Javascript Node.js Net模块，从回调函数中获取数据

所以我试着自己解决这个问题，用谷歌搜索了很多次，但我没能真正解决这个问题，尽管我认为这应该没那么难。因此，我正在做（或试图做）的是，我建立一个到服务器的简单telnet连接，并模拟SMTP会话的开始，以验证电子邮件是否存在（这是否给了我正确的结果是另一个问题）

我的代码如下所示：

const net = require('net');

async function TCPConnection(smtpServer, emailDomain, senderEmail) {

    const client = new net.Socket();
    client.setEncoding("utf-8");
    let completeData = '';

    client.connect({port: 25, host: smtpServer}, () => {
        console.log("TCP Connection established with the Server.");
    })

    client.write("ehlo " + emailDomain + "\r\n");
    client.write("mail from:<" + senderEmail + ">\r\n");
    client.write("rcpt to:<" + senderEmail + ">\r\n");


    client.on('data', function (data) {
        console.log(data);
    });

    function dataReceived(data){
        completeData += data;
    }

    client.on('end', function () {
        console.log('Requested an end to the TCP connection');
    });
}

TCPConnection('aspmx.l.google.com', 'mailtrap.io', 'new-recipient@mailtrap.io');

TCP Connection established with the Server.
220 mx.google.com ESMTP m17si1129948edf.309 - gsmtp

250-mx.google.com at your service, [217.84.87.66]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8

250 2.1.0 OK m17si1129948edf.309 - gsmtp

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1  https://support.google.com/mail/?p=NoSuchUser m17si1129948edf.309 - gsmtp

client.write("rcpt to:<" + senderEmail + ">\r\n","utf-8",()=>{
            console.log("third command written");
            client.end();
        });

client.on('data', function (data) {
        counterResponses++;
        console.log("Response Nr: " + counterResponses + '\r\n' + data);
        completeData.push(data);

        if (counterResponses === 4){
            console.log("4 responses received end connection");
            client.end();
        }
    });

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready

Response Nr: 2
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

因此，我想要实现的是从回调函数或TCPConnection函数中获取完整的数据（现在记录到控制台）。例如，在TCPConnection函数的末尾使用“return completeData；”

我想这样做的原因是，通过HTTP请求调用此函数（TCPConnection）。我想把结果发送给客户。完整的函数可能是这样的（但显然到目前为止还不起作用）：

我阅读了解决方案，可以在“end”事件发出后对数据执行我想执行的操作。但我的问题是，在我的三个“写命令”之后，服务器不会立即结束连接。如果我写这封信：

client.write("ehlo " + emailDomain + "\r\n");
client.write("mail from:<" + senderEmail + ">\r\n");
client.write("rcpt to:<" + senderEmail + ">\r\n");
client.end();

client.write（“ehlo”+emailDomain+”\r\n”）；
client.write（“邮件发件人：\r\n”）；
client.write（“rcpt to:\r\n”）；
client.end（）；

它在第二个和第三个命令得到响应之前结束连接。我试着用“等待客户。写…”来“等待”回复，但这显然行不通，因为我不知道是什么原因

---

如果你不想随便问的话，我希望你能知道我想做什么的要点。谢谢大家!

所以我认为我自己已经做到了，或者至少得到了一个在大多数情况下都能正常工作的解决方案。我所做的是在第三个write命令的回调中结束套接字，如下所示：

const net = require('net');

async function TCPConnection(smtpServer, emailDomain, senderEmail) {

    const client = new net.Socket();
    client.setEncoding("utf-8");
    let completeData = '';

    client.connect({port: 25, host: smtpServer}, () => {
        console.log("TCP Connection established with the Server.");
    })

    client.write("ehlo " + emailDomain + "\r\n");
    client.write("mail from:<" + senderEmail + ">\r\n");
    client.write("rcpt to:<" + senderEmail + ">\r\n");


    client.on('data', function (data) {
        console.log(data);
    });

    function dataReceived(data){
        completeData += data;
    }

    client.on('end', function () {
        console.log('Requested an end to the TCP connection');
    });
}

TCPConnection('aspmx.l.google.com', 'mailtrap.io', 'new-recipient@mailtrap.io');

TCP Connection established with the Server.
220 mx.google.com ESMTP m17si1129948edf.309 - gsmtp

250-mx.google.com at your service, [217.84.87.66]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8

250 2.1.0 OK m17si1129948edf.309 - gsmtp

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1  https://support.google.com/mail/?p=NoSuchUser m17si1129948edf.309 - gsmtp

client.write("rcpt to:<" + senderEmail + ">\r\n","utf-8",()=>{
            console.log("third command written");
            client.end();
        });

client.on('data', function (data) {
        counterResponses++;
        console.log("Response Nr: " + counterResponses + '\r\n' + data);
        completeData.push(data);

        if (counterResponses === 4){
            console.log("4 responses received end connection");
            client.end();
        }
    });

