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Appendices

History

GNUS was written by Masanobu UMEDA. When autumn crept up in '94, Lars Magne Ingebrigtsen grew bored and decided to rewrite Gnus.

If you want to investigate the person responsible for this outrage, you can point your (feh!) web browser to `http://www.stud.ifi.uio.no/~larsi/'. This is also the primary distribution point for the new and spiffy versions of Gnus, and is known as The Site That Destroys Newsrcs And Drives People Mad.

During the first extended alpha period of development, the new Gnus was called "(ding) Gnus". (ding) is, of course, short for ding is not Gnus, which is a total and utter lie, but who cares? (Besides, the "Gnus" in this abbreviation should probably be pronounced "news" as UMEDA intended, which makes it a more appropriate name, don't you think?)

In any case, after spending all that energy on coming up with a new and spunky name, we decided that the name was too spunky, so we renamed it back again to "Gnus". But in mixed case. "Gnus" vs. "GNUS". New vs. old.

The first "proper" release of Gnus 5 was done in November 1995 when it was included in the Emacs 19.30 distribution (132 (ding) Gnus releases plus 15 Gnus 5.0 releases).

In May 1996 the next Gnus generation (aka. "September Gnus" (after 99 releases)) was released under the name "Gnus 5.2" (40 releases).

On July 28th 1996 work on Red Gnus was begun, and it was released on January 25th 1997 (after 84 releases) as "Gnus 5.4" (67 releases).

On September 13th 1997, Quassia Gnus was started and lasted 37 releases. If was released as "Gnus 5.6 on March 8th 1998.

If you happen upon a version of Gnus that has a prefixed name -- "(ding) Gnus", "September Gnus", "Red Gnus", "Quassia Gnus" -- don't panic. Don't let it know that you're frightened. Back away. Slowly. Whatever you do, don't run. Walk away, calmly, until you're out of its reach. Find a proper released version of Gnus and snuggle up to that instead.

Why?

What's the point of Gnus?

I want to provide a "rad", "happening", "way cool" and "hep" newsreader, that lets you do anything you can think of. That was my original motivation, but while working on Gnus, it has become clear to me that this generation of newsreaders really belong in the stone age. Newsreaders haven't developed much since the infancy of the net. If the volume continues to rise with the current rate of increase, all current newsreaders will be pretty much useless. How do you deal with newsgroups that have thousands of new articles each day? How do you keep track of millions of people who post?

Gnus offers no real solutions to these questions, but I would very much like to see Gnus being used as a testing ground for new methods of reading and fetching news. Expanding on UMEDA-san's wise decision to separate the newsreader from the backends, Gnus now offers a simple interface for anybody who wants to write new backends for fetching mail and news from different sources. I have added hooks for customizations everywhere I could imagine it being useful. By doing so, I'm inviting every one of you to explore and invent.

May Gnus never be complete. C-u 100 M-x all-hail-emacs and C-u 100 M-x all-hail-xemacs.

Compatibility

Gnus was designed to be fully compatible with GNUS. Almost all key bindings have been kept. More key bindings have been added, of course, but only in one or two obscure cases have old bindings been changed.

Our motto is:

In a cloud bones of steel.

All commands have kept their names. Some internal functions have changed their names.

The gnus-uu package has changed drastically. See section Decoding Articles.

One major compatibility question is the presence of several summary buffers. All variables relevant while reading a group are buffer-local to the summary buffer they belong in. Although many important variables have their values copied into their global counterparts whenever a command is executed in the summary buffer, this change might lead to incorrect values being used unless you are careful.

All code that relies on knowledge of GNUS internals will probably fail. To take two examples: Sorting gnus-newsrc-alist (or changing it in any way, as a matter of fact) is strictly verboten. Gnus maintains a hash table that points to the entries in this alist (which speeds up many functions), and changing the alist directly will lead to peculiar results.

Old hilit19 code does not work at all. In fact, you should probably remove all hilit code from all Gnus hooks (gnus-group-prepare-hook and gnus-summary-prepare-hook). Gnus provides various integrated functions for highlighting. These are faster and more accurate. To make life easier for everybody, Gnus will by default remove all hilit calls from all hilit hooks. Uncleanliness! Away!

Packages like expire-kill will no longer work. As a matter of fact, you should probably remove all old GNUS packages (and other code) when you start using Gnus. More likely than not, Gnus already does what you have written code to make GNUS do. (Snicker.)

Even though old methods of doing things are still supported, only the new methods are documented in this manual. If you detect a new method of doing something while reading this manual, that does not mean you have to stop doing it the old way.

Gnus understands all GNUS startup files.

Overall, a casual user who hasn't written much code that depends on GNUS internals should suffer no problems. If problems occur, please let me know by issuing that magic command M-x gnus-bug.

If you are in the habit of sending bug reports very often, you may find the helpful help buffer annoying after a while. If so, set gnus-bug-create-help-buffer to nil to avoid having it pop up at you.

Conformity

No rebels without a clue here, ma'am. We conform to all standards known to (wo)man. Except for those standards and/or conventions we disagree with, of course.

RFC 822
There are no known breaches of this standard.
RFC 1036
There are no known breaches of this standard, either.
Son-of-RFC 1036
We do have some breaches to this one.
MIME
Gnus does no MIME handling, and this standard-to-be seems to think that MIME is the bees' knees, so we have major breakage here.
X-Newsreader
This is considered to be a "vanity header", while I consider it to be consumer information. After seeing so many badly formatted articles coming from tin and Netscape I know not to use either of those for posting articles. I would not have known that if it wasn't for the X-Newsreader header.

If you ever notice Gnus acting non-compliant with regards to the texts mentioned above, don't hesitate to drop a note to Gnus Towers and let us know.

Emacsen

Gnus should work on :

Gnus will absolutely not work on any Emacsen older than that. Not reliably, at least.

There are some vague differences between Gnus on the various platforms--XEmacs features more graphics (a logo and a toolbar)---but other than that, things should look pretty much the same under all Emacsen.

Contributors

The new Gnus version couldn't have been done without the help of all the people on the (ding) mailing list. Every day for over a year I have gotten billions of nice bug reports from them, filling me with joy, every single one of them. Smooches. The people on the list have been tried beyond endurance, what with my "oh, that's a neat idea <type type>, yup, I'll release it right away <ship off> no wait, that doesn't work at all <type type>, yup, I'll ship that one off right away <ship off> no, wait, that absolutely does not work" policy for releases. Micro$oft--bah. Amateurs. I'm much worse. (Or is that "worser"? "much worser"? "worsest"?)

I would like to take this opportunity to thank the Academy for... oops, wrong show.

This manual was proof-read by Adrian Aichner, with Ricardo Nassif, Mark Borges, and Jost Krieger proof-reading parts of the manual.

The following people have contributed many patches and suggestions:

Christopher Davis, Andrew Eskilsson, Kai Grossjohann, David Kågedal, Richard Pieri, Fabrice Popineau, Daniel Quinlan, Jason L. Tibbitts, III, and Jack Vinson.

