UTF8 in attachment filename is not encoded

[tumapav]

Version: 3.1.4

Bug Description

If the attachment file name contains UTF8 characters, the header is not RFC 2047 encoded, which causes email to rely on support of SMTPUTF8 extension, making the email undeliverable to destinations servers that don't support it (gmail supports it, but e.g. email.cz does not).

Steps To Reproduce

$mail = new Nette\Mail\Message;
$mail->setFrom('John <john@example.com>')
        ->addTo('peter@example.com')
        ->setSubject('Kůň v příloze')
        ->setBody("Test")
        ->addAttachment("kůň.txt", "test");

die($mail->generateMessage());

See resulting Content-Disposition header:

Content-Disposition: attachment; filename="kůň.txt"

Expected Behavior

Content-Disposition: attachment; filename="=?UTF-8?B?a8WvxYgudHh0?="

Possible Solution

This worked in the previous version, the bug was introduced with this change https://github.com/nette/mail/commit/6f333738075ba9ee152795dcbbd84569127a3182 which fixed #24, in this change, call to encodeHeader() has been removed. This call should be probably returned, but I'm not sure how exactly in order to not introduce back the issue #24.

I know a workaround is not to use utf8 in attachment file name with e.g. Strings::toAscii($filename), but as long as the encoding works well with other headers like Subject or From, I don't see a reason for this header to be an exception.

[milo]

It is hard to find some RFC for such situation. So, to find some working solution, I use Thunderbird. So I sent attachment named jůůůžě.txt via Thunderbird and GMail SMTP and I got:

Content-Type: text/plain; charset=UTF-8;
 name="=?UTF-8?B?asWvxa/Fr8W+xJsudHh0?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*=UTF-8''%6A%C5%AF%C5%AF%C5%AF%C5%BE%C4%9B%2E%74%78%74

[milo]

And this is via. GMail web interface:

Content-Type: text/plain; charset="UTF-8"; name="=?UTF-8?B?asWvxa/Fr8W+xJsudHh0?="
Content-Disposition: attachment; filename="=?UTF-8?B?asWvxa/Fr8W+xJsudHh0?="
Content-Transfer-Encoding: base64
Content-ID: <f_kfz6pkr50>
X-Attachment-Id: f_kfz6pkr50

[dg]

Milo, can you try to send files named ", \ and x? I am unable do it on Windows (except the third).

[milo]

Third char sould be x? I tried ů"\?x.txt and this is a result of Thunderbird 78.3.1 on Debian 10:

Content-Type: text/plain; charset=UTF-8;
 name="=?UTF-8?B?xa8iXD94LnR4dA==?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*=UTF-8''%C5%AF%22%5C%3F%78%2E%74%78%74

Correctly seen as ů"\?x.txt attachment in Thunderbird on Windows and when trying to save it, Thunderbird replaces name to ů___x.txt.

[milo]

And how encoded by GMail webface:

Content-Type: text/plain; charset="US-ASCII"; name="=?UTF-8?B?xa8iXD94LnR4dA==?="
Content-Disposition: attachment; filename="=?UTF-8?B?xa8iXD94LnR4dA==?="
Content-Transfer-Encoding: base64
X-Attachment-Id: f_kfzgl8310
Content-ID: <f_kfzgl8310>

[milo]

When sending ".txt. Thunderbird

Content-Type: text/plain; charset=UTF-8;
 name="\".txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="\".txt"

GMail

Content-Type: text/plain; charset="US-ASCII"; name="\".txt"
Content-Disposition: attachment; filename="\".txt"
Content-Transfer-Encoding: base64
Content-ID: <f_kfzgqenu0>
X-Attachment-Id: f_kfzgqenu0

[dg]

Thanks!

[dg]

Just to be sure, can you check also \ alone?

[milo]

Thunderbird "

Content-Type: text/plain; charset=UTF-8;
 name="\""
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="\""

\

Content-Type: text/plain; charset=UTF-8;
 name="\\"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="\\"

[milo]

And long ones (160 chars): 1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890 and ž23456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789ž

in Thunderbird:

Content-Type: text/plain; charset=UTF-8;
 name="1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*0="123456789012345678901234567890123456789012345678901234567890";
 filename*1="123456789012345678901234567890123456789012345678901234567890";
 filename*2="1234567890123456789012345678901234567890"

Content-Type: text/plain; charset=UTF-8;
 name="=?UTF-8?Q?=c5=be2345678901234567890123456789012345678901234567890123?=
 =?UTF-8?Q?45678901234567890123456789012345678901234567890123456789012?=
 =?UTF-8?Q?34567890123456789012345678901234567890123456789=c5=be?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*0*=UTF-8''%C5%BE%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*1*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*2*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*3*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*4*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*5*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*6*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*7*=%38%39%30%31%32%33%34%35%36%37%38%39%30%31%32%33%34%35%36%37;
 filename*8*=%38%39%C5%BE

via GMail webface

Content-Type: application/octet-stream; 
    name=1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
Content-Disposition: attachment; 
    filename=1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
Content-Transfer-Encoding: base64
Content-ID: <f_kg0oa0110>
X-Attachment-Id: f_kg0oa0110

Content-Type: application/octet-stream; 
    name="=?UTF-8?Q?=C5=BE23456789012345678901234567890123456789012345678901234567?=
    =?UTF-8?Q?890123456789012345678901234567890123456789012345678901234567?=
    =?UTF-8?Q?890123456789012345678901234567890123456789=C5=BE?="
Content-Disposition: attachment; 
    filename="=?UTF-8?Q?=C5=BE23456789012345678901234567890123456789012345678901234567?=
    =?UTF-8?Q?890123456789012345678901234567890123456789012345678901234567?=
    =?UTF-8?Q?890123456789012345678901234567890123456789=C5=BE?="
Content-Transfer-Encoding: base64
Content-ID: <f_kg0oa04b1>
X-Attachment-Id: f_kg0oa04b1

[dg]

Thanks! Now it should work correctly