aboutsummaryrefslogtreecommitdiffstats
path: root/src/mds-clipboard.c
blob: bf159ee20eb6c9c7f45fa42b6299348e87c5b5ef (plain) (blame)
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
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
/**
 * mds — A micro-display server
 * Copyright © 2014, 2015, 2016, 2017  Mattias Andrée (maandree@kth.se)
 * 
 * This program 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.
 * 
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include "mds-clipboard.h"

#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <libmdsserver/mds-message.h>

#include <errno.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define reconnect_to_display() -1



#define MDS_CLIPBOARD_VARS_VERSION 0



/**
 * This variable should declared by the actual server implementation.
 * It must be configured before `main` is invoked.
 * 
 * This tells the server-base how to behave
 */
server_characteristics_t server_characteristics = {
	.require_privileges = 0,
	.require_display = 1,
	.require_respawn_info = 1,
	.sanity_check_argc = 1,
	.fork_for_safety = 0,
	.danger_is_deadly = 1
};



/**
 * Value of the ‘Message ID’ header for the next message
 */
static uint32_t message_id = 1;

/**
 * Buffer for received messages
 */
static mds_message_t received;

/**
 * Whether the server is connected to the display
 */
static int connected = 1;

/**
 * The size of each clipstack
 */
static size_t clipboard_size[CLIPBOARD_LEVELS] = { 10, 1, 1 };

/**
 * The number of used elements in each clipstack
 */
static size_t clipboard_used[CLIPBOARD_LEVELS] = { 0, 0, 0 };

/**
 * The entries in each clipstack
 */
static clipitem_t *clipboard[CLIPBOARD_LEVELS];



/**
 * Send a full message even if interrupted
 * 
 * @param   message:const char*  The message to send
 * @param   length:size_t        The length of the message
 * @return  :int                 Zero on success, -1 on error
 */
#define full_send(message, length)\
	((full_send)(socket_fd, message, length))


/**
 * This function will be invoked before `initialise_server` (if not re-exec:ing)
 * or before `unmarshal_server` (if re-exec:ing)
 * 
 * @return  Non-zero on error
 */
int __attribute__((const))
preinitialise_server(void)
{
	return 0;
}


/**
 * This function should initialise the server,
 * and it not invoked after a re-exec.
 * 
 * @return  Non-zero on error
 */
int initialise_server(void)
{
	ssize_t i = 0;
	int stage = 0;
	const char* const message =
		"Command: intercept\n"
		"Message ID: 0\n"
		"Length: 33\n"
		"\n"
		"Command: clipboard\n"
		"Client closed\n";

	fail_if (full_send(message, strlen(message)));

	if (is_respawn) {
		const char* const crash_message =
			"Command: clipboard-info\n"
			"Event: crash\n"
			"Message ID: 1\n"
			"\n";

		fail_if (full_send(crash_message, strlen(crash_message)));
		message_id++;
	}

	stage++;
	fail_if (server_initialised() < 0);
	stage++;
	fail_if (mds_message_initialise(&received));

	for (i = 0; i < CLIPBOARD_LEVELS; i++)
		fail_if (xcalloc(clipboard[i], clipboard_size[i], clipitem_t));

	return 0;

fail:
	xperror(*argv);
	if (stage == 0) return 1;
	mds_message_destroy(&received);
	if (stage == 1) return 1;
	while (i--)
		free(clipboard[i]);
	return 1;
}


/**
 * This function will be invoked after `initialise_server` (if not re-exec:ing)
 * or after `unmarshal_server` (if re-exec:ing)
 * 
 * @return  Non-zero on error
 */
int
postinitialise_server(void)
{
	if (connected)
		return 0;

	fail_if (reconnect_to_display());
	connected = 1;
	return 0;
fail:
	mds_message_destroy(&received);
	return 1;
}


/**
 * Calculate the number of bytes that will be stored by `marshal_server`
 * 
 * On failure the program should `abort()` or exit by other means.
 * However it should not be possible for this function to fail.
 * 
 * @return  The number of bytes that will be stored by `marshal_server`
 */
size_t
marshal_server_size(void)
{
	size_t i, j, rc =  2 * sizeof(int) + sizeof(uint32_t) + mds_message_marshal_size(&received);
	clipitem_t clip;
	rc += 2 * CLIPBOARD_LEVELS * sizeof(size_t);
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		for (j = 0; j < clipboard_used[i]; j++) {
			clip = clipboard[i][j];
			rc += sizeof(size_t) + sizeof(time_t) + sizeof(long) + sizeof(uint64_t) + sizeof(int);
			rc += clip.length * sizeof(char);
		}
	}
	return rc;
}


