《计算机网络自顶向下》Socket Lab5 ICMPping

秒速五厘米 2022-09-11 00:14 182阅读 0赞

### 文章目录 ###

*   *  相关查阅博客链接
     *  前引
     *  Lab5 ICMPping
     *   *  Lab5 文档查阅
         *  客户端框架代码
         *  ICMP Ping 实现思路
         *   *  处理连接目的IP问题
             *  ICMP 响应报文字节处理问题
         *  ICMP Ping 实现代码
         *  ICMP Ping 测试效果

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## 相关查阅博客链接 ##

--------------------

**下面是我在完成Lab时所查阅的网页链接 基本上很多地方都对我完成Lab都有帮助 贴在下面 方便大家查阅**

**[ICMPping程序 GITHUB][ICMPping_ GITHUB]**  
**[python select模块详解][python select]**  
**[Python select.select 模块通信全过程详解][Python select.select]**  
**[Python中struct.pack()和struct.unpack()用法详细说明][Python_struct.pack_struct.unpack]**  
**[python常见模块命令(os/sys/platform)][python_os_sys_platform]**  
**[利用python发送icmp包详解(ping)][python_icmp_ping]**  
**[如何计算icmp校验和][icmp]**  
**[python struct.calcsize()函数（返回格式字符串fmt描述的结构的字节大小）][python struct.calcsize_fmt]**  
**[icmp回复报文\_ICMP协议详解][icmp_ICMP]**  
**[ICMP协议之ping实现][ICMP_ping]**

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## 前引 ##

--------------------

**各位看官好 今天又来完成这个套接字编程Lab了  
这篇博客主要是要完成 `ICMPping`这个客户程序 但是当我打开框架代码的时候 发现基本上代码全部都快填完了 我们只需要填很小一部分的 本来我还以为跟之前的代码一样都是大功夫 结果现在才发现不是 那今天还是很轻松的哈 哈哈**

**现在这段话是我在完成了Lab后写的 我差不多写了快3个小时 - - 我还以为框架代码基本上直接就可以用了 结果发现很多地方都需要修改 所以基本上代码很多地方我都进行了彻底的修改 其实也不是很简单很简单那种 有些地方没有思路也是借鉴的别人的代码 + 搜寻资料才能弄出来 对于这个Lab 我会很详细的把一些地方的点说一下 说完之后基本上注意到了这些地方的细节 这个Lab顺水推舟就可以做出来了 ^^**

**那话就先说到这里 现在在还没吃饭 待会写了再去吃饭 - -**

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## Lab5 ICMPping ##

--------------------

### Lab5 文档查阅 ###

--------------------

**方便大家下载相关文档 下面是下载链接 中文翻译找到`Python3 socket`即可**  
**[Pearson Computer Networking: a Top-Down Approach, 8th Edition][Pearson Computer Networking_ a Top-Down Approach_ 8th Edition]**

**中文翻译的图大概如下 看看就行了**  
![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16]

--------------------

### 客户端框架代码 ###

--------------------

**下面贴一下原版的代码 `尽管要修改很多 - -`**

from socket import * import os
    import sys 
    import struct 
    import time 
    import select 
    import binascii
    
    ICMP_ECHO_REQUEST = 8
    
    def checksum(string): 
    	csum = 0
    	countTo = (len(string) // 2) * 2 
    	count = 0
    	
    	while count < countTo:
    		thisVal = ord(string[count+1]) * 256 + ord(string[count]) 
    		csum = csum + thisVal
    		csum = csum & 0xffffffff 
    		count = count + 2
    	
    	if countTo < len(string):
    		csum = csum + ord(string[len(string) - 1]) 
    		csum = csum & 0xffffffff
    		
    	csum = (csum >> 16) + (csum & 0xffff)
    	csum = csum + (csum >> 16)
    	answer = ~csum
    	
    	answer = answer & 0xffff
    	answer = answer >> 8 | (answer << 8 & 0xff00) 
    	return answer
    
    
    def receiveOnePing(mySocket, ID, timeout, destAddr): 
    	timeLeft = timeout
    	while 1:
    		startedSelect = time.time()
    
    		whatReady = select.select([mySocket], [], [], timeLeft) 		
    		howLongInSelect = (time.time() - startedSelect)
    		if whatReady[0] == []: # Timeout 
    			return "Request timed out."
    		
