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, | |
…) ; |
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.
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.
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.
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.