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861345b4 | 1 | ;;; -*-lisp-*- |
2 | ;;; | |
3 | ;;; $Id$ | |
4 | ;;; | |
5 | ;;; Safely modify collections of files | |
6 | ;;; | |
7 | ;;; (c) 2005 Straylight/Edgeware | |
8 | ;;; | |
9 | ||
10 | ;;;----- Licensing notice --------------------------------------------------- | |
11 | ;;; | |
12 | ;;; This program is free software; you can redistribute it and/or modify | |
13 | ;;; it under the terms of the GNU General Public License as published by | |
14 | ;;; the Free Software Foundation; either version 2 of the License, or | |
15 | ;;; (at your option) any later version. | |
b2c12b4e | 16 | ;;; |
861345b4 | 17 | ;;; This program is distributed in the hope that it will be useful, |
18 | ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | ;;; GNU General Public License for more details. | |
b2c12b4e | 21 | ;;; |
861345b4 | 22 | ;;; You should have received a copy of the GNU General Public License |
23 | ;;; along with this program; if not, write to the Free Software Foundation, | |
24 | ;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
25 | ||
0b3651e5 | 26 | (defpackage #:safely |
623291d2 | 27 | (:use #:common-lisp #:mdw.base) |
861345b4 | 28 | (:export #:safely #:safely-close #:safely-delete-file |
29 | #:safely-open-output-stream #:safely-bail #:safely-commit | |
30 | #:safely-writing)) | |
0b3651e5 | 31 | (in-package #:safely) |
861345b4 | 32 | |
d7d81997 MW |
33 | #+(or cmu sbcl) |
34 | (eval-when (:compile-toplevel :execute) | |
35 | (import #+cmu '(ext:unix-namestring unix:unix-link) | |
2d9f4fc0 MW |
36 | #+sbcl '(sb-ext:native-namestring))) |
37 | #+cmu | |
38 | (progn | |
39 | (declaim (inline unix-namestring)) | |
40 | (defun native-namestring (pathname &key as-file) | |
41 | (declare (ignore as-file)) | |
42 | (unix-namestring pathname nil))) | |
d7d81997 | 43 | |
861345b4 | 44 | (defstruct (safely (:predicate safelyp)) |
45 | "Stores information about how to commit or undo safe writes." | |
46 | (streams nil) | |
47 | (trail nil)) | |
5e04ac39 | 48 | |
861345b4 | 49 | (defun safely-close (safe stream) |
50 | "Make sure that STREAM is closed when SAFE is finished." | |
51 | (push stream (safely-streams safe))) | |
5e04ac39 | 52 | |
861345b4 | 53 | (defun safely-delete-file (safe file) |
54 | "Delete FILE when SAFE is committed." | |
623291d2 MW |
55 | (push `(:delete ,file) (safely-trail safe))) |
56 | ||
57 | (defun generate-fresh-file-name (base tag &optional func) | |
58 | "Return a fresh file name constructed from BASE (a filespec) and TAG (some | |
59 | short descriptive string). The generated name has the same directory and | |
60 | type as the BASE name, but a different name. | |
61 | ||
62 | If FUNC is non-nil, then it is a function to call on the generated file | |
63 | name: generate-fresh-file-name runs in a loop, calling FUNC with generated | |
64 | file names until FUNC returns non-nil, at which point generate-fresh- | |
65 | file-name returns two values: the generated name, and the result of FUNC. | |
66 | generate-fresh-file-name catches errors of type file-error from FUNC, and | |
67 | just tries again with a new name. | |
68 | ||
69 | If FUNC is nil, it's treated the same as a function which always returns | |
70 | t. | |
71 | ||
72 | This is inspired by a similar facility in scsh." | |
73 | (let ((base (pathname base))) | |
74 | (dotimes (i 256 | |
75 | (error "Gave up trying to find a temporary ~A file for ~S." | |
76 | tag base)) | |
77 | (let* ((new (merge-pathnames | |
78 | (make-pathname | |
79 | :name (format nil "~A-~A-~X" | |
80 | (pathname-name base) | |
81 | tag | |
82 | (random most-positive-fixnum))) | |
83 | base)) | |
84 | (ret (and (not (probe-file new)) | |
85 | (if func | |
86 | (handler-case (funcall func new) | |
