gnu: services: admin: Add tailon.

* gnu/services/admin.scm
  (<tailon-configuration>, <tailon-configuration-file>): New record types.
  (tailon-configuration-files-string, tailon-shepherd-service): New
  procedures.
  (%tailon-accounts, tailon-service-type: New variables.
* doc/guix.texi (Monitoring Services: Document the Tailon service.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add gnu/tests/admin.scm.
* gnu/tests/admin.scm: New file.

doc/guix.texi

@@ -219,6 +219,7 @@ Services
 * Database Services::           SQL databases.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
+* Monitoring Services::         Monitoring services.
 * Kerberos Services::           Kerberos services.
 * Web Services::                Web servers.
 * DNS Services::                DNS daemons.
@@ -9011,6 +9012,7 @@ declaration.
 * Database Services::           SQL databases.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
+* Monitoring Services::         Monitoring services.
 * Kerberos Services::           Kerberos services.
 * Web Services::                Web servers.
 * DNS Services::                DNS daemons.
@@ -13599,6 +13601,94 @@ string, you could instantiate a prosody service like this:
           (prosody.cfg.lua "")))
 @end example
 
+@node Monitoring Services
+@subsubsection Monitoring Services
+
+@subsubheading Tailon Service
+
+@uref{https://tailon.readthedocs.io/, Tailon} is a web application for
+viewing and searching log files.
+
+The following example will configure the service with default values.
+By default, Tailon can be accessed on port 8080 (@code{http://localhost:8080}).
+
+@example
+(service tailon-service-type)
+@end example
+
+The following example customises more of the Tailon configuration,
+adding @command{sed} to the list of allowed commands.
+
+@example
+(service tailon-service-type
+         (tailon-configuration
+           (config-file
+             (tailon-configuration-file
+               (allowed-commands '("tail" "grep" "awk" "sed"))))))
+@end example
+
+
+@deftp {Data Type} tailon-configuration
+Data type representing the configuration of Tailon.
+This type has the following parameters:
+
+@table @asis
+@item @code{config-file} (default: @code{(tailon-configuration-file)})
+The configuration file to use for Tailon. This can be set to a
+@dfn{tailon-configuration-file} record value, or any gexp
+(@pxref{G-Expressions}).
+
+For example, to instead use a local file, the @code{local-file} function
+can be used:
+
+@example
+(service tailon-service-type
+         (tailon-configuration
+           (config-file (local-file "./my-tailon.conf"))))
+@end example
+
+@item @code{package} (default: @code{tailon})
+The tailon package to use.
+
+@end table
+@end deftp
+
+@deftp {Data Type} tailon-configuration-file
+Data type representing the configuration options for Tailon.
+This type has the following parameters:
+
+@table @asis
+@item @code{files} (default: @code{(list "/var/log")})
+List of files to display. The list can include strings for a single file
+or directory, or a list, where the first item is the name of a
+subsection, and the remaining items are the files or directories in that
+subsection.
+
+@item @code{bind} (default: @code{"localhost:8080"})
+Address and port to which Tailon should bind on.
+
+@item @code{relative-root} (default: @code{#f})
+URL path to use for Tailon, set to @code{#f} to not use a path.
+
+@item @code{allow-transfers?} (default: @code{#t})
+Allow downloading the log files in the web interface.
+
+@item @code{follow-names?} (default: @code{#t})
+Allow tailing of not-yet existent files.
+
+@item @code{tail-lines} (default: @code{200})
+Number of lines to read initially from each file.
+
+@item @code{allowed-commands} (default: @code{(list "tail" "grep" "awk")})
+Commands to allow running. By default, @code{sed} is disabled.
+
+@item @code{debug?} (default: @code{#f})
+Set @code{debug?} to @code{#t} to show debug messages.
+
+@end table
+@end deftp
+
+
 @node Kerberos Services
 @subsubsection Kerberos Services
 @cindex Kerberos

gnu/local.mk

@@ -478,6 +478,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/build/vm.scm				\
 						\
   %D%/tests.scm					\
+  %D%/tests/admin.scm				\
   %D%/tests/base.scm				\
   %D%/tests/dict.scm				\
   %D%/tests/nfs.scm				\

gnu/services/admin.scm

@@ -20,14 +20,19 @@
 (define-module (gnu services admin)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages base)
+  #:use-module (gnu packages logging)
   #:use-module (gnu services)
   #:use-module (gnu services mcron)
   #:use-module (gnu services shepherd)
+  #:use-module (gnu services web)
+  #:use-module (gnu system shadow)
   #:use-module (guix gexp)
+  #:use-module (guix store)
   #:use-module (guix packages)
   #:use-module (guix records)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 vlist)
+  #:use-module (ice-9 match)
   #:export (%default-rotations
             %rotated-files
 
