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