;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015, 2018 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix 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 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (gnu system nss)
#:use-module (rnrs enums)
#:use-module (guix records)
#:use-module (srfi srfi-9)
#:use-module (ice-9 match)
#:export (name-service-switch?
name-service-switch
name-service?
name-service
lookup-specification
%default-nss
%mdns-host-lookup-nss
%files
%compat
%dns
name-service-switch->string))
;;; Commentary:
;;;
;;; Bindings for libc's name service switch (NSS) configuration.
;;;
;;; Code:
(define-record-type* <name-service> name-service
make-name-service
name-service?
(name name-service-name)
(reaction name-service-reaction
(default (lookup-specification))))
;; Lookup specification (info "(libc) Actions in the NSS Configuration").
(define-enumeration lookup-action
(return continue)
make-lookup-action)
(define-enumeration lookup-status
(success
not-found
unavailable
try-again)
make-lookup-status)
(define-record-type <lookup-status-negation>
(lookup-status-negation status)
lookup-status-negation?
(status lookup-status-negation-status))
(define-record-type <lookup-reaction>
(make-lookup-reaction status action)
lookup-reaction?
(status lookup-reaction-status)
(action lookup-reaction-action))
(define-syntax lookup-reaction
(syntax-rules (not =>)
((_ ((not status) => action))
(make-lookup-reaction (lookup-status-negation (lookup-status status))
(lookup-action action)))
((_ (status => action))
(make-lookup-reaction (lookup-status status)
(lookup-action action)))))
(define-syntax-rule (lookup-specification reaction ...)
"Return an NSS lookup specification."
(list (lookup-reaction reaction) ...))
;;;
;;; Common name services and default NSS configuration.
;;;
(define %compat
;; Note: Starting from version 2.26, libc no longer provides libnss_compat
;; so this specification has become useless.
(name-service
(name "compat")
(reaction (lookup-specification (not-found => return)))))
(define %files
(name-service (name "files")))
(define %dns
;; DNS is supposed to be authoritative, so unless it's unavailable, return
;; what it finds.
(name-service
(name "dns")
(reaction (lookup-specification ((not unavailable) => return)))))
;; The NSS. We list all the databases here because that allows us to
;; statically ensure that the user's configuration refers to existing
;; databases. See libc/nss/databases.def for the list of databases. Default
;; values obtained by looking for "DEFAULT_CONFIG" in libc/nss/*.c.
;;
;; Although libc places 'dns' before 'files' in the default configurations of
;; the 'hosts' and 'networks' databases, we choose to put 'files' before 'dns'
;; by default, so that users can override host/address mappings in /etc/hosts
;; and bypass DNS to improve their privacy and escape NSA's MORECOWBELL.
(define-record-type* <name-service-switch> name-service-switch
make-name-service-switch
name-service-switch?
(aliases name-service-switch-aliases
(default '()))
(ethers name-service-switch-ethers
(default '()))
(group name-service-switch-group
(default (list %files)))
(gshadow name-service-switch-gshadow
(default '()))
(hosts name-service-switch-hosts
(default (list %files %dns)))
(initgroups name-service-switch-initgroups
(default '()))
(netgroup name-service-switch-netgroup
(default '()))
(networks name-service-switch-networks
(default (list %files %dns)))
(password name-service-switch-password
(default (list %files)))
(public-key name-service-switch-public-key
(default '()))
(rpc name-service-switch-rpc
(default '()))
(services name-service-switch-services
(default '()))
(shadow name-service-switch-shadow
(default (list %files))))
(define %default-nss
;; Default NSS configuration.
(name-service-switch))
(define %mdns-host-lookup-nss
(name-service-switch
(hosts (list %files ;first, check /etc/hosts
;; If the above did not succeed, try with 'mdns_minimal'.
(name-service
(name "mdns_minimal")
;; 'mdns_minimal' is authoritative for '.local'. When it
;; returns "not found", no need to try the next methods.
(reaction (lookup-specification
(not-found => return))))
;; Then fall back to DNS.
(name-service
(name "dns"))
;; Finally, try with the "full" 'mdns'.
(name-service
(name "mdns"))))))
;;;
;;; Serialization.
;;;
(define (lookup-status->string status)
(match status
('success "SUCCESS")
('not-found "NOTFOUND")
('unavailable "UNAVAIL")
('try-again "TRYAGAIN")
(($ <lookup-status-negation> status)
(string-append "!" (lookup-status->string status)))))
(define lookup-reaction->string
(match-lambda
(($ <lookup-reaction> status action)
(string-append (lookup-status->string status) "="
(symbol->string action)))))
(define name-service->string
(match-lambda
(($ <name-service> name ())
name)
(($ <name-service> name reactions)
(string-append name " ["
(string-join (map lookup-reaction->string reactions))
"]"))))
(define (name-service-switch->string nss)
"Return the 'nsswitch.conf' contents for NSS as a string. See \"NSS
Configuration File\" in the libc manual."
(let-syntax ((->string
(syntax-rules ()
((_ name field)
(match (field nss)
(() ;keep the default config
"")
((services (... ...))
(string-append name ":\t"
(string-join
(map name-service->string services))
"\n")))))))
(string-append (->string "aliases" name-service-switch-aliases)
(->string "ethers" name-service-switch-ethers)
(->string "group" name-service-switch-group)
(->string "gshadow" name-service-switch-gshadow)
(->string "hosts" name-service-switch-hosts)
(->string "initgroups" name-service-switch-initgroups)
(->string "netgroup" name-service-switch-netgroup)
(->string "networks" name-service-switch-networks)
(->string "passwd" name-service-switch-password)
(->string "publickey" name-service-switch-public-key)
(->string "rpc" name-service-switch-rpc)
(->string "services" name-service-switch-services)
(->string "shadow" name-service-switch-shadow))))
;;; Local Variables:
;;; eval: (put 'name-service 'scheme-indent-function 0)
;;; eval: (put 'name-service-switch 'scheme-indent-function 0)
;;; End:
;;; nss.scm ends here