Also thanks to the following for patches and stuff:

Jari Aalto, Adrian Aichner, Vladimir Alexiev, Russ Allbery, Peter Arius, Matt Armstrong, Marc Auslander, Frank Bennett, Robert Bihlmeyer, Chris Bone, Mark Borges, Mark Boyns, Lance A. Brown, Kees de Bruin, Martin Buchholz, Joe Buehler, Kevin Buhr, Alastair Burt, Joao Cachopo, Zlatko Calusic, Massimo Campostrini, Castor, David Charlap, Dan Christensen, Kevin Christian, Michael R. Cook, Glenn Coombs, Frank D. Cringle, Geoffrey T. Dairiki, Andre Deparade, Ulrik Dickow, Dave Disser, Rui-Tao Dong, Joev Dubach, Michael Welsh Duggan, Dave Edmondson, Paul Eggert, Enami Tsugutomo, Michael Ernst, Luc Van Eycken, Sam Falkner, Nelson Jose dos Santos Ferreira, Sigbjorn Finne, Decklin Foster, Gary D. Foster, Paul Franklin, Guy Geens, Arne Georg Gleditsch, David S. Goldberg, Michelangelo Grigni, D. Hall, Magnus Hammerin, Kenichi Handa, Raja R. Harinath, Yoshiki Hayashi, P. E. Jareth Hein, Hisashige Kenji, Marc Horowitz, Gunnar Horrigmo, Richard Hoskins, Brad Howes, François Felix Ingrand, Ishikawa Ichiro, Lee Iverson, Iwamuro Motonori, Rajappa Iyer, Andreas Jaeger, Randell Jesup, Fred Johansen, Gareth Jones, Simon Josefsson, Greg Klanderman, Karl Kleinpaste, Peter Skov Knudsen, Shuhei Kobayashi, Koseki Yoshinori, Thor Kristoffersen, Jens Lautenbacher, Martin Larose, Seokchan Lee, Carsten Leonhardt, James LewisMoss, Christian Limpach, Markus Linnala, Dave Love, Mike McEwan, Tonny Madsen, Shlomo Mahlab, Nat Makarevitch, Istvan Marko, David Martin, Jason R. Mastaler, Gordon Matzigkeit, Timo Metzemakers, Richard Mlynarik, Lantz Moore, Morioka Tomohiko, Erik Toubro Nielsen, Hrvoje Niksic, Andy Norman, Fred Oberhauser, C. R. Oldham, Alexandre Oliva, Ken Olstad, Masaharu Onishi, Hideki Ono, William Perry, Stephen Peters, Jens-Ulrik Holger Petersen, Ulrich Pfeifer, Matt Pharr, John McClary Prevost, Bill Pringlemeir, Mike Pullen, Jim Radford, Colin Rafferty, Lasse Rasinen, Lars Balker Rasmussen, Joe Reiss, Renaud Rioboo, Roland B. Roberts, Bart Robinson, Christian von Roques, Jason Rumney, Wolfgang Rupprecht, Jay Sachs, Dewey M. Sasser, Loren Schall, Dan Schmidt, Ralph Schleicher, Philippe Schnoebelen, Andreas Schwab, Randal L. Schwartz, Justin Sheehy, Danny Siu, Matt Simmons, Paul D. Smith, Jeff Sparkes, Toby Speight, Michael Sperber, Darren Stalder, Richard Stallman, Greg Stark, Sam Steingold, Paul Stodghill, Kurt Swanson, Samuel Tardieu, Teddy, Chuck Thompson, Philippe Troin, James Troup, Trung Tran-Duc, Aaron M. Ucko, Aki Vehtari, Didier Verna, Jan Vroonhof, Stefan Waldherr, Pete Ware, Barry A. Warsaw, Christoph Wedler, Joe Wells, Katsumi Yamaoka, and Shenghuo Zhu.

For a full overview of what each person has done, the ChangeLogs included in the Gnus alpha distributions should give ample reading (550kB and counting).

Apologies to everybody that I've forgotten, of which there are many, I'm sure.

Gee, that's quite a list of people. I guess that must mean that there actually are people who are using Gnus. Who'd'a thunk it!

New Features

These lists are, of course, just short overviews of the most important new features. No, really. There are tons more. Yes, we have feeping creaturism in full effect.

(ding) Gnus

New features in Gnus 5.0/5.1:

September Gnus

New features in Gnus 5.2/5.3:

Red Gnus

New features in Gnus 5.4/5.5:

Quassia Gnus

New features in Gnus 5.6:

Newest Features

Also known as the todo list. Sure to be implemented before the next millennium.

Be afraid. Be very afraid.

(That a feature appears in this list doesn't necessarily mean that I've decided to actually implement it. It just means that I think it sounds interesting.)

(Yes, this is the actual, up-to-the-second todo list.)

Terminology

news
This is what you are supposed to use this thing for--reading news. News is generally fetched from a nearby NNTP server, and is generally publicly available to everybody. If you post news, the entire world is likely to read just what you have written, and they'll all snigger mischievously. Behind your back.
mail
Everything that's delivered to you personally is mail. Some news/mail readers (like Gnus) blur the distinction between mail and news, but there is a difference. Mail is private. News is public. Mailing is not posting, and replying is not following up.
reply
Send a mail to the person who has written what you are reading.
follow up
Post an article to the current newsgroup responding to the article you are reading.
backend
Gnus gets fed articles from a number of backends, both news and mail backends. Gnus does not handle the underlying media, so to speak--this is all done by the backends.
native
Gnus will always use one method (and backend) as the native, or default, way of getting news.
foreign
You can also have any number of foreign groups active at the same time. These are groups that use non-native non-secondary backends for getting news.
secondary
Secondary backends are somewhere half-way between being native and being foreign, but they mostly act like they are native.
article
A message that has been posted as news.
mail message
A message that has been mailed.
message
A mail message or news article
head
The top part of a message, where administrative information (etc.) is put.
body
The rest of an article. Everything not in the head is in the body.
header
A line from the head of an article.
headers
A collection of such lines, or a collection of heads. Or even a collection of NOV lines.
NOV
When Gnus enters a group, it asks the backend for the headers of all unread articles in the group. Most servers support the News OverView format, which is more compact and much faster to read and parse than the normal HEAD format.
level
Each group is subscribed at some level or other (1-9). The ones that have a lower level are "more" subscribed than the groups with a higher level. In fact, groups on levels 1-5 are considered subscribed; 6-7 are unsubscribed; 8 are zombies; and 9 are killed. Commands for listing groups and scanning for new articles will all use the numeric prefix as working level.
killed groups
No information on killed groups is stored or updated, which makes killed groups much easier to handle than subscribed groups.
zombie groups
Just like killed groups, only slightly less dead.
active file
The news server has to keep track of what articles it carries, and what groups exist. All this information in stored in the active file, which is rather large, as you might surmise.
bogus groups
A group that exists in the `.newsrc' file, but isn't known to the server (i.e., it isn't in the active file), is a bogus group. This means that the group probably doesn't exist (any more).
activating
The act of asking the server for info on a group and computing the number of unread articles is called activating the group. Un-activated groups are listed with `*' in the group buffer.
server
A machine one can connect to and get news (or mail) from.
select method
A structure that specifies the backend, the server and the virtual server settings.
virtual server
A named select method. Since a select method defines all there is to know about connecting to a (physical) server, taking the thing as a whole is a virtual server.
washing
Taking a buffer and running it through a filter of some sort. The result will (more often than not) be cleaner and more pleasing than the original.
ephemeral groups
Most groups store data on what articles you have read. Ephemeral groups are groups that will have no data stored--when you exit the group, it'll disappear into the aether.
solid groups
This is the opposite of ephemeral groups. All groups listed in the group buffer are solid groups.
sparse articles
These are article placeholders shown in the summary buffer when gnus-build-sparse-threads has been switched on.
threading
To put responses to articles directly after the articles they respond to--in a hierarchical fashion.
root
The first article in a thread is the root. It is the ancestor of all articles in the thread.
parent
An article that has responses.
child
An article that responds to a different article--its parent.
digest
A collection of messages in one file. The most common digest format is specified by RFC1153.

