Re: Image handling in mutt
On Sun 10 Dec 2023 at 15:51:02 (-0500), Pocket wrote:
> > On Dec 10, 2023, at 3:05 PM, David Wright wrote:
> > On Fri 08 Dec 2023 at 16:29:12 (-0500), Paul M Foster wrote:
> >>> On Fri, Dec 08, 2023 at 11:04:54AM -0600, David Wright wrote:
> >>> On Fri 08 Dec 2023 at 11:56:12 (-0500), Paul M Foster wrote:
> >>>>
> >>>> I'm on Debian bookworm, using neomutt for email. Where there is an image to
> >>>> view, viewing it in neomutt calls up one of the ImageMagick programs. I've set
> >>>> the mailcap_path variable in my neomutt config to point to ~/.mailcap,
> >
> > Similarly, I point it to ~/.config/mutt/mailcap-mutt, which is
> > a specially crafted subset of /etc/mailcap with a few additions
> > (like converting webp to a jpeg rather than opening in gimp,
> > and playing midi files the way I want).
> >
> >>>> and
> >>>> set an entry in there for image/jpg to point to /usr/bin/feh. I've even set
> >>> ↑↑↑ try jpeg
> >>>
> >>>> the "display" alternative to feh with update-alternatives. Still, mutt is
> >>>> calling an imagemagick program to display jpgs.
> >>>>
> >>>> First, if alternatives doesn't point to the imagemagick program, and the
> >>>> mailcap file doesn't point to it, and there's nothing in the neomutt config
> >>>> pointing to the imagemagick program, then where the heck is it getting that
> >>>> as the program to use to display images?
> >
> > An email would contain headers with the attachment.
> >
> > ↓
> > Content-Type: image/jpeg
> > Content-Disposition: attachment; filename="don.jpg"
> > Content-Transfer-Encoding: base64
> >
> > By default, mutt searches six directories for a mailcap file. When
> > found, the line in the mailcap starting with image/jpeg selects the
> > program to run.
> >
> > If you see an extension in a mailcap field like nametemplate=%s.jpg
> > that's to show that a filename matching that pattern should be given
> > to a copy of the attachment to satisfy the program that's going to
> > read it. But it's the attachment /content type/ that selects the
> > program, not the extension¹.
> >
> >>>> Second, how do I fix this so that mutt uses feh to display images?
> >>
> >> I can't believe that worked. The /etc/mailcap has both (jpg and jpeg), and
> >> the files I was looking at had a "jpg" extension.
> >>
> >> But thanks for the tip.
> >
> > A couple of programs in my /etc/mailcap (gpicview and gm) have
> > image/jpg lines, duplicating the image/jpeg entries, perhaps
> > as a "catch-all" for malformed emails containing image/jpg.
> > I don't know whether image/jpg is an official legacy type/iana-token.
> >
> > ¹ Re the argument raging in this thread about "extension", the
> > term is clearly appropriate, as a glance at /etc/mime.types
> > demonstrates. The literature is full of the term.
> >
> > I wouldn't want to use "suffix" myself, as it's too general:
> > anything stuck on the end is a suffix, but not necessarily
> > a filename extension. Suffixes are used for other purposes.
>
> Suffix is the correct term.
> File names in Linux are a character string of 255 chars. Again there are not file extensions in a Linux file name.
>
> People are conflating the issue.
>
> Read the code, code good.
So you've said five or six times already. The trouble is that it's
difficult to square this with documentation not only of the OS in
the widest sense, but also the linux kernel itself, which uses the
term extension.
It's often stated, and has been in this thread, that the kernel uses
magic numbers at the start of executables rather than filename
extensions, and while this is true, it's not the only method.
Take a look, for example, at this file (choose your version):
linux-source-5.10/Documentation/admin-guide/binfmt-misc.rst
Kernel Support for miscellaneous Binary Formats (binfmt_misc)
=============================================================
This Kernel feature allows you to invoke almost (for restrictions
see below) every program by simply typing its name in the shell.
This includes for example compiled Java(TM), Python or Emacs programs.
To achieve this you must tell binfmt_misc which interpreter has to
be invoked with which binary. Binfmt_misc recognises the binary-type
by matching some bytes at the beginning of the file with a magic
byte sequence (masking out specified bits) you have supplied.
Binfmt_misc can also recognise a filename extension aka ``.com``
or ``.exe``.
[ … ]
``magic``
is the byte sequence binfmt_misc is matching for. The magic string
may contain hex-encoded characters like ``\x0a`` or ``\xA4``. Note
that you must escape any NUL bytes; parsing halts at the first one.
In a shell environment you might have to write ``\\x0a`` to prevent
the shell from eating your ``\``.
If you chose filename extension matching, this is the extension to be
recognised (without the ``.``, the ``\x0a`` specials are not allowed).
Extension matching is case sensitive, and slashes ``/`` are not allowed!
Cheers,
David.
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