Re: [Evolution] Opening pdf attachments

[Patrick O'Callaghan <poc usb ve>]

On Tue, 2009-12-15 at 22:30 -0500, Carpet Nailz wrote:
> On Wed, 2009-12-16 at 00:23 +0000, Patrick O'Callaghan wrote:
> > On Tue, 2009-12-15 at 17:30 -0500, Carpet Nailz wrote:
> > > I don't think it's the solution, though. In the case of the email with
> > > two pdfs attached, they both are type=application/pdf (according to
> > > the
> > > properties of the files once I save them to the desktop), yet one (in
> > > the email) give me as options to open Evince, Acrobat, OpenOffice
> > > writer, & GIMP; while the other (same type) only gives OOwriter/web
> > > and
> > > gedit. (On the desktop they both give me the same set of apps to open
> > > with: Evince, Acrobat, OpenOffice Writer and GIMP.)
> >
> > This is irrelevant. Evo looks at the MIME types encoded in the message
> > itself. Look at the MIME headers using View->Message Source or Ctrl-U.
> >
> > poc
> I took a look at the MIME info in the email Message Source. The
> attachment that gave me good "open with" results (Evince,OpenOffice
> Writer,Acrobat, Gimp) showed this:
>       Content-type: application/pdf; name="knutsonetal_NeuralPredictors.pdf";
> x-mac-creator="70727677"; x-mac-type="50444620"
>       Content-disposition: attachment;
> filename="knutsonetal_NeuralPredictors.pdf"
>       Content-transfer-encoding: base64
>
> The other message, which only offered OpenOffice Writer/web and gedit as
> open with options, showed this: 
>
>       Content-type: application/octet-stream; name="application of real-time
> fMRI.pdf"
>       Content-disposition: attachment; filename="application of real-time
> fMRI.pdf"
>       Content-transfer-encoding: base64
>       
> I guess I don't understand what determines the MIME type of a pdf.

It's not the "MIME type of a pdf", it's the MIME type of an attachment,
and it's determined entirely by the mailer used to send the message. If
the attachment is not properly described then Evo has no way of knowing
what's actually in it. I presume that's why it's falling back to
OpenOffice and gedit as apps that might be able to deal with it. Note
that the file extension (.pdf) plays no part in this, which is in line
with the MIME standard. It would be reasonable for Evo to use the
extension as a hint when it's not sure, but that would require asking
for an enhancement.

What's happening here is that one mailer is working and the other isn't.
There's not much you can do about that other than exhort the user of the
broken mailer to use a working one.

> From
> what I see when investigating MIME types on the web, there should be a
> close relationship between file type (eg, pdf) and mime type.

The association of an extension (.pdf) with a file type is highly
system-dependent (e.g. consider .html vs .htm) which is why MIME tries
to be independent of such things.

> I haven't
> been able to find anything but cursory explanations of MIME types that
> just link them with file types such as pdf.

Standards documents tend to be highly generic. I'm sure a Google search
will turn up lots of info on this.

> Other items:
> One forum discussing this included this strange bit of advice, "Inform
> the clueless sender about the proper MIME types." Can the sender change
> the MIME type of an existing pdf?

The recommendation is correct (modulo the language). However although
the "clueless sender" doesn't have to do anything at all to their PDF
file, they do have to configure their system properly. This often
involves editing a configuration file somewhere that makes the
association between file extensions and MIME types explicit for that
system. How to do this depends on the system of course. For an example,
take a look at /etc/mime.types on most Linux systems.

> The email I'm focusing on included this statement in the message source:
> "This message is in MIME format. Since your mail reader does not
> understand this format, some or all of this message may not be legible."
> Why would Evolution not understand MIME format?

You're misreading the statement (which could be better phrased in fact).
What it's saying is that Evo knows this is a MIME attachment but can't
figure out what type it is since the header doesn't say.

> When I went to my wife's Mac (OS X 5) to see what it could tell me about
> the pdfs that she sent to me, I couldn't fine anything at all about MIME
> type in the "Get Info" for the documents. Each was just described as
> "Kind: Portable Document Format," although they had different encoding
> software indicated.

Again, this is because MIME type is not something recorded in the file
itself. A quick search on Google turned up this:
http://mac.softpedia.com/get/System-Utilities/RCDefaultApp.shtml which
might be illustrative.

poc