Merge remote-tracking branch 'upstream/patch_disable-gnutls-verify' into main

[elpher.git] / elpher.texi

\input texinfo @c -*-texinfo-*-

@setfilename elpher.info
@settitle Elpher Manual v2.10.0

@dircategory Emacs
@direntry
* Elpher: (elpher).     A gopher and gemini client for Emacs.
@end direntry

@copying
This manual documents Elpher, a gopher and gemini client for Emacs.

Copyright @copyright{} 2019, 2020 Tim Vaughan

@quotation
The source and documentation of Elpher is free software.  You can
redistribute it and/or modify it under the terms of the GNU General
Public License as published by the Free Software Foundation; either
version 3, or (at your option) any later version.

Elpher is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNElpher FOR A PARTICULAR PURPOSE. See the GNU General Public License in
the file COPYING in the same directory as this file for more details.
@end quotation
@end copying

@titlepage
@title Elpher Gopher and Gemini Client Manual
@author Tim Vaughan

@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top, Introduction, (dir), (dir)
@top Elpher

@insertcopying
@end ifnottex

@macro keycmd{key,cmd}
@item \key\  (@code{\cmd\})
@findex \cmd\
@end macro

@menu
* Introduction::                Elpher Overview: what's this all about?
* Installation::                Installing Elpher
* Quick Start::                 Get up and running quickly
* Navigation::                  Fundamentals of Elpher navigation
* Bookmarks::                   How to record and visit bookmarks
* Gopher character encodings::  How Elpher selects encodings for gopher pages
* Encrypted gopher connections::       How and when TLS is enabled for gopher
* Gemini support::              Support for the Gemini protocol
* Finger support::              Support for the Finger protocol
* Customization::               How to customize various aspects of Elpher
* Command Index::

@detailmenu
 --- The Detailed Node Listing ---

Navigation

* Within-page navigation::      Moving about within a page
* Between-page navigation::     Commands for moving between pages
* History and Caching::         Explanation of how Elpher represents history

@end detailmenu
@end menu

@node Introduction, Installation, Top, Top
@chapter Introduction

Elpher aims to be a capable and practical gopher and gemini client for
Emacs.  Its focus is on easy keyboard-driven navigation based on
sensible default bindings (with out-of-the-box support for Evil).  It is
intended to be robust and behave in non-surprising ways at all times.
Additionally, Elpher provides the following bells and whistles:

@itemize
@item
followable web and gopher links in plain text,

@item
an easily navigable history, sporting caching of visited pages (both
content and cursor position),

@item
auto-completing menu item navigation,

@item
direct visualization of image files where supported (no writing to
disk),

@item
a bookmark management system,

@item
basic support for the new ``heavier than gopher, lighter than the web'' Gemini protocol,

@item
support for the Finger protocol.

@end itemize

Elpher is still under active development.  Although we try very hard to
ensure that releases are bug-free, this cannot be guaranteed.  However,
this also means that any usability features that you feel are missing
can likely by incorporated quickly, so please get in touch if you
have some ideas.

@node Installation, Quick Start, Introduction, Top
@chapter Installation

Elpher is available from the MELPA package repository.  If you have
never installed packages from this repository before, you'll need
to follow the instructions at @url{https://melpa.org/#/getting-started}.

@noindent To install Elpher, enter the following:

@example
@kbd{M-x package-install @key{RET} elpher @key{RET}}
@end example

@noindent To uninstall, use

@example
@kbd{M-x package-delete @key{RET} elpher @key{RET}}.
@end example

While not recommended, it is also possible to install Elpher directly by
downloading the file @file{elpher.el} from
@url{gopher://thelambdalab.xyz/1/projects/elpher/}, adding it to a directory in
your @code{load-path}, and then adding

@example
(require 'elpher)
@end example

@noindent to your Emacs initialization file.

@node Quick Start, Navigation, Installation, Top
@chapter Quick Start

Before diving into the minutiae of the different commands available,
we will quickly describe how to get up and running with Elpher.

Once installed, you can launch Elpher using

@example
@kbd{M-x elpher @key{RET}}
@end example

@noindent This will switch to the *Elpher* buffer and display a start
page, with information on each of the default keyboard bindings.

From here you can move point between links (which may be menu items or
inline URLs in text files) by using @key{TAB} and @kbd{S-@key{TAB}},
as in Info.  You can also jump directly to a menu item using @key{m}, or
use the standard Emacs or Evil motion and search commands to find your
way around.  To open a link, press @key{RET}.  (Where a mouse is
available, Clicking on a link with the mouse cursor has the same
effect.)

