通过完成本实验，您将更加了解SMTP协议。您还将学到使用Python实现标准协议的经验。

您的任务是开发一个简单的邮件客户端，将邮件发送给任意收件人。您的客户端将需要连接到邮件服务器，使用SMTP协议与邮件服务器进行对话，并向邮件服务器发送电子邮件。 Python提供了一个名为smtplib的模块，它内置了使用SMTP协议发送邮件的方法。但是我们不会在本实验中使用此模块，因为它隐藏了SMTP和套接字编程的细节。

为了限制垃圾邮件，一些邮件服务器不接受来源随意的TCP连接。对于下面所述的实验，您可能需要尝试连接到您的大学邮件服务器和流行的Webmail服务器（如AOL邮件服务器）。您也可以尝试从您的家和您的大学校园进行连接。

代码

下面你会找到客户端的代码框架。您将完成代码框架。您需要填写代码的地方标有#Fill in start和#Fill in end。每个地方都可能需要不止一行代码。

附加说明

在某些情况下，接收邮件服务器可能会将您的电子邮件分类为垃圾邮件。当您查找从客户端发送的电子邮件时，请检查垃圾邮件文件夹。

要上交的内容

在您的上交内容中，你需要提供完整的SMTP邮件客户端的代码以及一张能显示您确实收到电子邮件的屏幕截图。

邮件客户端的Python代码框架

from socket import *
msg = "\r\n I love computer networks!"
endmsg = "\r\n.\r\n"
# Choose a mail server (e.g. Google mail server) and call it mailserver 
mailserver = #Fill in start   #Fill in end
# Create socket called clientSocket and establish a TCP connection with mailserver
#Fill in start
#Fill in end
recv = clientSocket.recv(1024)
print recv
if recv[:3] != '220':
    print '220 reply not received from server.'
# Send HELO command and print server response.
heloCommand = 'HELO Alice\r\n'
clientSocket.send(heloCommand)
recv1 = clientSocket.recv(1024)
print recv1
if recv1[:3] != '250':
    print '250 reply not received from server.'
# Send MAIL FROM command and print server response.
# Fill in start
# Fill in end
# Send RCPT TO command and print server response.
# Fill in start
# Fill in end
# Send DATA command and print server response.
# Fill in start
# Fill in end
# Send message data.
# Fill in start
# Fill in end 
# Message ends with a single period.
# Fill in start
# Fill in end
# Send QUIT command and get server response.
# Fill in start
# Fill in end

可选练习

1. 类似Google邮件的服务器（如地址：smtp.gmail.com，端口：587））要求您的客户端在发送MAIL FROM命令之前，需要为了身份验证和安全原因添加传输层安全（TLS）或安全套接字层（SSL）。将TLS / SSL命令添加到现有的命令中，并使用上述地址和端口为Google邮件服务器实现客户端。
2. 您当前的SMTP邮件客户端只能在电子邮件正文中发送文本消息。修改您的客户端，使其可以发送包含文本和图像的电子邮件。

