bus: parse matches locally and allow registration of callbacks for them

This includes code to parse and split up match strings which will also
be useful to calculate bloom filter masks when the time comes.

1 files changed, 978 insertions, 0 deletions

diff --git a/src/libsystemd-bus/bus-match.c b/src/libsystemd-bus/bus-match.c
new file mode 100644
index 0000000000..ff1edfaaed
--- /dev/null
+++ b/src/libsystemd-bus/bus-match.c
@@ -0,0 +1,978 @@
+/*-*- 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(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,
+                int ret,
+                sd_bus_message *m) {
+
+
+        const char *test_str = NULL;
+        uint8_t test_u8 = 0;
+        int r;
+
+        assert(m);
+
+        if (!node)
+                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, ret, 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, ret, m);
+
+        case BUS_MATCH_LEAF:
+
+                /* Run the callback. And then invoke siblings. */
+                assert(node->leaf.callback);
+                r = node->leaf.callback(bus, ret, m, node->leaf.userdata);
+                if (r != 0)
+                        return r;
+
+                return bus_match_run(bus, node->next, ret, 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, ret, 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, ret, m);
+                        if (r != 0)
+                                return r;
+                }
+        }
+
+        /* And now, let's invoke our siblings */
+        return bus_match_run(bus, node->next, ret, 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_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_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((void**) &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((void**) &components, &components_allocated,
+                                    (n_components + 1) * sizeof(struct match_component))) {
+                        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_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_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);
+}