@@ -41,7 +46,27 @@
             rottlog-configuration
             rottlog-configuration?
             rottlog-service
-            rottlog-service-type))
+            rottlog-service-type
+
+            <tailon-configuration-file>
+            tailon-configuration-file
+            tailon-configuration-file?
+            tailon-configuration-file-files
+            tailon-configuration-file-bind
+            tailon-configuration-file-relative-root
+            tailon-configuration-file-allow-transfers?
+            tailon-configuration-file-follow-names?
+            tailon-configuration-file-tail-lines
+            tailon-configuration-file-allowed-commands
+            tailon-configuration-file-debug?
+
+            <tailon-configuration>
+            tailon-configuration
+            tailon-configuration?
+            tailon-configuration-config-file
+            tailon-configuration-package
+
+            tailon-service-type))
 
 ;;; Commentary:
 ;;;
@@ -172,4 +197,128 @@ for ROTATION."
                                  rotations)))))
    (default-value (rottlog-configuration))))
 
+
+;;;
+;;; Tailon
+;;;
+
+(define-record-type* <tailon-configuration-file>
+  tailon-configuration-file make-tailon-configuration-file
+  tailon-configuration-file?
+  (files                   tailon-configuration-file-files
+                           (default '("/var/log")))
+  (bind                    tailon-configuration-file-bind
+                           (default "localhost:8080"))
+  (relative-root           tailon-configuration-file-relative-root
+                           (default #f))
+  (allow-transfers?        tailon-configuration-file-allow-transfers?
+                           (default #t))
+  (follow-names?           tailon-configuration-file-follow-names?
+                           (default #t))
+  (tail-lines              tailon-configuration-file-tail-lines
+                           (default 200))
+  (allowed-commands        tailon-configuration-file-allowed-commands
+                           (default '("tail" "grep" "awk")))
+  (debug?                  tailon-configuration-file-debug?
+                           (default #f)))
+
+(define (tailon-configuration-files-string files)
+  (string-append
+   "\n"
+   (string-join
+    (map
+     (lambda (x)
+       (string-append
+        "  - "
+        (cond
+         ((string? x)
+          (simple-format #f "'~A'" x))
+         ((list? x)
+          (string-join
+           (cons (simple-format #f "'~A':" (car x))
+                 (map
+                  (lambda (x) (simple-format #f "      - '~A'" x))
+                  (cdr x)))
+           "\n"))
+         (else (error x)))))
+     files)
+    "\n")))
+
+(define-gexp-compiler (tailon-configuration-file-compiler
+                       (file <tailon-configuration-file>) system target)
+  (match file
+    (($ <tailon-configuration-file> files bind relative-root
+                                    allow-transfers? follow-names?
+                                    tail-lines allowed-commands debug?)
+     (text-file
+      "tailon-config.yaml"
+      (string-concatenate
+       (filter-map
+        (match-lambda
+         ((key . #f) #f)
+         ((key . value) (string-append key ": " value "\n")))
+
+        `(("files" . ,(tailon-configuration-files-string files))
+          ("bind" . ,bind)
+          ("relative-root" . ,relative-root)
+          ("allow-transfers" . ,(if allow-transfers? "true" "false"))
+          ("follow-names" . ,(if follow-names? "true" "false"))
+          ("tail-lines" . ,(number->string tail-lines))
+          ("commands" . ,(string-append "["
+                                        (string-join allowed-commands ", ")
+                                        "]"))
+          ,@(if debug? '(("debug" . "true")) '()))))))))
+
+(define-record-type* <tailon-configuration>
+  tailon-configuration make-tailon-configuration
+  tailon-configuration?
+  (config-file tailon-configuration-config-file
+               (default (tailon-configuration-file)))
+  (package tailon-configuration-package
+           (default tailon)))
+
+(define tailon-shepherd-service
+  (match-lambda
+    (($ <tailon-configuration> config-file package)
+     (list (shepherd-service
+            (provision '(tailon))
+            (documentation "Run the tailon daemon.")
+            (start #~(make-forkexec-constructor
+                      `(,(string-append #$package "/bin/tailon")
+                        "-c" ,#$config-file)
+                      #:user "tailon"
+                      #:group "tailon"))
+            (stop #~(make-kill-destructor)))))))
+
+(define %tailon-accounts
+  (list (user-group (name "tailon") (system? #t))
+        (user-account
+         (name "tailon")
+         (group "tailon")
+         (system? #t)
+         (comment "tailon")
+         (home-directory "/var/empty")
+         (shell (file-append shadow "/sbin/nologin")))))
+
+(define tailon-service-type
+  (service-type
+   (name 'tailon)
+   (extensions
+    (list (service-extension shepherd-root-service-type
+                             tailon-shepherd-service)
+          (service-extension account-service-type
+                             (const %tailon-accounts))))
+   (compose concatenate)
+   (extend (lambda (parameter files)
+             (tailon-configuration
+              (inherit parameter)
+              (config-file
+               (let ((old-config-file
+                      (tailon-configuration-config-file parameter)))
+                 (tailon-configuration-file
+                  (inherit old-config-file)
+                  (files (append (tailon-configuration-file-files old-config-file)
+                                 files))))))))
+   (default-value (tailon-configuration))))
+
 ;;; admin.scm ends here

