summaryrefslogtreecommitdiff
path: root/src/libsystemd-bus/bus-match.c
blob: ed871d9d7799912a6a553926f6216b940fe9dc2d (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
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
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2013 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include "bus-internal.h"
#include "bus-message.h"
#include "bus-match.h"

/* Example:
 *
 *  A: type=signal,sender=foo,interface=bar
 *  B: type=signal,sender=quux,interface=fips
 *  C: type=signal,sender=quux,interface=waldo
 *  D: type=signal,member=test
 *  E: sender=miau
 *  F: type=signal
 *  G: type=signal
 *
 *  results in this tree:
 *
 *  BUS_MATCH_ROOT
 *  + BUS_MATCH_MESSAGE_TYPE
 *  | ` BUS_MATCH_VALUE: value == signal
 *  |   + DBUS_MATCH_SENDER
 *  |   | + BUS_MATCH_VALUE: value == foo
 *  |   | | ` DBUS_MATCH_INTERFACE
 *  |   | |   ` BUS_MATCH_VALUE: value == bar
 *  |   | |     ` BUS_MATCH_LEAF: A
 *  |   | ` BUS_MATCH_VALUE: value == quux
 *  |   |   ` DBUS_MATCH_INTERFACE
 *  |   |     | BUS_MATCH_VALUE: value == fips
 *  |   |     | ` BUS_MATCH_LEAF: B
 *  |   |     ` BUS_MATCH_VALUE: value == waldo
 *  |   |       ` BUS_MATCH_LEAF: C
 *  |   + DBUS_MATCH_MEMBER
 *  |   | ` BUS_MATCH_VALUE: value == test
 *  |   |   ` BUS_MATCH_LEAF: D
 *  |   + BUS_MATCH_LEAF: F
 *  |   ` BUS_MATCH_LEAF: G
 *  ` BUS_MATCH_SENDER
 *    ` BUS_MATCH_VALUE: value == miau
 *      ` BUS_MATCH_LEAF: E
 */

static inline bool BUS_MATCH_IS_COMPARE(enum bus_match_node_type t) {
        return t >= BUS_MATCH_MESSAGE_TYPE && t <= BUS_MATCH_ARG_NAMESPACE_LAST;
}

static inline bool BUS_MATCH_CAN_HASH(enum bus_match_node_type t) {
        return (t >= BUS_MATCH_MESSAGE_TYPE && t <= BUS_MATCH_PATH) ||
                (t >= BUS_MATCH_ARG && t <= BUS_MATCH_ARG_LAST);
}

static void bus_match_node_free(struct bus_match_node *node) {
        assert(node);
        assert(node->parent);
        assert(!node->child);
        assert(node->type != BUS_MATCH_ROOT);
        assert(node->type < _BUS_MATCH_NODE_TYPE_MAX);

        if (node->parent->child) {
                /* We are apparently linked into the parent's child
                 * list. Let's remove us from there. */
                if (node->prev) {
                        assert(node->prev->next == node);
                        node->prev->next = node->next;
                } else {
                        assert(node->parent->child == node);
                        node->parent->child = node->next;
                }

                if (node->next)
                        node->next->prev = node->prev;
        }

        if (node->type == BUS_MATCH_VALUE) {
                /* We might be in the parent's hash table, so clean
                 * this up */

                if (node->parent->type == BUS_MATCH_MESSAGE_TYPE)
                        hashmap_remove(node->parent->compare.children, UINT_TO_PTR(node->value.u8));
                else if (BUS_MATCH_CAN_HASH(node->parent->type) && node->value.str)
                        hashmap_remove(node->parent->compare.children, node->value.str);

                free(node->value.str);
        }

        if (BUS_MATCH_IS_COMPARE(node->type)) {
                assert(hashmap_isempty(node->compare.children));
                hashmap_free(node->compare.children);
        }

        free(node);
}

static bool bus_match_node_maybe_free(struct bus_match_node *node) {
        assert(node);

        if (node->child)
                return false;

        if (BUS_MATCH_IS_COMPARE(node->type) && !hashmap_isempty(node->compare.children))
                return true;

        bus_match_node_free(node);
        return true;
}

static bool value_node_test(
                struct bus_match_node *node,
                enum bus_match_node_type parent_type,
                uint8_t value_u8,
                const char *value_str) {

        assert(node);
        assert(node->type == BUS_MATCH_VALUE);