Customization

All variables are properly documented elsewhere in this manual. This section is designed to give general pointers on how to customize Gnus for some quite common situations.

Slow/Expensive NNTP Connection

If you run Emacs on a machine locally, and get your news from a machine over some very thin strings, you want to cut down on the amount of data Gnus has to get from the NNTP server.

gnus-read-active-file
Set this to nil, which will inhibit Gnus from requesting the entire active file from the server. This file is often v. large. You also have to set gnus-check-new-newsgroups and gnus-check-bogus-newsgroups to nil to make sure that Gnus doesn't suddenly decide to fetch the active file anyway.
gnus-nov-is-evil
This one has to be nil. If not, grabbing article headers from the NNTP server will not be very fast. Not all NNTP servers support XOVER; Gnus will detect this by itself.

Slow Terminal Connection

Let's say you use your home computer for dialing up the system that runs Emacs and Gnus. If your modem is slow, you want to reduce (as much as possible) the amount of data sent over the wires.

gnus-auto-center-summary
Set this to nil to inhibit Gnus from re-centering the summary buffer all the time. If it is vertical, do only vertical re-centering. If it is neither nil nor vertical, do both horizontal and vertical recentering.
gnus-visible-headers
Cut down on the headers included in the articles to the minimum. You can, in fact, make do without them altogether--most of the useful data is in the summary buffer, anyway. Set this variable to `^NEVVVVER' or `From:', or whatever you feel you need.
gnus-article-display-hook
Set this hook to all the available hiding commands:
(setq gnus-article-display-hook
      '(gnus-article-hide-headers
        gnus-article-hide-signature
        gnus-article-hide-citation))
gnus-use-full-window
By setting this to nil, you can make all the windows smaller. While this doesn't really cut down much generally, it means that you have to see smaller portions of articles before deciding that you didn't want to read them anyway.
gnus-thread-hide-subtree
If this is non-nil, all threads in the summary buffer will be hidden initially.
gnus-updated-mode-lines
If this is nil, Gnus will not put information in the buffer mode lines, which might save some time.

Little Disk Space

The startup files can get rather large, so you may want to cut their sizes a bit if you are running out of space.

gnus-save-newsrc-file
If this is nil, Gnus will never save `.newsrc'---it will only save `.newsrc.eld'. This means that you will not be able to use any other newsreaders than Gnus. This variable is t by default.
gnus-save-killed-list
If this is nil, Gnus will not save the list of dead groups. You should also set gnus-check-new-newsgroups to ask-server and gnus-check-bogus-newsgroups to nil if you set this variable to nil. This variable is t by default.

Slow Machine

If you have a slow machine, or are just really impatient, there are a few things you can do to make Gnus run faster.

Set gnus-check-new-newsgroups and gnus-check-bogus-newsgroups to nil to make startup faster.

Set gnus-show-threads, gnus-use-cross-reference and gnus-nov-is-evil to nil to make entering and exiting the summary buffer faster.

Set gnus-article-display-hook to nil to make article processing a bit faster.

Troubleshooting

Gnus works so well straight out of the box--I can't imagine any problems, really.

Ahem.

  1. Make sure your computer is switched on.
  2. Make sure that you really load the current Gnus version. If you have been running GNUS, you need to exit Emacs and start it up again before Gnus will work.
  3. Try doing an M-x gnus-version. If you get something that looks like `Gnus v5.46; nntp 4.0' you have the right files loaded. If, on the other hand, you get something like `NNTP 3.x' or `nntp flee', you have some old `.el' files lying around. Delete these.
  4. Read the help group (G h in the group buffer) for a FAQ and a how-to.
  5. Gnus works on many recursive structures, and in some extreme (and very rare) cases Gnus may recurse down "too deeply" and Emacs will beep at you. If this happens to you, set max-lisp-eval-depth to 500 or something like that.

If all else fails, report the problem as a bug.

If you find a bug in Gnus, you can report it with the M-x gnus-bug command. M-x set-variable RET debug-on-error RET t RET, and send me the backtrace. I will fix bugs, but I can only fix them if you send me a precise description as to how to reproduce the bug.

You really can never be too detailed in a bug report. Always use the M-x gnus-bug command when you make bug reports, even if it creates a 10Kb mail each time you use it, and even if you have sent me your environment 500 times before. I don't care. I want the full info each time.

It is also important to remember that I have no memory whatsoever. If you send a bug report, and I send you a reply, and then you just send back "No, it's not! Moron!", I will have no idea what you are insulting me about. Always over-explain everything. It's much easier for all of us--if I don't have all the information I need, I will just mail you and ask for more info, and everything takes more time.

If the problem you're seeing is very visual, and you can't quite explain it, copy the Emacs window to a file (with xwd, for instance), put it somewhere it can be reached, and include the URL of the picture in the bug report.

If you just need help, you are better off asking on `gnu.emacs.gnus'. I'm not very helpful.

You can also ask on the ding mailing list---`ding@gnus.org'. Write to `ding-request@gnus.org' to subscribe.

A Programmer's Guide to Gnus

It is my hope that other people will figure out smart stuff that Gnus can do, and that other people will write those smart things as well. To facilitate that I thought it would be a good idea to describe the inner workings of Gnus. And some of the not-so-inner workings, while I'm at it.

You can never expect the internals of a program not to change, but I will be defining (in some details) the interface between Gnus and its backends (this is written in stone), the format of the score files (ditto), data structures (some are less likely to change than others) and general methods of operation.

