aboutsummaryrefslogtreecommitdiffstats
path: root/transact.scm
blob: 59a06fe95d4aa40aa84cd5f0f2e25fb8f0d6a1e9 (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
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
;;; "transact.scm" Interface to programs.
; Copyright 1997, 1998, 2002 Aubrey Jaffer
;
;Permission to copy this software, to modify it, to redistribute it,
;to distribute modified versions, and to use it for any purpose is
;granted, subject to the following restrictions and understandings.
;
;1.  Any copy made of this software must include this copyright notice
;in full.
;
;2.  I have made no warranty or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3.  In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.

(require 'string-search)
(require 'filename)
(require 'line-i/o)
(require 'system)
(require 'printf)
(require 'scanf)
(require 'byte)
(require-if 'compiling 'directory)

;;@subsubheading File Locking
;;
;;@noindent
;;Unix file-locking is focussed on write permissions for segments of a
;;existing file.  While this might be employed for (binary) database
;;access, it is not used for everyday contention (between users) for
;;text files.
;;
;;@noindent
;;Microsoft has several file-locking protocols.  Their model denies
;;write access to a file if any reader has it open.  This is too
;;restrictive.  Write access is denied even when the reader has
;;reached end-of-file.  And tracking read access (which is much more
;;common than write access) causes havoc when remote hosts crash or
;;disconnect.
;;
;;@noindent
;;It is bizarre that the concept of multi-user contention for
;;modifying files has not been adequately addressed by either of the
;;large operating system development efforts.  There is further irony
;;that both camps support contention detection and resolution only
;;through weak conventions of some their document editing programs.
;;
;;@noindent
;;@cindex file-lock
;;The @dfn{file-lock} procedures implement a transaction method for file
;;replacement compatible with the methods used by the GNU @dfn{emacs}
;;text editor on Unix systems and the Microsoft @dfn{Word} editor.
;;@cindex emacs
;;
;;@noindent
;;@cindex certificate
;;Both protocols employ what I term a @dfn{certificate} containing the
;;user, hostname, time, and (on Unix) process-id.
;;Intent to replace @var{file} is indicated by adding to @var{file}'s
;;directory a certificate object whose name is derived from
;;@var{file}.
;;
;;@noindent
;;The Microsoft Word certificate is contained in a 162 byte file named
;;for the visited @var{file} with a @samp{~$} prefix.
;;Emacs/Unix creates a symbolic link to a certificate named for the
;;visited @var{file} prefixed with @samp{.#}.
;;Because Unix systems can import Microsoft file systems, these
;;routines maintain and check both Emacs and Word certificates.

;;Returns a string naming the path of the emacs-style file-lock symbolic
;;link associated with @1.
(define (emacs-lock:path path)
  (let* ((dir (pathname->vicinity path))
	 (file (substring path (string-length dir) (string-length path))))
    (in-vicinity dir (string-append ".#" file))))

;;Returns a string naming the path of the ms-word style lock file
;;associated with @1.
(define (word-lock:path path)
  (let* ((dir (pathname->vicinity path))
	 (file (substring path (string-length dir) (string-length path)))
	 (filen (string-length file)))
    (in-vicinity
     dir (string-append
	  "~$" (substring file (min 2 (max 0 (- filen 10))) filen)))))

