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## Name

sd_bus_path_encode, sd_bus_path_decode — Convert an external identifier into an object path and back

## Synopsis

    #include <systemd/sd-bus.h>

`int sd_bus_path_encode(` | const char *prefix,
| const char *external_id,
| char **ret_path`)`;

`int sd_bus_path_decode(` | const char *path,
| const char *prefix,
| char **ret_external_id`)`;

## 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_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 "`_`".

## 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

`sd_bus_path_encode()` and `sd_bus_path_decode()` are available as a shared library, which can be compiled and linked to with the `libsystemd` pkg-config(1) file.

## See Also

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