Subject: Re: [bug#37295] [PATCHv3] services: ntp: Support different NTP server types and options.

From: Maxim Cournoyer <[email-masked]>
Date: Tue, 03 Sep 2019 17:04:27 +0900

Hello Efraim,

Efraim Flashner <[email-masked]> writes:

> Can you check how this affects the openntpd service? It currently also
> uses %ntp-servers

I had overlooked this important detail; thanks for pointing it out!

I made the simplest change possible, by introducing a %openntpd-servers
variable that holds a list of addresses (strings), which is defined as
(map ntp-server-address %ntp-servers).  This variable is used as the new
default value for the "servers" field of the openntpd-configuration
record.  See the attached patch for details.

>From 98d246ba9c0119e6a2441c635193cc34b7218b4e Mon Sep 17 00:00:00 2001
From: Maxim Cournoyer <[email-masked]>
Date: Tue, 3 Sep 2019 10:14:59 +0900
Subject: [PATCH] services: ntp: Support different NTP server types and
 options.

* gnu/services/networking.scm (ntp-server-types): New enum.
(<ntp-server>): New record type.
(ntp-server->string): New procedure.
(%ntp-servers): Define in terms of <htp-server> records.  Use the first
entrypoint server as a pool instead of a list of static servers.  This is more
resilient since a new server of the pool can be interrogated on every
request.  Add the 'iburst' options.
(ntp-configuration-servers): Define a custom accessor that warns but honors
the now deprecated server format.
(<ntp-configuration>): Use it.
(%openntpd-servers): New variable,
(<openntpd-configuration>): Use it, as a pool ('servers' field) instead of a
regular server.
* tests/networking.scm: New file.
* Makefile.am (SCM_TESTS): Register it.
* doc/guix.texi: Update documentation.
---
 Makefile.am                 |   1 +
 doc/guix.texi               |  40 +++++++++++--
 gnu/services/networking.scm | 108 ++++++++++++++++++++++++++++++------
 tests/networking.scm        |  50 +++++++++++++++++
 4 files changed, 177 insertions(+), 22 deletions(-)
 create mode 100644 tests/networking.scm

diff --git a/Makefile.am b/Makefile.am
index fa6bf8fe80..32d518acbd 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -399,6 +399,7 @@ SCM_TESTS =					\
   tests/modules.scm				\
   tests/monads.scm				\
   tests/nar.scm				\
+  tests/networking.scm				\
   tests/opam.scm				\
   tests/packages.scm				\
   tests/pack.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 9de0957d14..12bb1c18e2 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -12988,8 +12988,9 @@ This is the data type for the NTP service configuration.
 
 @table @asis
 @item @code{servers} (default: @code{%ntp-servers})
-This is the list of servers (host names) with which @command{ntpd} will be
-synchronized.
+This is the list of servers (@code{<ntp-server>} records) with which
+@command{ntpd} will be synchronized.  See the @code{ntp-server} data type
+definition below.
 
 @item @code{allow-large-adjustment?} (default: @code{#t})
 This determines whether @command{ntpd} is allowed to make an initial
@@ -13005,6 +13006,32 @@ List of host names used as the default NTP servers.  These are servers of the
 @uref{https://www.ntppool.org/en/, NTP Pool Project}.
 @end defvr
 
+@deftp {Data Type} ntp-server
+The data type representing the configuration of a NTP server.
+
+@table @asis
+@item @code{type} (default: @code{'server})
+The type of the NTP server, given as a symbol. One of @code{'pool},
+@code{'server}, @code{'peer}, @code{'broadcast} or @code{'manycastclient}.
+
+@item @code{address}
+The address of the server, as a string.
+
+@item @code{options}
+NTPD options to use with that specific server, given as a list of option names
+and/or of option names and values tuples. The following example define a server
+to use with the options @option{iburst} and @option{prefer}, as well as
+@option{version} 3 and a @option{maxpoll} time of 16 seconds.
+
+@example
+(ntp-server
+ (type 'server)
+ (address "some.ntp.server.org")
+ (options `(iburst (version 3) (maxpoll 16) prefer))))
+@end example
+@end table
+@end deftp
+
 @cindex OpenNTPD
 @deffn {Scheme Procedure} openntpd-service-type
 Run the @command{ntpd}, the Network Time Protocol (NTP) daemon, as implemented
@@ -13024,6 +13051,11 @@ clock synchronized with that of the given servers.
 @end example
 @end deffn
 
