sd_bus_message_append — Attach parts of message based on a format string
#include <systemd/sd-bus.h>
int sd_bus_message_append( | sd_bus_message *m, |
const char *types, | |
...) ; |
The sd_bus_message_append
function appends
a sequence of items to message m
. The
format string types
describes the types of
arguments that follow.
The format string is composed of the elements shown in the
table below. It contains zero or more single "complete types".
Each complete type may be one of the basic types or a fully
described container type. A container type may be a structure, a
variant type code, an array with its element type, or a dictionary
with its entry type. The format string is
NUL
-terminated.
In case of a basic type, one argument of the corresponding type is expected.
A structure is denoted by a sequence of complete types
between "(
" and ")
". This
sequence cannot be empty — it must contain at least one type.
Arguments corresponding to this nested sequence follow the same
rules as if they were not nested.
A variant is denoted by "v
". Correspoding
arguments must include a format string denoting a complete type,
and following that, arguments corresponding to the specified type.
An array is denoted by "a
" followed by a
complete type. Corresponding arguments must include the size of
the array, and then repeated this number of times, arguments
corresponding to the nested type.
A dictionary is an array of dictionary entries, denoted by
"a
" followed by a pair of complete types between
"{
" and "}
". The first of those
types must be a basic type. Corresponding arguments must include
the size of the dictionary, and then repeated this number of
times, arguments corresponding to each of the two nested
types.
Table 1. Item format specifiers
Specifier | Constant | Description | Size |
---|---|---|---|
"y " | SD_BUS_TYPE_BYTE | unsigned integer | 1 byte |
"b " | SD_BUS_TYPE_BOOLEAN | boolean | 4 bytes |
"n " | SD_BUS_TYPE_INT16 | signed integer | 2 bytes |
"q " | SD_BUS_TYPE_UINT16 | unsigned integer | 2 bytes |
"i " | SD_BUS_TYPE_INT32 | signed integer | 4 bytes |
"u " | SD_BUS_TYPE_UINT32 | unsigned integer | 4 bytes |
"x " | SD_BUS_TYPE_INT64 | signed integer | 8 bytes |
"t " | SD_BUS_TYPE_UINT64 | unsigned integer | 8 bytes |
"d " | SD_BUS_TYPE_DOUBLE | floating-point | 8 bytes |
"s " | SD_BUS_TYPE_STRING | Unicode string | variable |
"o " | SD_BUS_TYPE_OBJECT_PATH | object path | variable |
"g " | SD_BUS_TYPE_SIGNATURE | signature | variable |
"h " | SD_BUS_TYPE_UNIX_FD | UNIX file descriptor | 4 bytes |
"a " | SD_BUS_TYPE_ARRAY | array | determined by array type and size |
"v " | SD_BUS_TYPE_VARIANT | variant | determined by the type argument |
"( " | SD_BUS_TYPE_STRUCT_BEGIN | array start | determined by the nested types |
") " | SD_BUS_TYPE_STRUCT_END | array end | |
"{ " | SD_BUS_TYPE_DICT_ENTRY_BEGIN | dictionary entry start | determined by the nested types |
"} " | SD_BUS_TYPE_DICT_ENTRY_END | dictionary entry end |
types ::= complete_type* complete_type ::= basic_type | variant | structure | array | dictionary basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" | "b" | "h" | "s" | "o" | "g" variant ::= "v" structure ::= "(" complete_type+ ")" array ::= "a" complete_type dictionary ::= "a" "{" basic_type complete_type "}"
Append a single basic type (the string "a string
"):
sd_bus_message *m; ... sd_bus_message_append(m, "s", "a string");
Append all types of integers:
uint8_t y = 1; int16_t n = 2; uint16_t q = 3; int32_t i = 4; uint32_t u = 5; int32_t x = 6; uint32_t t = 7; double d = 8.0; sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);
Append a structure composed of string and a D-Bus path:
sd_bus_message_append(m, "(so)", "a string", "/a/path");
Append an array of UNIX file descriptors:
sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
Append a variant, with the real type "g" (signature), and value "sdbusisgood":
sd_bus_message_append(m, "v", "g", "sdbusisgood");
Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
On success, this call returns 0 or a positive integer. On failure, this call returns a negative errno-style error code.
sd_bus_open_user()
and other functions
described here are available as a shared library, which can be
compiled and linked to with the
libsystemd-bus
pkg-config(1)
file.