    		timeReceived = time.time()
    		recPacket, addr = mySocket.recvfrom(1024)
    		#Fill in start
    		#Fetch the ICMP header from the IP packet
    		#Fill in end
    
    		timeLeft = timeLeft - howLongInSelect 
    		if timeLeft <= 0:
    			return "Request timed out."
    			
    def sendOnePing(mySocket, destAddr, ID):
    	# Header is type (8), code (8), checksum (16), id (16), sequence (16)
    	myChecksum = 0
    	# Make a dummy header with a 0 checksum
    	# struct -- Interpret strings as packed binary data
    	
    	header = struct.pack("bbHHh", ICMP_ECHO_REQUEST, 0, myChecksum, ID, 1) 
    	data = struct.pack("d", time.time())
    	# Calculate the checksum on the data and the dummy header. 
    	myChecksum = checksum(str(header + data))
    
    	# Get the right checksum, and put in the header 
    	if sys.platform == 'darwin':
    	# Convert 16-bit integers from host to network byte order 
    		myChecksum = htons(myChecksum) & 0xffff
    	else:
    		myChecksum = htons(myChecksum)
    	
    	header = struct.pack("bbHHh", ICMP_ECHO_REQUEST, 0, myChecksum, ID, 1) 
    	packet = header + data
    	
    	mySocket.sendto(packet, (destAddr, 1)) 
    	# AF_INET address must be tuple, not str # Both LISTS and TUPLES consist of a number of objects
    	# which can be referenced by their position number within the object.
    	
    def doOnePing(destAddr, timeout): 
    	icmp = getprotobyname("icmp")
    	# SOCK_RAW is a powerful socket type. For more details: http://sock- raw.org/papers/sock_raw
    	mySocket = socket(AF_INET, SOCK_RAW, icmp)
    	myID = os.getpid() & 0xFFFF	# Return the current process i 		
    	sendOnePing(mySocket, destAddr, myID)
    	delay = receiveOnePing(mySocket, myID, timeout, destAddr)
    	mySocket.close() 
    	return delay
    
    def ping(host, timeout=1):
    	
    	# timeout=1 means: If one second goes by without a reply from the server,
    	# the client assumes that either the client's ping or the server's pong is lost 
    	dest = gethostbyname(host)
    	print("Pinging " + dest + " using Python:") print("")
    	# Send ping requests to a server separated by approximately one second 
    	while 1 :
    		delay = doOnePing(dest, timeout) 
    		print(delay)
    		time.sleep(1)# one second 
    		return delay

--------------------

### ICMP Ping 实现思路 ###

--------------------

**其实刚开始我们可以看一下我们的框架代码干了什么**  
**`1、得到目的网址的IP地址`**  
**`2、创建套接字 协议为ICMP 对目的地址发起连接`**  
**`3、sendoneping 主要就是把相关参数设置好 然后向得到的ip发送icmp请求`**  
**`4、recvoneping 套接字得到响应报文 我们要做的就是对于响应报文处理`**

--------------------

#### 处理连接目的IP问题 ####

--------------------

**我们要做的仅是处理响应报文 如果有机智的hxd刚开始想到 我们先试一下连接如何 往我们需要填的地方填入`print(recPacket)` 那就和我想到一块去了 ^^ 我们先试一下 - - 结果发现没有响应报文 无法连接 如下**

![在这里插入图片描述][f8ef65329227461ebf15b3da77e59340.png]

--------------------

**正在热锅上的我 处理不了下面的程序 忽然灵机一动 想到了一个软件 老朋友`wireshark` 不如看一下我们的`wireshark`发生了什么 我们打开捕获 再次重新启动程序 过滤器输入`icmp` 得到如下结果**

![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16 1]

--------------------

**我们根据书上写的 `Type为8` `Code为0` 对的啊 怎么发不出去呢 我们可以仔细看一下 `Wireshark`提示我们发出去的包`checksum incorrect` 怎么会`checksum incorrect`呢 那问题就出现在了这里**

**这里先贴一下关于`icmp协议`的`checksum`怎么用的 再贴一下我们的数据怎么用`pack`包装住的**  
**[利用python发送icmp包详解(ping)][python_icmp_ping]**  
**[Python中struct.pack()和struct.unpack()用法详细说明][Python_struct.pack_struct.unpack]**