+@defvr {Scheme Variable} %openntpd-servers
+This variable is a list of the server addresses defined in
+@var{%ntp-servers}.
+@end defvr
+
 @deftp {Data Type} openntpd-configuration
 @table @asis
 @item @code{openntpd} (default: @code{(file-append openntpd "/sbin/ntpd")})
@@ -13037,9 +13069,9 @@ Specify a list of timedelta sensor devices ntpd should use.  @code{ntpd}
 will listen to each sensor that actually exists and ignore non-existent ones.
 See @uref{https://man.openbsd.org/ntpd.conf, upstream documentation} for more
 information.
-@item @code{server} (default: @var{%ntp-servers})
+@item @code{server} (default: @code{'()})
 Specify a list of IP addresses or hostnames of NTP servers to synchronize to.
-@item @code{servers} (default: @code{'()})
+@item @code{servers} (default: @var{%openntp-servers})
 Specify a list of IP addresses or hostnames of NTP pools to synchronize to.
 @item @code{constraint-from} (default: @code{'()})
 @code{ntpd} can be configured to query the ‘Date’ from trusted HTTPS servers via TLS.
diff --git a/gnu/services/networking.scm b/gnu/services/networking.scm
index 13a5c6c98d..c45bfcdad9 100644
--- a/gnu/services/networking.scm
+++ b/gnu/services/networking.scm
@@ -51,6 +51,7 @@
   #:use-module (guix records)
   #:use-module (guix modules)
   #:use-module (guix deprecation)
+  #:use-module (rnrs enums)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
@@ -72,13 +73,22 @@
             dhcpd-configuration-pid-file
             dhcpd-configuration-interfaces
 
-            %ntp-servers
-
             ntp-configuration
             ntp-configuration?
+            ntp-configuration-ntp
+            ntp-configuration-servers
+            ntp-allow-large-adjustment?
+
+            %ntp-servers
+            ntp-server
+            ntp-server-type
+            ntp-server-address
+            ntp-server-options
+
             ntp-service
             ntp-service-type
 
+            %openntpd-servers
             openntpd-configuration
             openntpd-configuration?
             openntpd-service-type
@@ -292,31 +302,87 @@ Protocol (DHCP) client, on all the non-loopback network interfaces."
     (list (service-extension shepherd-root-service-type dhcpd-shepherd-service)
           (service-extension activation-service-type dhcpd-activation)))))
 
-(define %ntp-servers
-  ;; Default set of NTP servers. These URLs are managed by the NTP Pool project.
-  ;; Within Guix, Leo Famulari <[email-masked]> is the administrative contact
-  ;; for this NTP pool "zone".
-  '("0.guix.pool.ntp.org"
-    "1.guix.pool.ntp.org"
-    "2.guix.pool.ntp.org"
-    "3.guix.pool.ntp.org"))
-
 
 ;;;
 ;;; NTP.
 ;;;
 
-;; TODO: Export.
+(define ntp-server-types (make-enumeration
+                          '(pool
+                            server
+                            peer
+                            broadcast
+                            manycastclient)))
+
+(define-record-type* <ntp-server>
+  ntp-server make-ntp-server
+  ntp-server?
+  ;; The type can be one of the symbols of the NTP-SERVER-TYPE? enumeration.
+  (type ntp-server-type
+        (default 'server))
+  (address ntp-server-address)    ; a string
+  ;; The list of options can contain single option names or tuples in the form
+  ;; '(name value).
+  (options ntp-server-options
+           (default '())))
+
+(define (ntp-server->string ntp-server)
+  ;; Serialize the NTP server object as a string, ready to use in the NTP
+  ;; configuration file.
+  (define (flatten lst)
+    (reverse
+     (let loop ((x lst)
+                (res '()))
+       (if (list? x)
+           (fold loop res x)
+           (cons (format #f "~s" x) res)))))
+
+  (match ntp-server
+    (($ <ntp-server> type address options)
+     ;; XXX: It'd be neater if fields were validated at the syntax level (for
+     ;; static ones at least).  Perhaps the Guix record type could support a
+     ;; predicate property on a field?
+     (unless (enum-set-member? type ntp-server-types)
+       (error "Invalid NTP server type" type))
+     (string-join (cons* (symbol->string type)
+                         address
+                         (flatten options))))))
+
+(define %ntp-servers
+  ;; Default set of NTP servers. These URLs are managed by the NTP Pool project.
+  ;; Within Guix, Leo Famulari <[email-masked]> is the administrative contact
+  ;; for this NTP pool "zone".
+  (list
+   (ntp-server
+    (type 'pool)
+    (address "0.guix.pool.ntp.org")
+    (options '("iburst")))))               ;as recommended in the ntpd manual
+
 (define-record-type* <ntp-configuration>
   ntp-configuration make-ntp-configuration
   ntp-configuration?
   (ntp      ntp-configuration-ntp
             (default ntp))
-  (servers  ntp-configuration-servers
+  (servers  %ntp-configuration-servers   ;list of <ntp-server> objects
             (default %ntp-servers))
   (allow-large-adjustment? ntp-allow-large-adjustment?
                            (default #t))) ;as recommended in the ntpd manual
 