/**
 * `memset`, but the compiler does not know that
 */
void *(*volatile mds_clipboard_my_explicit_memset)(void *s, int c, size_t n) = memset;


/**
 * Wipe a memory area and free it
 * 
 * @param  s  The memory area
 * @param  n  The number of bytes to write
 */
static inline void
wipe_and_free(void *s, size_t n)
{
	if (s)
		free(mds_clipboard_my_explicit_memset(s, 0, n));
}


/**
 * Marshal server implementation specific data into a buffer
 * 
 * @param   state_buf  The buffer for the marshalled data
 * @return             Non-zero on error
 */
int
marshal_server(char *state_buf)
{
	size_t i, j;
	clipitem_t clip;

	buf_set_next(state_buf, int, MDS_CLIPBOARD_VARS_VERSION);
	buf_set_next(state_buf, int, connected);
	buf_set_next(state_buf, uint32_t, message_id);
	mds_message_marshal(&received, state_buf);

	/* Removed entires from the clipboard that may not be marshalled. */
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		for (j = 0; j < clipboard_used[i]; j++) {
			clip = clipboard[i][j];

			if (clip.autopurge == CLIPITEM_AUTOPURGE_NEVER)
				continue;

			wipe_and_free(clip.content, clip.length * sizeof(char));

			memmove(clipboard[i] + j, clipboard[i] + j + 1, (clipboard_used[i] - j - 1) * sizeof(clipitem_t));
			clipboard_used[i]--;
			j--;
		}
	}

	/* Marshal clipboard. */
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		buf_set_next(state_buf, size_t, clipboard_size[i]);
		buf_set_next(state_buf, size_t, clipboard_used[i]);
		for (j = 0; j < clipboard_used[i]; j++) {
			clip = clipboard[i][j];
			buf_set_next(state_buf, size_t, clip.length);
			buf_set_next(state_buf, time_t, clip.dethklok.tv_sec);
			buf_set_next(state_buf, long, clip.dethklok.tv_nsec);
			buf_set_next(state_buf, uint64_t, clip.client);
			buf_set_next(state_buf, int, clip.autopurge);
			memcpy(state_buf, clip.content, clip.length * sizeof(char));
			state_buf += clip.length;
			
			free(clip.content);
		}
		free(clipboard[i]);
	}

	mds_message_destroy(&received);
	return 0;
}


/**
 * Unmarshal server implementation specific data and update the servers state accordingly
 * 
 * On critical failure the program should `abort()` or exit by other means.
 * That is, do not let `reexec_failure_recover` run successfully, if it unrecoverable
 * error has occurred or one severe enough that it is better to simply respawn.
 * 
 * @param   state_buf  The marshalled data that as not been read already
 * @return             Non-zero on error
 */
int
unmarshal_server(char *state_buf)
{
	size_t i, j;
	clipitem_t *clip;

	for (i = 0; i < CLIPBOARD_LEVELS; i++)
		clipboard[i] = NULL;

	/* buf_get_next(state_buf, int, MDS_CLIPBOARD_VARS_VERSION); */
	buf_next(state_buf, int, 1);
	buf_get_next(state_buf, int, connected);
	buf_get_next(state_buf, uint32_t, message_id);
	fail_if (mds_message_unmarshal(&received, state_buf));

	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		buf_get_next(state_buf, size_t, clipboard_size[i]);
		buf_get_next(state_buf, size_t, clipboard_used[i]);
		fail_if (xcalloc(clipboard[i], clipboard_size[i], clipitem_t));

		for (j = 0; j < clipboard_used[i]; j++) {
			clip = clipboard[i] + j;
			buf_get_next(state_buf, size_t, clip->length);
			buf_get_next(state_buf, time_t, clip->dethklok.tv_sec);
			buf_get_next(state_buf, long, clip->dethklok.tv_nsec);
			buf_get_next(state_buf, uint64_t, clip->client);
			buf_get_next(state_buf, int, clip->autopurge);
			fail_if (xmemdup(clip->content, state_buf, clip->length, char));
			state_buf += clip->length;
		}
	}

	return 0;
fail:
	xperror(*argv);
	mds_message_destroy(&received);
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		if (clipboard[i] != NULL) {
			for (j = 0; j < clipboard_used[i]; j++)
				free(clipboard[i][j].content);
			free(clipboard[i]);
		}
	}
	abort();
	return -1;
}