        /* Tests parameters against this value node, doing prefix
         * magic and stuff. */

        switch (parent_type) {

        case BUS_MATCH_MESSAGE_TYPE:
                return node->value.u8 == value_u8;

        case BUS_MATCH_SENDER:
        case BUS_MATCH_DESTINATION:
        case BUS_MATCH_INTERFACE:
        case BUS_MATCH_MEMBER:
        case BUS_MATCH_PATH:
        case BUS_MATCH_ARG ... BUS_MATCH_ARG_LAST:
                return streq_ptr(node->value.str, value_str);

        case BUS_MATCH_ARG_NAMESPACE ... BUS_MATCH_ARG_NAMESPACE_LAST:
                return namespace_simple_pattern(node->value.str, value_str);

        case BUS_MATCH_PATH_NAMESPACE:
                return path_simple_pattern(node->value.str, value_str);

        case BUS_MATCH_ARG_PATH ... BUS_MATCH_ARG_PATH_LAST:
                return path_complex_pattern(node->value.str, value_str);

        default:
                assert_not_reached("Invalid node type");
        }
}

static bool value_node_same(
                struct bus_match_node *node,
                enum bus_match_node_type parent_type,
                uint8_t value_u8,
                const char *value_str) {

        /* Tests parameters against this value node, not doing prefix
         * magic and stuff, i.e. this one actually compares the match
         * itself.*/

        assert(node);
        assert(node->type == BUS_MATCH_VALUE);

        switch (parent_type) {

        case BUS_MATCH_MESSAGE_TYPE:
                return node->value.u8 == value_u8;

        case BUS_MATCH_SENDER:
        case BUS_MATCH_DESTINATION:
        case BUS_MATCH_INTERFACE:
        case BUS_MATCH_MEMBER:
        case BUS_MATCH_PATH:
        case BUS_MATCH_ARG ... BUS_MATCH_ARG_LAST:
        case BUS_MATCH_ARG_NAMESPACE ... BUS_MATCH_ARG_NAMESPACE_LAST:
        case BUS_MATCH_PATH_NAMESPACE:
        case BUS_MATCH_ARG_PATH ... BUS_MATCH_ARG_PATH_LAST:
                return streq(node->value.str, value_str);

        default:
                assert_not_reached("Invalid node type");
        }
}

int bus_match_run(
                sd_bus *bus,
                struct bus_match_node *node,
                sd_bus_message *m) {


        const char *test_str = NULL;
        uint8_t test_u8 = 0;
        int r;

        assert(m);

        if (!node)
                return 0;

        if (bus && bus->match_callbacks_modified)
                return 0;

        /* Not these special semantics: when traversing the tree we
         * usually let bus_match_run() when called for a node
         * recursively invoke bus_match_run(). There's are two
         * exceptions here though, which are BUS_NODE_ROOT (which
         * cannot have a sibling), and BUS_NODE_VALUE (whose siblings
         * are invoked anyway by its parent. */

        switch (node->type) {

        case BUS_MATCH_ROOT:

                /* Run all children. Since we cannot have any siblings
                 * we won't call any. The children of the root node
                 * are compares or leaves, they will automatically
                 * call their siblings. */
                return bus_match_run(bus, node->child, m);

        case BUS_MATCH_VALUE:

                /* Run all children. We don't execute any siblings, we
                 * assume our caller does that. The children of value
                 * nodes are compares or leaves, they will
                 * automatically call their siblings */

                assert(node->child);
                return bus_match_run(bus, node->child, m);

        case BUS_MATCH_LEAF:

                if (bus) {
                        if (node->leaf.last_iteration == bus->iteration_counter)
                                return 0;