+(define (ntp-configuration-servers ntp-configuration)
+  ;; A wrapper to support the deprecated form of this field.
+  (let ((ntp-servers (%ntp-configuration-servers ntp-configuration)))
+    (match ntp-servers
+      (((? string?) (? string?) ...)
+       (format (current-error-port) "warning: Defining NTP servers as strings is \
+deprecated.  Please use <ntp-server> records instead.\n")
+       (map (lambda (addr)
+              (ntp-server
+               (type 'server)
+               (address addr)
+               (options '()))) ntp-servers))
+      ((($ <ntp-server>) ($ <ntp-server>) ...)
+       ntp-servers))))
+
 (define ntp-shepherd-service
   (match-lambda
     (($ <ntp-configuration> ntp servers allow-large-adjustment?)
@@ -324,8 +390,7 @@ Protocol (DHCP) client, on all the non-loopback network interfaces."
        ;; TODO: Add authentication support.
        (define config
          (string-append "driftfile /var/run/ntpd/ntp.drift\n"
-                        (string-join (map (cut string-append "server " <>)
-                                          servers)
+                        (string-join (map ntp-server->string servers)
                                      "\n")
                         "
 # Disable status queries as a workaround for CVE-2013-5211:
@@ -335,7 +400,11 @@ restrict -6 default kod nomodify notrap nopeer noquery limited
 
 # Yet, allow use of the local 'ntpq'.
 restrict 127.0.0.1
-restrict -6 ::1\n"))
+restrict -6 ::1
+
+# This is required to use servers from a pool directive when using the 'nopeer'
+# option by default, as documented in the 'ntp.conf' manual.
+restrict source notrap nomodify noquery\n"))
 
        (define ntpd.conf
          (plain-file "ntpd.conf" config))
@@ -409,6 +478,9 @@ make an initial adjustment of more than 1,000 seconds."
 ;;; OpenNTPD.
 ;;;
 
+(define %openntpd-servers
+  (map ntp-server-address %ntp-servers))
+
 (define-record-type* <openntpd-configuration>
   openntpd-configuration make-openntpd-configuration
   openntpd-configuration?
@@ -422,9 +494,9 @@ make an initial adjustment of more than 1,000 seconds."
   (sensor                  openntpd-sensor
                            (default '()))
   (server                  openntpd-server
-                           (default %ntp-servers))
-  (servers                 openntpd-servers
                            (default '()))
+  (servers                 openntpd-servers
+                           (default %openntpd-servers))
   (constraint-from         openntpd-constraint-from
                            (default '()))
   (constraints-from        openntpd-constraints-from
diff --git a/tests/networking.scm b/tests/networking.scm
new file mode 100644
index 0000000000..001d7df74d
--- /dev/null
+++ b/tests/networking.scm
@@ -0,0 +1,50 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Maxim Cournoyer <[email-masked]>
+;;;
+;;; 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 (tests networking)
+  #:use-module (gnu services networking)
+  #:use-module (srfi srfi-64))
+
+;;; Tests for the (gnu services networking) module.
+
+(define ntp-server->string (@@ (gnu services networking) ntp-server->string))
+
+(define %ntp-server-sample
+  (ntp-server
+   (type 'server)
+   (address "some.ntp.server.org")
+   (options `(iburst (version 3) (maxpoll 16) prefer))))
+
+(test-begin "networking")
+
+(test-equal "ntp-server->string"
+  (ntp-server->string %ntp-server-sample)
+  "server some.ntp.server.org iburst version 3 maxpoll 16 prefer")
+
+(test-equal "ntp configuration servers deprecated form"
+  (ntp-configuration-servers
+   (ntp-configuration
+    (servers (list (ntp-server
+                    (type 'server)
+                    (address "example.pool.ntp.org")
+                    (options '()))))))
+  (ntp-configuration-servers
+   (ntp-configuration
+    (servers (list "example.pool.ntp.org")))))
+
+(test-end "networking")
-- 
2.23.0

We could also overhaul the code of the openntpd-service-type so that it'd
be possible to provide different server types and options like for the
'ntp-service-type', but I'm not sure it's worth it, given that OpenNTPD
is more spartan than NTP (it only supports two server types ('server' vs
'servers'), already captured as fields in its configuration record; and
its server directives only support one option, 'weight', which can
currently be included in the server string if desired).

However, I noticed that the configuration file produced by the openntpd
service, while valid, is not very clean.

For the documented following openntpd-service-type definition:

--8<---------------cut here---------------start------------->8---
(openntpd-configuration
            (listen-on '("127.0.0.1" "::1"))
            (sensor '("udcf0 correction 70000"))
            (constraint-from '("www.gnu.org"))
            (constraints-from '("https://www.google.com/"))
            (allow-large-adjustment? #t)))
--8<---------------cut here---------------end--------------->8---

The following configuration file is generated:

--8<---------------cut here---------------start------------->8---
listen on 127.0.0.1
 listen on ::1
constraints from "https://www.google.com/"
constraints from "https://www.google.com/"
sensor udcf0 correction 70000
constraints from "https://www.google.com/"
constraints from "https://www.google.com/"
servers 0.guix.pool.ntp.org
constraints from "https://www.google.com/"
constraint from www.gnu.org
--8<---------------cut here---------------end--------------->8---

This is reproducible when testing without my changes (with the difference
that multiple servers were used instead of a single "pool" entry point).

I've opened an issue so that this issue can be tracked separately here:
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=37318.

Thank you!

Maxim