Gnus Utility Functions

When writing small functions to be run from hooks (and stuff), it's vital to have access to the Gnus internal functions and variables. Below is a list of the most common ones.

gnus-newsgroup-name
This variable holds the name of the current newsgroup.
gnus-find-method-for-group
A function that returns the select method for group.
gnus-group-real-name
Takes a full (prefixed) Gnus group name, and returns the unprefixed name.
gnus-group-prefixed-name
Takes an unprefixed group name and a select method, and returns the full (prefixed) Gnus group name.
gnus-get-info
Returns the group info list for group.
gnus-group-unread
The number of unread articles in group, or t if that is unknown.
gnus-active
The active entry for group.
gnus-set-active
Set the active entry for group.
gnus-add-current-to-buffer-list
Adds the current buffer to the list of buffers to be killed on Gnus exit.
gnus-continuum-version
Takes a Gnus version string as a parameter and returns a floating point number. Earlier versions will always get a lower number than later versions.
gnus-group-read-only-p
Says whether group is read-only or not.
gnus-news-group-p
Says whether group came from a news backend.
gnus-ephemeral-group-p
Says whether group is ephemeral or not.
gnus-server-to-method
Returns the select method corresponding to server.
gnus-server-equal
Says whether two virtual servers are equal.
gnus-group-native-p
Says whether group is native or not.
gnus-group-secondary-p
Says whether group is secondary or not.
gnus-group-foreign-p
Says whether group is foreign or not.
group-group-find-parameter
Returns the parameter list of group. If given a second parameter, returns the value of that parameter for group.
gnus-group-set-parameter
Takes three parameters; group, parameter and value.
gnus-narrow-to-body
Narrows the current buffer to the body of the article.
gnus-check-backend-function
Takes two parameters, function and group. If the backend group comes from supports function, return non-nil.
(gnus-check-backend-function "request-scan" "nnml:misc")
=> t
gnus-read-method
Prompts the user for a select method.

Backend Interface

Gnus doesn't know anything about NNTP, spools, mail or virtual groups. It only knows how to talk to virtual servers. A virtual server is a backend and some backend variables. As examples of the first, we have nntp, nnspool and nnmbox. As examples of the latter we have nntp-port-number and nnmbox-directory.

When Gnus asks for information from a backend--say nntp---on something, it will normally include a virtual server name in the function parameters. (If not, the backend should use the "current" virtual server.) For instance, nntp-request-list takes a virtual server as its only (optional) parameter. If this virtual server hasn't been opened, the function should fail.

Note that a virtual server name has no relation to some physical server name. Take this example:

(nntp "odd-one"
      (nntp-address "ifi.uio.no")
      (nntp-port-number 4324))

Here the virtual server name is `odd-one' while the name of the physical server is `ifi.uio.no'.

The backends should be able to switch between several virtual servers. The standard backends implement this by keeping an alist of virtual server environments that they pull down/push up when needed.

There are two groups of interface functions: required functions, which must be present, and optional functions, which Gnus will always check for presence before attempting to call 'em.

All these functions are expected to return data in the buffer nntp-server-buffer (` *nntpd*'), which is somewhat unfortunately named, but we'll have to live with it. When I talk about resulting data, I always refer to the data in that buffer. When I talk about return value, I talk about the function value returned by the function call. Functions that fail should return nil as the return value.

Some backends could be said to be server-forming backends, and some might be said not to be. The latter are backends that generally only operate on one group at a time, and have no concept of "server" -- they have a group, and they deliver info on that group and nothing more.

In the examples and definitions I will refer to the imaginary backend nnchoke.

Required Backend Functions

(nnchoke-retrieve-headers ARTICLES &optional GROUP SERVER FETCH-OLD)
articles is either a range of article numbers or a list of Message-IDs. Current backends do not fully support either--only sequences (lists) of article numbers, and most backends do not support retrieval of Message-IDs. But they should try for both. The result data should either be HEADs or NOV lines, and the result value should either be headers or nov to reflect this. This might later be expanded to various, which will be a mixture of HEADs and NOV lines, but this is currently not supported by Gnus. If fetch-old is non-nil it says to try fetching "extra headers", in some meaning of the word. This is generally done by fetching (at most) fetch-old extra headers less than the smallest article number in articles, and filling the gaps as well. The presence of this parameter can be ignored if the backend finds it cumbersome to follow the request. If this is non-nil and not a number, do maximum fetches. Here's an example HEAD:
221 1056 Article retrieved.
Path: ifi.uio.no!sturles
From: sturles@ifi.uio.no (Sturle Sunde)
Newsgroups: ifi.discussion
Subject: Re: Something very droll
Date: 27 Oct 1994 14:02:57 +0100
Organization: Dept. of Informatics, University of Oslo, Norway
Lines: 26
Message-ID: <38o8e1$a0o@holmenkollen.ifi.uio.no>
References: <38jdmq$4qu@visbur.ifi.uio.no>
NNTP-Posting-Host: holmenkollen.ifi.uio.no
.
So a headers return value would imply that there's a number of these in the data buffer. Here's a BNF definition of such a buffer:
headers        = *head
head           = error / valid-head
error-message  = [ "4" / "5" ] 2number " " <error message> eol
valid-head     = valid-message *header "." eol
valid-message  = "221 " <number> " Article retrieved." eol
header         = <text> eol
If the return value is nov, the data buffer should contain network overview database lines. These are basically fields separated by tabs.
nov-buffer = *nov-line
nov-line   = 8*9 [ field <TAB> ] eol
field      = <text except TAB>
For a closer look at what should be in those fields, see section Headers.
(nnchoke-open-server SERVER &optional DEFINITIONS)
server is here the virtual server name. definitions is a list of (VARIABLE VALUE) pairs that define this virtual server. If the server can't be opened, no error should be signaled. The backend may then choose to refuse further attempts at connecting to this server. In fact, it should do so. If the server is opened already, this function should return a non-nil value. There should be no data returned.
(nnchoke-close-server &optional SERVER)
Close connection to server and free all resources connected to it. Return nil if the server couldn't be closed for some reason. There should be no data returned.
(nnchoke-request-close)
Close connection to all servers and free all resources that the backend have reserved. All buffers that have been created by that backend should be killed. (Not the nntp-server-buffer, though.) This function is generally only called when Gnus is shutting down. There should be no data returned.
(nnchoke-server-opened &optional SERVER)
If server is the current virtual server, and the connection to the physical server is alive, then this function should return a non-nil vlue. This function should under no circumstances attempt to reconnect to a server we have lost connection to. There should be no data returned.
(nnchoke-status-message &optional SERVER)
This function should return the last error message from server. There should be no data returned.
(nnchoke-request-article ARTICLE &optional GROUP SERVER TO-BUFFER)
The result data from this function should be the article specified by article. This might either be a Message-ID or a number. It is optional whether to implement retrieval by Message-ID, but it would be nice if that were possible. If to-buffer is non-nil, the result data should be returned in this buffer instead of the normal data buffer. This is to make it possible to avoid copying large amounts of data from one buffer to another, while Gnus mainly requests articles to be inserted directly into its article buffer. If it is at all possible, this function should return a cons cell where the car is the group name the article was fetched from, and the cdr is the article number. This will enable Gnus to find out what the real group and article numbers are when fetching articles by Message-ID. If this isn't possible, t should be returned on successful article retrieval.
(nnchoke-request-group GROUP &optional SERVER FAST)
Get data on group. This function also has the side effect of making group the current group. If FAST, don't bother to return useful data, just make group the current group. Here's an example of some result data and a definition of the same:
211 56 1000 1059 ifi.discussion
The first number is the status, which should be 211. Next is the total number of articles in the group, the lowest article number, the highest article number, and finally the group name. Note that the total number of articles may be less than one might think while just considering the highest and lowest article numbers, but some articles may have been canceled. Gnus just discards the total-number, so whether one should take the bother to generate it properly (if that is a problem) is left as an exercise to the reader.
group-status = [ error / info ] eol
error        = [ "4" / "5" ] 2<number> " " <Error message>
info         = "211 " 3* [ <number> " " ] <string>
(nnchoke-close-group GROUP &optional SERVER)
Close group and free any resources connected to it. This will be a no-op on most backends. There should be no data returned.
(nnchoke-request-list &optional SERVER)
Return a list of all groups available on server. And that means all. Here's an example from a server that only carries two groups:
ifi.test 0000002200 0000002000 y
ifi.discussion 3324 3300 n
On each line we have a group name, then the highest article number in that group, the lowest article number, and finally a flag.
active-file = *active-line
active-line = name " " <number> " " <number> " " flags eol
name        = <string>
flags       = "n" / "y" / "m" / "x" / "j" / "=" name
The flag says whether the group is read-only (`n'), is moderated (`m'), is dead (`x'), is aliased to some other group (`=other-group') or none of the above (`y').
(nnchoke-request-post &optional SERVER)
This function should post the current buffer. It might return whether the posting was successful or not, but that's not required. If, for instance, the posting is done asynchronously, it has generally not been completed by the time this function concludes. In that case, this function should set up some kind of sentinel to beep the user loud and clear if the posting could not be completed. There should be no result data from this function.

