How to parse email attachments in node.js using mailparser npm module?

Question

I am using the mailparser npm module, typescript and node 14. I am reading a message and trying to parse the attachment. This email message has one file attachment and that is a csv file, at least to the eye.

So in the code, I have the following:

const MailParser = require('mailparser').MailParser;

where I process the correct email message, I have

const parser = new MailParser();

    parser.on('headers', headers => {
        console.log(headers.get('subject'));
    });

    parser.on('data', data => {
        if (data.type === 'attachment') {
            console.log(data.filename);
            console.log(data.contentType);
            data.content.pipe(process.stdout);
            data.content.on('end', () => data.release());
        }
    });

What I see is the following as the output, I am truncating some of the control characters:

Outlook-dxbeseix.png
image/png
�PNG

IHDR�SLs IDATx�wtW�-z�zo���[��߽?ۀ ��y���4Nc�gl�x<cόA�Ev�1��8�4��d����[�d���������A��~k�%5
....
�)IEND�B`�2020-8-24-20-4-24 (1).csv
application/vnd.ms-excel
IMEI,Result
353071093175234,UNPAID
356759089843552,UNLOCKED
358709098168945,UNLOCKED

So I see a png stream ending with the actual attached file. Can someone explain what is going on here? And how to find the csv file attachment content in this buffer so I can parse it?

Answer 1

When using MailParser class content is not a Buffer but a Stream.

I have added some code comments

parser.on('data', data => {
    if (data.type === 'attachment') {
        // prints the file name of the attachment
        console.log(data.filename);

        // prints the contentType of the attachment
        console.log(data.contentType);

        // Content is a stream which is piped to stdout
        data.content.pipe(process.stdout);

        // call release after attachment processing to continue
        // message processing. Message processing will be paused
        // until release is called
        data.content.on('end', () => data.release());
    }
});

how to find the csv file attachment content

You can use the data.contentType to get the csv attachment stream like the following

// RFC 7111 and MS Excel types
const csvContentTypes = ['text/csv','application/vnd.ms-excel'];

parser.on('data', data => {
    if (data.type === 'attachment') {
        if(csvContentTypes.includes(data.contentType)) {
          // stream to a file, s3 etc

          // call release
          data.content.on('end', () => data.release());
        } else {
          // skip the attachment
          data.release();
        }
    }
});