[Feature Request] Avoid fetching attachments if it's already downloaded

[yrccondor]

I'm using this library for a while, and it's really helpful!

I noticed that when I dealing with mails with multiple inline iamges (cid:...), IncommingMail::embedImageAttachments() took a very long time to process (I've set $attachmentsDir to null). I found that for
every call to IncomingMailAttachment::getContents() will eventually call imap_fetchbody in Imap::fetchbody(), which took a long time to fetch.

Since we already have attachment data in DataPartInfo::data, can we just return it in DataPartInfo::fetch() if data is set or add a getter for DataPartInfo::data?

I'm not really familiar with imap, sorry if I'm wrong.

[yrccondor]

I've made a quick fix. This works for me.

DataPartInfo::fetch():

public function fetch(): string
{
    if (0 === $this->part) {
        $this->data = Imap::body($this->mail->getImapStream(), $this->id, $this->options);
    } else {
        if (null !== $this->data) {
            return $this->data;
        }
        $this->data = Imap::fetchbody($this->mail->getImapStream(), $this->id, $this->part, $this->options);
    }

    return $this->decodeAfterFetch();
}

BTW, since only a "Content-ID" is also enough:

php-imap/src/PhpImap/IncomingMail.php

Lines 222 to 226 in e933976

	/**
	* Inline images can contain a "Content-Disposition: inline", but only a "Content-ID" is also enough.
	* See https://github.com/barbushin/php-imap/issues/569
	*/
	if ($attachment->contentId == $cid || 'inline' == \mb_strtolower((string) $attachment->disposition)) {

It's may better to change this line to if ($attachment->contentId == $cid) {, otherwise in some cases we'll get a wrong image.

[Sebbo94BY]

Thank you very much for this code improvement @yrccondor!

I've implemented and tested it.

[Sebbo94BY]

This feature/change has been released in version 4.5.0.