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|
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016, 2018 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016, 2021 Mark H Weaver <mhw@netris.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 build graft)
#:use-module (guix build utils)
#:use-module (guix build debug-link)
#:use-module (rnrs bytevectors)
#:use-module (ice-9 vlist)
#:use-module (ice-9 match)
#:use-module (ice-9 threads)
#:use-module (ice-9 binary-ports)
#:use-module (srfi srfi-1) ; list library
#:use-module (srfi srfi-26) ; cut and cute
#:export (replace-store-references
rewrite-directory
graft))
;;; Commentary:
;;;
;;; This module supports "grafts". Grafting a directory means rewriting it,
;;; with references to some specific items replaced by references to other
;;; store items---the grafts.
;;;
;;; This method is used to provide fast security updates as only the leaves of
;;; the dependency graph need to be grafted, even when the security updates
;;; affect a core component such as Bash or libc. It is based on the idea of
;;; 'replace-dependency' implemented by Shea Levy in Nixpkgs.
;;;
;;; Code:
(define-constant hash-length 32)
(define nix-base32-char?
(cute char-set-contains?
;; ASCII digits and lower case letters except e o t u
(string->char-set "0123456789abcdfghijklmnpqrsvwxyz")
<>))
(define (nix-base32-char-or-nul? c)
"Return true if C is a nix-base32 character or NUL, otherwise return false."
(or (nix-base32-char? c)
(char=? c #\nul)))
(define (possible-utf16-hash? buffer i w)
"Return true if (I - W) is large enough to hold a UTF-16 encoded
nix-base32 hash and if BUFFER contains NULs in all positions where NULs
are to be expected in a UTF-16 encoded hash+dash pattern whose dash is
found at position I. Otherwise, return false."
(and (<= (* 2 hash-length) (- i w))
(let loop ((j (+ 1 (- i (* 2 hash-length)))))
(or (>= j i)
(and (zero? (bytevector-u8-ref buffer j))
(loop (+ j 2)))))))
(define (possible-utf32-hash? buffer i w)
"Return true if (I - W) is large enough to hold a UTF-32 encoded
nix-base32 hash and if BUFFER contains NULs in all positions where NULs
are to be expected in a UTF-32 encoded hash+dash pattern whose dash is
found at position I. Otherwise, return false."
(and (<= (* 4 hash-length) (- i w))
(let loop ((j (+ 1 (- i (* 4 hash-length)))))
(or (>= j i)
(and (zero? (bytevector-u8-ref buffer j))
(zero? (bytevector-u8-ref buffer (+ j 1)))
(zero? (bytevector-u8-ref buffer (+ j 2)))
(loop (+ j 4)))))))
(define (insert-nuls char-size bv)
"Given a bytevector BV, return a bytevector containing the same bytes but
with (CHAR-SIZE - 1) NULs inserted between every two adjacent bytes from BV.
For example, (insert-nuls 4 #u8(1 2 3)) => #u8(1 0 0 0 2 0 0 0 3)."
(if (= char-size 1)
bv
(let* ((len (bytevector-length bv))
(bv* (make-bytevector (+ 1 (* char-size
(- len 1)))
0)))
(let loop ((i 0))
(when (< i len)
(bytevector-u8-set! bv* (* i char-size)
(bytevector-u8-ref bv i))
(loop (+ i 1))))
bv*)))
(define* (replace-store-references input output replacement-table
#:optional (store (%store-directory)))
"Read data from INPUT, replacing store references according to
REPLACEMENT-TABLE, and writing the result to OUTPUT. REPLACEMENT-TABLE is a
vhash that maps strings (original hashes) to bytevectors (replacement strings
comprising the replacement hash, a dash, and a string).
Note: We use string keys to work around the fact that guile-2.0 hashes all
bytevectors to the same value."
(define (lookup-replacement s)
(match (vhash-assoc s replacement-table)
((origin . replacement)
replacement)
(#f #f)))
(define (optimize-u8-predicate pred)
(cute vector-ref
(list->vector (map pred (iota 256)))
<>))
(define nix-base32-byte-or-nul?