To return to the page you just followed the link from, press @key{u}.

Elpher caches (for the duration of an Emacs session) both page contents
and the position of point on each of the pages (gopher menus, gemini
pages, query results, or text pages) you visit, restoring these when you
next visit the same page.  Thus, pressing @key{u} displays the previous
page in exactly the same state as when you left, meaning that you can
quickly and visually explore the different documents in a menu without
having to wait for anything to reload.

Of course, sometimes you'll @emph{want} to reload the current page
rather than stick with the cached version.  To do this use @key{R}.
(This is particularly useful for search query results, where this
allows you to perform a different search.)

That's more-or-less it. Elpher supports a number of other features, such
as bookmarking, support for different coding schemes and TLS encryption,
and a variety of customization options, all of which are explained in
the rest of this document.  However the emphasis is on keeping the basic
navigation experience as intuitive and responsive as possible.

@node Navigation, Bookmarks, Quick Start, Top
@chapter Navigation
Throughout this manual, we use the word ``page'' to refer to any
visualization of a response from a gopher or gemini server, be it a
menu/directory, query result, text file or image.  We use

Elpher's navigation interface is inspired by the Emacs Info mode.
Movement within a page is essentially the same as moving
around any other text file in Emacs, but with special keys
for quickly jumping between menu items and URLs in text files.
Movement between pages is facilitated by a simple linear history
coupled with caching of pages and cursor position.

@menu
* Within-page navigation::      Moving about within a page
* Between-page navigation::     Commands for moving between pages
* History and Caching::         Explanation of how Elpher represents history
@end menu


@node Within-page navigation, Between-page navigation, Navigation, Navigation
@section Within-page navigation

To move about within a page, you should be able use the same keys you usually
use to browse files in Emacs.  This is even true when Evil mode is
enabled. Paragraph hopping, searching etc should work as usual.

In addition, the following commands are provided for quickly moving between
links and menu items.

@table @asis
@keycmd{@key{TAB}, elpher-next-link}
Move to the next link or menu item in the file.

@keycmd{@kbd{Shift-@key{TAB}}/@key{backtab}, @code{elpher-prev-link}}
Move to the previous link or menu item in the file.

@keycmd{@key{m}, elpher-jump}
Jump directly to a link within a file by specifying its display string
or link text.  (Unlike the previous two commands, this immediately opens
the selected link.
@end table

The following commands can be used to retrieve information about the
current page, or the address of the link at point:

@table @asis
@keycmd{@key{i}, elpher-info-link}
Display host, port and selector information for the link at point.

@keycmd{@key{I}, elpher-info-current}
Display host, port and selector information for the current page.

@keycmd{@key{c}, elpher-copy-link-url}
Add URL representing address of link at point to the kill-ring and the
system clipboard (if available).

@keycmd{@key{C}, elpher-copy-current-url}
Add URL representing address of the current page to the kill-ring and
the system clipboard (if available).

@keycmd{@key{d}, elpher-download}
Download link at point and save the result as a file.  The minibuffer
will prompt for the name of the file to write, with the default name being
the display string (if available) associated with the link.

@keycmd{@key{D}, elpher-download-current}
This is similar to @code{elpher-download}, but instead applies to the
current page rather than a link.

@keycmd{@key{.}, elpher-view-raw}
This displays the raw server response for the current page.  While not
useful for general browsing, it is useful for debugging incorrect rendering
or out-of-spec server responses.
@end table

@node Between-page navigation, History and Caching, Within-page navigation, Navigation
@section Between-page navigation

Moving to a different page can be accomplished in several ways,
described by the following command:

@table @asis
@keycmd{@key{RET}\, @kbd{mouse-1}, elpher-follow-link}
Follow the menu item or link at point (or selected with the mouse).

Exactly what is meant by ``follow'' depends on the kind of item selected:

@itemize
@item
For text or menu type items or links, the current page text is replaced
by the text of this item.  Unless the customization variable
@code{elpher-use-header} (@pxref{Customization}) is 
@code{nil}, the display string of the link is displayed in the buffer header.
Links to images behave similarly on Emacs systems supporting the display of
bitmap graphics, however their content is not cached in memory by default.

@item
When followed, links to search/query items (type 7) prompt for input in
the minibuffer then display the results in the same way as for text and menu
items.