(define (word-lock:certificate lockpath)
  (define iport (open-file lockpath "rb"))
  (and
   iport
   (call-with-open-ports
    (lambda (iport)
      (define len (read-byte iport))
      (define pos 1)
      (and (number? len)
	   (let ((name (make-string len)))
	     (define (discard cnt)
	       (do ((cnt (+ -1 cnt) (+ -1 cnt)))
		   ((or (eof-object? (peek-char iport)) (negative? cnt))
		    (negative? cnt))
		 (or (eof-object? (read-byte iport)) (set! pos (+ 1 pos)))))
	     (define (read-field)
	       (define len (read-byte iport))
	       (set! pos (+ 1 pos))
	       (or (eof-object? (read-byte iport)) (set! pos (+ 1 pos)))
	       (and (number? len)
		    (let ((str (make-string len)))
		      (do ((idx 0 (+ 1 idx)))
			  ((or (eof-object? (peek-char iport)) (>= idx len))
			   (and (>= idx len) str))
			(string-set! str idx (read-char iport))
			(or (eof-object? (read-char iport)) (set! pos (+ 2 pos)))))))
;;; read compact name
	     (do ((idx 0 (+ 1 idx)))
		 ((or (eof-object? (peek-char iport)) (>= idx len)))
	       (string-set! name idx (read-char iport))
	       (set! pos (+ 1 pos)))
;;; read expanded names (interleaved with nul)
	     (let* ((name2 (and (discard (- 54 pos)) (read-field)))
		    (company (and (discard 6) (read-field)))
		    (name3 (and (discard 8) (read-field))))
	       (define (check field fieldname)
		 (cond ((not field) (slib:warn 'missing fieldname))
		       ((equal? name field))
		       (else (slib:warn fieldname 'mismatch name field))))
	       (check name2 'name2)
	       (check name3 'name3)
	       (or (and (eof-object? (peek-char iport)) (= pos 162))
		   (and (not (and (discard (- 162 pos))
				  (eof-object? (peek-char iport))))
			(slib:error lockpath 'length pos '(not = 162))))
	       (and name company (sprintf #f "%s@%s" name company))))))
    iport)))

(define (emacs-lock:certificate lockpath)
  (define conflict
    (system->line (sprintf #f "ls -ld %#a 2>/dev/null" lockpath)))
  (cond ((and conflict (substring? "-> " conflict))
	 => (lambda (idx)
	      (substring conflict (+ 3 idx) (string-length conflict))))
	(conflict (slib:error 'bad 'emacs 'lock lockpath conflict))
	(else #f)))

(define (file-lock:certificate path)
  (or (case (software-type)
	((UNIX COHERENT PLAN9)
	 (emacs-lock:certificate (emacs-lock:path path)))
	(else #f))
      (word-lock:certificate (word-lock:path path))))

;;@body
;;Returns the string @samp{@var{user}@@@var{hostname}} associated with
;;the lock owner of file @1 if locked; and #f otherwise.
(define (file-lock-owner path)
  (or (emacs-lock:certificate (emacs-lock:path path))
      (word-lock:certificate (word-lock:path path))))

(define (word:lock! path email)
  (define lockpath (word-lock:path path))
  (define at (substring? "@" email))
  (let ((user (substring email 0 at))
	(hostname (substring email (+ 1 at) (string-length email)))
	(oport (open-file lockpath "wb")))
    (define userlen (string-length user))
    (and oport (call-with-open-ports
		oport (lambda (oport)
			(define pos 1)
			(define (nulls cnt)
			  (display (make-bytes cnt 0) oport)
			  (set! pos (+ cnt pos)))
			(define (write-field field)
			  (define len (string-length field))
			  (write-byte len oport)
			  (write-byte 0 oport)
			  (set! pos (+ 2 pos))
			  (do ((idx 0 (+ 1 idx)))
			      ((>= idx len))
			    (write-char (string-ref field idx) oport)
			    (write-byte 0 oport)
			    (set! pos (+ 2 pos))))
			(write-byte userlen oport)
			(display user oport) (set! pos (+ userlen pos))
;;; write expanded names (interleaved with nul)
			(nulls (- 54 pos))
			(write-field user)
			(nulls 6)
			(write-field hostname)
			(nulls 8)
			(write-field user)
			(nulls (- 162 pos))
			(and (not (eqv? 162 pos))
			     (slib:error lockpath 'length pos '(not = 162)))
			(let ((certificate (word-lock:certificate lockpath)))
			  (and (equal? email certificate) email)))))))

