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guix/guix/narinfo.scm

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013-2022 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2014 Nikita Karetnikov <nikita@karetnikov.org>
;;; Copyright © 2018 Kyle Meyer <kyle@kyleam.com>
;;;
;;; 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 narinfo)
#:use-module (guix pki)
#:use-module (guix i18n)
#:use-module (guix base32)
#:use-module (guix base64)
#:use-module (guix records)
#:use-module (guix diagnostics)
#:use-module (gcrypt hash)
#:use-module (gcrypt pk-crypto)
#:use-module (rnrs bytevectors)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-26)
#:use-module (ice-9 match)
#:use-module (ice-9 binary-ports)
#:use-module (web uri)
#:export (narinfo-signature->canonical-sexp
narinfo?
narinfo-path
narinfo-uris
narinfo-uri-base
narinfo-compressions
narinfo-file-hashes
narinfo-file-sizes
narinfo-hash
narinfo-size
narinfo-references
narinfo-deriver
narinfo-system
narinfo-signature
narinfo-contents
narinfo-hash-algorithm+value
narinfo-hash->sha256
narinfo-preferred-uris
narinfo-best-uri
valid-narinfo?
read-narinfo
write-narinfo
string->narinfo
narinfo->string
equivalent-narinfo?))
(define-record-type <narinfo>
(%make-narinfo path uri-base uris compressions file-sizes file-hashes
nar-hash nar-size references deriver system
signature contents)
narinfo?
(path narinfo-path)
(uri-base narinfo-uri-base) ;URI of the cache it originates from
(uris narinfo-uris) ;list of strings
(compressions narinfo-compressions) ;list of strings
(file-sizes narinfo-file-sizes) ;list of (integers | #f)
(file-hashes narinfo-file-hashes)
(nar-hash narinfo-hash)
(nar-size narinfo-size)
(references narinfo-references)
(deriver narinfo-deriver)
(system narinfo-system)
(signature narinfo-signature) ; canonical sexp
;; The original contents of a narinfo file. This field is needed because we
;; want to preserve the exact textual representation for verification purposes.
;; See <https://lists.gnu.org/archive/html/guix-devel/2014-02/msg00340.html>
;; for more information.
(contents narinfo-contents))
(define (narinfo-hash-algorithm+value narinfo)
"Return two values: the hash algorithm used by NARINFO and its value as a
bytevector."
(match (string-tokenize (narinfo-hash narinfo)
(char-set-complement (char-set #\:)))
((algorithm base32)
(values (lookup-hash-algorithm (string->symbol algorithm))
(nix-base32-string->bytevector base32)))
(_
(raise (formatted-message
(G_ "invalid narinfo hash: ~s") (narinfo-hash narinfo))))))
(define (narinfo-hash->sha256 hash)
"If the string HASH denotes a sha256 hash, return it as a bytevector.
Otherwise return #f."
(and (string-prefix? "sha256:" hash)
(nix-base32-string->bytevector (string-drop hash 7))))
(define (narinfo-signature->canonical-sexp str)
"Return the value of a narinfo's 'Signature' field as a canonical sexp."
(match (string-split str #\;)
((version host-name sig)
(let ((maybe-number (string->number version)))
(cond ((not (number? maybe-number))
(leave (G_ "signature version must be a number: ~s~%")
version))
;; Currently, there are no other versions.
((not (= 1 maybe-number))
(leave (G_ "unsupported signature version: ~a~%")
maybe-number))
(else
(let ((signature (utf8->string (base64-decode sig))))
(catch 'gcry-error
(lambda ()
(string->canonical-sexp signature))
(lambda (key proc err)
(leave (G_ "signature is not a valid \
s-expression: ~s~%")
signature))))))))
(x
(leave (G_ "invalid format of the signature field: ~a~%") x))))
(define (narinfo-maker str cache-url)
"Return a narinfo constructor for narinfos originating from CACHE-URL. STR
must contain the original contents of a narinfo file."
(lambda (path urls compressions file-hashes file-sizes
nar-hash nar-size references deriver system
signature)
"Return a new <narinfo> object."
(define len (length urls))
(%make-narinfo path cache-url
;; Handle the case where URL is a relative URL.
(map (lambda (url)
(or (string->uri url)
(string->uri
(if (string-suffix? "/" cache-url)
(string-append cache-url url)
(string-append cache-url "/" url)))))
urls)
compressions
(match file-sizes
(() (make-list len #f))
((lst ...) (map string->number lst)))
(match file-hashes
(() (make-list len #f))
((lst ...) (map string->number lst)))
nar-hash
(and=> nar-size string->number)
(string-tokenize references)
(match deriver
((or #f "") #f)
(_ deriver))
system
(false-if-exception
(and=> signature narinfo-signature->canonical-sexp))
str)))
(define fields->alist
;; The narinfo format is really just like recutils.
recutils->alist)
(define* (read-narinfo port #:optional url
#:key size)
"Read a narinfo from PORT. If URL is true, it must be a string used to
build full URIs from relative URIs found while reading PORT. When SIZE is
true, read at most SIZE bytes from PORT; otherwise, read as much as possible.
No authentication and authorization checks are performed here!"
(let ((str (utf8->string (if size
(get-bytevector-n port size)
(get-bytevector-all port)))))
(alist->record (call-with-input-string str fields->alist)
(narinfo-maker str url)
'("StorePath" "URL" "Compression"
"FileHash" "FileSize" "NarHash" "NarSize"
"References" "Deriver" "System"
"Signature")
'("URL" "Compression" "FileSize" "FileHash"))))
(define (narinfo-sha256 narinfo)
"Return the sha256 hash of NARINFO as a bytevector, or #f if NARINFO lacks a
'Signature' field."
