Python3中telnetlib模块连接网络设备及字节处理详解

telnetlib模块基础与编码问题

Python标准库中内置了telnetlib模块，专门用于实现基于Telnet协议的通信功能。

在Python3环境下使用telnetlib连接网络设备时，开发者常会遭遇字节流与字符串之间的编码不匹配问题。

具体的错误提示信息如下所示：

import telnetlib
Host = "10.10.10.10"
# 连接Telnet服务器
tn = telnetlib.Telnet(Host, port=23, timeout=10)
tn.set_debuglevel(0)

# 输入登录用户名
tn.read_until(b'login: ')
tn.write(b"admin" + b'\n')

# 输入登录密码
tn.read_until(b'Password: ')
tn.write(b"Admin@1234" + b'\n')

tn.read_until(b'#')
tn.write(b"cd /home/sd" + b'\n')

tn.read_until(b'#')
tn.write(b"ls -al" + b'\n')

r = tn.read_until(b'#').decode('ASCII')
r1 = r.split(r"\r\n")
for i in r1:
  print(i)

tn.close()

以下为一个典型的网络设备交互实例。

>>> tn=telnetlib.Telnet("10.10.0.6",timeout=2)
>>> tn.read_until(b'login: ',timeout=2)
b"\r\n******************************************************************
****\r\n* Copyright (c) 2004-2018 New H3C Technologies Co., Ltd. All rig
rved.*\r\n* Without the owner's prior written consent,
    *\r\n* no decompiling or reverse-engineering shall be allowed.
     *\r\n**********************************************************
************\r\n\r\nlogin: "
>>> tn.write(b'admin'+b'\n')
>>> tn.read_until(b'Password: ',timeout=2)
b'jgtl\r\r\nPassword: '
>>> tn.write(b'Admin@123'+b'\n')
>>> tn.read_until(b'>')
b'\r\n<bangong-01>'
>>> tn.write(b'ping 10.10.0.7')
>>> tn.read_until(b'>')

上述过程展示了命令行手动执行的结果。若将其转化为自动化脚本，主要需解决两个核心问题：一是如何对替换变量进行正确的编码与解码处理，二是对设备返回的输出结果进行解码操作。

#-*- coding:utf-8 -*-
import telnetlib
import re
import csv
import sys
import time
from datetime import datetime

host_dict={
  "ip":"10.10.0.6",
  "user":"admin",
  "pwd":"Admin@123"
}

def get_loss(addrlist):
  host=host_dict["ip"]
  user=host_dict["user"]
  pwd=host_dict["pwd"]
  print (host)
  resultlist = []
  #try:
  tn = telnetlib.Telnet(host, timeout=2)
  print ("AA")
  if len(host_dict["pwd"]) and len(host_dict["user"]):
    print ("BB")
    tn.read_until(b"login: ", timeout=3)
    #tn.write(b"admin"+b"\n")
    tn.write(user.encode()+b"\n")
    tn.read_until(b"Password: ", timeout=3)
    #tn.write(b"Admin@123"+b"\n")
    tn.write(pwd.encode()+ b"\n")
    # p_error = re.compile("found at")

  if tn.read_until(b">", timeout=4).find(b">") != -1:
    print("Connect to {host} ...... ".format(host=host))
    tn.write(b"ping 127.0.0.1\n")
    print (tn.read_until(b'01>'))
  else:
    print("%s Wrong username or password!!!" % host)
    return ""
  #tn.read_until(b">")

  if len(addrlist) != 0:
    for i in range(len(addrlist)-1):
      tep = {}
      command = "ping " + addrlist[i]
      print("command:", command)
      tn.write(command.encode() + b"\n")
      result = str(tn.read_until(b"01>"))
      print(result)
      re_loss = re.compile("\d+\.\d+%")
      loss = re_loss.findall(result)
      tep[host] = loss[0]
      resultlist.append(tep)
      #if p_error.search(result.decode()):
      #  print("There is a error in this command: {0}".format(c.decode()))
  tn.close()
  #except Exception as e:
    #if e:
    #  print ("Connect to {host} Failed!!!".format(host=host),e)
    #return ""
  return resultlist

if __name__=="__main__":
  addrlist=['10.10.0.2','10.10.0.5']
  print ("get_loss",get_loss(addrlist))

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