                        node->leaf.last_iteration = bus->iteration_counter;
                }

                r = sd_bus_message_rewind(m, true);
                if (r < 0)
                        return r;

                /* Run the callback. And then invoke siblings. */
                assert(node->leaf.callback);
                r = node->leaf.callback(bus, m, node->leaf.userdata);
                if (r != 0)
                        return r;

                return bus_match_run(bus, node->next, m);

        case BUS_MATCH_MESSAGE_TYPE:
                test_u8 = m->header->type;
                break;

        case BUS_MATCH_SENDER:
                test_str = m->sender;
                /* FIXME: resolve test_str from a well-known to a unique name first */
                break;

        case BUS_MATCH_DESTINATION:
                test_str = m->destination;
                break;

        case BUS_MATCH_INTERFACE:
                test_str = m->interface;
                break;

        case BUS_MATCH_MEMBER:
                test_str = m->member;
                break;

        case BUS_MATCH_PATH:
        case BUS_MATCH_PATH_NAMESPACE:
                test_str = m->path;
                break;

        case BUS_MATCH_ARG ... BUS_MATCH_ARG_LAST:
                test_str = bus_message_get_arg(m, node->type - BUS_MATCH_ARG);
                break;

        case BUS_MATCH_ARG_PATH ... BUS_MATCH_ARG_PATH_LAST:
                test_str = bus_message_get_arg(m, node->type - BUS_MATCH_ARG_PATH);
                break;

        case BUS_MATCH_ARG_NAMESPACE ... BUS_MATCH_ARG_NAMESPACE_LAST:
                test_str = bus_message_get_arg(m, node->type - BUS_MATCH_ARG_NAMESPACE);
                break;

        default:
                assert_not_reached("Unknown match type.");
        }

        if (BUS_MATCH_CAN_HASH(node->type)) {
                struct bus_match_node *found;

                /* Lookup via hash table, nice! So let's jump directly. */

                if (test_str)
                        found = hashmap_get(node->compare.children, test_str);
                else if (node->type == BUS_MATCH_MESSAGE_TYPE)
                        found = hashmap_get(node->compare.children, UINT_TO_PTR(test_u8));
                else
                        found = NULL;

                if (found) {
                        r = bus_match_run(bus, found, m);
                        if (r != 0)
                                return r;
                }
        } else {
                struct bus_match_node *c;

                /* No hash table, so let's iterate manually... */

                for (c = node->child; c; c = c->next) {
                        if (!value_node_test(c, node->type, test_u8, test_str))
                                continue;

                        r = bus_match_run(bus, c, m);
                        if (r != 0)
                                return r;
                }
        }

        if (bus && bus->match_callbacks_modified)
                return 0;

        /* And now, let's invoke our siblings */
        return bus_match_run(bus, node->next, m);
}

static int bus_match_add_compare_value(
                struct bus_match_node *where,
                enum bus_match_node_type t,
                uint8_t value_u8,
                const char *value_str,
                struct bus_match_node **ret) {

        struct bus_match_node *c = NULL, *n = NULL;
        int r;

        assert(where);
        assert(where->type == BUS_MATCH_ROOT || where->type == BUS_MATCH_VALUE);
        assert(BUS_MATCH_IS_COMPARE(t));
        assert(ret);

        for (c = where->child; c && c->type != t; c = c->next)
                ;

        if (c) {
                /* Comparison node already exists? Then let's see if
                 * the value node exists too. */

                if (t == BUS_MATCH_MESSAGE_TYPE)
                        n = hashmap_get(c->compare.children, UINT_TO_PTR(value_u8));
                else if (BUS_MATCH_CAN_HASH(t))
                        n = hashmap_get(c->compare.children, value_str);
                else {
                        for (n = c->child; n && !value_node_same(n, t, value_u8, value_str); n = n->next)
                                ;
                }

