summaryrefslogtreecommitdiff
path: root/guix/build/graft.scm
blob: c119ee71d1cc2dfafce8d73a40bb16c7ed421695 (about) (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016, 2018 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016 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-syntax-rule (define-inline name val)
  (define-syntax name (identifier-syntax val)))

(define-inline 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* (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?
    (optimize-u8-predicate
     (compose nix-base32-char?
              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.  To accommodate large files,
  ;; we do not read the entire file, but instead work on buffers of up to
  ;; 'request-size' bytes.  To ensure that every 33-byte sequence appears
  ;; entirely within exactly one buffer, adjacent buffers must overlap,
  ;; i.e. they must share 32 byte positions.  We accomplish this by
  ;; "ungetting" the last 32 bytes 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)))
    (let loop ()
      ;; Note: We avoid 'get-bytevector-n' to work around
      ;; <http://bugs.gnu.org/17466>.
      (match (get-bytevector-n! input buffer 0 request-size)
        ((? eof-object?) 'done)
        (end
         ;; We scan the buffer for dashes that might be preceded by a
         ;; nix-base32 hash.  The key optimization here is that whenever we
         ;; find a NON-nix-base32 character at position 'i', we know that it
         ;; cannot be part of a hash, so the earliest position where the next
         ;; hash could start is i+1 with the following dash at position i+33.
         ;;
         ;; Since nix-base32 characters comprise only 1/8 of the 256 possible
         ;; byte values, and exclude some of the most common letters in
         ;; English text (e t o u), in practice we can advance by 33 positions
         ;; most of the time.
         (let scan-from ((i hash-length) (written 0))
           ;; 'i' is the first position where we look for a dash.  'written'
           ;; is the number of bytes in the buffer that have already been
           ;; written.
           (if (< i end)
               (let ((byte (bytevector-u8-ref buffer i)))
                 (cond ((and (dash? byte)
                             ;; We've found a dash.  Note that we do not know
                             ;; whether the preceeding 32 bytes are nix-base32
                             ;; characters, but we do not need to know.  If
                             ;; they are not, the following lookup will fail.
                             (lookup-replacement
                              (string-tabulate (lambda (j)
                                                 (integer->char
                                                  (bytevector-u8-ref buffer
                                                   (+ j (- i hash-length)))))
                                               hash-length)))
                        => (lambda (replacement)
                             ;; 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 written
                                             (- i hash-length written))
                             ;; Now write the replacement string.
                             (put-bytevector output replacement)
                             ;; Since the byte at position 'i' is a dash,
                             ;; which is not a nix-base32 char, the earliest
                             ;; position where the next hash might start is
                             ;; i+1, and the earliest position where the
                             ;; following dash might start is (+ i 1
                             ;; hash-length).  Also, increase the write
                             ;; position to account for REPLACEMENT.
                             (let ((len (bytevector-length replacement)))
                               (scan-from (+ i 1 len)
                                          (+ i (- len hash-length))))))
                       ;; If the byte at position 'i' is a nix-base32 char,
                       ;; then the dash we're looking for might be as early as
                       ;; the following byte, so we can only advance by 1.
                       ((nix-base32-byte? byte)
                        (scan-from (+ i 1) written))
                       ;; If the byte at position 'i' is NOT a nix-base32
                       ;; char, then the earliest position where the next hash
                       ;; might start is i+1, with the following dash at
                       ;; position (+ i 1 hash-length).
                       (else
                        (scan-from (+ i 1 hash-length) written))))

               ;; 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
               ;; 'hash-length' bytes (32 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.
               (begin
                 (if (> written end)
                     (get-bytevector-n! input buffer 0 (- written end))
                     (let* ((unwritten  (- end written))
                            (unget-size (if (= end request-size)
                                            (min hash-length unwritten)
                                            0))
                            (write-size (- unwritten unget-size)))
                       (put-bytevector output buffer written write-size)
                       (unget-bytevector input buffer (+ written write-size)
                                         unget-size)))
                 (loop)))))))))

(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