(define (emacs:lock! path email)
  (define lockpath (emacs-lock:path path))
  (define certificate (sprintf #f "%s.%s:%d"
			       email
			       (or (system->line "echo $PPID") "")
			       (current-time)))
  (and (eqv? 0 (system (sprintf #f "ln -s %#a %#a" certificate lockpath)))
       (let ((e-cert (emacs-lock:certificate lockpath)))
	 (and (equal? certificate e-cert)
	      certificate))))

;;@args path email
;;@args path
;;
;;@1 must be a string naming the file to be locked.  If supplied, @2
;;must be a string formatted as @samp{@var{user}@@@var{hostname}}.  If
;;absent, @2 defaults to the value returned by @code{user-email-address}.
;;
;;If @1 is already locked, then @0 returns @samp{#f}.  If @1 is
;;unlocked, then @0 returns the certificate string associated with the
;;new lock for file @1.
(define (file-lock! path . email)
  (set! email (if (null? email) (user-email-address) (car email)))
  (and (string? email)
       (not (file-lock:certificate path))
       (let ((wl (word:lock! path email)))
	 (case (software-type)
	   ((UNIX COHERENT PLAN9)
	    ;; file-system may not support symbolic links.
	    (or (emacs:lock! path email) wl))
	   (else wl)))))

;;@body
;;@1 must be a string naming the file to be unlocked.  @2 must be the
;;string returned by @code{file-lock!} for @1.
;;
;;If @1 is locked with @2, then @0 removes the locks and returns
;;@samp{#t}.  Otherwise, @0 leaves the file system unaltered and returns
;;@samp{#f}.
(define (file-unlock! path certificate)
  (define w-path (word-lock:path path))
  (let ((w-cert (word-lock:certificate w-path)))
    (cond ((not w-cert) #f)
	  ((not certificate) #f)
	  ((equal? w-cert certificate)	; my word certificate
	   (delete-file w-path))
	  ((not (eqv? 0 (substring? w-cert certificate)))
	   ;; word certificate doesn't match emacs certificate
	   (slib:warn 'file-unlock! w-path 'mismatch certificate) #f)
	  (else
	   (let ((e-path (emacs-lock:path path)))
	     (define e-cert (emacs-lock:certificate e-path))
	     (case (software-type)
	       ((UNIX COHERENT PLAN9)
		(cond ((not (equal? e-cert certificate))
		       (slib:warn 'file-unlock! e-path 'mismatch certificate)
		       #f)
		      (else (and (delete-file e-path)
				 (delete-file w-path)))))
	       (else (delete-file w-path))))))))

;;;@subsubheading File Transactions

(define (emacs:backup-number path)
  (let* ((dir (pathname->vicinity path))
	 (file (substring path (string-length dir) (string-length path)))
	 (largest #f))
    (require 'directory)
    (if (equal? "" dir) (set! dir "./"))
    (directory-for-each
     (lambda (str)
       (define left.~ (substring? ".~" str))
       (cond ((not left.~))
	     ((not (equal? file (substring str 0 left.~))))
	     ((string->number (substring str
					 (+ 2 left.~)
					 (string-reverse-index str #\~)))
	      => (lambda (number)
		   (set! largest (max number (or largest number)))))))
     dir (string-append file "*~*[0-9]~"))
    largest))

;;@body
;;@1 must be a string.  @2 must be a symbol.  Depending on @2, @0
;;returns:
;;@table @r
;;@item none
;;#f
;;@item simple
;;the string "@1~"
;;@item numbered
;;the string "@1.~@var{n}~", where @var{n} is one greater than the
;;highest number appearing in a filename matching "@1.~*~".  @var{n}
;;defauls to 1 when no filename matches.
;;@item existing
;;the string "@1.~@var{n}~" if a numbered backup already exists in
;;this directory; otherwise. "@1~"
;;@item orig
;;the string "@1.orig"
;;@item bak
;;the string "@1.bak"
;;@end table
(define (emacs:backup-name path backup-style)
  (define (numbered bn) (sprintf #f "%s.~%d~" path (+ 1 (or bn 0))))
  (define (simple) (string-append path "~"))
  (case backup-style
    ((none #f) #f)
    ((simple) (simple))
    ((numbered) (numbered (emacs:backup-number path)))
    ((existing) (let ((bn (emacs:backup-number path)))
		  (if bn (numbered bn) (simple))))
    ((orig bak) (sprintf #f "%s.%s" path backup-style))
    (else
     (slib:error 'emacs:backup-name 'unknown 'backup-style backup-style))))