@item
Following links to binary files (and image files on unsupported systems)
causes Elpher to prompt for a filename in which to save the content.

@item
Following links of type `h' with a selector having the `URL:' prefix, or
unsuported URLs in text files, will result in Elpher using an external
programme to open the URL.  This will be either the default system browser
or, if the @code{elpher-open-urls-with-eww} customization variable is non-nil,
Emacs' own EWW browser. (See @pxref{Customization}.) 

@end itemize

Once a text, menu or query response page has been displayed, its contents are
cached for the duration of the Emacs session. 

@keycmd{@key{g}, elpher-go}
Open a particular page by specifying either its full URL or just entering
a gopher host name. (The protocol defaults to gopher, so gemini links must include the @code{gemini://} prefix.

If a unsupported protocol is used in the URL the result will be the same
as following a URL link of the same type from a link in a page.

@keycmd{@key{o}, elpher-go-current}
Prompts for a URL similar to @code{elpher-go}, but initialized to the URL
of the current page.  This allows you to easily try other selectors for the
same server.

Remember however, that the Gopher RFC 1436 provides @emph{no} guarantees about the
structure of selectors.

@keycmd{@key{O}, elpher-root-dir}
Open the root page (empty selector) on the current host.

@keycmd{@key{u}\, @kbd{mouse-3}, elpher-back}
Return to the previous page, where ``previous'' means the page where the
page which was displayed immediately before the current page.
@end table


@node History and Caching,  , Between-page navigation, Navigation
@section History and Caching 

The history and caching strategy in Elpher is extremely simple, but
may be confusing without a good mental model of how it works.  That
is what this section attempts to provide.

Essentially, @strong{every} time you navigate to a new page, either
by clicking or pressing @key{RET} on a link, using @key{g} to jump
to a new page by its address, or using @key{O} to open the root selector,
the following two things occur:

@enumerate
@item
the cursor position and content for the original page are recorded in an
in-memory cache, and

@item
the original page is set as the ``parent'' of the new page.
@end enumerate

The only way to return to pages in this history is by using @key{u},
which returns to the previous of the current page.  @footnote{The
addition of the new page to the history happens even if the new page is
one that has been seen before. This is mostly the desired behaviour.
However, opening an explicit ``back'' link provided by a gopher menu or
gemini page will also add a new entry to the history.  Unless you
haven't yet visited that menu, it's therefore better to use @key{u} to
go back in this case.}

One aspect that may seem peculiar is that Elpher lacks a corresponding ``next'' or
``forward'' command.  However, since Elpher caches the position of point,
this will be automatically positioned on the link that was most recently followed
from a given page.  This means that, at least for links followed from menus
and text files, the inverse of @key{u} is actually just @key{RET}.


@node Bookmarks, Gopher character encodings, Navigation, Top
@chapter Bookmarks

Elpher has a very simple link bookmarking system involving the
following commands:

@table @asis
@keycmd{@key{a}, elpher-bookmark-link}
Add a bookmark for the link at point.  The minibuffer will prompt for
a name for the bookmark, which defaults to the display string.

@keycmd{@key{A}, elpher-bookmark-current}
Add a bookmark for the current page.  The minibuffer will prompt for
a name for the bookmark, defaulting to the display string associated
with the link that was followed to reach the current page.

@keycmd{@key{x}, elpher-unbookmark-link}
Immediately remove the bookmark (if one exists) to the link at point.

@keycmd{@key{X}, elpher-unbookmark-current}
Immediately remove the bookmark (if one exists) to the current page.

@keycmd{@key{B}, elpher-bookmarks}
Open a page displaying all current bookmarks.  Note that this bookmark
page is added to the history just as if you had opened it using a link.
Thus to return to the previous page, use @kbd{u}.  This also means
that you can peruse the various bookmarks by visiting them in turn, 
using @kbd{u} to return to the bookmark page (where the position of point
is cached), then moving to another bookmarked link and so on.
@end table

Bookmarks are stored as a s-exp in the file @file{elpher-bookmarks}
in the user emacs directory (usually @file{~/.emacs.d/}).
Any command which modifies the list of bookmarks immediately updates
this file.

@node Gopher character encodings, Encrypted gopher connections, Bookmarks, Top
@chapter Gopher character encodings

Responses Elpher retrieves from servers are initially read as pure
binary data.  When the data is intended to be interpreted as textual (as
determined by the type parameter of the gopher menu item or the gopher
URL), this data needs to be @emph{decoded} into a sequence of
characters.  To do this properly requires knowledge of the encoding
system used by whoever authored the document.

