sd_bus_message_append — Attach fields to a D-Bus message based on a type 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 fields to the D-Bus message object
m
. The type string
types
describes the types of the field
arguments that follow. For each type specified in the type string,
one or more arguments need to be specified, in the same order as
declared in the type string.
The type 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 with
the contained types, a variant, an array with its element type, or
a dictionary entry with the contained types. The type 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
". Corresponding
arguments must begin with a type 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 begin with the number of
entries in the array, followed by the entries themselves,
matching the element type of the array.
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 begin
with the number of dictionary entries, followed by a pair of
values for each entry matching the element type of
the dictionary entries.
For further details on the D-Bus type system, please consult the D-Bus Specification.
Table 1. Item type specifiers
Specifier | Constant | Description | Size | Expected C Type |
---|---|---|---|---|
"y " | SD_BUS_TYPE_BYTE | unsigned integer | 1 byte | uint8_t |
"b " | SD_BUS_TYPE_BOOLEAN | boolean | 4 bytes | int |
"n " | SD_BUS_TYPE_INT16 | signed integer | 2 bytes | int16_t |
"q " | SD_BUS_TYPE_UINT16 | unsigned integer | 2 bytes | uint16_t |
"i " | SD_BUS_TYPE_INT32 | signed integer | 4 bytes | int32_t |
"u " | SD_BUS_TYPE_UINT32 | unsigned integer | 4 bytes | uint32_t |
"x " | SD_BUS_TYPE_INT64 | signed integer | 8 bytes | int64_t |
"t " | SD_BUS_TYPE_UINT64 | unsigned integer | 8 bytes | uint64_t |
"d " | SD_BUS_TYPE_DOUBLE | floating-point | 8 bytes | double |
"s " | SD_BUS_TYPE_STRING | Unicode string | variable | char[] |
"o " | SD_BUS_TYPE_OBJECT_PATH | object path | variable | char[] |
"g " | SD_BUS_TYPE_SIGNATURE | signature | variable | char[] |
"h " | SD_BUS_TYPE_UNIX_FD | UNIX file descriptor | 4 bytes | int |
"a " | SD_BUS_TYPE_ARRAY | array | determined by array type and size | int, followed by array contents |
"v " | SD_BUS_TYPE_VARIANT | variant | determined by the type argument | signature string, followed by variant contents |
"( " | SD_BUS_TYPE_STRUCT_BEGIN | array start | determined by the nested types | structure contents |
") " | SD_BUS_TYPE_STRUCT_END | array end | ||
"{ " | SD_BUS_TYPE_DICT_ENTRY_BEGIN | dictionary entry start | determined by the nested types | dictionary contents |
"} " | 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 a 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.