Cómo leer y guardar archivos adjuntos usando node-imap

Ten en cuenta que en las ciencias un error casi siempre tiene diferentes soluciones, no obstante nosotros aquí te mostramos lo más óptimo y mejor.

Solución:

Lo descubrí gracias a la ayuda de @arnt y mscdex. Aquí hay un script completo y en funcionamiento que transmite todos los archivos adjuntos como archivos al disco mientras los decodifica en base64 sobre la marcha. Bastante escalable en términos de uso de memoria.

var inspect = require('util').inspect;
var fs      = require('fs');
var base64  = require('base64-stream');
var Imap    = require('imap');
var imap    = new Imap(
  user: '[email protected]',
  password: 'mygmailpassword',
  host: 'imap.gmail.com',
  port: 993,
  tls: true
  //,debug: function(msg)console.log('imap:', msg);
);

function toUpper(thing)  return thing && thing.toUpperCase ? thing.toUpperCase() : thing;

function findAttachmentParts(struct, attachments)   [];
  for (var i = 0, len = struct.length, r; i < len; ++i) 
    if (Array.isArray(struct[i])) 
      findAttachmentParts(struct[i], attachments);
     else 
      if (struct[i].disposition && ['INLINE', 'ATTACHMENT'].indexOf(toUpper(struct[i].disposition.type)) > -1) 
        attachments.push(struct[i]);
      
    
  
  return attachments;


function buildAttMessageFunction(attachment) 
  var filename = attachment.params.name;
  var encoding = attachment.encoding;

  return function (msg, seqno) 
    var prefix = '(#' + seqno + ') ';
    msg.on('body', function(stream, info) 
      //Create a write stream so that we can stream the attachment to file;
      console.log(prefix + 'Streaming this attachment to file', filename, info);
      var writeStream = fs.createWriteStream(filename);
      writeStream.on('finish', function() 
        console.log(prefix + 'Done writing to file %s', filename);
      );

      //stream.pipe(writeStream); this would write base64 data to the file.
      //so we decode during streaming using 
      if (toUpper(encoding) === 'BASE64') 
        //the stream is base64 encoded, so here the stream is decode on the fly and piped to the write stream (file)
        stream.pipe(base64.decode()).pipe(writeStream);
       else  
        //here we have none or some other decoding streamed directly to the file which renders it useless probably
        stream.pipe(writeStream);
      
    );
    msg.once('end', function() 
      console.log(prefix + 'Finished attachment %s', filename);
    );
  ;


imap.once('ready', function() 
  imap.openBox('INBOX', true, function(err, box) 
    if (err) throw err;
    var f = imap.seq.fetch('1:3', 
      bodies: ['HEADER.FIELDS (FROM TO SUBJECT DATE)'],
      struct: true
    );
    f.on('message', function (msg, seqno) 
      console.log('Message #%d', seqno);
      var prefix = '(#' + seqno + ') ';
      msg.on('body', function(stream, info) 
        var buffer = '';
        stream.on('data', function(chunk) 
          buffer += chunk.toString('utf8');
        );
        stream.once('end', function() 
          console.log(prefix + 'Parsed header: %s', Imap.parseHeader(buffer));
        );
      );
      msg.once('attributes', function(attrs) 
        var attachments = findAttachmentParts(attrs.struct);
        console.log(prefix + 'Has attachments: %d', attachments.length);
        for (var i = 0, len=attachments.length ; i < len; ++i) 
          var attachment = attachments[i];
          /*This is how each attachment looks like 
              partID: '2',
              type: 'application',
              subtype: 'octet-stream',
              params:  name: 'file-name.ext' ,
              id: null,
              description: null,
              encoding: 'BASE64',
              size: 44952,
              md5: null,
              disposition:  type: 'ATTACHMENT', params:  filename: 'file-name.ext'  ,
              language: null
            
          */
          console.log(prefix + 'Fetching attachment %s', attachment.params.name);
          var f = imap.fetch(attrs.uid ,  //do not use imap.seq.fetch here
            bodies: [attachment.partID],
            struct: true
          );
          //build function to process attachment message
          f.on('message', buildAttMessageFunction(attachment));
        
      );
      msg.once('end', function() 
        console.log(prefix + 'Finished email');
      );
    );
    f.once('error', function(err) 
      console.log('Fetch error: ' + err);
    );
    f.once('end', function() 
      console.log('Done fetching all messages!');
      imap.end();
    );
  );
);

imap.once('error', function(err) 
  console.log(err);
);

imap.once('end', function() 
  console.log('Connection ended');
);

imap.connect();

Si te gusta la programación, puedes dejar una sección acerca de qué le añadirías a esta división.

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