                if (n) {
                        *ret = n;
                        return 0;
                }
        } else {
                /* Comparison node, doesn't exist yet? Then let's
                 * create it. */

                c = new0(struct bus_match_node, 1);
                if (!c) {
                        r = -ENOMEM;
                        goto fail;
                }

                c->type = t;
                c->parent = where;
                c->next = where->child;
                if (c->next)
                        c->next->prev = c;
                where->child = c;

                if (t == BUS_MATCH_MESSAGE_TYPE) {
                        c->compare.children = hashmap_new(trivial_hash_func, trivial_compare_func);
                        if (!c->compare.children) {
                                r = -ENOMEM;
                                goto fail;
                        }
                } else if (BUS_MATCH_CAN_HASH(t)) {
                        c->compare.children = hashmap_new(string_hash_func, string_compare_func);
                        if (!c->compare.children) {
                                r = -ENOMEM;
                                goto fail;
                        }
                }
        }

        n = new0(struct bus_match_node, 1);
        if (!n) {
                r = -ENOMEM;
                goto fail;
        }

        n->type = BUS_MATCH_VALUE;
        n->value.u8 = value_u8;
        if (value_str) {
                n->value.str = strdup(value_str);
                if (!n->value.str) {
                        r = -ENOMEM;
                        goto fail;
                }
        }

        n->parent = c;
        if (c->compare.children) {

                if (t == BUS_MATCH_MESSAGE_TYPE)
                        r = hashmap_put(c->compare.children, UINT_TO_PTR(value_u8), n);
                else
                        r = hashmap_put(c->compare.children, n->value.str, n);

                if (r < 0)
                        goto fail;
        } else {
                n->next = c->child;
                if (n->next)
                        n->next->prev = n;
                c->child = n;
        }

        *ret = n;
        return 1;

fail:
        if (c)
                bus_match_node_maybe_free(c);

        if (n) {
                free(n->value.str);
                free(n);
        }

        return r;
}

static int bus_match_find_compare_value(
                struct bus_match_node *where,
                enum bus_match_node_type t,
                uint8_t value_u8,
                const char *value_str,
                struct bus_match_node **ret) {

        struct bus_match_node *c, *n;

        assert(where);
        assert(where->type == BUS_MATCH_ROOT || where->type == BUS_MATCH_VALUE);
        assert(BUS_MATCH_IS_COMPARE(t));
        assert(ret);

        for (c = where->child; c && c->type != t; c = c->next)
                ;

        if (!c)
                return 0;

        if (t == BUS_MATCH_MESSAGE_TYPE)
                n = hashmap_get(c->compare.children, UINT_TO_PTR(value_u8));
        else if (BUS_MATCH_CAN_HASH(t))
                n = hashmap_get(c->compare.children, value_str);
        else {
                for (n = c->child; !value_node_same(n, t, value_u8, value_str); n = n->next)
                        ;
        }

        if (n) {
                *ret = n;
                return 1;
        }

        return 0;
}

static int bus_match_add_leaf(
                struct bus_match_node *where,
                sd_bus_message_handler_t callback,
                void *userdata,
                struct bus_match_node **ret) {

        struct bus_match_node *n;

        assert(where);
        assert(where->type == BUS_MATCH_ROOT || where->type == BUS_MATCH_VALUE);
        assert(ret);

        n = new0(struct bus_match_node, 1);
        if (!n)
                return -ENOMEM;

        n->type = BUS_MATCH_LEAF;
        n->parent = where;
        n->next = where->child;
        if (n->next)
                n->next->prev = n;
        n->leaf.callback = callback;
        n->leaf.userdata = userdata;

        where->child = n;