;;@args proc path backup-style certificate
;;@args proc path backup-style
;;@args proc path
;;
;;@2 must be a string naming an existing file.  @3 is one of the
;;symbols @r{none}, @r{simple}, @r{numbered}, @r{existing}, @r{orig},
;;@r{bak} or @r{#f}; with meanings described above; or a string naming
;;the location of a backup file.  @3 defaults to @r{#f}.  If supplied,
;;@4 is the certificate with which @2 is locked.
;;
;;@1 must be a procedure taking two string arguments:
;;@itemize @bullet
;;@item
;;@2, the original filename (to be read); and
;;@item
;;a temporary file-name.
;;@end itemize
;;
;;If @2 is locked by other than @4, or if @4 is supplied and @2 is not
;;locked, then @0 returns #f.  If @4 is not supplied, then, @0 creates
;;temporary (Emacs and Word) locks for @2 during the transaction.  The
;;lock status of @2 will be restored before @0 returns.
;;
;;@0 calls @1 with @2 (which should not be modified) and a temporary
;;file path to be written.
;;If @1 returns any value other than @r{#t}, then the file named by @2
;;is not altered and @0 returns @r{#f}.
;;Otherwise, @code{emacs:backup-name} is called with @2 and @3.  If it
;;returns a string, then @2 is renamed to it.
;;
;;Finally, the temporary file is renamed @2.
;;@0 returns #t if @2 was successfully replaced; and #f otherwise.
(define (transact-file-replacement proc path . args)
  (define certificate (case (length args)
			((2) (cadr args))
			((1 0) #f)
			(else (slib:error 'transact-file-replacement
					  (+ 2 (length args)) 'args))))
  (define backup-style (if (null? args) #f (car args)))
  (define move (case (software-type)
		 ((UNIX COHERENT PLAN9) "mv -f")
		 ((MS-DOS WINDOWS OS/2 ATARIST) "MOVE /Y")
		 (else (slib:error (software-type) 'move?))))
  (define (move? tmpfn path)
    (eqv? 0 (system (sprintf #f "%s %#a %#a" move tmpfn path))))
  (let* ((dir (pathname->vicinity path))
	 (file (substring path (string-length dir) (string-length path)))
	 (tmpfn (in-vicinity dir (string-append "#" file "#"))))
    (cond ((not (file-exists? path)) (slib:warn 'file path 'missing) #f)
	  (else
	   (let ((f-cert (file-lock:certificate path)))
	     (cond ((and f-cert (not (equal? certificate f-cert)))
		    (slib:warn 'file path 'locked 'by f-cert) #f)
		   ((and (file-exists? tmpfn)
			 (slib:warn 'file tmpfn 'exists)
			 (not (delete-file tmpfn)))
		    #f)
		   ((or certificate (file-lock! path))
		    => (lambda (cert)
			 (define result (proc path tmpfn))
			 (cond
			  ((not (eqv? #t result))
			   (delete-file tmpfn)
			   (or f-cert (file-unlock! path cert)) #f)
			  (else
			   (let ((bakf
				  (if (symbol? backup-style)
				      (emacs:backup-name path backup-style)
				      backup-style)))
			     (cond
			      ((and bakf (not (move? path bakf)))
			       (or f-cert (file-unlock! path cert)) #f)
			      ((not (move? tmpfn path))
			       (or f-cert (file-unlock! path cert)) #f)
			      (else
			       (or f-cert (file-unlock! path cert)) #t)))))))
		   (else (slib:warn 'could 'not 'lock path) #f)))))))

