X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=src%2Flibelogind%2Fsd-bus%2Fbus-util.c;fp=src%2Flibelogind%2Fsd-bus%2Fbus-util.c;h=ee002a55f54370e83f86ed080482faa086b0222b;hb=b78378a2ba194084d85810dd5721217bb4337edc;hp=c4e44b1fa4d5003c33c8ea5c5681e493cda3ea3c;hpb=78e252953ddc56a371986bfc0656f755acf61475;p=elogind.git diff --git a/src/libelogind/sd-bus/bus-util.c b/src/libelogind/sd-bus/bus-util.c index c4e44b1fa..ee002a55f 100644 --- a/src/libelogind/sd-bus/bus-util.c +++ b/src/libelogind/sd-bus/bus-util.c @@ -34,6 +34,7 @@ #include "sd-bus.h" #include "bus-error.h" +#include "bus-label.h" #include "bus-message.h" #include "bus-util.h" #include "bus-internal.h" @@ -1903,3 +1904,130 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet) { return 0; } + +/** + * bus_path_encode_unique() - encode unique object path + * @b: bus connection or NULL + * @prefix: object path prefix + * @sender_id: unique-name of client, or NULL + * @external_id: external ID to be chosen by client, or NULL + * @ret_path: storage for encoded object path pointer + * + * Whenever we provide a bus API that allows clients to create and manage + * server-side objects, we need to provide a unique name for these objects. If + * we let the server choose the name, we suffer from a race condition: If a + * client creates an object asynchronously, it cannot destroy that object until + * it received the method reply. It cannot know the name of the new object, + * thus, it cannot destroy it. Furthermore, it enforces a round-trip. + * + * Therefore, many APIs allow the client to choose the unique name for newly + * created objects. There're two problems to solve, though: + * 1) Object names are usually defined via dbus object paths, which are + * usually globally namespaced. Therefore, multiple clients must be able + * to choose unique object names without interference. + * 2) If multiple libraries share the same bus connection, they must be + * able to choose unique object names without interference. + * The first problem is solved easily by prefixing a name with the + * unique-bus-name of a connection. The server side must enforce this and + * reject any other name. The second problem is solved by providing unique + * suffixes from within sd-bus. + * + * This helper allows clients to create unique object-paths. It uses the + * template '/prefix/sender_id/external_id' and returns the new path in + * @ret_path (must be freed by the caller). + * If @sender_id is NULL, the unique-name of @b is used. If @external_id is + * NULL, this function allocates a unique suffix via @b (by requesting a new + * cookie). If both @sender_id and @external_id are given, @b can be passed as + * NULL. + * + * Returns: 0 on success, negative error code on failure. + */ +int bus_path_encode_unique(sd_bus *b, const char *prefix, const char *sender_id, const char *external_id, char **ret_path) { + _cleanup_free_ char *sender_label = NULL, *external_label = NULL; + char external_buf[DECIMAL_STR_MAX(uint64_t)], *p; + int r; + + assert_return(b || (sender_id && external_id), -EINVAL); + assert_return(object_path_is_valid(prefix), -EINVAL); + assert_return(ret_path, -EINVAL); + + if (!sender_id) { + r = sd_bus_get_unique_name(b, &sender_id); + if (r < 0) + return r; + } + + if (!external_id) { + xsprintf(external_buf, "%"PRIu64, ++b->cookie); + external_id = external_buf; + } + + sender_label = bus_label_escape(sender_id); + if (!sender_label) + return -ENOMEM; + + external_label = bus_label_escape(external_id); + if (!external_label) + return -ENOMEM; + + p = strjoin(prefix, "/", sender_label, "/", external_label, NULL); + if (!p) + return -ENOMEM; + + *ret_path = p; + return 0; +} + +/** + * bus_path_decode_unique() - decode unique object path + * @path: object path to decode + * @prefix: object path prefix + * @ret_sender: output parameter for sender-id label + * @ret_external: output parameter for external-id label + * + * This does the reverse of bus_path_encode_unique() (see its description for + * details). Both trailing labels, sender-id and external-id, are unescaped and + * returned in the given output parameters (the caller must free them). + * + * Note that this function returns 0 if the path does not match the template + * (see bus_path_encode_unique()), 1 if it matched. + * + * Returns: Negative error code on failure, 0 if the given object path does not + * match the template (return parameters are set to NULL), 1 if it was + * parsed successfully (return parameters contain allocated labels). + */ +int bus_path_decode_unique(const char *path, const char *prefix, char **ret_sender, char **ret_external) { + const char *p, *q; + char *sender, *external; + + assert(object_path_is_valid(path)); + assert(object_path_is_valid(prefix)); + assert(ret_sender); + assert(ret_external); + + p = object_path_startswith(path, prefix); + if (!p) { + *ret_sender = NULL; + *ret_external = NULL; + return 0; + } + + q = strchr(p, '/'); + if (!q) { + *ret_sender = NULL; + *ret_external = NULL; + return 0; + } + + sender = bus_label_unescape_n(p, q - p); + external = bus_label_unescape(q + 1); + if (!sender || !external) { + free(sender); + free(external); + return -ENOMEM; + } + + *ret_sender = sender; + *ret_external = external; + return 1; +}