elinks/doc/mime.txt

Introduction to MIME handling
-----------------------------

At some time along the 0.4 prereleases, ELinks replaced the old Links file
configuration system with its own one. Now, the configuration is stored in
elinks.conf, much more complete and featuring a new syntax. You can set most
options from the UI (so usually there is no need to deal with elinks.conf),
and that used to be true for setting MIME handlers and extensions as well; but
now the associations menu is gone temporarily, forcing you to set the handlers
from the configuration file.

The comments provided within elinks.conf for the MIME options are not much
helpful, and those options may seem a bit obscure or confusing at first.  This
document is a basic introduction to setting of MIME associations for ELinks.
If you want to know how to automatically launch a program to view some kind of
file (like images), then read on. Some basic knowledge of MIME is recommended.


Handling MIME types, the ELinks way
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

What are MIME types and why may you want to use them?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If, while browsing with ELinks, you need to display files that it can't show
(like images or PDF documents), then you will likely want to pass them to
other programs that are suitable for this task. While you may do it manually
(saving the file to disk, running the auxiliary program to show it and then
removing the file when finished), ELinks provides a method to do this
automatically using MIME types.

ELinks usually knows what the MIME type is for any file (which is a kind of
description of its format), thus you only need to specify how to manage the
MIME types for the files you want to open. If you don't tell ELinks how to
manage a given MIME type then it will show you on screen the contents of the
file (as if it was ASCII text) instead of calling an external program to show
them.

Associating files to MIME types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the file is fetched from a web server then this web server should tell
ELinks what its MIME type is, so you should have generally no need to care
about it. However, the web server might send an incorrect type, or you may be
retrieving it by FTP or from your local filesystem, so sometimes ELinks needs
to guess it.

The easiest method to guess a MIME type for a file is to just look at its name
trusting it was given the right extension.  ELinks supports this, letting you
to specify a type for any given extension.

Managing a given MIME type
^^^^^^^^^^^^^^^^^^^^^^^^^^

This usually means specifying programs to open files of this type and the
conditions in which those programs may be used. For instance, you may want to
use zgv (a popular svgalib image viewer) when you are using the text console,
but xli (a image viewer for X) when running the X window system.


Binding it to a handler
+++++++++++++++++++++++

Instead of directly attaching a program to a MIME type, ELinks lets you
associate an abstract handler to each type. Then you can specify which
programs implement the handler and how are they used.

For instance, you may create an image_viewer handler and assign it to MIME
types image/jpeg, image/png and image/gif. Then you would associate to
image_viewer the programs you would like to use for viewing images and the
details on how to use them. This is less cumbersome than repeating all these
details for each MIME type.


Specifying the details for a handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

There are three issues to specify for a handler: the program associated to it,
whether you want confirmation before using it and whether you want the
terminal to be blocked while it is being used.

When specifying any of these issues, you must tell ELinks the situation in
which it gets applied, which is typically either the text console or the X
window system. So you can specify that you don't want confirmation before
running the program when running X, and that you want it otherwise.
Similarly, when you are attaching a program (name it foo) to this handler you
must tell if it's for X or not (you can attach a second program for the other
choice if you want).

Attaching a program to it::

	You must tell ELinks the exact command for running it (with any
	options you wish). In place of the filename you must enter %.

Choosing whether you want confirmation before applying it::

	This is rather simple. If you choose not to do so, then the handler
	will be automatically called upon when you demand ELinks to show
	something attached to this handler. Otherwise, if you ask for
	confirmation, you will be prompted to open it with a external program,
	with additional choices that include cancelling the operation and
	viewing it with ELinks. E.g: you may use this option for programs
	written in C so that you may always choose if you want to read the
	source with ELinks, or if you want to save it, or if you want to use
	indent to display it with less.

Choosing whether to block the terminal::

	If you don't want to allow going back to ELinks (or any other program
	from the same terminal) before the external program ends, then you
	should ask to block the terminal.


Setting up elinks.conf
~~~~~~~~~~~~~~~~~~~~~~

If you have old configuration files from old ELinks versions or from Links,
then you may use the conf-links2elinks.pl script (which is placed at
contrib/conv/ on the source distribution) to convert them to the new format.
If you don't use it you will need to edit the configuration file, and here you
will find how.

Associating a file extension to a MIME type
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can still do this with the UI, from the the Setup->File Extensions
submenu.

If you want to do so from the configuration file, enter set mime.extension.ext
= "type", replacing ext with the appropriate file extension, and type with its
MIME type. E.g. you may want to have set mime.extension.jpg = "image/jpeg".


Defining a handler
^^^^^^^^^^^^^^^^^^

For each handler you must define three items, specifying in what context the
value of the item should be applied. You must enter set
mime.handler.handler-name.item.context = value, replacing handler-name with
the name for the handler you are defining, item with the item you are defining
for this handler, context with the context this item value is to be applied,
and value with the value you want to assign to the item. You must do so for
each of the available items: program, ask and block.

The value for program is a string with the exact command you want to be issued
to view the file, placing % were you would put the file name. The values for
ask and block are either 0 (no) or 1 (yes). Available contexts include unix
and unix-xwin, which mean UNIX text terminal and X respectively (others can be
os2, win32, beos, riscos, ...). The latter does not mean you are running
ELinks from X, just that the DISPLAY variable is set so that ELinks may run an
X program.

To illustrate it, here is an example. Suppose you want to define the
image_viewer handler which should be used to view images.  The configuration
file may look like this:

--------------------------------------------------------------------------------
set mime.handler.image_viewer.unix.ask = 1
set mime.handler.image_viewer.unix-xwin.ask = 0

set mime.handler.image_viewer.unix.block = 1
set mime.handler.image_viewer.unix-xwin.block = 0

set mime.handler.image_viewer.unix.program = "zgv %"
set mime.handler.image_viewer.unix-xwin.program = "xli %"
--------------------------------------------------------------------------------

In this example the image_viewer handler uses the svgalib image viewer zgv
when X is not available, and the X image viewer xli when it is. The terminal
would be blocked when X is not available and it would not be when it's
available. Finally, ELinks would ask for confirmation before using the handler
only with X not available.

Associating a MIME type to a handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Just enter set mime.type.class.name = "handler", replacing class with the
class for the mime type, name with the specific name within that class, and
handler with the name for the handler you want to assign to the MIME type.
E.g. you may want to have set mime.type.image.jpeg = "image_viewer".