   答案

   作业3答案

   ```python

   改为Python3格式

   from socket import * import base64

   Choose a mail server (e.g. Google mail server) and call it mailserver

   mailserver = “smtp.163.com” mailUser = ‘jz163wy’ mailFromAddress = ‘jz163wy@163.com’ mailPassWord = ‘**‘ mailToAddress = ‘ecnujz@qq.com’

msg = ‘FROM: ‘ + mailFromAddress + ‘\r\n’ msg += ‘TO: ‘ + mailToAddress + ‘\r\n’ msg += ‘Subject: ‘ + ‘test’ + ‘\r\n’ msg += “\r\n I love computer networks!” endmsg = “\r\n.\r\n”

Create socket called clientSocket and establish a TCP connection with mailserver

clientSocket = socket(AF_INET, SOCK_STREAM) clientSocket.connect((mailserver, 25))

recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] != ‘220’: print(‘220 reply not received from server.’)

Send HELO command and print server response.

heloCommand = ‘HELO mailserver\r\n’ while True: clientSocket.send(heloCommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘250’: break

登录过程

loginCommand = ‘auth login\r\n’ while True: clientSocket.send(loginCommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘334’: break

邮箱账户经过base64编码

userCommand = base64.b64encode(mailUser.encode()) + b’\r\n’ while True: clientSocket.send(userCommand) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘334’: break

邮箱密码经过base64编码 这里不展示密码了

passCommand = base64.b64encode(mailPassWord.encode()) + b’\r\n’ while True: clientSocket.send(passCommand) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘235’: break

Send MAIL FROM command and print server response.

MFCommand = ‘MAIL FROM: <’+ mailFromAddress + ‘>\r\n’ while True: clientSocket.send(MFCommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘250’: break

Send RCPT TO command and print server response.

RTCommand = ‘RCPT TO: <’+ mailToAddress + ‘>\r\n’ while True: clientSocket.send(RTCommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘250’: break

Send DATA command and print server response.

DATACommand = ‘DATA\r\n’ while True: clientSocket.send(DATACommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘354’: break

Send message data.

clientSocket.send(msg.encode())

Message ends with a single period.

while True: clientSocket.send(endmsg.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘250’: break

Send QUIT command and get server response.

QUITCommand = ‘QUIT\r\n’ while True: clientSocket.send(QUITCommand.encode()) recv = clientSocket.recv(1024) recv = recv.decode() print(recv) if recv[:3] == ‘221’: break

<a name="PmTCl"></a>
## 可选练习1答案
```python
#改为Python3格式
from socket import *
import sys
import os
if len(sys.argv) <= 1:
    print('Usage : "python ProxyServer.py server_ip"\n[server_ip : It is the IP Address Of Proxy Server')
    sys.exit(2)
# Create a server socket, bind it to a port and start listening
tcpSerSock = socket(AF_INET, SOCK_STREAM)
tcpSerPort = int(sys.argv[1])
tcpSerSock.bind(("", tcpSerPort))
print(tcpSerPort)
tcpSerSock.listen(10)
while 1:
    # Strat receiving data from the client
    print('Ready to serve...')
    tcpCliSock, addr = tcpSerSock.accept()
    print('Received a connection from:', addr)
    message = tcpCliSock.recv(1024)
    message = message.decode()
    print("message:", message)
    if(message == ''):
        continue
    # Extract the filename from the given message
    print("message.split()[1]:", message.split()[1])
    filename = message.split()[1].partition("/")[2]
    print("filename:", filename)
    fileExist = "false"
    filetouse = "/" + filename
    print("filetouse:", filetouse)
    try:
        # Check wether the file exist in the cache
        f = open("WEB/" + filetouse[1:], "rb")
        outputdata = f.read()
        f.close()
        fileExist = "true"
        # ProxyServer finds a cache hit and generates a response message
        tcpCliSock.send("HTTP/1.1 200 OK\r\n".encode())
        tcpCliSock.send("Content-Type:text/html\r\n\r\n".encode())
        tcpCliSock.send(outputdata)
        print('Read from cache')
    # Error handling for file not found in cache
    except IOError:
        if fileExist == "false":
            # Create a socket on the proxyserver
            c = socket(AF_INET, SOCK_STREAM)
            hostn = filename.replace("www.","",1)
            print("hostn:", hostn)
            try:
                # Connect to the socket to port 80
                serverName = hostn.partition("/")[0]
                serverPort = 80
                print((serverName, serverPort))
                c.connect((serverName, serverPort))
                askFile = ''.join(filename.partition('/')[1:])
                print("askFile:", askFile)
                # Create a temporary file on this socket and ask port 80
                # for the file requested by the client
                fileobj = c.makefile('rwb', 0)
                fileobj.write("GET ".encode() + askFile.encode() + " HTTP/1.0\r\nHost: ".encode() + serverName.encode() + "\r\n\r\n".encode())
                # Read the response into buffer
                serverResponse = fileobj.read()
                if serverResponse.split()[0] != b'404':
                    print('404')
                    tcpCliSock.send("HTTP/1.1 404 Not Found\r\n\r\n".encode())
                    tcpCliSock.close()
                    continue
                # Create a new file in the cache for the requested file.
                # Also send the response in the buffer to client socket and the corresponding file in the cache
                filename = "WEB/" + filename
                filesplit = filename.split('/')
                for i in range(0, len(filesplit) - 1):
                    if not os.path.exists("/".join(filesplit[0:i+1])):
                        os.makedirs("/".join(filesplit[0:i+1]))
                tmpFile = open(filename, "wb")
                print(serverResponse)
                serverResponse = serverResponse.split(b'\r\n\r\n')[1]
                print(serverResponse)
                tmpFile.write(serverResponse)
                tmpFile.close()
                tcpCliSock.send("HTTP/1.1 200 OK\r\n".encode())
                tcpCliSock.send("Content-Type:text/html\r\n\r\n".encode())
                tcpCliSock.send(serverResponse)
            except:
                print("Illegal request")
            c.close()
        else:
            # HTTP response message for file not found
            print("NET ERROR")
    # Close the client and the server sockets
    tcpCliSock.close()
tcpSerSock.close()