**在根据别人的代码和我查询资料得到的 发现需要前面要加`!` 使包装按照大端序 即字节顺序不反过来储存 对于这个大端序 小端序 大家如果没有学习过计算机组成原理的话 大家可以去网上搜一下资料 尽管我计组也没有完全学完 但是在之前自己编写操作系统的时候是用到过的**

**`pack`前面如果没有加`!` 则是小端序发出 加了则是大端序 由于字节编码顺序的问题 就会导致下面的情况 这个也是在我尝试后和别人的编写的程序对比后发现的 我们现在都先改过来 并且把一个`htons`删除了 再把`checksum` `python`程序调试正确 再来看看`wireshark`的包是怎么样的**

--------------------

**这次就正确了 并且还有`reply` 关于这部分就解决了**  
![在这里插入图片描述][0498cede58c54bd1807b27344955ebdf.png]

--------------------

#### ICMP 响应报文字节处理问题 ####

--------------------

**关于这个问题 我先说一下延迟怎么计算 由于我们输出过去的时候 载荷里面的是我们的发出时间 于是延迟在我们之后再接收到包的时候 用此刻的时间减去`ICMP`包里面的数据（也就是和我们发出的数据前8字节一样 以确认相同的ICMP） 也就得到了**

**我们最后得到的数据包是包括了`IP协议报的首部` 则我们根据`wireshark`中详细的每个字节的位置 对应在详细数据中的位置 提取即可**  
**提取方法详细的话 就要看切片语法那些的了 这些我就不详细说了**  
**`TTL`跳步数的话 是在`IP`协议首部的 这个自己提取即可**

**剩下的就是自己发挥了 感觉也没什么好说的了**

--------------------

### ICMP Ping 实现代码 ###

--------------------

from socket import *
    import os
    import sys
    import struct
    import time
    import select
    import binascii
    
    ICMP_ECHO_REQUEST = 8
    def checksum(string):
        csum = 0
        countTo = (len(string) // 2) * 2
        count = 0
        while count < countTo:
            thisVal = string[count + 1] * 256 + string[count]
            csum = csum + thisVal
            csum = csum & 0xffffffff
            count = count + 2
    
        if countTo < len(string):
            csum = csum + string[len(string) - 1]
            csum = csum & 0xffffffff
        csum = (csum >> 16) + (csum & 0xffff)
        csum = csum + (csum >> 16)
        answer = ~csum
        answer = answer & 0xffff
        answer = answer >> 8 | (answer << 8 & 0xff00)
        return answer
    
    
    def receiveOnePing(mySocket, ID, timeout, destAddr):
        timeLeft = timeout
        startedSelect = time.time()
        whatReady = select.select([mySocket], [], [], timeLeft)
        howLongInSelect = (time.time() - startedSelect)
        if whatReady[0] == []:  # Timeout
            print("Request timed out.")
            return None
        timeReceived = time.time()
        recPacket, addr = mySocket.recvfrom(1024)
    
        leftbytes = recPacket[:-8]
        icmpheader = leftbytes[-8:]
        type,code,checksum,id,seq = struct.unpack("!bbHHh",icmpheader)
        if type != 0 or id != ID:
            print("Echo Reply failed")
            return None
        else:
            ipheader = leftbytes[:20]
            icmpdata_bytes = struct.calcsize("d")
            ttl = struct.unpack("!b",ipheader[8:9])[0]
            timeSend = struct.unpack("!d",recPacket[28:])[0]
            delay = timeReceived - timeSend
            return (icmpdata_bytes,delay,ttl)
    
    def sendOnePing(mySocket, destAddr, ID,seq):
        # Header is type (8), code (8), checksum (16), id (16), sequence (16)
        myChecksum = 0
        # Calculate the checksum on the data and the dummy header. myChecksum = checksum(str(header + data))
        # Get the right checksum, and put in the header
        header = struct.pack("!bbHHh", ICMP_ECHO_REQUEST, 0, myChecksum, ID, seq)
        data = struct.pack("!d", time.time())
        myChecksum = checksum(header+data)
        header = struct.pack("!bbHHh", ICMP_ECHO_REQUEST, 0, myChecksum, ID, seq)
        packet = header + data
        mySocket.sendto(packet, (destAddr, 1))  # AF_INET address must be tuple, not str # Both LISTS and TUPLES consist of a number of objects
        # which can be referenced by their position number within the object.
    