Optional Backend Functions

(nnchoke-retrieve-groups GROUPS &optional SERVER)
groups is a list of groups, and this function should request data on all those groups. How it does it is of no concern to Gnus, but it should attempt to do this in a speedy fashion. The return value of this function can be either active or group, which says what the format of the result data is. The former is in the same format as the data from nnchoke-request-list, while the latter is a buffer full of lines in the same format as nnchoke-request-group gives.
group-buffer = *active-line / *group-status
(nnchoke-request-update-info GROUP INFO &optional SERVER)
A Gnus group info (see section Group Info) is handed to the backend for alterations. This comes in handy if the backend really carries all the information (as is the case with virtual and imap groups). This function should destructively alter the info to suit its needs, and should return the (altered) group info. There should be no result data from this function.
(nnchoke-request-type GROUP &optional ARTICLE)
When the user issues commands for "sending news" (F in the summary buffer, for instance), Gnus has to know whether the article the user is following up on is news or mail. This function should return news if article in group is news, mail if it is mail and unknown if the type can't be decided. (The article parameter is necessary in nnvirtual groups which might very well combine mail groups and news groups.) Both group and article may be nil. There should be no result data from this function.
(nnchoke-request-update-mark GROUP ARTICLE MARK)
If the user tries to set a mark that the backend doesn't like, this function may change the mark. Gnus will use whatever this function returns as the mark for article instead of the original mark. If the backend doesn't care, it must return the original mark, and not nil or any other type of garbage. The only use for this I can see is what nnvirtual does with it--if a component group is auto-expirable, marking an article as read in the virtual group should result in the article being marked as expirable. There should be no result data from this function.
(nnchoke-request-scan &optional GROUP SERVER)
This function may be called at any time (by Gnus or anything else) to request that the backend check for incoming articles, in one way or another. A mail backend will typically read the spool file or query the POP server when this function is invoked. The group doesn't have to be heeded--if the backend decides that it is too much work just scanning for a single group, it may do a total scan of all groups. It would be nice, however, to keep things local if that's practical. There should be no result data from this function.
(nnchoke-request-group-description GROUP &optional SERVER)
The result data from this function should be a description of group.
description-line = name <TAB> description eol
name             = <string>
description      = <text>
(nnchoke-request-list-newsgroups &optional SERVER)
The result data from this function should be the description of all groups available on the server.
description-buffer = *description-line
(nnchoke-request-newgroups DATE &optional SERVER)
The result data from this function should be all groups that were created after `date', which is in normal human-readable date format. The data should be in the active buffer format.
(nnchoke-request-create-group GROUP &optional SERVER)
This function should create an empty group with name group. There should be no return data.
(nnchoke-request-expire-articles ARTICLES &optional GROUP SERVER FORCE)
This function should run the expiry process on all articles in the articles range (which is currently a simple list of article numbers.) It is left up to the backend to decide how old articles should be before they are removed by this function. If force is non-nil, all articles should be deleted, no matter how new they are. This function should return a list of articles that it did not/was not able to delete. There should be no result data returned.
(nnchoke-request-move-article ARTICLE GROUP SERVER ACCEPT-FORM
&optional LAST) This function should move article (which is a number) from group by calling accept-form. This function should ready the article in question for moving by removing any header lines it has added to the article, and generally should "tidy up" the article. Then it should eval accept-form in the buffer where the "tidy" article is. This will do the actual copying. If this eval returns a non-nil value, the article should be removed. If last is nil, that means that there is a high likelihood that there will be more requests issued shortly, so that allows some optimizations. The function should return a cons where the car is the group name and the cdr is the article number that the article was entered as. There should be no data returned.
(nnchoke-request-accept-article GROUP &optional SERVER LAST)
This function takes the current buffer and inserts it into group. If last in nil, that means that there will be more calls to this function in short order. The function should return a cons where the car is the group name and the cdr is the article number that the article was entered as. There should be no data returned.
(nnchoke-request-replace-article ARTICLE GROUP BUFFER)
This function should remove article (which is a number) from group and insert buffer there instead. There should be no data returned.
(nnchoke-request-delete-group GROUP FORCE &optional SERVER)
This function should delete group. If force, it should really delete all the articles in the group, and then delete the group itself. (If there is such a thing as "the group itself".) There should be no data returned.
(nnchoke-request-rename-group GROUP NEW-NAME &optional SERVER)
This function should rename group into new-name. All articles in group should move to new-name. There should be no data returned.

Error Messaging

The backends should use the function nnheader-report to report error conditions--they should not raise errors when they aren't able to perform a request. The first argument to this function is the backend symbol, and the rest are interpreted as arguments to format if there are multiple of them, or just a string if there is one of them. This function must always returns nil.

(nnheader-report 'nnchoke "You did something totally bogus")

(nnheader-report 'nnchoke "Could not request group %s" group)

Gnus, in turn, will call nnheader-get-report when it gets a nil back from a server, and this function returns the most recently reported message for the backend in question. This function takes one argument--the server symbol.

Internally, these functions access backend-status-string, so the nnchoke backend will have its error message stored in nnchoke-status-string.

Writing New Backends

Many backends are quite similar. nnml is just like nnspool, but it allows you to edit the articles on the server. nnmh is just like nnml, but it doesn't use an active file, and it doesn't maintain overview databases. nndir is just like nnml, but it has no concept of "groups", and it doesn't allow editing articles.

It would make sense if it were possible to "inherit" functions from backends when writing new backends. And, indeed, you can do that if you want to. (You don't have to if you don't want to, of course.)

All the backends declare their public variables and functions by using a package called nnoo.