/**
 * Attempt to recover from a re-exec failure that has been
 * detected after the server successfully updated it execution image
 * 
 * @return  Non-zero on error
 */
int __attribute__((const))
reexec_failure_recover(void)
{
	return -1;
}


/**
 * Perform the server's mission
 * 
 * @return  Non-zero on error
 */
int
master_loop(void)
{
	int rc = 1, r;
	size_t i, j;

	while (!reexecing && !terminating) {
		if (danger) {
			danger = 0;
			clipboard_danger();
		}

		if (r = mds_message_read(&received, socket_fd), r == 0)
			if (r = handle_message(), r == 0)
				continue;

		if (r == -2) {
			eprint("corrupt message received, aborting.");
			goto done;
		} else if (errno == EINTR) {
			continue;
		} else {
			fail_if (errno != ECONNRESET);
		}

		eprint("lost connection to server.");
		mds_message_destroy(&received);
		mds_message_initialise(&received);
		connected = 0;
		fail_if (reconnect_to_display());
		connected = 1;
	}

	rc = 0;
	goto done;
 fail:
	xperror(*argv);
 done:
	if (!rc && reexecing)
		return 0;
	mds_message_destroy(&received);
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		if (clipboard[i] != NULL) {
			for (j = 0; j < clipboard_used[i]; j++)
				wipe_and_free(clipboard[i][j].content, clipboard[i][j].length);
			free(clipboard[i]);
		}
	}
	return rc;
}


/**
 * Handle the received message
 * 
 * @return  Zero on success, -1 on error
 */
int
handle_message(void)
{
	/* Fetch message headers. */

	const char *recv_client_id = "0:0";
	const char *recv_message_id = NULL;
	const char *recv_length = NULL;
	const char *recv_level = NULL;
	const char *recv_action = NULL;
	const char *recv_size = NULL;
	const char *recv_index = "0";
	const char *recv_time_to_live = "forever";
	const char *recv_client_closed = NULL;
	size_t i;
	int level;

#define __get_header(storage, header)\
	(startswith(received.headers[i], header))\
		storage = received.headers[i] + strlen(header)

	for (i = 0; i < received.header_count; i++) {
		if      __get_header(recv_client_id,     "Client ID: ");
		else if __get_header(recv_message_id,    "Message ID: ");
		else if __get_header(recv_length,        "Length: ");
		else if __get_header(recv_action,        "Action: ");
		else if __get_header(recv_level,         "Level: ");
		else if __get_header(recv_size,          "Size: ");
		else if __get_header(recv_index,         "Index: ");
		else if __get_header(recv_time_to_live,  "Time to live: ");
		else if __get_header(recv_client_closed, "Client closed: ");
	}

#undef __get_header

	/* Validate headers and take appropriate action. */

	if (!recv_message_id)
		return eprint("received message without ID, ignoring, master server is misbehaving."), 0;

	if (recv_client_closed) {
		if (strequals(recv_client_closed, "0:0"))
			return 0;
		return clipboard_death(recv_client_closed);
	}

	if (!recv_action)
		return eprint("received message without any action, ignoring."), 0;
	if (!recv_level)
		return eprint("received message without specified clipboard level, ignoring."), 0;
	level = atoi(recv_level);
	if ((level < 0) || (CLIPBOARD_LEVELS <= level))
		return eprint("received message without invalid clipboard level, ignoring."), 0;
	if (strequals(recv_client_id, "0:0"))
		if (strequals(recv_action, "read") || strequals(recv_action, "get-size"))
			return eprint("received information request from an anonymous client, ignoring."), 0;

	if (strequals(recv_action, "add")) {
		if (recv_length == NULL)
			return eprint("received request for adding a clipboard entry "
			              "but did not receive any content, ignoring."), 0;
		if ((strequals(recv_client_id, "0:0")) && startswith(recv_time_to_live, "until-death"))
			return eprint("received request new clipboard entry with autopurge upon "
			              "client close from an anonymous client, ignoring."), 0;
		return clipboard_add(level, recv_time_to_live, recv_client_id);
	} else if (strequals(recv_action, "read")) {
		return clipboard_read(level, atoz(recv_index), recv_client_id, recv_message_id);
	} else if (strequals(recv_action, "clear")) {
		return clipboard_clear(level);
	} else if (strequals(recv_action, "set-size")) {
		if (recv_size == NULL)
			return eprint("received request for clipboard resizing without a new size, ignoring."), 0;
		return clipboard_set_size(level, atoz(recv_size));
	} else if (strequals(recv_action, "get-size")) {
		return clipboard_get_size(level, recv_client_id, recv_message_id);
	}

	eprint("received message with invalid action, ignoring.");
	return 0;
}


/**
 * Free an entry from the clipboard
 * 
 * @param  entry  The clipboard entry to free
 */
static inline void __attribute__((nonnull))
free_clipboard_entry(clipitem_t *entry)
{
	if (entry->autopurge == CLIPITEM_AUTOPURGE_NEVER)
		free(entry->content);
	else
		wipe_and_free(entry->content, entry->length);
	entry->content = NULL;
}