        *ret = n;
        return 1;
}

static int bus_match_find_leaf(
                struct bus_match_node *where,
                sd_bus_message_handler_t callback,
                void *userdata,
                struct bus_match_node **ret) {

        struct bus_match_node *c;

        assert(where);
        assert(where->type == BUS_MATCH_ROOT || where->type == BUS_MATCH_VALUE);
        assert(ret);

        for (c = where->child; c; c = c->next) {
                if (c->type == BUS_MATCH_LEAF &&
                    c->leaf.callback == callback &&
                    c->leaf.userdata == userdata) {
                        *ret = c;
                        return 1;
                }
        }

        return 0;
}

enum bus_match_node_type bus_match_node_type_from_string(const char *k, size_t n) {
        assert(k);

        if (n == 4 && memcmp(k, "type", 4) == 0)
                return BUS_MATCH_MESSAGE_TYPE;
        if (n == 6 && memcmp(k, "sender", 6) == 0)
                return BUS_MATCH_SENDER;
        if (n == 11 && memcmp(k, "destination", 11) == 0)
                return BUS_MATCH_DESTINATION;
        if (n == 9 && memcmp(k, "interface", 9) == 0)
                return BUS_MATCH_INTERFACE;
        if (n == 6 && memcmp(k, "member", 6) == 0)
                return BUS_MATCH_MEMBER;
        if (n == 4 && memcmp(k, "path", 4) == 0)
                return BUS_MATCH_PATH;
        if (n == 14 && memcmp(k, "path_namespace", 14) == 0)
                return BUS_MATCH_PATH_NAMESPACE;

        if (n == 4 && memcmp(k, "arg", 3) == 0) {
                int j;

                j = undecchar(k[3]);
                if (j < 0)
                        return -EINVAL;

                return BUS_MATCH_ARG + j;
        }

        if (n == 5 && memcmp(k, "arg", 3) == 0) {
                int a, b;
                enum bus_match_node_type t;

                a = undecchar(k[3]);
                b = undecchar(k[4]);
                if (a <= 0 || b < 0)
                        return -EINVAL;

                t = BUS_MATCH_ARG + a * 10 + b;
                if (t > BUS_MATCH_ARG_LAST)
                        return -EINVAL;

                return t;
        }

        if (n == 8 && memcmp(k, "arg", 3) == 0 && memcmp(k + 4, "path", 4) == 0) {
                int j;

                j = undecchar(k[3]);
                if (j < 0)
                        return -EINVAL;

                return BUS_MATCH_ARG_PATH + j;
        }

        if (n == 9 && memcmp(k, "arg", 3) == 0 && memcmp(k + 5, "path", 4) == 0) {
                enum bus_match_node_type t;
                int a, b;

                a = undecchar(k[3]);
                b = undecchar(k[4]);
                if (a <= 0 || b < 0)
                        return -EINVAL;

                t = BUS_MATCH_ARG_PATH + a * 10 + b;
                if (t > BUS_MATCH_ARG_PATH_LAST)
                        return -EINVAL;

                return t;
        }

        if (n == 13 && memcmp(k, "arg", 3) == 0 && memcmp(k + 4, "namespace", 9) == 0) {
                int j;

                j = undecchar(k[3]);
                if (j < 0)
                        return -EINVAL;

                return BUS_MATCH_ARG_NAMESPACE + j;
        }

        if (n == 14 && memcmp(k, "arg", 3) == 0 && memcmp(k + 5, "namespace", 9) == 0) {
                enum bus_match_node_type t;
                int a, b;

                a = undecchar(k[3]);
                b = undecchar(k[4]);
                if (a <= 0 || b < 0)
                        return -EINVAL;

                t = BUS_MATCH_ARG_NAMESPACE + a * 10 + b;
                if (t > BUS_MATCH_ARG_NAMESPACE_LAST)
                        return -EINVAL;

                return t;
        }

        return -EINVAL;
}

struct match_component {
        enum bus_match_node_type type;
        uint8_t value_u8;
        char *value_str;
};

static int match_component_compare(const void *a, const void *b) {
        const struct match_component *x = a, *y = b;

        if (x->type < y->type)
                return -1;
        if (x->type > y->type)
                return 1;

        return 0;
}

static void free_components(struct match_component *components, unsigned n_components) {
        unsigned i;