87 | (file-error (cond) | |
88 | (unless (pathname-match-p | |
89 | (file-error-pathname cond) | |
90 | new) | |
91 | (error cond)) | |
92 | nil)) | |
93 | t)))) | |
94 | (when ret | |
95 | (return (values new ret))))))) | |
5e04ac39 | 96 | |
861345b4 | 97 | (defun safely-open-output-stream (safe file &rest open-args) |
98 | "Create an output stream which will be named FILE when SAFE is committed. | |
0ff9df03 | 99 | Other OPEN-ARGS are passed to open." |
623291d2 MW |
100 | (multiple-value-bind |
101 | (name stream) | |
102 | (generate-fresh-file-name file "new" | |
103 | (lambda (name) | |
104 | (apply #'open name | |
105 | :direction :output | |
106 | :if-exists nil | |
107 | open-args))) | |
861345b4 | 108 | (safely-close safe stream) |
623291d2 | 109 | (push `(:shunt ,name ,file) |
861345b4 | 110 | (safely-trail safe)) |
111 | stream)) | |
5e04ac39 | 112 | |
9224720f MW |
113 | #+clisp |
114 | (progn | |
115 | (ffi:def-call-out %rename (:name "rename") | |
116 | (:language :stdc) | |
4b53d23c | 117 | (:library "libc.so.6") |
9224720f MW |
118 | (:arguments (from ffi:c-string) |
119 | (to ffi:c-string)) | |
120 | (:return-type ffi:int))) | |
121 | ||
443fcfc4 MW |
122 | (declaim (inline rename)) |
123 | (defun rename (old new) | |
9224720f | 124 | #-clisp |
562ed2dd MW |
125 | (let ((target (make-pathname :directory '(:relative) |
126 | :defaults new))) | |
9224720f MW |
127 | (rename-file old target)) |
128 | ||
129 | #+clisp | |
130 | (let ((rc (%rename (namestring old) (namestring new)))) | |
131 | (when (= rc -1) | |
132 | (error "Failed to rename ~S to ~S: ~A" old new (posix:strerror))))) | |
443fcfc4 | 133 | |
861345b4 | 134 | (defun delete-file-without-moaning (file) |
135 | "Delete the FILE, ignoring errors." | |
623291d2 MW |
136 | (handler-case (delete-file file) |
137 | (file-error () nil))) | |
5e04ac39 | 138 | |
861345b4 | 139 | (defun rename-file-without-moaning (old new) |
140 | "Rename OLD to NEW, ignoring errors, and without doing any stupid name | |
0ff9df03 | 141 | mangling." |
443fcfc4 | 142 | (handler-case (rename old new) |
623291d2 | 143 | (file-error () nil))) |
5e04ac39 | 144 | |
861345b4 | 145 | (defun safely-unwind (trail) |
146 | "Roll back the TRAIL of operations." | |
147 | (dolist (job trail) | |
148 | (ecase (car job) | |
623291d2 MW |
149 | (:shunt (destructuring-bind (new file) (cdr job) |
150 | (declare (ignore file)) | |
861345b4 | 151 | (delete-file-without-moaning new))) |
152 | (:delete) | |
623291d2 | 153 | (:rmtmp (destructuring-bind (file) (cdr job) |
861345b4 | 154 | (delete-file-without-moaning file))) |
623291d2 | 155 | (:revert (destructuring-bind (old new) (cdr job) |
861345b4 | 156 | (rename-file-without-moaning old new)))))) |
5e04ac39 | 157 | |
861345b4 | 158 | (defun safely-reset (safe) |
159 | "Reset SAFE to its initial state." | |
160 | (setf (safely-streams safe) nil) | |
161 | (setf (safely-trail safe) nil)) | |
5e04ac39 | 162 | |
861345b4 | 163 | (defun safely-bail (safe) |
164 | "Abort the operations in SAFE, unwinding all the things that have been | |
0ff9df03 | 165 | done. Streams are closed, new files are removed." |
861345b4 | 166 | (dolist (stream (safely-streams safe)) |
167 | (close stream :abort t)) | |
168 | (safely-unwind (safely-trail safe)) | |
169 | (safely-reset safe)) | |
5e04ac39 | 170 | |
d7d81997 MW |
171 | #+sbcl |
172 | (defun unix-link (from to) | |
173 | (sb-unix::int-syscall ("link" sb-alien:c-string sb-alien:c-string) | |
174 | from to)) | |
175 | ||
623291d2 MW |
176 | (defun safe-copy (file tag) |
177 | "Make a copy of the FILE. Return the new name." | |
178 | ||
d7d81997 | 179 | #+(or cmu sbcl) |
623291d2 MW |
180 | ;; Use link(2) where available. |
181 | (generate-fresh-file-name file tag | |
182 | (lambda (name) | |
2d9f4fc0 MW |