/**
 * Broadcast notification about an automatic removal of an entry
 * 
 * @param   level  The clipboard level
 * @param   index  The index in the clipstack of the removed entry
 * @return         Zero on success, -1 on error, `errno` will be set accordingly
 */
static int
clipboard_notify_pop(int level, size_t index)
{
	size_t size = clipboard_size[level];
	size_t used = clipboard_used[level];
	char message[10 + 3 * (sizeof(int) + 3 * sizeof(size_t)) +
		     sizeof("Command: clipboard-info\n"
			    "Event: crash\n"
			    "Message ID: \n"
			    "Level: \n"
			    "Popped: \n"
			    "Size: \n"
			    "Used: \n"
			    "\n") / sizeof(char)];

	sprintf(message,
	        "Command: clipboard-info\n"
	        "Event: crash\n"
	        "Message ID: %" PRIu32 "\n"
	        "Level: %i\n"
	        "Popped: %zu\n"
	        "Size: %zu\n"
	        "Used: %zu\n"
	        "\n",
	        message_id, level, index, size, used);

	message_id = message_id == UINT32_MAX ? 0 : (message_id + 1);
	fail_if (full_send(message, strlen(message)) ? -1 : 0);
	return 0;
fail:
	return -1;
}


/**
 * Remove old entries from a clipstack
 * 
 * @param   level      The clipboard level
 * @param   client_id  The ID of the client that has newly closed, `NULL` if none
 * @return             Zero on success, -1 on error
 */
static int
clipboard_purge(int level, const char *client_id)
{
	uint64_t client = client_id ? parse_client_id(client_id) : 0;
	struct timespec now;
	clipitem_t *clip;
	size_t i;

	fail_if (monotone(&now));

	for (i = 0; i < clipboard_used[level]; i++) {
		clip = clipboard[level] + i;
		if ((clip->autopurge & CLIPITEM_AUTOPURGE_UPON_DEATH)) {
			if (clip->client == client)
				goto removed;
		}
		if ((clip->autopurge & CLIPITEM_AUTOPURGE_UPON_CLOCK)) {
			if (clip->dethklok.tv_sec > now.tv_sec)
				goto removed;
			if (clip->dethklok.tv_sec == now.tv_sec)
				if (clip->dethklok.tv_nsec >= now.tv_nsec)
					goto removed;
		}

		continue;
	removed:
		free_clipboard_entry(clipboard[level] + i);
		clipboard_used[level]--;
		fail_if (clipboard_notify_pop(level, i));
		memmove(clipboard[level] + i, clipboard[level] + i + 1, (clipboard_used[level] - i) * sizeof(clipitem_t));
		i--;
	}

	return 0;
fail:
	xperror(*argv);
	return -1;
}


/**
 * Remove expired entries
 * 
 * @return  Zero on success, -1 on error
 */
int
clipboard_danger(void)
{
	int i;
	for (i = 0; i < CLIPBOARD_LEVELS; i++)
		fail_if (clipboard_purge(i, NULL));
	return 0;
fail:
	return -1;
}


/**
 * Remove entries in the clipboard added by a client
 * 
 * @param   recv_client_id  The ID of the client
 * @return                  Zero on success, -1 on error
 */
int
clipboard_death(const char *recv_client_id)
{
	int i;
	for (i = 0; i < CLIPBOARD_LEVELS; i++)
		fail_if (clipboard_purge(i, recv_client_id));
	return 0;
fail:
	return -1;
}