(optimize-u8-predicate
(compose nix-base32-char-or-nul?
integer->char)))
(define (dash? byte) (= byte 45))
(define request-size (expt 2 20)) ; 1 MiB
;; We scan the file for the following 33-byte pattern: 32 bytes of
;; nix-base32 characters followed by a dash. When we find such a pattern
;; whose hash is in REPLACEMENT-TABLE, we perform the required rewrite and
;; continue scanning.
;;
;; To support UTF-16 and UTF-32 store references, the 33 bytes comprising
;; this hash+dash pattern may optionally be interspersed by extra NUL bytes.
;; This simple approach works because the characters we are looking for are
;; restricted to ASCII. UTF-16 hashes are interspersed with single NUL
;; bytes ("\0"), and UTF-32 hashes are interspersed with triplets of NULs
;; ("\0\0\0"). Note that we require NULs to be present only *between* the
;; other bytes, and not at either end, in order to be insensitive to byte
;; order.
;;
;; To accommodate large files, we do not read the entire file at once, but
;; instead work on buffers of up to REQUEST-SIZE bytes. To ensure that
;; every hash+dash pattern appears in its entirety in at least one buffer,
;; adjacent buffers must overlap by one byte less than the maximum size of a
;; hash+dash pattern. We accomplish this by "ungetting" a suffix of each
;; buffer before reading the next buffer, unless we know that we've reached
;; the end-of-file.
(let ((buffer (make-bytevector request-size)))
(define-syntax-rule (byte-at i)
(bytevector-u8-ref buffer i))
(let outer-loop ()
(match (get-bytevector-n! input buffer 0 request-size)
((? eof-object?) 'done)
(end
(define (scan-from i w)
;; Scan the buffer for dashes that might be preceded by nix hashes,
;; where I is the minimum position where such a dash might be
;; found, and W is the number of bytes in the buffer that have been
;; written so far. We assume that I - W >= HASH-LENGTH.
;;
;; The key optimization here is that whenever we find a byte at
;; position I that cannot occur within a nix hash (because it's
;; neither a nix-base32 character nor NUL), we can infer that the
;; earliest position where the next hash could start is at I + 1,
;; and therefore the earliest position for the following dash is
;; (+ I 1 HASH-LENGTH), which is I + 33.
;;
;; Since nix-base32-or-nul characters comprise only about 1/8 of
;; the 256 possible byte values, and exclude some of the most
;; common letters in English text (e t o u), we can advance 33
;; positions much of the time.
(if (< i end)
(let ((byte (byte-at i)))
(cond ((dash? byte)
(found-dash i w))
((nix-base32-byte-or-nul? byte)
(scan-from (+ i 1) w))
(else
(not-part-of-hash i w))))
(finish-buffer i w)))
(define (not-part-of-hash i w)
;; Position I is known to not be within a nix hash that we must
;; rewrite. Therefore, the earliest position where the next hash
;; might start is I + 1, and therefore the earliest position of
;; the following dash is (+ I 1 HASH-LENGTH).
(scan-from (+ i 1 hash-length) w))
(define (found-dash i w)
;; We know that there is a dash '-' at position I, and that
;; I - W >= HASH-LENGTH. The immediately preceding bytes *might*
;; contain a nix-base32 hash, but that is not yet known. Here,
;; we rule out all but one possible encoding (ASCII, UTF-16,
;; UTF-32) by counting how many NULs precede the dash.
(cond ((not (zero? (byte-at (- i 1))))
;; The dash is *not* preceded by a NUL, therefore it
;; cannot possibly be a UTF-16 or UTF-32 hash. Proceed
;; to check for an ASCII hash.
(found-possible-hash 1 i w))
((not (zero? (byte-at (- i 2))))
;; The dash is preceded by exactly one NUL, therefore it
;; cannot be an ASCII or UTF-32 hash. Proceed to check
;; for a UTF-16 hash.