Unfortunately gopher lacks a systematic way of acquiring this necessary
information. Thus, the details of the coding system must be either inferred from the binary data,
or must be specified by the user.

By default, Elpher applies Emacs' built-in character encoding detection
system to the full (undecoded) response data and uses this to attempt to
convert it into a character string.
(See @pxref{Recognize coding, Recognizing coding systems, ,emacs}.) While
this approach can be okay, it is important to realize that its inference
algorithm is extremely primitive and depends heavily on assumptions based
on the language settings of your emacs system.

The alternative is to explicitly set the coding system used for decoding
using the following command:

@table @asis
@keycmd{@key{S},elpher-set-coding-system}
Causes a elpher to prompt for a coding system to use for decoding
future gopher text.  The @key{TAB} key can be used at this prompt to display a
list of alternatives (which is extensive) and to auto-complete.  An empty
response will cause Elpher to return to its default auto-detection
behaviour.
@end table

Note that changing the coding system only affects newly loaded text.
Thus, if text has already been decoded using an incorrect system, you
will need to select the correct coding and then reload the text using
@key{R}.


@node Encrypted gopher connections, Gemini support, Gopher character encodings, Top
@chapter Encrypted gopher connections

While RFC 1436 does not broach the topic of encryption at all, several
modern gopher servers can serve content over encrypted connections,
and a common choice for this is TLS.

Elpher can retrieve selectors using Emacs' built-in TLS support which
uses the GnuTLS library. (It is possible to build emacs without
GnuTLS, in which case encryption is not supported.)

To retrieve documents using TLS, Elpher's TLS mode must be enabled.
This can be directly toggled using @key{T}, but note that just as with
the character encoding, changing this mode only affects subsequent
connections.

Alternatively, TLS mode is @emph{automatically} enabled whenever
gopher URLs starting with @code{gophers://} are followed.

The mode is sticky, so it remains active until switched off.
It can also be automatically switched off when a TLS connection fails.
In this case Elpher will prompt for your confirmation to ensure that
you can't accidentally make a non-TLS connection.

@node Gemini support, Finger support, Encrypted gopher connections, Top
@chapter Gemini support

@uref{gopher://gemini.circumlunar.space, Gemini}
is a new protocol being developed by several members of
gopherspace.  It aims to solve some of the long-standing technical
issues associated with gopher as a protocol, while keeping the major benefits.
For instance, it _requires_ encrypted connections, it does away with
the selector type, and allows servers to explicitly specify the
character coding scheme used for text documents.

The latest versions of Elpher aim to provide seamless transitions between
gemini and gopher documents.  Basically you should be able to open,
bookmark, download and otherwise interact with gemini pages in exactly
the same way as you do with other non-gemini pages.  The only major
difference from your perspective as a user is that you should no longer
have to worry about manually toggling TLS on or off (for gemini it's
always on), and you should never have to manually set a character coding
scheme.

The gemini protocol specification recommends a Trust on First Use (TOFU)
behaviour when validating gemini server TLS certificates.  This is
because many gemini servers rely on self-signed certificates rather
than certificates signed by a CA. Sadly however, this TOFU behaviour is
far from straight-forward to configure using Emacs' existing Network
Security Manager.  For this reason, elpher defaults to performing no
certificate verification by default.  This behaviour can be easily
customized by setting the @code{elpher-gemini-TLS-cert-checks}
customization variable to non-nil.

The gemini specification concerns both the protocol and a simple text
document format (mimetype text/gemini) which is like a mixture between
gophermap files and markdown-formatted files but simpler than both.
Elpher renders gemini responses which are provided in this format in
line with the rules in the spec.  This includes wrapping long lines at
word boundaries.  The specific column at which this text is wrapped is
defined by the customization variable
@code{elpher-gemini-max-fill-width}, which is set to 80 columns by
default. (This is slightly wider than Emacs' default fill width of 70
columns due to the fact that there are a significant amount of older
gemini content which, against the advice of the current spec, hard wraps
at <80 columns.  The larger default allows this to still look okay,
while still keeping content without hard wraps looking pleasant.)

The text/gemini format also possesses a section header syntax similar to
markdown.  Elpher allows different header levels to be drawn with
different, customizable, faces.  By default, on graphically-capable
emacs systems, these faces are given different heights to distinguish
among levels.  On terminal systems, the level is indicated by the
number of preceding # symbols.

