Error Messaging Backend Interface Hooking New Backends Into Gnus
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
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
To inherit functions from other backends (and allow other backends to inherit functions from the current backend), you should use the following macros:
This macro declares the first parameter to be a child of the subsequent parameters. For instance:
This macro is equivalent to
In addition to the normal
This means that
This macro defines some common functions that almost all backends should have.
This macro is just like
This macro allows mapping of functions from the current backend to functions from the parent backends.
This means that when
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.
This means that calls to
Below is a slightly shortened version of the
;;; 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)