        for (i = 0; i < n_components; i++)
                free(components[i].value_str);

        free(components);
}

static int parse_match(
                const char *match,
                struct match_component **_components,
                unsigned *_n_components) {

        const char *p = match;
        struct match_component *components = NULL;
        size_t components_allocated = 0;
        unsigned n_components = 0, i;
        _cleanup_free_ char *value = NULL;
        int r;

        assert(match);
        assert(_components);
        assert(_n_components);

        while (*p != 0) {
                const char *eq, *q;
                enum bus_match_node_type t;
                unsigned j = 0;
                size_t value_allocated = 0;
                bool escaped = false;
                uint8_t u;

                eq = strchr(p, '=');
                if (!eq)
                        return -EINVAL;

                if (eq[1] != '\'')
                        return -EINVAL;

                t = bus_match_node_type_from_string(p, eq - p);
                if (t < 0)
                        return -EINVAL;

                for (q = eq + 2;; q++) {

                        if (*q == 0) {
                                r = -EINVAL;
                                goto fail;
                        }

                        if (!escaped) {
                                if (*q == '\\') {
                                        escaped = true;
                                        continue;
                                }
                                if (*q == '\'') {
                                        if (value)
                                                value[j] = 0;
                                        break;
                                }
                        }

                        if (!GREEDY_REALLOC(value, value_allocated, j + 2)) {
                                r = -ENOMEM;
                                goto fail;
                        }

                        value[j++] = *q;
                        escaped = false;
                }

                if (t == BUS_MATCH_MESSAGE_TYPE) {
                        r = bus_message_type_from_string(value, &u);
                        if (r < 0)
                                goto fail;

                        free(value);
                        value = NULL;
                } else
                        u = 0;

                if (!GREEDY_REALLOC(components, components_allocated, n_components + 1)) {
                        r = -ENOMEM;
                        goto fail;
                }

                components[n_components].type = t;
                components[n_components].value_str = value;
                components[n_components].value_u8 = u;
                n_components++;

                value = NULL;

                if (q[1] == 0)
                        break;

                if (q[1] != ',') {
                        r = -EINVAL;
                        goto fail;
                }

                p = q + 2;
        }

        /* Order the whole thing, so that we always generate the same tree */
        qsort(components, n_components, sizeof(struct match_component), match_component_compare);

        /* Check for duplicates */
        for (i = 0; i+1 < n_components; i++)
                if (components[i].type == components[i+1].type) {
                        r = -EINVAL;
                        goto fail;
                }

        *_components = components;
        *_n_components = n_components;

        return 0;

fail:
        free_components(components, n_components);
        return r;
}

int bus_match_add(
                struct bus_match_node *root,
                const char *match,
                sd_bus_message_handler_t callback,
                void *userdata,
                struct bus_match_node **ret) {

        struct match_component *components = NULL;
        unsigned n_components = 0, i;
        struct bus_match_node *n;
        int r;

        assert(root);
        assert(match);
        assert(callback);

        r = parse_match(match, &components, &n_components);
        if (r < 0)
                return r;

        n = root;
        for (i = 0; i < n_components; i++) {
                r = bus_match_add_compare_value(
                                n, components[i].type,
                                components[i].value_u8, components[i].value_str, &n);
                if (r < 0)
                        goto finish;
        }

        r = bus_match_add_leaf(n, callback, userdata, &n);
        if (r < 0)
                goto finish;

        if (ret)
                *ret = n;

finish:
        free_components(components, n_components);
        return r;
}

int bus_match_remove(
                struct bus_match_node *root,
                const char *match,
                sd_bus_message_handler_t callback,
                void *userdata) {

        struct match_component *components = NULL;
        unsigned n_components = 0, i;
        struct bus_match_node *n, **gc;
        int r;

        assert(root);
        assert(match);

        r = parse_match(match, &components, &n_components);
        if (r < 0)
                return r;

        gc = newa(struct bus_match_node*, n_components);

        n = root;
        for (i = 0; i < n_components; i++) {
                r = bus_match_find_compare_value(
                                n, components[i].type,
                                components[i].value_u8, components[i].value_str,
                                &n);
                if (r <= 0)
                        goto finish;

                gc[i] = n;
        }

        r = bus_match_find_leaf(n, callback, userdata, &n);
        if (r <= 0)
                goto finish;