I should emphasize however that, while it is definitely functional,
Elpher's gemini support is still experimental, and various aspects will
change as the protocol develops further.

@section Client Certificates for Gemini

Gemini makes explicit use of the client certificate mechanism that TLS
provides for allowing clients to authenticate themselves with servers.
The Gemini specification suggests two distinct classes of client
certificates: short-lived certificates used to identify you for a single
session, and more permanent certificates used to identify you over a
longer time period.

When Elpher receives a request for a client certificate from a server,
it will present you with the option to create and use a single-use
``throwaway'' certificate, or to use a ``persistent''
certificate (optionally creating it or installing pre-existing key and
certificate files).

Certificate creation in Elpher requires an installation of OpenSSL, and
---in particular---that Elpher be able to run the @command{openssl} command-line
utility.  By default, Elpher assumes that the @command{openssl} is on the
system path, but the precise location can be set by customizing the
@code{elpher-openssl-command} variable.

Each generated certificate results in the creation of a .key file and
a .crt file.  In the case of a throwaway certificate, these files are
stored in the temporary directory indicated by the Emacs variable
@code{temporary-file-directory} and are deleted when ``forgotten''
(as described below).

In the case of persistent certificates, these files are stored in the
folder defined by the Elpher variable
@code{elpher-certificate-directory}, and are never deleted by Elpher.
(Of course you can delete them yourself whenever you like.)
The base name of the files (i.e. sans extension) is what Elpher uses
to identify the certificate.

Using throwaway certificates is as simple as pressing the @key{t} 
key at the prompt which appears following a certificate request from
a server.  There is nothing more to do.

Using a persistent certificate requires instead selecting @key{p} from the same
menu.  This will result in Elpher asking you for the name identifying
the certificate.  This entry autocompletes to the list of known certificate
names, so you can use @key{TAB} to display the list.

In the case that you choose a name that does not belong to the list of
known certificates, Elpher will offer to create one for you or to
``install'' one from existing key and certificate files.
Pressing the @key{n} key will cause Elpher to begin the process of
creating a new persistent certificate, using some additional
details for which you will be prompted.
Alternatively, pressing the @key{i} key will cause Elpher to ask for the
locations of edisting key and certificate files to add to
@code{elpher-certificate-directory} under the chosen name.

Once a certificate is selected, it will be used for all subsequent TLS
transactions to the host for which the certificate was created.
It is immediately ``forgotten'' when a TLS connection to another host
is attempted, or the following command is issued:

@table @asis
@keycmd{@key{F},elpher-forget-certificate}
Causes Elpher to immediately forget any currently-loaded client certificate.
@end table

In either case, ``forgetting'' means that the details of the key and
certificate file pair are erased from memory.  Furthermore, in the case
of throw-away certificates, the corresponding files are deleted.


@node Finger support, Customization, Gemini support, Top
@chapter Finger support

Incidentally, Elpher has native support for querying finger servers.
Of course, one could argue that this functionality is more easily
provided by one's local telnet client.  However finger URLs do appear
on occasion in gopherspace, and it's nice to be able to open them
in place.

Elpher interprets @code{finger://} URLs as follows:

@itemize

@item
The host is determined by the host name portion of the URL.

@item
In the case that the @emph{file name} portion of the URL is non-empty (besides
the leading slash), this is interpreted as the user to finger.

@item
Otherwise, the @emph{user} portion of the URL is interpreted as the user to finger.

@item
If no user is provided, the root directory of the finger server is requested.

@end itemize

Thus @code{finger://user@@hostname} and @code{finger://hostname/user} are both equivalent.

(The precedence of the /user notation over the user@ notation reflects a
preference of the community.)

@node Customization, Command Index, Finger support, Top
@chapter Customization

Various parts of Elpher can be customized via the 
variables belonging to the elpher customization group, accessible
using

@example
@kbd{M-x customize-group elpher @key{RET}}
@end example

@noindent This group contains a number of faces that can be modified to change
the appearance of Elpher, including one face per menu item type.

The group also contains variables for customizing the behaviour of
Elpher.  This includes how to open arbitrary (non-gopher) URLs, whether
to display buffer headers, how to deal with ANSI escape sequences in
text, the timeout to impose on network connections, and whether to
prompt for confirmation when switching away from TLS.

See the customization group itself for details.

@node Command Index,  , Customization, Top
@unnumbered Command Index

@printindex fn

@bye