    
    def doOnePing(destAddr, timeout,seq):
        icmp = getprotobyname("icmp")
        # SOCK_RAW is a powerful socket type. For more details: http://sock- raw.org/papers/sock_raw
        mySocket = socket(AF_INET, SOCK_RAW, icmp)
        myID = os.getpid() & 0xFFFF  # Return the current process i
        sendOnePing(mySocket, destAddr, myID, seq)
        delay = receiveOnePing(mySocket, myID, timeout, destAddr)
        mySocket.close()
        return delay
    
    
    def ping(host, timeout=1):
        # timeout=1 means: If one second goes by without a reply from the server,
        # the client assumes that either the client's ping or the server's pong is lost
        dest = gethostbyname(host)
        print("\nPinging " + dest + " using Python:")
        print("")
        loss = timeavg = 0;totalsend = 5
        minDelay = 1000
        maxDelay = 0
        # Send ping requests to a server separated by approximately one second
        for i in range(0,totalsend):
            recv = doOnePing(dest, timeout,i)
            if recv == None:
                loss += 1
            else:
                tmptime = int(recv[1]*1000)
                print("From {:} reply: bytes={:} delay={:}ms TTL={:}".format(dest,recv[0],tmptime,recv[2]))
                minDelay = min(tmptime,minDelay);maxDelay = max(tmptime,maxDelay)
                timeavg += tmptime
            time.sleep(1)  # one second
        print("\n{:} Ping Statistic:".format(dest))
        print("\tData Packet: Sended = {:}, Recved = {:}, Loss = {:}({:}% Loss),".format(totalsend,totalsend-loss,loss,(int)(loss/totalsend*100)))
        print("Delay Estimated Time(ms):\n\tShortest = {:}ms, Longest = {:}ms, aver = {:}ms".format(minDelay,maxDelay,timeavg//totalsend))
    
    ping('www.baidu.com')

--------------------

### ICMP Ping 测试效果 ###

--------------------

**下面是测试的`baidu.com` `ping` 格式模仿的是`windows dos` `ping`**  
**都快两点了 还没吃饭 那就先写到这里辣 哈哈哈 各位再见**  
![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16 2]

[ICMPping_ GITHUB]: https://codechina.csdn.net/mirrors/moranzcw/Computer-Networking-A-Top-Down-Approach-NOTES/-/blob/master/SocketProgrammingAssignment/%E4%BD%9C%E4%B8%9A5-ICMPping%E7%A8%8B%E5%BA%8F/%E4%BD%9C%E4%B8%9A5-ICMPping%E7%A8%8B%E5%BA%8F-%E8%A7%A3%E7%AD%94.md
[python select]: https://www.cnblogs.com/huchong/p/8613308.html
[Python select.select]: https://blog.csdn.net/nanhuaibeian/article/details/103082269
[Python_struct.pack_struct.unpack]: https://blog.csdn.net/weiwangchao_/article/details/80395941
[python_os_sys_platform]: https://blog.csdn.net/B_H_L/article/details/17289397
[python_icmp_ping]: https://jianfensec.com/
[icmp]: https://blog.csdn.net/zhj082/article/details/80518322
[python struct.calcsize_fmt]: https://blog.csdn.net/Dontla/article/details/103754612
[icmp_ICMP]: https://blog.csdn.net/weixin_42299244/article/details/112490245
[ICMP_ping]: https://blog.csdn.net/qy532846454/article/details/5429700
[Pearson Computer Networking_ a Top-Down Approach_ 8th Edition]: https://media.pearsoncmg.com/ph/esm/ecs_kurose_compnetwork_8/cw/
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16]: /images/20220829/f86e68ead25a45d7a51d7fcb9553e641.png
[f8ef65329227461ebf15b3da77e59340.png]: /images/20220829/e6f5cae57695406391514f1105f36a85.png
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16 1]: /images/20220829/ab71522760e849328e47f09e41875d9b.png
[0498cede58c54bd1807b27344955ebdf.png]: /images/20220829/8b40998f890e4b09848b6219327d1644.png
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBATG92ZSA2_size_20_color_FFFFFF_t_70_g_se_x_16 2]: /images/20220829/4a769344571e4bf089f0e3638c2a3bc1.png