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready

Response Nr: 2
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

因为我想在收到4个命令响应后结束套接字，所以我使用if语句来检查响应的数量。但问题是，有时多个响应可以作为一个响应发送。例如，响应可能如下所示：

const net = require('net');

async function TCPConnection(smtpServer, emailDomain, senderEmail) {

    const client = new net.Socket();
    client.setEncoding("utf-8");
    let completeData = '';

    client.connect({port: 25, host: smtpServer}, () => {
        console.log("TCP Connection established with the Server.");
    })

    client.write("ehlo " + emailDomain + "\r\n");
    client.write("mail from:<" + senderEmail + ">\r\n");
    client.write("rcpt to:<" + senderEmail + ">\r\n");


    client.on('data', function (data) {
        console.log(data);
    });

    function dataReceived(data){
        completeData += data;
    }

    client.on('end', function () {
        console.log('Requested an end to the TCP connection');
    });
}

TCPConnection('aspmx.l.google.com', 'mailtrap.io', 'new-recipient@mailtrap.io');

TCP Connection established with the Server.
220 mx.google.com ESMTP m17si1129948edf.309 - gsmtp

250-mx.google.com at your service, [217.84.87.66]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8

250 2.1.0 OK m17si1129948edf.309 - gsmtp

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1  https://support.google.com/mail/?p=NoSuchUser m17si1129948edf.309 - gsmtp

client.write("rcpt to:<" + senderEmail + ">\r\n","utf-8",()=>{
            console.log("third command written");
            client.end();
        });

client.on('data', function (data) {
        counterResponses++;
        console.log("Response Nr: " + counterResponses + '\r\n' + data);
        completeData.push(data);

        if (counterResponses === 4){
            console.log("4 responses received end connection");
            client.end();
        }
    });

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready

Response Nr: 2
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

但也像这样：

const net = require('net');

async function TCPConnection(smtpServer, emailDomain, senderEmail) {

    const client = new net.Socket();
    client.setEncoding("utf-8");
    let completeData = '';

    client.connect({port: 25, host: smtpServer}, () => {
        console.log("TCP Connection established with the Server.");
    })

    client.write("ehlo " + emailDomain + "\r\n");
    client.write("mail from:<" + senderEmail + ">\r\n");
    client.write("rcpt to:<" + senderEmail + ">\r\n");


    client.on('data', function (data) {
        console.log(data);
    });

    function dataReceived(data){
        completeData += data;
    }

    client.on('end', function () {
        console.log('Requested an end to the TCP connection');
    });
}

TCPConnection('aspmx.l.google.com', 'mailtrap.io', 'new-recipient@mailtrap.io');

TCP Connection established with the Server.
220 mx.google.com ESMTP m17si1129948edf.309 - gsmtp

250-mx.google.com at your service, [217.84.87.66]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8

250 2.1.0 OK m17si1129948edf.309 - gsmtp

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1  https://support.google.com/mail/?p=NoSuchUser m17si1129948edf.309 - gsmtp

client.write("rcpt to:<" + senderEmail + ">\r\n","utf-8",()=>{
            console.log("third command written");
            client.end();
        });

client.on('data', function (data) {
        counterResponses++;
        console.log("Response Nr: " + counterResponses + '\r\n' + data);
        completeData.push(data);

        if (counterResponses === 4){
            console.log("4 responses received end connection");
            client.end();
        }
    });

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready

Response Nr: 2
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

Response Nr: 1
220 mtaproxy104.free.mail.ir2.yahoo.com ESMTP ready
250-mtaproxy104.free.mail.ir2.yahoo.com
250-PIPELINING
250-SIZE 41943040
250-8BITMIME
250 STARTTLS

因此，2个响应作为一个响应发送。这使得我很难评估自己是否得到了所有需要得到的回答。这就是为什么我在最后一个写命令之后才结束套接字

在client.on（'end'）函数中，我将完成的数据发送回客户端

client.on('end', function () {
        console.log('Requested an end to the TCP connection');
        console.log(completeData);

        res.status(200).json(completeData);
    });

唯一仍然困扰我的是我的数组（我用每个发出的“数据”事件推送数据）的长度是可变的。这会让确认电子邮件是否被找到变得有点困难。但是，由于这应该始终是最后一个响应，因此如果我只测试数组的最后一个条目中是否包含状态代码“250”或“550”，那么在大多数情况下，它都会起作用

我希望这至少对某些人有所帮助。让我知道它是否对你有帮助，或者如果你对此有任何疑问。同时，由于我确信有更好的方法可以做到这一点，所以仍然可以寻求更好的解决方案