[Dovecot] Dovecot failing to parse some UTF-8 encoded attachment filenames, returning empty string instead

[Timo Sirainen]

On 22.9.2011, at 1.59, Andrew Richards wrote:

> I'm seeing a strange problem with some attachment filenames that are
> UTF-8 encoded. The problem seems to be related to spaces and/or
> unusual characters in filenames, like accented characters (or perhaps
> just to filenames if UTF-8 encoded; I've not explored that fully).

The problem is that the client sends it wrong:

> Content-Type: application/octet-stream;
> 	name==?UTF-8?B?dGhpc19mYWlscy50eHQ=?=
> Content-Disposition: attachment;
> 	filename==?UTF-8?B?dGhpc19mYWlscy50eHQ=?=

These are both wrong. First of all they are illegal because they have = and ? characters, from RFC 2045:

>      parameter := attribute "=" value
>      value := token / quoted-string
>      token := 1*<any (US-ASCII) CHAR except SPACE, CTLs,
>                  or tspecials>
>      tspecials :=  "(" / ")" / "<" / ">" / "@" /
>                    "," / ";" / ":" / "\" / <">
>                    "/" / "[" / "]" / "?" / "="
>                    ; Must be in quoted-string,
>                    ; to use within parameter values


Also from RFC 2047 (encoded-word is the =?UTF-8?...?= thing):

>    + An 'encoded-word' MUST NOT be used in parameter of a MIME
>      Content-Type or Content-Disposition field, or in any structured
>      field body except within a 'comment' or 'phrase'.

The proper way to do this would be to use RFC 2184, which looks something like this:

> Content-Disposition: attachment;
>         filename*=iso-8859-1''p%E4%E4

Looks like Apple Mail also sends:

> Content-Type: application/octet-stream;
>         name="=?iso-8859-1?Q?p=E4=E4?="

That is inside a quoted-string, so it's not broken, but clients aren't really supposed to decode that string in there either.

Anyway .. I'll check tomorrow if I can easily add code to workaround your problem. If it's just a minor change I'll do it.