Python套接字连接FTP未收到预期数据

Question

我正在使用Python的socket库连接ftp.rediris.es，但在发送数据后没有收到我期待的回复。我用我的代码和回复来更清楚地说明这个问题：

#!/usr/bin/env python

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

print "Socket Created"

port = 21

host = "ftp.rediris.es"

ip = socket.gethostbyname(host)

print ip

print "ip of " +host+ " is " +ip

s.connect ((ip, port))

print "Socket Connected to "+host+" on ip "+ ip

message = "HELP\r\n"

s.sendall(message)

reply = s.recv(65565)

print reply

这是我运行代码时得到的回复：

 python test.py
Socket Created
130.206.1.5
ip of ftp.rediris.es is 130.206.1.5
Socket Connected to ftp.rediris.es on ip 130.206.1.5
220-  Bienvenido al FTP anónimo de RedIRIS.
220-Welcome to the RedIRIS anonymous FTP server.
220 Only anonymous FTP is allowed here

而这是我期待的回复：

telnet
telnet> open ftp.rediris.es 21
Trying 130.206.1.5...
Connected to zeppo.rediris.es.
Escape character is '^]'.
220-  Bienvenido al FTP anónimo de RedIRIS.
220-Welcome to the RedIRIS anonymous FTP server.
220 Only anonymous FTP is allowed here
HELP
214-The following SITE commands are recognized
 ALIAS
 CHMOD
 IDLE
 UTIME

我在端口80上尝试过连接www.google.com，发送了GET / HTTP/1.1\r\n\r\n，并且完美地看到了头信息。 这是怎么回事呢？我是不是没有正确地向服务器发送命令呢？谢谢大家！

Answer 1

你可以在发送 HELP 消息之前，先检查一下最后一行是否收到了 220 Only anonymous FTP is allowed here，这就像在 telnetlib 中使用 read_until 一样。

像这样，我试过是有效的：

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print "Socket Created"
port = 21
host = "ftp.rediris.es"
ip = socket.gethostbyname(host)

print ip
print "ip of " +host+ " is " +ip

s.connect ((ip, port))
print "Socket Connected to "+host+" on ip "+ ip

reply = ''
while True:
    message = "HELP\r\n"
    reply += s.recv(1024)
    if not reply:
        break
    if '220 Only anonymous FTP is allowed here' in reply:
        s.sendall(message)
        break    
reply += s.recv(65535)
print reply

输出结果：

Socket Created
130.206.1.5
ip of ftp.rediris.es is 130.206.1.5
Socket Connected to ftp.rediris.es on ip 130.206.1.5
220-  Bienvenido al FTP anónimo de RedIRIS.
220-Welcome to the RedIRIS anonymous FTP server.
220 Only anonymous FTP is allowed here
214-The following SITE commands are recognized
 ALIAS
 CHMOD
 IDLE
 UTIME
214 Pure-FTPd - http://pureftpd.org/

不过，我有点不明白你为什么一开始没有选择更合适的模块，比如 ftplib 或 telnetlib。