(define (windows:user-email-address user hostname)
  (define compname (getenv "COMPUTERNAME")) ;without domain
  (define workgroup #f)
  (define netdir
    (or (getenv "windir")
	(getenv "winbootdir")
	(and (getenv "SYSTEMROOT")
	     (string-append (getenv "SYSTEMROOT") "\\system32"))
	"C:\\windows"))
  (call-with-tmpnam
   (lambda (tmp)
     (define (net . cmd)
       (zero? (system (apply string-append
			     (or netdir "")
			     (if netdir "\\" "")
			     "NET " cmd))))
     (and (zero? (system (string-append
			  (or netdir "")
			  (if netdir "\\" "")
			  "IPCONFIG /ALL > " tmp " ")))
	  (file-exists? tmp)	    ;(print tmp '=) (display-file tmp)
	  (call-with-input-file tmp
	    (lambda (port)
	      (find-string-from-port? "Host Name" port)
	      (fscanf port " %*[. ]: %s" hostname)))
	  (delete-file tmp))
     (and (net "START /LIST >" tmp)
	  (file-exists? tmp)
	  (not (eof-object? (call-with-input-file tmp read-char)))
	  (cond ((call-with-input-file tmp
		   (lambda (port)
		     (find-string-from-port? "o network servic" port)))
		 (and (net "CONFIG /YES >" tmp) (net "STOP /YES")))
		(else (net "CONFIG /YES >" tmp)))
	  (call-with-input-file tmp
	    (lambda (port)
	      (do ((line (read-line port) (read-line port)))
		  ((eof-object? line))
		(sscanf line " Workstation root directory %s" netdir)
		(sscanf line " Computer name \\\\%s" compname)
		(sscanf line " Workstation Domain %s" workgroup)
		(sscanf line " Workgroup %s" workgroup)
		(sscanf line " User name %s" user)))))))
  
  (and netdir (not (and user hostname))
       (set! netdir (string-append netdir "\\system.ini"))
       (file-exists? netdir)
       (call-with-input-file netdir
	 (lambda (port) (and (find-string-from-port? "[DNS]" port)
			     (read-line port) ;past newline
			     (do ((line (read-line port) (read-line port)))
				 ((not (and (string? line)
					    (string-index line #\=))))
			       (sscanf line "HostName=%s" compname)
			       (sscanf line "DomainName=%s" workgroup)))))
       (not user)
       (call-with-input-file netdir
	 (lambda (port) (and (find-string-from-port? "[Network]" port)
			     (read-line port) ;past newline
			     (do ((line (read-line port) (read-line port)))
				 ((not (and (string? line)
					    (string-index line #\=))))
			       (sscanf line "UserName=%s" user))))))

  (string-append (or user "John_Doe") "@"
		 (if (and compname (not hostname))
		     (string-append compname "." (or workgroup "localnet"))
		     (or hostname "localhost"))))

;;@subsubheading Identification

;;@args
;;@0 returns a string of the form @samp{username@r{@@}hostname}.  If
;;this e-mail address cannot be obtained, #f is returned.
(define (user-email-address)
  (define user (or (getenv "USER") (getenv "USERNAME")))
  (define hostname (getenv "HOSTNAME")) ;with domain
  (cond ((and user hostname) (string-append user "@" hostname))
	(else (case (software-type)
		;;((AMIGA)				)
		;;((MACOS THINKC)			)
		((MS-DOS WINDOWS OS/2 ATARIST)
		 (windows:user-email-address user hostname))
		;;((NOSVE)				)
		;;((VMS)				)
		((UNIX COHERENT PLAN9)
		 (call-with-tmpnam
		  (lambda (tmp)
		    (if (not user) (set! user (system->line "whoami" tmp)))
		    (if (not hostname) (set! hostname (system->line "hostname" tmp)))
		    (if (not user) (set! user "John_Doe"))
		    (if (not hostname) (set! hostname "localhost"))))
		 (string-append user "@" hostname))))))