(define %mandatory-fields
;; List of fields that must be signed. If they are not signed, the
;; narinfo is considered unsigned.
'("StorePath" "NarHash" "References"))
(let ((contents (narinfo-contents narinfo)))
(match (string-contains contents "Signature:")
(#f #f)
(index
(let* ((above-signature (string-take contents index))
(signed-fields (match (call-with-input-string above-signature
fields->alist)
(((fields . values) ...) fields))))
(and (every (cut member <> signed-fields) %mandatory-fields)
(sha256 (string->utf8 above-signature))))))))
(define* (valid-narinfo? narinfo #:optional (acl (current-acl))
#:key verbose?)
"Return #t if NARINFO's signature is valid and made by one of the keys in
ACL."
(let ((hash (narinfo-sha256 narinfo))
(signature (narinfo-signature narinfo))
(uri (uri->string (first (narinfo-uris narinfo)))))
(and hash signature
(signature-case (signature hash acl)
(valid-signature #t)
(invalid-signature
(when verbose?
(format (current-error-port)
"invalid signature for substitute at '~a'~%"
uri))
#f)
(hash-mismatch
(when verbose?
(format (current-error-port)
"hash mismatch for substitute at '~a'~%"
uri))
#f)
(unauthorized-key
(when verbose?
(format (current-error-port)
"substitute at '~a' is signed by an \
unauthorized party~%"
uri))
#f)
(corrupt-signature
(when verbose?
(format (current-error-port)
"corrupt signature for substitute at '~a'~%"
uri))
#f)))))
(define (write-narinfo narinfo port)
"Write NARINFO to PORT."
(put-bytevector port (string->utf8 (narinfo-contents narinfo))))
(define (narinfo->string narinfo)
"Return the external representation of NARINFO."
(call-with-output-string (cut write-narinfo narinfo <>)))
(define (string->narinfo str cache-uri)
"Return the narinfo represented by STR. Assume CACHE-URI as the base URI of
the cache STR originates form."
(call-with-input-string str (cut read-narinfo <> cache-uri)))
(define (equivalent-narinfo? narinfo1 narinfo2)
"Return true if NARINFO1 and NARINFO2 are equivalent--i.e., if they describe
the same store item. This ignores unnecessary metadata such as the Nar URL."
(and (string=? (narinfo-hash narinfo1)
(narinfo-hash narinfo2))
;; The following is not needed if all we want is to download a valid
;; nar, but it's necessary if we want valid narinfo.
(string=? (narinfo-path narinfo1)
(narinfo-path narinfo2))
(equal? (narinfo-references narinfo1)
(narinfo-references narinfo2))
(= (narinfo-size narinfo1)
(narinfo-size narinfo2))))
(define %compression-methods
;; Known compression methods and a thunk to determine whether they're
;; supported. See 'decompressed-port' in (guix utils).
`(("gzip" . ,(const #t))
("lzip" . ,(const #t))
("zstd" . ,(lambda ()
(resolve-module '(zstd) #t #f #:ensure #f)))
("xz" . ,(const #t))
("bzip2" . ,(const #t))
("none" . ,(const #t))))
(define (supported-compression? compression)
"Return true if COMPRESSION, a string, denotes a supported compression
method."
(match (assoc-ref %compression-methods compression)
(#f #f)
(supported? (supported?))))
(define (compresses-better? compression1 compression2)
"Return true if COMPRESSION1 generally compresses better than COMPRESSION2;
this is a rough approximation."
(match compression1
("none" #f)
("gzip" (string=? compression2 "none"))
("lzip" #t)
(_ (or (string=? compression2 "none")
(string=? compression2 "gzip")))))
(define (decompresses-faster? compression1 compression2)
"Return true if COMPRESSION1 generally has a higher decompression throughput
than COMPRESSION2."
(match compression1
("none" #t)
("zstd" #t)
("gzip" (string=? compression2 "lzip"))
(_ #f)))
(define* (narinfo-preferred-uris narinfo #:key fast-decompression?)
"Return the sorted list of \"preferred\" nar URIs from NARINFO (preferred
comes first) where each entry is a tuple containing: the URI, its compression
method (a string), and the compressed file size.
When FAST-DECOMPRESSION? is true, prefer substitutes with faster
decompression (typically zstd) rather than substitutes with a higher
compression ratio (typically lzip)."
(define choices
(filter (match-lambda
((uri compression file-size)
(supported-compression? compression)))
(zip (narinfo-uris narinfo)
(narinfo-compressions narinfo)
(narinfo-file-sizes narinfo))))
(define (file-size<? c1 c2)
(match c1
((uri1 compression1 (? integer? file-size1))
(match c2
((uri2 compression2 (? integer? file-size2))
(< file-size1 file-size2))
(_ #t)))
((uri compression1 #f)
(match c2
((uri2 compression2 _)
(compresses-better? compression1 compression2))))
(_ #f))) ;we can't tell
(define (speed<? c1 c2)
(match c1
((uri1 compression1 . _)
(match c2
((uri2 compression2 . _)
(decompresses-faster? compression2 compression1))))))
(sort choices (if fast-decompression? (negate speed<?) file-size<?)))
(define* (narinfo-best-uri narinfo #:key fast-decompression?)
"Select the \"best\" URI to download NARINFO's nar, and return three values:
the URI, its compression method (a string), and the compressed file size.
When FAST-DECOMPRESSION? is true, prefer substitutes with faster
decompression (typically zstd) rather than substitutes with a higher
compression ratio (typically lzip)."
(match (narinfo-preferred-uris narinfo
#:fast-decompression? fast-decompression?)
(((uri compression file-size) _ ...)
(values uri compression file-size))))
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