/**
 * Add a new entry to the clipboard
 * 
 * @param   level           The clipboard level
 * @param   time_to_live    When the entry should be removed
 * @param   recv_client_id  The ID of the client
 * @return                  Zero on success, -1 on error
 */
int
clipboard_add(int level, const char *time_to_live, const char *recv_client_id)
{
	int autopurge = CLIPITEM_AUTOPURGE_UPON_CLOCK;
	uint64_t client = parse_client_id(recv_client_id);
	clipitem_t new_clip;
	struct timespec dethklok;

	fail_if (clipboard_purge(level, NULL));

	if (strequals(time_to_live, "forever")) {
		autopurge = CLIPITEM_AUTOPURGE_NEVER;
	} else if (strequals(time_to_live, "until-death")) {
		autopurge = CLIPITEM_AUTOPURGE_UPON_DEATH;
	} else if (startswith(time_to_live, "until-death ")) {
		autopurge = CLIPITEM_AUTOPURGE_UPON_DEATH_OR_CLOCK;
		time_to_live += strlen("until-death ");
	}

	if ((autopurge & CLIPITEM_AUTOPURGE_UPON_CLOCK)) {
		fail_if (monotone(&dethklok));
		dethklok.tv_sec += (time_t)atoll(time_to_live);
		/* It should really be `atol`, but we want to be future-proof. */
		new_clip.dethklok = dethklok;
	} else {
		new_clip.dethklok.tv_sec = 0;
		new_clip.dethklok.tv_nsec = 0;
	}

	new_clip.client = client;
	new_clip.autopurge = autopurge;
	new_clip.length = received.payload_size;

	fail_if (xmemdup(new_clip.content, received.payload, new_clip.length, char));

	if (clipboard_used[level] == clipboard_size[level])
		free_clipboard_entry(clipboard[level] + clipboard_used[level] - 1);
	memmove(clipboard[level] + 1, clipboard[level], (clipboard_used[level] - 1) * sizeof(clipitem_t));
	clipboard[level][0] = new_clip;

	return 0;
fail:
	xperror(*argv);
	return -1;
}


/**
 * Read an entry to the clipboard
 * 
 * @param   level            The clipboard level
 * @param   index            The index of the clipstack element
 * @param   recv_client_id   The ID of the client
 * @param   recv_message_id  The message ID of the received message
 * @return                   Zero on success, -1 on error
 */
int
clipboard_read(int level, size_t index, const char *recv_client_id, const char *recv_message_id)
{
	char *message = NULL;
	clipitem_t *clip = NULL;
	size_t n;

	fail_if (clipboard_purge(level, NULL));

	if (clipboard_used[level] == 0) {
		n = sizeof("To: \n"
			   "In response to: \n"
			   "Message ID: \n"
			   "Origin command: clipboard\n"
			   "\n") / sizeof(char);
		n += strlen(recv_client_id) + strlen(recv_message_id) + 10;

		fail_if (xmalloc(message, n, char));

		sprintf(message,
			"To: %s\n"
			"In response to: %s\n"
			"Message ID: %" PRIu32 "\n"
			"Origin command: clipboard\n"
			"\n",
			recv_client_id, recv_message_id, message_id);

		goto send;
	}

	if (index >= clipboard_used[level])
		index = clipboard_used[level] - 1;

	clip = clipboard[level] + index;

	n = sizeof("To: \n"
	           "In response to: \n"
	           "Message ID: \n"
	           "Origin command: clipboard\n"
	           "Length: \n"
	           "\n") / sizeof(char);
	n += strlen(recv_client_id) + strlen(recv_message_id) + 10 + 3 * sizeof(size_t);

	fail_if (xmalloc(message, n, char));

	sprintf(message,
	        "To: %s\n"
	        "In response to: %s\n"
	        "Message ID: %" PRIu32 "\n"
	        "Origin command: clipboard\n"
	        "Length: %zu\n"
	        "\n",
	        recv_client_id, recv_message_id, message_id, clip->length);

send:
	message_id = message_id == INT32_MAX ? 0 : (message_id + 1);
	fail_if (full_send(message, strlen(message)));
	if (clip)
		fail_if (full_send(clip->content, clip->length));

	free(message);
	return 0;
fail:
	xperror(*argv);
	free(message);
	return errno = 0, -1;
}


/**
 * Clear a clipstack
 * 
 * @param   level  The clipboard level
 * @return         Zero on success, -1 on error
 */
int
clipboard_clear(int level)
{
	size_t i;
	for (i = 0; i < clipboard_used[level]; i++)
		free_clipboard_entry(clipboard[level] + i);
	clipboard_used[level] = 0;
	return 0;
}