gnu/tests/admin.scm

@@ -0,0 +1,128 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2017 Christopher Baines <mail@cbaines.net>
+;;;
+;;; 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 tests admin)
+  #:use-module (gnu tests)
+  #:use-module (gnu system)
+  #:use-module (gnu system file-systems)
+  #:use-module (gnu system shadow)
+  #:use-module (gnu system vm)
+  #:use-module (gnu services)
+  #:use-module (gnu services admin)
+  #:use-module (gnu services networking)
+  #:use-module (guix gexp)
+  #:use-module (guix store)
+  #:use-module (guix monads)
+  #:export (%test-tailon))
+
+(define %tailon-os
+  ;; Operating system under test.
+  (simple-operating-system
+   (dhcp-client-service)
+   (service tailon-service-type
+            (tailon-configuration
+             (config-file
+              (tailon-configuration-file
+               (bind "0.0.0.0:8080")))))))
+
+(define* (run-tailon-test #:optional (http-port 8081))
+  "Run tests in %TAILON-OS, which has tailon running and listening on
+HTTP-PORT."
+  (define os
+    (marionette-operating-system
+     %tailon-os
+     #:imported-modules '((gnu services herd)
+                          (guix combinators))))
+
+  (define vm
+    (virtual-machine
+     (operating-system os)
+     (port-forwardings `((,http-port . 8080)))))
+
+  (define test
+    (with-imported-modules '((gnu build marionette))
+      #~(begin
+          (use-modules (srfi srfi-11) (srfi srfi-64)
+                       (ice-9 match)
+                       (gnu build marionette)
+                       (web uri)
+                       (web client)
+                       (web response))
+
+          (define marionette
+            ;; Forward the guest's HTTP-PORT, where tailon is listening, to
+            ;; port 8080 in the host.
+            (make-marionette (list #$vm)))
+
+          (mkdir #$output)
+          (chdir #$output)
+
+          (test-begin "tailon")
+
+          (test-eq "service running"
+            'running!
+            (marionette-eval
+             '(begin
+                (use-modules (gnu services herd))
+                (start-service 'tailon)
+                'running!)
+             marionette))
+
+          (define* (retry-on-error f #:key times delay)
+            (let loop ((attempt 1))
+              (match (catch
+                      #t
+                      (lambda ()
+                        (cons #t
+                              (f)))
+                      (lambda args
+                        (cons #f
+                              args)))
+                ((#t . return-value)
+                 return-value)
+                ((#f . error-args)
+                 (if (>= attempt times)
+                     error-args
+                     (begin
+                       (sleep delay)
+                       (loop (+ 1 attempt))))))))
+
+          (test-equal "http-get"
+            200
+            (retry-on-error
+             (lambda ()
+               (let-values (((response text)
+                             (http-get #$(format
+                                          #f
+                                          "http://localhost:~A/"
+                                          http-port)
+                                       #:decode-body? #t)))
+                 (response-code response)))
+             #:times 10
+             #:delay 5))
+
+          (test-end)
+          (exit (= (test-runner-fail-count (test-runner-current)) 0)))))
+
+  (gexp->derivation "tailon-test" test))
+
+(define %test-tailon
+  (system-test
+   (name "tailon")
+   (description "Connect to a running Tailon server.")
+   (value (run-tailon-test))))