Description¶

sd_bus_path_encode() and sd_bus_path_decode() convert external identifier strings into object paths and back. These functions are useful to map application-specific string identifiers of any kind into bus object paths in a simple, reversible and safe way.

sd_bus_path_encode() takes a bus path prefix and an external identifier string as arguments, plus a place to store the returned bus path string. The bus path prefix must be a valid bus path, starting with a slash "/", and not ending in one. The external identifier string may be in any format, may be the empty string, and has no restrictions on the charset — however, it must always be NUL-terminated. The returned string will be the concatenation of the bus path prefix plus an escaped version of the external identifier string. This operation may be reversed with sd_bus_path_decode(). It is recommended to only use external identifiers that generally require little escaping to be turned into valid bus path identifiers (for example, by sticking to a 7-bit ASCII character set), in order to ensure the resulting bus path is still short and easily processed.

sd_bus_path_decode() reverses the operation of sd_bus_path_encode() and thus regenerates an external identifier string from a bus path. It takes a bus path and a prefix string, plus a place to store the returned external identifier string. If the bus path does not start with the specified prefix, 0 is returned and the returned string is set to NULL. Otherwise, the string following the prefix is unescaped and returned in the external identifier string.

The escaping used will replace all characters which are invalid in a bus object path by "_", followed by a hexadecimal value. As a special case, the empty string will be replaced by a lone "_".

sd_bus_path_encode_many() works like its counterpart sd_bus_path_encode(), but takes a path template as argument and encodes multiple labels according to its embedded directives. For each "%" character found in the template, the caller must provide a string via varargs, which will be encoded and embedded at the position of the "%" character. Any other character in the template is copied verbatim into the encoded path.

sd_bus_path_decode_many() does the reverse of sd_bus_path_encode_many(). It decodes the passed object path according to the given path template. For each "%" character in the template, the caller must provide an output storage ("char **") via varargs. The decoded label will be stored there. Each "%" character will only match the current label. It will never match across labels. Furthermore, only a single directive is allowed per label. If NULL is passed as output storage, the label is verified but not returned to the caller.

Return Value¶

On success, sd_bus_path_encode() returns positive or 0, and a valid bus path in the return argument. On success, sd_bus_path_decode() returns a positive value if the prefixed matched, or 0 if it did not. If the prefix matched, the external identifier is returned in the return parameter. If it did not match, NULL is returned in the return parameter. On failure, a negative errno-style error number is returned by either function. The returned strings must be free(3)'d by the caller.

Notes¶

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.

See Also¶

systemd(1), sd-bus(3), free(3)