如何使用Node.js Net发送SMTP邮件(无Nodemailer)

Question

第一：不要告诉我使用nodemailer。我正在努力学习网络编程，并希望用多种语言从头开始。

我正在尝试做一个相当简单的任务：使用TCP套接字发送SMTP电子邮件。我在Python 3.6中有一个工作实现：

from socket import socket, AF_INET, SOCK_STREAM
# Choose a mail server (e.g. Google mail server) and call it mailserver
mailserver = 'gmail-smtp-in.l.google.com'
# Create socket called clientSocket and establish a TCP connection with mailserver
clientSocket = socket(AF_INET, SOCK_STREAM)
def recv():
print(clientSocket.recv(1024).decode())
# Port number may change according to the mail server
clientSocket.connect((mailserver, 25))
recv()
# Send HELO command and print server response.
clientSocket.send('HELO gmail rn'.encode())
recv()
# Send MAIL FROM command and print server response.
clientSocket.send('MAIL FROM: <[e-mail]>rn'.encode())
recv()
# Send RCPT TO command and print server response. 
clientSocket.send('RCPT TO: <[e-mail]>rn'.encode())
recv()
# Send DATA command and print server response. 
clientSocket.send('DATArn'.encode())
recv()
# Send message data. Make sure to include header lines: From, To, Subject
clientSocket.send('FROM: <[e-mail]>rn'.encode())
clientSocket.send('TO: <[e-mail]>rn'.encode())
clientSocket.send('SUBJECT: Testingrn'.encode())
clientSocket.send('This is cool!rn'.encode())
# Message ends with a single period.
clientSocket.send('.rn'.encode())
recv()
# Send QUIT command and get server response
clientSocket.send('QUITrn'.encode())
recv()

它工作并将以下内容输出到我的控制台：

220 mx.google.com ESMTP m30si710943qtg.40 - gsmtp
250 mx.google.com at your service
250 2.1.0 OK m30si710943qtg.40 - gsmtp
250 2.1.5 OK m30si710943qtg.40 - gsmtp
354  Go ahead m30si710943qtg.40 - gsmtp
250 2.0.0 OK 1548694151 m30si710943qtg.40 - gsmtp
221 2.0.0 closing connection m30si710943qtg.40 - gsmtp

我现在尝试使用Node.js 11.7.0和Net模块来实现同样的东西。我的代码：

const net = require('net')
const socket = net.createConnection(25, 'gmail-smtp-in.l.google.com', () => {
console.log('Connected!')
socket.write('HELO gmailrn')
socket.write('MAIL FROM: <[e-mail]>rn')
socket.write('RCPT TO: <[e-mail]>rn')
socket.write('DATArn')
socket.write('FROM: <[e-mail]>rn')
socket.write('TO: <[e-mail]>rn')
socket.write('SUBJECT: Testingrn')
socket.write('This is cool!rn')
socket.write('.rn')
socket.write('QUITrn')
})
socket.on('data', buff => console.log(buff.toString()))

此代码不起作用，并导致以下终端输出：

Connected!
220 mx.google.com ESMTP 88si682318qte.245 - gsmtp
250 mx.google.com at your service
451 4.5.0 SMTP protocol violation, see RFC 2821 88si682318qte.245 - gsmtp

451错误说明不了什么。我认为问题不在于编码，因为Node.js和Python3都默认为UTF-8。

我想我的错误与我如何调用.write有关。就像SMTP服务器在有机会响应前一个命令之前就收到了命令一样。这让我相信，我的Node.js实现中缺少了一些东西，这些东西是Python3版本默认提供的。

任何线索或其他想法都将不胜感激。

我希望我的Node.js实现能像Python3实现一样工作。

Answer 1

socket.write是异步函数。不能只列出socket.write并期望它们按顺序运行。

您必须使用回调并编写类似的内容

socket.write( msg1 , () =>
socket.write( msg2 , () => {
[ .. ]
} );
} );

Answer 2

在nodejs/help中发布了这篇文章并得到了答案(https://github.com/nodejs/help/issues/1741)

归根结底，Python有阻塞套接字。调用recv()方法会阻塞TCP流，直到从服务器返回一些内容为止。Node.js不这样做，它们也无法阻止套接字(按设计)。因此，我需要利用data事件来继续我的套接字通信。