[horde] Email attachments with special filenames

[Jens Wahnes]

Jan Schneider wrote:
>
> Zitat von Jens Wahnes <wahnes at uni-koeln.de>:
>
>> Hi,
>>
>> today, I looked into the encoding employed by Horde to properly
>> transmit the file name of attachments sent through Imp. We've had some
>> users complaining about files they sent not being displayed properly
>> at the recipient's side (which uses some non Horde email client).
>> Horde uses RFC 2231 encoding where appropriate, which is good, of
>> course, even though not every other mail client is able to handle RFC
>> 2231 encoded file names properly.
>>
>> However, it seems to me that Horde is generating those RFC 2231
>> headers incorrectly in some cases.  Consider an attachment that has
>> got a file name containing special non-ASCII characters, but the
>> contents of the file are pure ASCII, i.e. "text/plain" as per MIME
>> with no declaration of character set required.  If such a file is
>> attached, the file name is encoded according to RFC 2231 rules, but
>> the charset of the encoded file name (given before the first single
>> quote character in the encoded line) is set to "us-ascii", which is
>> wrong.
>>
>> To make things clearer, here is an example of email headers generated
>> by Horde in the case described before:
>>
>> ---
>>
>> Subject: File with strange filename but pure ASCII content is attached
>> User-Agent: Horde Application Framework 5
>> Content-Type: multipart/mixed; boundary="=_m5H-xgvB12M0GEygFUEQ7FY"
>> MIME-Version: 1.0
>>
>> This message is in MIME format.
>>
>> --=_m5H-xgvB12M0GEygFUEQ7FY
>> Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
>> Content-Disposition: inline
>>
>> This message has got an attachment that contains pure ASCII text, but
>> the file name of the attachment is somewhat eccentric.
>>
>> --=_m5H-xgvB12M0GEygFUEQ7FY
>> Content-Type: text/plain;
>>
>> name*0*=us-ascii''File%20with%20a%20long%20name%20co%F1ta%EFning%20str%E5ng;
>>
>>  name*1*=e%20characters%20but%20pure%20ASCII%20content.txt
>> Content-Disposition: attachment; size=27;
>>
>> filename*0*=us-ascii''File%20with%20a%20long%20name%20co%F1ta%EFning%20str;
>>
>>  filename*1*=%E5nge%20characters%20but%20pure%20ASCII%20content.txt
>>
>> Hello Peter, how are you?
>>
>> --=_m5H-xgvB12M0GEygFUEQ7FY--
>>
>> ---
>>
>> I hope the above information is sent correctly, considering I'm trying
>> to discuss MIME matters in an email using MIME. ;-)
>>
>> The name of the attached file should read "File with a long name
>> coñtaïning strånge characters but pure ASCII content.txt".
>>
>> As you can see, the non-ASCII characters in the file name like "ñ" in
>> the word "coñtaïning" are encoded in the "first" (number 0) "name" and
>> "filename" lines with two hex chars (0xF1), or one byte (octet if you
>> will).  So the actual character set used is ISO-8859-1 or similar, as
>> opposed to the declared charset "us-ascii", which would not even
>> contain the "ñ" character, as there is no character with hex code
>> above 0x7F available in ASCII anyway.
>>
>> It seems that this only happens on attachments that have got pure
>> ASCII content.  When the attached file itself contains e.g. UTF-8
>> characters and the file name contains non-ASCII characters too, the
>> file name is encoded correctly, e.g. an "ñ" in the filename is
>> represented by "%C3%B1" (two bytes in UTF-8) in that case and the
>> charset declared is "utf-8".
>>
>> So, in conclusion, could it be that Horde is using the charset of the
>> attachment's /content/ in the place where it should use the charset of
>> the attachment's /filename/?
>> If so, I'm not sure where a bug report should go.  Is this an issue of
>> Imp?  Or of Horde_Mime?  Or some other package I'm not even aware of?
>>
>> If you need more info to reproduce this, I'll be glad to provide it.
>> The assessments above where made using Imp 6.2.18, Horde 5.2.14, and
>> Horde_Mime 2.10.3.
>>
>> Thanks,
>>
>> Jens
>
> This clearly sounds like a bug, and you should start reporting it to the
> IMP queue. We can always categorize it differently later.

Thanks, I filed a bug report. <https://bugs.horde.org/ticket/14618>


Jens


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