To inherit functions from other backends (and allow other backends to inherit functions from the current backend), you should use the following macros:

nnoo-declare
This macro declares the first parameter to be a child of the subsequent parameters. For instance:
(nnoo-declare nndir
  nnml nnmh)
nndir has declared here that it intends to inherit functions from both nnml and nnmh.
defvoo
This macro is equivalent to defvar, but registers the variable as a public server variable. Most state-oriented variables should be declared with defvoo instead of defvar. In addition to the normal defvar parameters, it takes a list of variables in the parent backends to map the variable to when executing a function in those backends.
(defvoo nndir-directory nil
  "Where nndir will look for groups."
  nnml-current-directory nnmh-current-directory)
This means that nnml-current-directory will be set to nndir-directory when an nnml function is called on behalf of nndir. (The same with nnmh.)
nnoo-define-basics
This macro defines some common functions that almost all backends should have.
(nnoo-define-basics nndir)
deffoo
This macro is just like defun and takes the same parameters. In addition to doing the normal defun things, it registers the function as being public so that other backends can inherit it.
nnoo-map-functions
This macro allows mapping of functions from the current backend to functions from the parent backends.
(nnoo-map-functions nndir
  (nnml-retrieve-headers 0 nndir-current-group 0 0)
  (nnmh-request-article 0 nndir-current-group 0 0))
This means that when nndir-retrieve-headers is called, the first, third, and fourth parameters will be passed on to nnml-retrieve-headers, while the second parameter is set to the value of nndir-current-group.
nnoo-import
This macro allows importing functions from backends. It should be the last thing in the source file, since it will only define functions that haven't already been defined.
(nnoo-import nndir
  (nnmh
   nnmh-request-list
   nnmh-request-newgroups)
  (nnml))
This means that calls to nndir-request-list should just be passed on to nnmh-request-list, while all public functions from nnml that haven't been defined in nndir yet should be defined now.

Below is a slightly shortened version of the nndir backend.

;;; nndir.el -- single directory newsgroup access for Gnus
;; Copyright (C) 1995,96 Free Software Foundation, Inc.

;;; Code:

(require 'nnheader)
(require 'nnmh)
(require 'nnml)
(require 'nnoo)
(eval-when-compile (require 'cl))

(nnoo-declare nndir
  nnml nnmh)

(defvoo nndir-directory nil
  "Where nndir will look for groups."
  nnml-current-directory nnmh-current-directory)

(defvoo nndir-nov-is-evil nil
  "*Non-nil means that nndir will never retrieve NOV headers."
  nnml-nov-is-evil)

(defvoo nndir-current-group "" nil nnml-current-group nnmh-current-group)
(defvoo nndir-top-directory nil nil nnml-directory nnmh-directory)
(defvoo nndir-get-new-mail nil nil nnml-get-new-mail nnmh-get-new-mail)

(defvoo nndir-status-string "" nil nnmh-status-string)
(defconst nndir-version "nndir 1.0")

;;; Interface functions.

(nnoo-define-basics nndir)

(deffoo nndir-open-server (server &optional defs)
  (setq nndir-directory
        (or (cadr (assq 'nndir-directory defs))
            server))
  (unless (assq 'nndir-directory defs)
    (push `(nndir-directory ,server) defs))
  (push `(nndir-current-group
          ,(file-name-nondirectory (directory-file-name nndir-directory)))
        defs)
  (push `(nndir-top-directory
          ,(file-name-directory (directory-file-name nndir-directory)))
        defs)
  (nnoo-change-server 'nndir server defs))

(nnoo-map-functions nndir
  (nnml-retrieve-headers 0 nndir-current-group 0 0)
  (nnmh-request-article 0 nndir-current-group 0 0)
  (nnmh-request-group nndir-current-group 0 0)
  (nnmh-close-group nndir-current-group 0))

(nnoo-import nndir
  (nnmh
   nnmh-status-message
   nnmh-request-list
   nnmh-request-newgroups))

(provide 'nndir)

Hooking New Backends Into Gnus

Having Gnus start using your new backend is rather easy--you just declare it with the gnus-declare-backend functions. This will enter the backend into the gnus-valid-select-methods variable.

gnus-declare-backend takes two parameters--the backend name and an arbitrary number of abilities.

Here's an example:

(gnus-declare-backend "nnchoke" 'mail 'respool 'address)

The abilities can be:

mail
This is a mailish backend--followups should (probably) go via mail.
post
This is a newsish backend--followups should (probably) go via news.
post-mail
This backend supports both mail and news.
none
This is neither a post nor mail backend--it's something completely different.
respool
It supports respooling--or rather, it is able to modify its source articles and groups.
address
The name of the server should be in the virtual server name. This is true for almost all backends.
prompt-address
The user should be prompted for an address when doing commands like B in the group buffer. This is true for backends like nntp, but not nnmbox, for instance.

Mail-like Backends

One of the things that separate the mail backends from the rest of the backends is the heavy dependence by the mail backends on common functions in `nnmail.el'. For instance, here's the definition of nnml-request-scan:

(deffoo nnml-request-scan (&optional group server)
  (setq nnml-article-file-alist nil)
  (nnmail-get-new-mail 'nnml 'nnml-save-nov nnml-directory group))

It simply calls nnmail-get-new-mail with a few parameters, and nnmail takes care of all the moving and splitting of the mail.

This function takes four parameters.

method
This should be a symbol to designate which backend is responsible for the call.
exit-function
This function should be called after the splitting has been performed.
temp-directory
Where the temporary files should be stored.
group
This optional argument should be a group name if the splitting is to be performed for one group only.

nnmail-get-new-mail will call backend-save-mail to save each article. backend-active-number will be called to find the article number assigned to this article.

The function also uses the following variables: backend-get-new-mail (to see whether to get new mail for this backend); and backend-group-alist and backend-active-file to generate the new active file. backend-group-alist should be a group-active alist, like this:

(("a-group" (1 . 10))
 ("some-group" (34 . 39)))

Score File Syntax

Score files are meant to be easily parseable, but yet extremely mallable. It was decided that something that had the same read syntax as an Emacs Lisp list would fit that spec.

Here's a typical score file:

(("summary"
  ("win95" -10000 nil s)
  ("Gnus"))
 ("from"
  ("Lars" -1000))
 (mark -100))

