I am using the NPM package postal-mime to process inbound emails through cloudflare workers. Similar code to on this guide.

https://docs.emailengine.app/how-to-parse-emails-with-cloudflare-email-workers/

The link states this about attachments.

Attachment support.

PostalMime parses all attachments into Uint8Array objects. If you want to process the contents of an attachment as a regular string (which makes sense for textual attachments but not for binary files like images), you can use the TextDecoder class for it.

const decoder = new TextDecoder('utf-8');
const attachmentText = decoder.decode(email.attachments[0].content);

Everything is working as expected when I send an email with a CSV attachment, I can read the CSV and send the data to my server.

However I now have a 3rd party sending the CSV inside a zip file.

The data that arrives at my server is not a valid zip file, presumably since it has been decoded into a text format rather than kept as binary. The guide specifically states this doesn’t make sense for binary files.

If I send the raw email.attachments[0].content to the server all I get is an empty array.

How can I process this Uint8Array object into a form that will allow me to post to my server, then decode it as a valid binary zip file?

import PostalMime from 'postal-mime';

export default {
  async email(message, env, ctx) {
    const parser = new PostalMime();
    const email = await parser.parse(message.raw);

    console.log('Subject', email.subject);
    console.log('HTML', email.html);
    console.log(message);
    const webhookUrl = 'https://example.com/webhook';
    
    var attach;
    var attach_binary;
    email.attachments.forEach((attachment) => {
      let decoder = new TextDecoder('utf-8');
        console.log('Attachment', attachment.filename, 
        decoder.decode(attachment.content));
        if(attachment.mimeType == 'application/zip'){
            attach_binary =  '';//DO SOMETHING HERE
        }else{
            attach = decoder.decode(attachment.content);
        }
    });
    
    
    const webhookPayload = JSON.stringify({
      subject: email.subject,
      sender: message.from,
      email_html: email.html,
      email_text: email.text,
      email: message.to,
      csv: attach ,
      csv_binary: attach_binary 
    });

    try {
      const response = await fetch(webhookUrl, {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
        },
        body: webhookPayload,
      });

      if (response.ok) {
        console.log('Webhook request successful');
      } else {
        console.error('Webhook request failed:', response.status);
      }
    } catch (error) {
      console.error('Error sending webhook request:', error);
    }
  },
};