可选练习2答案

#改为Python3格式
from socket import *
import base64
import ssl
# Choose a mail server (e.g. Google mail server) and call it mailserver
mailserver = "smtp.163.com"
mailUser = 'jz163wy'
mailFromAddress = 'jz163wy@163.com'
mailPassWord = '******'
mailToAddress = 'ecnujz@qq.com'
# transfer image and html
with open("timg.jpg","rb") as f:
    image_data = base64.b64encode(f.read())
with open("hello.html","rb") as f:
    html_data = base64.b64encode(f.read())
# 构造邮件正文
msg = 'FROM: ' + mailFromAddress + '\r\n'
msg += 'TO: ' + mailToAddress +  '\r\n'
msg += 'Subject: ' + 'text and picture' +  '\r\n'
msg += 'Content-Type:multipart/related; boundary="----=_NextPart_000_0012345JZ"\r\n'
msg += 'MIME-Version: 1.0\r\n'
msg += '\r\n'
msg = msg.encode()
msg += '------=_NextPart_000_0012345JZ\r\n'.encode()
msg += 'Content-Type: text/html; charset=UTF-8\r\n'.encode()
msg += 'Content-Transfer-Encoding: base64\r\n'.encode()
msg += '\r\n'.encode()
msg += html_data
msg += '\r\n'.encode()
msg += '\r\n'.encode()
msg += '------=_NextPart_000_0012345JZ\r\n'.encode()
msg += 'Content-Type: image/jpeg; name="timg.jpg"\r\n'.encode()
msg += 'Content-Transfer-Encoding: base64\r\n'.encode()
msg += 'Content-ID: JZJZJZJZJZJZJZJZ'.encode()
msg += '\r\n'.encode()
msg += image_data + "\r\n".encode()
msg += '\r\n'.encode()
msg += '------=_NextPart_000_0012345JZ--\r\n'.encode()
endmsg = "\r\n.\r\n"
# Create socket called clientSocket and establish a TCP connection with mailserver
context = ssl.create_default_context()
clientSocket = socket(AF_INET, SOCK_STREAM)
clientSocket.connect((mailserver, 465))
clientSocketSSL = context.wrap_socket(clientSocket, server_hostname=mailserver)
recv = clientSocketSSL.recv(1024)
recv = recv.decode()
print(recv)
if recv[:3] != '220':
    print('220 reply not received from server.')
# Send HELO command and print server response.
heloCommand = 'HELO mailserver\r\n'
while True:
    clientSocketSSL.send(heloCommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '250':
        break
# 登录过程
loginCommand = 'auth login\r\n'
while True:
    clientSocketSSL.send(loginCommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '334':
        break
# 邮箱账户经过base64编码
userCommand = base64.b64encode(mailUser.encode()) + b'\r\n'
while True:
    clientSocketSSL.send(userCommand)
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '334':
        break
# 邮箱密码经过base64编码 这里不展示密码了
passCommand = base64.b64encode(mailPassWord.encode()) + b'\r\n'
while True:
    clientSocketSSL.send(passCommand)
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '235':
        break
# Send MAIL FROM command and print server response.
MFCommand = 'MAIL FROM: <'+ mailFromAddress + '>\r\n'
while True:
    clientSocketSSL.send(MFCommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '250':
        break
# Send RCPT TO command and print server response.
RTCommand = 'RCPT TO: <'+ mailToAddress + '>\r\n'
while True:
    clientSocketSSL.send(RTCommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '250':
        break
# Send DATA command and print server response.
DATACommand = 'DATA\r\n'
while True:
    clientSocketSSL.send(DATACommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '354':
        break
# Send message data.
clientSocketSSL.send(msg)
# Message ends with a single period.
while True:
    clientSocketSSL.send(endmsg.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '250':
        break
# Send QUIT command and get server response.
QUITCommand = 'QUIT\r\n'
while True:
    clientSocketSSL.send(QUITCommand.encode())
    recv = clientSocketSSL.recv(1024)
    recv = recv.decode()
    print(recv)
    if recv[:3] == '221':
        break
clientSocketSSL.close()