/**
 * Resize a clipstack
 * 
 * @param   level  The clipboard level
 * @param   size   The new clipstack size
 * @return         Zero on success, -1 on error
 */
int
clipboard_set_size(int level, size_t size)
{
	size_t i, old_used;
	clipitem_t* old;

	fail_if (clipboard_purge(level, NULL));

	if (size < clipboard_size[level]) {
		old_used = clipboard_used[level];
		if (size < old_used) {
			clipboard_used[level] = size;
			for (i = size; i < old_used; i++)
				free_clipboard_entry(clipboard[level] + i);
		}
	}

	if (size != clipboard_size[level]) {
		old = clipboard[level];
		if (xrealloc(clipboard[level], size, clipitem_t)) {
			clipboard[level] = old;
			fail_if (1);
		}
		clipboard_size[level] = size;
	}

	return 0;
fail:
	xperror(*argv);
	return -1;
}


/**
 * Get the size of a clipstack and how many entries it contains
 * 
 * @param   level            The clipboard level
 * @param   recv_client_id   The ID of the client
 * @param   recv_message_id  The message ID of the received message
 * @return                   Zero on success, -1 on error
 */
int
clipboard_get_size(int level, const char *recv_client_id, const char *recv_message_id)
{
	char *message = NULL;
	size_t n;

	fail_if (clipboard_purge(level, NULL));

	n = sizeof("To: \n"
	           "In response to: \n"
	           "Message ID: \n"
	           "Origin command: clipboard\n"
	           "Size: \n"
	           "Used: \n"
	           "\n") / sizeof(char);
	n += strlen(recv_client_id) + strlen(recv_message_id) + 10 + 2 * 3 * sizeof(size_t);

	fail_if (xmalloc(message, n, char));
	sprintf(message,
	        "To: %s\n"
	        "In response to: %s\n"
	        "Message ID: %" PRIu32 "\n"
	        "Origin command: clipboard\n"
	        "Size: %zu\n"
	        "Used: %zu\n"
	        "\n",
		recv_client_id, recv_message_id, message_id, clipboard_size[level], clipboard_used[level]);

	message_id = message_id == INT32_MAX ? 0 : (message_id + 1);

	fail_if (full_send(message, strlen(message)));

	free(message);
	return 0;
fail:
	xperror(*argv);
	free(message);
	return errno = 0, -1;
}


/**
 * This function is called when a signal that
 * signals that the system to dump state information
 * and statistics has been received
 * 
 * @param  signo  The signal that has been received
 */
void
received_info(int signo)
{
	SIGHANDLER_START;
	clipitem_t clipitem;
	size_t i, j, n;
	struct timespec now;
	if (monotone(&now) < 0)
		iprint("(unable to get current time)");
	else
		iprintf("current time: %ji.%09li", (intmax_t)(now.tv_sec), (long)(now.tv_nsec));
	iprintf("next message ID: %" PRIu32, message_id);
	iprintf("connected: %s", connected ? "yes" : "no");
	for (i = 0; i < CLIPBOARD_LEVELS; i++) {
		n = clipboard_used[i];
		iprintf("clipstack %zu: allocated: %zu", i, clipboard_size[i]);
		iprintf("clipstack %zu: used: %zu", i, n);
		for (j = 0; j < n; j++) {
			clipitem = clipboard[i][j];
			iprintf("clipstack %zu: item %zu:", i, j);
			iprintf("  autopurge: %s",
			        clipitem.autopurge == CLIPITEM_AUTOPURGE_NEVER ? "as needed" :
			        clipitem.autopurge == CLIPITEM_AUTOPURGE_UPON_DEATH ? "upon death or as needed" :
			        clipitem.autopurge == CLIPITEM_AUTOPURGE_UPON_CLOCK ? "timeout or as needed" :
			        clipitem.autopurge == CLIPITEM_AUTOPURGE_UPON_DEATH_OR_CLOCK ? "upon death, timeout or as needed" :
			        "unrecognised rule, something is wrong here!");
			iprintf("  client: %" PRIu32 ":%" PRIu32,
			        (uint32_t)(clipitem.client >> 32),
			        (uint32_t)(clipitem.client));
			if (clipitem.autopurge & CLIPITEM_AUTOPURGE_UPON_CLOCK)
				iprintf("  timeout: %ji.%09li",
				        (intmax_t)(clipitem.dethklok.tv_sec),
				        (long)(clipitem.dethklok.tv_nsec));
			iprintf("  butes: %zu", clipitem.length);
			iprintf("  content (possibily truncated): %.*s",
			        (int)strnlen(clipitem.content, clipitem.length > 50 ? (size_t)50 : clipitem.length),
			        clipitem.content);
		}
	}
	SIGHANDLER_END;
	(void) signo;
}