'localhost'
PORT = 21
FTP_ROOT = '/path/to/ftp/root'

class FTPHandler:
    def __init__(self, conn):
        self.conn = conn
        self.cwd = FTP_ROOT

    def handle(self):
        self.conn.sendall(b'220 Welcome to FTP server\r\n')
        while True:
            data = self.conn.recv(1024)
            if not data:
                break
            cmd = data.strip().decode()
            args = cmd.split(' ')
            func = getattr(self, 'cmd_' + args[0].lower(), None)
            if func:
                try:
                    response = func(*args[1:])
                except Exception as e:
                    response = f'500 Error: {str(e)}\r\n'
            else:
                response = f'502 Command not implemented: {cmd}\r\n'
            self.conn.sendall(response.encode())

    def cmd_user(self, username):
        return '331 OK.\r\n'

    def cmd_pass(self, password):
        return '230 OK.\r\n'

    def cmd_syst(self):
        return '215 UNIX Type: L8\r\n'

    def cmd_pwd(self):
        return f'257 "{self.cwd}" is the current directory.\r\n'

    def cmd_cwd(self, path):
        if not os.path.isabs(path):
            path = os.path.normpath(os.path.join(self.cwd, path))
        if not path.startswith(FTP_ROOT):
            return '550 Permission denied.\r\n'
        if not os.path.exists(path) or not os.path.isdir(path):
            return f'550 Directory not found: {path}\r\n'
        self.cwd = path
        return f'250 OK.\r\n'

    def cmd_list(self, path='.'):
        fullpath = os.path.normpath(os.path.join(self.cwd, path))
        if not fullpath.startswith(FTP_ROOT):
            return '550 Permission denied.\r\n'
        if not os.path.exists(fullpath):
            return f'550 File not found: {path}\r\n'
        if os.path.isfile(fullpath):
            return f'550 Not a directory: {path}\r\n'
        files = os.listdir(fullpath)
        response = '226 Transfer complete.\r\n'
        for filename in files:
            filepath = os.path.join(fullpath, filename)
            filemode = os.stat(filepath).st_mode
            if os.path.isdir(filepath):
                response += f'drwxr-xr-x    2 1000     1000         4096 Nov 11 09:06 {filename}\r\n'
            else:
                response += f'-rw-r--r--    1 1000     1000           18 Nov 11 09:06 {filename}\r\n'
        return response

def main():
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        sock.bind((HOST, PORT))
        sock.listen(1)
        while True:
            conn, addr = sock.accept()
            with conn:
                handler = FTPHandler(conn)
                handler.handle()

if __name__ == '__main__':
    main()

这个 FTP 服务器只支持基本命令。你可以在 `FTPHandler` 类中添加更多命令的实现。在 `cmd_list` 方法中，我们只是简单地模拟了文件列表。在实际的实现中，你需要使用 `os.listdir` 和 `os.stat` 函数来读取目录和文件信息。