(if (possible-utf16-hash? buffer i w)
(found-possible-hash 2 i w)
(not-part-of-hash i w)))
(else
;; The dash is preceded by at least two NULs, therefore
;; it cannot be an ASCII or UTF-16 hash. Proceed to
;; check for a UTF-32 hash.
(if (possible-utf32-hash? buffer i w)
(found-possible-hash 4 i w)
(not-part-of-hash i w)))))
(define (found-possible-hash char-size i w)
;; We know that there is a dash '-' at position I, that
;; I - W >= CHAR-SIZE * HASH-LENGTH, and that the only
;; possible encoding for the preceding hash is as indicated by
;; CHAR-SIZE. Here we check to see if the given hash is in
;; REPLACEMENT-TABLE, and if so, we perform the required
;; rewrite.
(let* ((hash (string-tabulate
(lambda (j)
(integer->char
(byte-at (- i (* char-size
(- hash-length j))))))
hash-length))
(replacement* (lookup-replacement hash))
(replacement (and replacement*
(insert-nuls char-size replacement*))))
(cond
((not replacement)
(not-part-of-hash i w))
(else
;; We've found a hash that needs to be replaced.
;; First, write out all bytes preceding the hash
;; that have not yet been written.
(put-bytevector output buffer w
(- i (* char-size hash-length) w))
;; Now write the replacement string.
(put-bytevector output replacement)
;; Now compute the new values of W and I and continue.
(let ((w (+ (- i (* char-size hash-length))
(bytevector-length replacement))))
(scan-from (+ w hash-length) w))))))
(define (finish-buffer i w)
;; We have finished scanning the buffer. Now we determine how many
;; bytes have not yet been written, and how many bytes to "unget".
;; If END is less than REQUEST-SIZE then we read less than we asked
;; for, which indicates that we are at EOF, so we needn't unget
;; anything. Otherwise, we unget up to (* 4 HASH-LENGTH) bytes.
;; However, we must be careful not to unget bytes that have already
;; been written, because that would cause them to be written again
;; from the next buffer. In practice, this case occurs when a
;; replacement is made near or beyond the end of the buffer. When
;; REPLACEMENT went beyond END, we consume the extra bytes from
;; INPUT.
(if (> w end)
(get-bytevector-n! input buffer 0 (- w end))
(let* ((unwritten (- end w))
(unget-size (if (= end request-size)
(min (* 4 hash-length)
unwritten)
0))
(write-size (- unwritten unget-size)))
(put-bytevector output buffer w write-size)
(unget-bytevector input buffer (+ w write-size)
unget-size)))
(outer-loop))
(scan-from hash-length 0))))))
(define (rename-matching-files directory mapping)
"Apply MAPPING to the names of all the files in DIRECTORY, where MAPPING is
a list of store file name pairs."
(let* ((mapping (map (match-lambda
((source . target)
(cons (basename source) (basename target))))
mapping))
(matches (find-files directory
(lambda (file stat)
(assoc-ref mapping (basename file)))
#:directories? #t)))
;; XXX: This is not quite correct: if MAPPING contains "foo", and
;; DIRECTORY contains "bar/foo/foo", we first rename "bar/foo" and then
;; "bar/foo/foo" no longer exists so we fail. Oh well, surely that's good
;; enough!
(for-each (lambda (file)
(let ((target (assoc-ref mapping (basename file))))
(rename-file file
(string-append (dirname file) "/" target))))
matches)))
(define (exit-on-exception proc)
"Return a procedure that wraps PROC so that 'primitive-exit' is called when
an exception is caught."
(lambda (arg)
(catch #t
(lambda ()
(proc arg))
(lambda (key . args)
;; Since ports are not thread-safe as of Guile 2.0, reopen stderr.
(let ((port (fdopen 2 "w0")))
(print-exception port #f key args)
(primitive-exit 1))))))
;; We need this as long as we support Guile < 2.0.13.