BNF definition of a score file:

score-file       = "" / "(" *element ")"
element          = rule / atom
rule             = string-rule / number-rule / date-rule
string-rule      = "(" quote string-header quote space *string-match ")"
number-rule      = "(" quote number-header quote space *number-match ")"
date-rule        = "(" quote date-header quote space *date-match ")"
quote            = <ascii 34>
string-header    = "subject" / "from" / "references" / "message-id" /
                   "xref" / "body" / "head" / "all" / "followup"
number-header    = "lines" / "chars"
date-header      = "date"
string-match     = "(" quote <string> quote [ "" / [ space score [ "" /
                   space date [ "" / [ space string-match-t ] ] ] ] ] ")"
score            = "nil" / <integer>
date             = "nil" / <natural number>
string-match-t   = "nil" / "s" / "substring" / "S" / "Substring" /
                   "r" / "regex" / "R" / "Regex" /
                   "e" / "exact" / "E" / "Exact" /
                   "f" / "fuzzy" / "F" / "Fuzzy"
number-match     = "(" <integer> [ "" / [ space score [ "" /
                   space date [ "" / [ space number-match-t ] ] ] ] ] ")"
number-match-t   = "nil" / "=" / "<" / ">" / ">=" / "<="
date-match       = "(" quote <string> quote [ "" / [ space score [ "" /
                   space date [ "" / [ space date-match-t ] ] ] ] ")"
date-match-t     = "nil" / "at" / "before" / "after"
atom             = "(" [ required-atom / optional-atom ] ")"
required-atom    = mark / expunge / mark-and-expunge / files /
                   exclude-files / read-only / touched
optional-atom    = adapt / local / eval
mark             = "mark" space nil-or-number
nil-or-number    = "nil" / <integer>
expunge          = "expunge" space nil-or-number
mark-and-expunge = "mark-and-expunge" space nil-or-number
files            = "files" *[ space <string> ]
exclude-files    = "exclude-files" *[ space <string> ]
read-only        = "read-only" [ space "nil" / space "t" ]
adapt            = "adapt" [ space "ignore" / space "t" / space adapt-rule ]
adapt-rule       = "(" *[ <string> *[ "(" <string> <integer> ")" ] ")"
local            = "local" *[ space "(" <string> space <form> ")" ]
eval             = "eval" space <form>
space            = *[ " " / <TAB> / <NEWLINE> ]

Any unrecognized elements in a score file should be ignored, but not discarded.

As you can see, white space is needed, but the type and amount of white space is irrelevant. This means that formatting of the score file is left up to the programmer--if it's simpler to just spew it all out on one looong line, then that's ok.

The meaning of the various atoms are explained elsewhere in this manual (see section Score File Format).

Headers

Internally Gnus uses a format for storing article headers that corresponds to the NOV format in a mysterious fashion. One could almost suspect that the author looked at the NOV specification and just shamelessly stole the entire thing, and one would be right.

Header is a severely overloaded term. "Header" is used in RFC1036 to talk about lines in the head of an article (e.g., From). It is used by many people as a synonym for "head"---"the header and the body". (That should be avoided, in my opinion.) And Gnus uses a format internally that it calls "header", which is what I'm talking about here. This is a 9-element vector, basically, with each header (ouch) having one slot.

These slots are, in order: number, subject, from, date, id, references, chars, lines, xref. There are macros for accessing and setting these slots--they all have predictable names beginning with mail-header- and mail-header-set-, respectively.

The xref slot is really a misc slot. Any extra info will be put in there.

Ranges

GNUS introduced a concept that I found so useful that I've started using it a lot and have elaborated on it greatly.

The question is simple: If you have a large amount of objects that are identified by numbers (say, articles, to take a wild example) that you want to qualify as being "included", a normal sequence isn't very useful. (A 200,000 length sequence is a bit long-winded.)

The solution is as simple as the question: You just collapse the sequence.

(1 2 3 4 5 6 10 11 12)

is transformed into

((1 . 6) (10 . 12))

To avoid having those nasty `(13 . 13)' elements to denote a lonesome object, a `13' is a valid element:

((1 . 6) 7 (10 . 12))

This means that comparing two ranges to find out whether they are equal is slightly tricky:

((1 . 5) 7 8 (10 . 12))

and

((1 . 5) (7 . 8) (10 . 12))

are equal. In fact, any non-descending list is a range:

(1 2 3 4 5)

is a perfectly valid range, although a pretty long-winded one. This is also valid:

(1 . 5)

and is equal to the previous range.

Here's a BNF definition of ranges. Of course, one must remember the semantic requirement that the numbers are non-descending. (Any number of repetition of the same number is allowed, but apt to disappear in range handling.)

range           = simple-range / normal-range
simple-range    = "(" number " . " number ")"
normal-range    = "(" start-contents ")"
contents        = "" / simple-range *[ " " contents ] /
                  number *[ " " contents ]

Gnus currently uses ranges to keep track of read articles and article marks. I plan on implementing a number of range operators in C if The Powers That Be are willing to let me. (I haven't asked yet, because I need to do some more thinking on what operators I need to make life totally range-based without ever having to convert back to normal sequences.)

Group Info

Gnus stores all permanent info on groups in a group info list. This list is from three to six elements (or more) long and exhaustively describes the group.

Here are two example group infos; one is a very simple group while the second is a more complex one:

("no.group" 5 (1 . 54324))

("nnml:my.mail" 3 ((1 . 5) 9 (20 . 55))
                ((tick (15 . 19)) (replied 3 6 (19 . 3)))
                (nnml "")
                ((auto-expire . t) (to-address . "ding@gnus.org")))

The first element is the group name---as Gnus knows the group, anyway. The second element is the subscription level, which normally is a small integer. (It can also be the rank, which is a cons cell where the car is the level and the cdr is the score.) The third element is a list of ranges of read articles. The fourth element is a list of lists of article marks of various kinds. The fifth element is the select method (or virtual server, if you like). The sixth element is a list of group parameters, which is what this section is about.

Any of the last three elements may be missing if they are not required. In fact, the vast majority of groups will normally only have the first three elements, which saves quite a lot of cons cells.

Here's a BNF definition of the group info format:

info          = "(" group space ralevel space read
                [ "" / [ space marks-list [ "" / [ space method [ "" /
                space parameters ] ] ] ] ] ")"
group         = quote <string> quote
ralevel       = rank / level
level         = <integer in the range of 1 to inf>
rank          = "(" level "." score ")"
score         = <integer in the range of 1 to inf>
read          = range
marks-lists   = nil / "(" *marks ")"
marks         = "(" <string> range ")"
method        = "(" <string> *elisp-forms ")"
parameters    = "(" *elisp-forms ")"

Actually that `marks' rule is a fib. A `marks' is a `<string>' consed on to a `range', but that's a bitch to say in pseudo-BNF.

If you have a Gnus info and want to access the elements, Gnus offers a series of macros for getting/setting these elements.

gnus-info-group
gnus-info-set-group
Get/set the group name.
gnus-info-rank
gnus-info-set-rank
Get/set the group rank (see section Group Score).
gnus-info-level
gnus-info-set-level
Get/set the group level.
gnus-info-score
gnus-info-set-score
Get/set the group score (see section Group Score).
gnus-info-read
gnus-info-set-read
Get/set the ranges of read articles.
gnus-info-marks
gnus-info-set-marks
Get/set the lists of ranges of marked articles.
gnus-info-method
gnus-info-set-method
Get/set the group select method.
gnus-info-params
gnus-info-set-params
Get/set the group parameters.

All the getter functions take one parameter--the info list. The setter functions take two parameters--the info list and the new value.

The last three elements in the group info aren't mandatory, so it may be necessary to extend the group info before setting the element. If this is necessary, you can just pass on a non-nil third parameter to the three final setter functions to have this happen automatically.

Extended Interactive

Gnus extends the standard Emacs interactive specification slightly to allow easy use of the symbolic prefix (see section Symbolic Prefixes). Here's an example of how this is used:

(defun gnus-summary-increase-score (&optional score symp)
  (interactive (gnus-interactive "P\ny"))
  ...
  )

The best thing to do would have been to implement gnus-interactive as a macro which would have returned an interactive form, but this isn't possible since Emacs checks whether a function is interactive or not by simply doing an assq on the lambda form. So, instead we have gnus-interactive function that takes a string and returns values that are usable to interactive.

