Closes #656

use libmagic to detect valid file formats

init_parse_options calls feh_prepare_filelist, which in turn calls
feh_file_info_preload if opt.preload is set. This function will load all
images in the filelist to determine their attributes, so we need to initialize
libmagic before calling init_parse_options.

Add a global `magic_t magic` and initialize it just once.

Also `feh_is_image()` now calls itself to check compressed files, saving
some duplicate code.

Writing our own magic bytes detection is prone to errors and an
everlasting catch-up-game. Let's use libmagic to get things right,
this is less code and makes things more reliable.

Building without libmagic is still possible. That will make the code
act like specifying FEH_SKIP_MAGIC=1, effectively passing everything
to imlib2.

When _POSIX_C_SOURCE is defined, macOS hides the definitions of mkdtemp
and mkstemps, among others. Define _DARWIN_C_SOURCE to counteract that.

Guilherme Janczak authored Jan 11, 2022 and derf committed Jan 16, 2022

getopt_long() is widely supported these days, removing it from the
source tree should be okay.

Here's documentation or the implementation of getopt_long on many
systems:

All the BSDs:
https://man.netbsd.org/NetBSD-9.2-STABLE/getopt_long.3
https://man.openbsd.org/OpenBSD-7.0/getopt_long
https://www.freebsd.org/cgi/man.cgi?query=getopt_long
https://leaf.dragonflybsd.org/cgi/web-man?command=getopt_long

Illumos (OpenSolaris fork):
https://illumos.org/man/3c/getopt_long

The musl, newlib, and uclibc-ng libcs:
https://gogs.waldemar-brodkorb.de/oss/uclibc-ng/src/master/libc/unistd/getopt_long-simple.c#L49-L52
https://git.musl-libc.org/cgit/musl/tree/src/misc/getopt_long.c#n140
https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/stdlib/getopt.c;h=d4f225a7a735dc741d2874eb6c131b6fce2967c5;hb=HEAD#l475

Mingw-w64:
https://github.com/mirror/mingw-w64/blob/master/mingw-w64-crt/misc/getopt.c#L542-L549

Mac OS X:
https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/getopt_long.3.html

Closes #642

Imlib2 v1.7.5 introduces automatic (and transparent) orientation adjustment
based on EXIF orientation tags. This makes feh's --auto-rotate function
both superfluous and erroneous: It doesn't know about Imlib2's adjustments,
so it rotates an image which is already correctly oriented, leading to
incorrect orientation.

I am not aware of a simple run-time check for detecting whethen running
Imlib2 < 1.7.5 or ≥ 1.7.5. For now, feh disables --auto-rotate entirely when
compiled on a system with Imlib2 1.7.5+ and outputs a warning when the
option is used.

Rationale: The Imlib2 version available at run-time should in most cases be
at least as recent as the Imlib2 version used at compile-time. So, while there
may be cases where feh was compiled with Imlib2 1.7.4 and exhibits erroneous
auto-rotate behaviour on an Imlib2 1.7.5 system, the inverse case
(a feh with disabled auto-rotate support running on Imlib2 1.7.4) should be
sufficiently rare. If it does occur, it can be remedied by compiling feh
from source locally.

Possible caveat: Imlib2 only adjusts for EXIF orientation when loading JPEG
and TIFF images. If there are additional EXIF-aware file formats supported by
feh, but not Imlib2, they lose auto-rotate support.

Reference: GitHub issue #642

See GitHub issue #642

Closes #639

Useful to make feh quit (or execute actions) on mouse movement

Closes #568

If stdin is not connected, the X11 connection may use FD 0, which is
traditionally used for STDIN. Do not attempt reads from fd 0 unless it
_really_ is connected to a terminal on stdin.

Reported by https://github.com/pvanstam, thanks a lot!

Closes #631
Closes #632

This allows feh to load .gif images via libcurl, as some imlib2 versions only
load gif images if the suffix is correct. It's also more convenient when using
--keep-http.

To achieve this, feh needs to use mkstemps. mkstemps is a non-standard
extension that is available on several systems. Compile feh with
"mkstemps=0" to use mkstemp instead.

Closes #630

Needs further testing

Tobias Stoeckmann authored Jul 23, 2021 and derf committed Jul 23, 2021

The snprintf string argument should not be duplicated.
It is not needed and also not released afterwards.

Tobias Stoeckmann authored Jul 23, 2021 and derf committed Jul 23, 2021

Calling feh with an empty argument leads to out of boundary access.
This can be seen best when compiled with asan:

$ feh ""

* Fix out of boundary access

The while-loop is not finished when pos is set to EXIF_MAX_DATA.
Instead, the loop continues and therefore tries to access data outside
of the array.

This is triggered when compiled with exif=1 and asan:

$ feh --draw-exif image.jpg

* Fixed formatting

No functional change but makes previous commit easier verifiable
(independent of tab space setup).

* Call break; instead of setting pos2 to a magic value

This is in line with the following else clause

* Another cosmetic adjustment

Co-authored-by: Daniel Friesel <derf@finalrewind.org>

Fix feh_is_image for tiny (<16 byte) image files

Alistair authored Jun 09, 2021 and derf committed Jun 09, 2021

Note that Imlib2 does not support JXL images out of the box.  However, the
imlib2-jxl loader (https://github.com/alistair7/imlib2-jxl) does.

This is consistent with --scroll-step (option name) and --zoom (percentage)

"screen" and "display" are different X11 terms; we're actually talking about
"monitors"

This should help answer questions such as #605 in the future