(define* (mkdir-p* dir #:optional (mode #o755))
"This is a variant of 'mkdir-p' that works around
<http://bugs.gnu.org/24659> by passing MODE explicitly in each 'mkdir' call."
(define absolute?
(string-prefix? "/" dir))
(define not-slash
(char-set-complement (char-set #\/)))
(let loop ((components (string-tokenize dir not-slash))
(root (if absolute?
""
".")))
(match components
((head tail ...)
(let ((path (string-append root "/" head)))
(catch 'system-error
(lambda ()
(mkdir path mode)
(loop tail path))
(lambda args
(if (= EEXIST (system-error-errno args))
(loop tail path)
(apply throw args))))))
(() #t))))
(define* (rewrite-directory directory output mapping
#:optional (store (%store-directory)))
"Copy DIRECTORY to OUTPUT, replacing strings according to MAPPING, a list of
file name pairs."
(define hash-mapping
;; List of hash/replacement pairs, where the hash is a nix-base32 string
;; and the replacement is a string that includes the replacement's name,
;; like "r837zajjc1q8z9hph4b6860a9c05blyy-openssl-1.0.2j".
(let* ((prefix (string-append store "/"))
(start (string-length prefix))
(end (+ start hash-length)))
(define (valid-hash? h)
(every nix-base32-char? (string->list h)))
(define (hash+rest s)
(and (< end (string-length s))
(let ((hash (substring s start end))
(all (substring s start)))
(and (string-prefix? prefix s)
(valid-hash? hash)
(eqv? #\- (string-ref s end))
(list hash all)))))
(map (match-lambda
(((= hash+rest (origin-hash origin-string))
.
(= hash+rest (replacement-hash replacement-string)))
(unless (= (string-length origin-string)
(string-length replacement-string))
(error "replacement length differs from the original length"
origin-string replacement-string))
(cons origin-hash (string->utf8 replacement-string)))
((origin . replacement)
(error "invalid replacement" origin replacement)))
mapping)))
(define replacement-table
(alist->vhash hash-mapping))
(define prefix-len
(string-length directory))
(define (destination file)
(string-append output (string-drop file prefix-len)))
(define (rewrite-leaf file)
(let ((stat (lstat file))
(dest (destination file)))
(mkdir-p* (dirname dest))
(case (stat:type stat)
((symlink)
(let ((target (readlink file)))
(symlink (call-with-output-string
(lambda (output)
(replace-store-references (open-input-string target)
output replacement-table
store)))
dest)))
((regular)
(call-with-input-file file
(lambda (input)
(call-with-output-file dest
(lambda (output)
(replace-store-references input output replacement-table
store)
(chmod output (stat:perms stat)))))))
((directory)
(mkdir-p* dest))
(else
(error "unsupported file type" stat)))))
;; Use 'exit-on-exception' to force an exit upon I/O errors, given that
;; 'n-par-for-each' silently swallows exceptions.
;; See <http://bugs.gnu.org/23581>.
(n-par-for-each (parallel-job-count)
(exit-on-exception rewrite-leaf)
(find-files directory (const #t)
#:directories? #t))
(rename-matching-files output mapping))
(define %graft-hooks
;; Default list of hooks run after grafting.
(list graft-debug-links))
(define* (graft old-outputs new-outputs mapping
#:key (log-port (current-output-port))
(hooks %graft-hooks))
"Apply the grafts described by MAPPING on OLD-OUTPUTS, leading to
NEW-OUTPUTS. MAPPING must be a list of file name pairs; OLD-OUTPUTS and
NEW-OUTPUTS are lists of output name/file name pairs."
(for-each (lambda (input output)
(format log-port "grafting '~a' -> '~a'...~%" input output)
(force-output)
(rewrite-directory input output mapping))
(match old-outputs
(((names . files) ...)
files))
(match new-outputs
(((names . files) ...)
files)))
(for-each (lambda (hook)
(hook old-outputs new-outputs mapping
#:log-port log-port))
hooks))
;;; graft.scm ends here
|