        /* Free the leaf */
        bus_match_node_free(n);

        /* Prune the tree above */
        for (i = n_components; i > 0; i --) {
                struct bus_match_node *p = gc[i-1]->parent;

                if (!bus_match_node_maybe_free(gc[i-1]))
                        break;

                if (!bus_match_node_maybe_free(p))
                        break;
        }

finish:
        free_components(components, n_components);
        return r;
}

void bus_match_free(struct bus_match_node *node) {
        struct bus_match_node *c;

        if (!node)
                return;

        if (BUS_MATCH_CAN_HASH(node->type)) {
                Iterator i;

                HASHMAP_FOREACH(c, node->compare.children, i)
                        bus_match_free(c);

                assert(hashmap_isempty(node->compare.children));
        }

        while ((c = node->child))
                bus_match_free(c);

        if (node->type != BUS_MATCH_ROOT)
                bus_match_node_free(node);
}

const char* bus_match_node_type_to_string(enum bus_match_node_type t, char buf[], size_t l) {
        switch (t) {

        case BUS_MATCH_ROOT:
                return "root";

        case BUS_MATCH_VALUE:
                return "value";

        case BUS_MATCH_LEAF:
                return "leaf";

        case BUS_MATCH_MESSAGE_TYPE:
                return "type";

        case BUS_MATCH_SENDER:
                return "sender";

        case BUS_MATCH_DESTINATION:
                return "destination";

        case BUS_MATCH_INTERFACE:
                return "interface";

        case BUS_MATCH_MEMBER:
                return "member";

        case BUS_MATCH_PATH:
                return "path";

        case BUS_MATCH_PATH_NAMESPACE:
                return "path_namespace";

        case BUS_MATCH_ARG ... BUS_MATCH_ARG_LAST:
                snprintf(buf, l, "arg%i", t - BUS_MATCH_ARG);
                return buf;

        case BUS_MATCH_ARG_PATH ... BUS_MATCH_ARG_PATH_LAST:
                snprintf(buf, l, "arg%ipath", t - BUS_MATCH_ARG_PATH);
                return buf;

        case BUS_MATCH_ARG_NAMESPACE ... BUS_MATCH_ARG_NAMESPACE_LAST:
                snprintf(buf, l, "arg%inamespace", t - BUS_MATCH_ARG_NAMESPACE);
                return buf;

        default:
                return NULL;
        }
}

void bus_match_dump(struct bus_match_node *node, unsigned level) {
        struct bus_match_node *c;
        _cleanup_free_ char *pfx = NULL;
        char buf[32];

        if (!node)
                return;

        pfx = strrep("  ", level);
        printf("%s[%s]", strempty(pfx), bus_match_node_type_to_string(node->type, buf, sizeof(buf)));

        if (node->type == BUS_MATCH_VALUE) {
                if (node->parent->type == BUS_MATCH_MESSAGE_TYPE)
                        printf(" <%u>\n", node->value.u8);
                else
                        printf(" <%s>\n", node->value.str);
        } else if (node->type == BUS_MATCH_ROOT)
                puts(" root");
        else if (node->type == BUS_MATCH_LEAF)
                printf(" %p/%p\n", node->leaf.callback, node->leaf.userdata);
        else
                putchar('\n');

        if (BUS_MATCH_CAN_HASH(node->type)) {
                Iterator i;

                HASHMAP_FOREACH(c, node->compare.children, i)
                        bus_match_dump(c, level + 1);
        }

        for (c = node->child; c; c = c->next)
                bus_match_dump(c, level + 1);
}