;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015 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 (guix scripts challenge)
  #:use-module (guix ui)
  #:use-module (guix scripts)
  #:use-module (guix store)
  #:use-module (guix utils)
  #:use-module (guix monads)
  #:use-module (guix base32)
  #:use-module (guix packages)
  #:use-module (guix serialization)
  #:use-module (guix scripts substitute)
  #:use-module (rnrs bytevectors)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-37)
  #:use-module (ice-9 match)
  #:use-module (ice-9 vlist)
  #:use-module (ice-9 format)
  #:use-module (web uri)
  #:export (discrepancies

            discrepancy?
            discrepancy-item
            discrepancy-local-sha256
            discrepancy-narinfos

            guix-challenge))

;;; Commentary:
;;;
;;; Challenge substitute servers, checking whether they provide the same
;;; binaries as those built locally.
;;;
;;; Here we completely bypass the daemon to access substitutes.  This is
;;; because we want to be able to report fine-grain information about
;;; discrepancies: We need to show the URL of the offending nar, its hash, and
;;; so on.
;;;
;;; Code:

(define ensure-store-item                         ;XXX: move to (guix ui)?
  (@@ (guix scripts size) ensure-store-item))

;; Representation of a hash mismatch for ITEM.
(define-record-type <discrepancy>
  (discrepancy item local-sha256 narinfos)
  discrepancy?
  (item         discrepancy-item)                   ;string, /gnu/store/… item
  (local-sha256 discrepancy-local-sha256)           ;bytevector | #f
  (narinfos     discrepancy-narinfos))              ;list of <narinfo>

(define (locally-built? store item)
  "Return true if ITEM was built locally."
  ;; XXX: For now approximate it by checking whether there's a build log for
  ;; ITEM.  There could be false negatives, if logs have been removed.
  (->bool (log-file store item)))

(define (query-locally-built-hash item)
  "Return the hash of ITEM, a store item, if ITEM was built locally.
Otherwise return #f."
  (lambda (store)
    (guard (c ((nix-protocol-error? c)
               (values #f store)))
      (if (locally-built? store item)
          (values (query-path-hash store item) store)
          (values #f store)))))

(define-syntax-rule (report args ...)
  (format (current-error-port) args ...))

(define (discrepancies items servers)
  "Challenge the substitute servers whose URLs are listed in SERVERS by
comparing the hash of the substitutes of ITEMS that they serve.  Return the
list of discrepancies.

This procedure does not authenticate narinfos from SERVERS, nor does it verify
that they are signed by an authorized public keys.  The reason is that, by
definition, we may want to target unknown servers.  Furthermore, no risk is
taken since we do not import the archives."
  (define (compare item reference)
    ;; Return a procedure to compare the hash of ITEM with REFERENCE.
    (lambda (narinfo url)
      (if (not narinfo)
          (begin
            (warning (_ "~a: no substitute at '~a'~%")
                     item url)
            #t)
          (let ((value (narinfo-hash->sha256 (narinfo-hash narinfo))))
            (bytevector=? reference value)))))

  (define (select-reference item narinfos urls)
    ;; Return a "reference" narinfo among NARINFOS.
    (match narinfos
      ((first narinfos ...)
       (match servers
         ((url urls ...)
          (if (not first)
              (select-reference item narinfos urls)
              (narinfo-hash->sha256 (narinfo-hash first))))))
      (()
       (leave (_ "no substitutes for '~a'~%") item))))

  (mlet* %store-monad ((local     (mapm %store-monad
                                        query-locally-built-hash items))
                       (remote -> (append-map (cut lookup-narinfos <> items)
                                              servers))
                       ;; No 'assert-valid-narinfo' on purpose.
                       (narinfos -> (fold (lambda (narinfo vhash)
                                            (if narinfo
                                                (vhash-cons (narinfo-path narinfo) narinfo
                                                            vhash)
                                                vhash))
                                          vlist-null
                                          remote)))
    (return (filter-map (lambda (item local)
                          (let ((narinfos (vhash-fold* cons '() item narinfos)))
                            (define reference
                              (or local
                                  (begin
                                    (warning (_ "no local build for '~a'~%") item)
                                    (select-reference item narinfos servers))))

                            (if (every (compare item reference)
                                       narinfos servers)
                                #f
                                (discrepancy item local narinfos))))
                        items
                        local))))

(define* (summarize-discrepancy discrepancy
                                #:key (hash->string
                                       bytevector->nix-base32-string))
  "Write to the current error port a summary of DISCREPANCY, a <discrepancy>
object that denotes a hash mismatch."
  (match discrepancy
    (($ <discrepancy> item local (narinfos ...))
     (report (_ "~a contents differ:~%") item)
     (if local
         (report (_ "  local hash: ~a~%") (hash->string local))
         (warning (_ "no local build for '~a'~%") item))

     (for-each (lambda (narinfo)
                 (if narinfo
                     (report (_ "  ~50a: ~a~%")
                             (uri->string (narinfo-uri narinfo))
                             (hash->string
                              (narinfo-hash->sha256 (narinfo-hash narinfo))))
                     (report (_ "  ~50a: unavailable~%")
                             (uri->string (narinfo-uri narinfo)))))
               narinfos))))


;;;
;;; Command-line options.
;;;

(define (show-help)
  (display (_ "Usage: guix challenge [PACKAGE...]
Challenge the substitutes for PACKAGE... provided by one or more servers.\n"))
  (display (_ "
      --substitute-urls=URLS
                         compare build results with those at URLS"))
  (newline)
  (display (_ "
  -h, --help             display this help and exit"))
  (display (_ "
  -V, --version          display version information and exit"))
  (newline)
  (show-bug-report-information))

(define %options
  (list  (option '(#\h "help") #f #f
                 (lambda args
                   (show-help)
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
                   (show-version-and-exit "guix challenge")))

         (option '("substitute-urls") #t #f
                 (lambda (opt name arg result . rest)
                   (apply values
                          (alist-cons 'substitute-urls
                                      (string-tokenize arg)
                                      (alist-delete 'substitute-urls result))
                          rest)))))

(define %default-options
  `((system . ,(%current-system))
    (substitute-urls . ,%default-substitute-urls)))


;;;
;;; Entry point.
;;;

(define (guix-challenge . args)
  (with-error-handling
    (let* ((opts     (parse-command-line args %options (list %default-options)))
           (files    (filter-map (match-lambda
                                   (('argument . file) file)
                                   (_ #f))
                                 opts))
           (system   (assoc-ref opts 'system))
           (urls     (assoc-ref opts 'substitute-urls)))
      (leave-on-EPIPE
       (with-store store
         (let ((files (match files
                        (()
                         (filter (cut locally-built? store <>)
                                 (live-paths store)))
                        (x
                         files))))
           (set-build-options store
                              #:use-substitutes? #f)

           (run-with-store store
             (mlet* %store-monad ((items  (mapm %store-monad
                                               ensure-store-item files))
                                  (issues (discrepancies items urls)))
               (for-each summarize-discrepancy issues)
               (return (null? issues)))
             #:system system)))))))

;;; challenge.scm ends here
