# sd_bus_path_encode

systemd

sd_bus_path_encode

3

sd_bus_path_encode

sd_bus_path_encode_many

sd_bus_path_decode

sd_bus_path_decode_many

Convert an external identifier into an object path and back

\#include \<systemd/sd-bus.h\>

int

sd_bus_path_encode

const char \*

prefix

const char \*

external_id

char \*\*

ret_path

int

sd_bus_path_encode_many

char \*\*

out

const char \*

path_template

…

int

sd_bus_path_decode

const char \*

path

const char \*

prefix

char \*\*

ret_external_id

int

sd_bus_path_decode_many

const char \*

path

const char \*

path_template

…

# 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.

# History

`sd_bus_path_encode()` and `sd_bus_path_decode()` were added in version 211.

`sd_bus_path_encode_many()` and `sd_bus_path_decode_many()` were added in version 227.

# See Also

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