183 | (let ((from (native-namestring file |
184 | :as-file t)) | |
185 | (to (native-namestring name | |
186 | :as-file t))) | |
623291d2 | 187 | (and from to |
d7d81997 | 188 | (unix-link from to))))) |
623291d2 | 189 | |
443fcfc4 MW |
190 | #+clisp |
191 | (generate-fresh-file-name file tag | |
192 | (lambda (name) | |
6a115035 MW |
193 | (posix:copy-file (namestring file) |
194 | (namestring name) | |
195 | :method :hardlink | |
196 | :if-exists nil))) | |
197 | ||
1a50efd8 | 198 | #-(or cmu sbcl clisp) |
623291d2 MW |
199 | ;; Otherwise just copy the file contents and hope for the best. |
200 | (with-open-file (input file :element-type :default) | |
201 | (multiple-value-bind | |
202 | (copy output) | |
203 | (generate-fresh-file-name file tag | |
204 | (lambda (name) | |
205 | (open name | |
206 | :direction :output | |
207 | :if-exists nil | |
208 | :element-type :default))) | |
209 | (unwind-protect | |
210 | (progn | |
211 | (let ((buffer (make-array 8192 | |
212 | :element-type (stream-element-type | |
213 | input)))) | |
214 | (loop | |
215 | (let ((read (read-sequence buffer input))) | |
216 | (when (plusp read) | |
217 | (write-sequence buffer output :end read)) | |
218 | (when (< read (length buffer)) | |
219 | (return copy)))))) | |
220 | (close output))))) | |
b2c12b4e | 221 | |
861345b4 | 222 | (defun safely-commit (safe) |
223 | "Commit SAFE. The files deleted by safely-delete-file are deleted; the | |
0ff9df03 MW |
224 | files created by safely-open-output-stream are renamed over the old |
225 | versions, if any. If a problem occurs during this stage, everything is | |
226 | rewound and no changes are made." | |
861345b4 | 227 | (let ((trail (safely-trail safe)) |
228 | (revert nil) | |
229 | (cleanup nil)) | |
230 | (unwind-protect | |
231 | (progn | |
232 | (dolist (stream (safely-streams safe)) | |
233 | (close stream)) | |
234 | (loop | |
235 | (unless trail | |
236 | (return)) | |
6e1633e7 MW |
237 | (let ((job (pop trail))) |
238 | (ecase (car job) | |
239 | (:shunt (destructuring-bind (tag new file) job | |
240 | (declare (ignore tag)) | |
241 | (push `(:rmtmp ,new) revert) | |
242 | (if (probe-file file) | |
243 | (let ((old (safe-copy file "old"))) | |
244 | (push `(:rmtmp ,old) cleanup) | |
245 | (push `(:revert ,old ,file) revert)) | |
246 | (push `(:rmtmp ,file) revert)) | |
247 | (rename new file))) | |
248 | (:delete (destructuring-bind (tag file) job | |
249 | (declare (ignore tag)) | |
250 | (let ((old (safe-copy file "delete"))) | |
251 | (push `(:revert ,old ,file) revert) | |
252 | (push `(:rmtmp ,old) cleanup) | |
253 | (delete-file file))))))) | |
861345b4 | 254 | (setf revert nil)) |
255 | (safely-unwind trail) | |
256 | (safely-unwind revert) | |
257 | (safely-unwind cleanup) | |
258 | (safely-reset safe)))) | |
5e04ac39 | 259 | |
861345b4 | 260 | (defmacro safely ((safe &key) &body body) |
261 | "Do stuff within the BODY safely. If BODY completes without errors, the | |
0ff9df03 | 262 | SAFE is committed; otherwise it's bailed." |
861345b4 | 263 | `(let ((,safe (make-safely))) |
264 | (unwind-protect | |
265 | (progn | |
266 | ,@body | |
267 | (safely-commit ,safe) | |
268 | (setf ,safe nil)) | |
269 | (when ,safe | |
270 | (safely-bail ,safe))))) | |
5e04ac39 | 271 | |
861345b4 | 272 | (defmacro safely-writing ((stream file &rest open-args) &body body) |
273 | "Simple macro for writing a single file safely. STREAM is opened onto a | |
0ff9df03 | 274 | temporary file, and if BODY completes, it is renamed to FILE." |
861345b4 | 275 | (with-gensyms safe |
276 | `(safely (,safe) | |
7413889a | 277 | (let ((,stream (safely-open-output-stream ,safe ,file ,@open-args))) |
861345b4 | 278 | ,@body)))) |
279 | ||
280 | ;;;----- That's all, folks -------------------------------------------------- |