This function accepts (almost) all normal interactive specs, but adds a few more.

`y'
The current symbolic prefix--the gnus-current-prefix-symbol variable.
`Y'
A list of the current symbolic prefixes--the gnus-current-prefix-symbol variable.
`A'
The current article number--the gnus-summary-article-number function.
`H'
The current article header--the gnus-summary-article-header function.
`g'
The current group name--the gnus-group-group-name function.

Emacs/XEmacs Code

While Gnus runs under Emacs, XEmacs and Mule, I decided that one of the platforms must be the primary one. I chose Emacs. Not because I don't like XEmacs or Mule, but because it comes first alphabetically.

This means that Gnus will byte-compile under Emacs with nary a warning, while XEmacs will pump out gigabytes of warnings while byte-compiling. As I use byte-compilation warnings to help me root out trivial errors in Gnus, that's very useful.

I've also consistently used Emacs function interfaces, but have used Gnusey aliases for the functions. To take an example: Emacs defines a run-at-time function while XEmacs defines a start-itimer function. I then define a function called gnus-run-at-time that takes the same parameters as the Emacs run-at-time. When running Gnus under Emacs, the former function is just an alias for the latter. However, when running under XEmacs, the former is an alias for the following function:

(defun gnus-xmas-run-at-time (time repeat function &rest args)
  (start-itimer
   "gnus-run-at-time"
   `(lambda ()
      (,function ,@args))
   time repeat))

This sort of thing has been done for bunches of functions. Gnus does not redefine any native Emacs functions while running under XEmacs--it does this defalias thing with Gnus equivalents instead. Cleaner all over.

In the cases where the XEmacs function interface was obviously cleaner, I used it instead. For example gnus-region-active-p is an alias for region-active-p in XEmacs, whereas in Emacs it is a function.

Of course, I could have chosen XEmacs as my native platform and done mapping functions the other way around. But I didn't. The performance hit these indirections impose on Gnus under XEmacs should be slight.

Various File Formats

Active File Format

The active file lists all groups available on the server in question. It also lists the highest and lowest current article numbers in each group.

Here's an excerpt from a typical active file:

soc.motss 296030 293865 y
alt.binaries.pictures.fractals 3922 3913 n
comp.sources.unix 1605 1593 m
comp.binaries.ibm.pc 5097 5089 y
no.general 1000 900 y

Here's a pseudo-BNF definition of this file:

active      = *group-line
group-line  = group space high-number space low-number space flag <NEWLINE>
group       = <non-white-space string>
space       = " "
high-number = <non-negative integer>
low-number  = <positive integer>
flag        = "y" / "n" / "m" / "j" / "x" / "=" group

For a full description of this file, see the manual pages for `innd', in particular `active(5)'.

Newsgroups File Format

The newsgroups file lists groups along with their descriptions. Not all groups on the server have to be listed, and not all groups in the file have to exist on the server. The file is meant purely as information to the user.

The format is quite simple; a group name, a tab, and the description. Here's the definition:

newsgroups    = *line
line          = group tab description <NEWLINE>
group         = <non-white-space string>
tab           = <TAB>
description   = <string>

Emacs for Heathens

Believe it or not, but some people who use Gnus haven't really used Emacs much before they embarked on their journey on the Gnus Love Boat. If you are one of those unfortunates whom "M-C-a", "kill the region", and "set gnus-flargblossen to an alist where the key is a regexp that is used for matching on the group name" are magical phrases with little or no meaning, then this appendix is for you. If you are already familiar with Emacs, just ignore this and go fondle your cat instead.

Keystrokes

Yes, when you use Emacs, you are apt to use the control key, the shift key and the meta key a lot. This is very annoying to some people (notably vile users), and the rest of us just love the hell out of it. Just give up and submit. Emacs really does stand for "Escape-Meta-Alt-Control-Shift", and not "Editing Macros", as you may have heard from other disreputable sources (like the Emacs author).

The shift keys are normally located near your pinky fingers, and are normally used to get capital letters and stuff. You probably use it all the time. The control key is normally marked "CTRL" or something like that. The meta key is, funnily enough, never marked as such on any keyboard. The one I'm currently at has a key that's marked "Alt", which is the meta key on this keyboard. It's usually located somewhere to the left hand side of the keyboard, usually on the bottom row.

Now, us Emacs people don't say "press the meta-control-m key", because that's just too inconvenient. We say "press the M-C-m key". M- is the prefix that means "meta" and "C-" is the prefix that means "control". So "press C-k" means "press down the control key, and hold it down while you press k". "Press M-C-k" means "press down and hold down the meta key and the control key and then press k". Simple, ay?

This is somewhat complicated by the fact that not all keyboards have a meta key. In that case you can use the "escape" key. Then M-k means "press escape, release escape, press k". That's much more work than if you have a meta key, so if that's the case, I respectfully suggest you get a real keyboard with a meta key. You can't live without it.

Emacs Lisp

Emacs is the King of Editors because it's really a Lisp interpreter. Each and every key you tap runs some Emacs Lisp code snippet, and since Emacs Lisp is an interpreted language, that means that you can configure any key to run any arbitrary code. You just, like, do it.

Gnus is written in Emacs Lisp, and is run as a bunch of interpreted functions. (These are byte-compiled for speed, but it's still interpreted.) If you decide that you don't like the way Gnus does certain things, it's trivial to have it do something a different way. (Well, at least if you know how to write Lisp code.) However, that's beyond the scope of this manual, so we are simply going to talk about some common constructs that you normally use in your `.emacs' file to customize Gnus.

If you want to set the variable gnus-florgbnize to four (4), you write the following:

(setq gnus-florgbnize 4)

This function (really "special form") setq is the one that can set a variable to some value. This is really all you need to know. Now you can go and fill your .emacs file with lots of these to change how Gnus works.

If you have put that thing in your .emacs file, it will be read and evaled (which is lisp-ese for "run") the next time you start Emacs. If you want to change the variable right away, simply say C-x C-e after the closing parenthesis. That will eval the previous "form", which is a simple setq statement here.

Go ahead--just try it, if you're located at your Emacs. After you C-x C-e, you will see `4' appear in the echo area, which is the return value of the form you evaled.

Some pitfalls:

If the manual says "set gnus-read-active-file to some", that means:

(setq gnus-read-active-file 'some)

On the other hand, if the manual says "set gnus-nntp-server to `nntp.ifi.uio.no'", that means:

(setq gnus-nntp-server "nntp.ifi.uio.no")

So be careful not to mix up strings (the latter) with symbols (the former). The manual is unambiguous, but it can be confusing.

Frequently Asked Questions

This is the Gnus Frequently Asked Questions list. If you have a Web browser, the official hypertext version is at `http://www.ccs.neu.edu/software/gnus/', and has probably been updated since you got this manual.

Installation

Customization

Reading News

Reading Mail


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