SD_BUS_MESSAGE_APPEND(3) sd_bus_message_append SD_BUS_MESSAGE_APPEND(3)
NAME
sd_bus_message_append, sd_bus_message_appendv - Attach fields to a
D-Bus message based on a type string
SYNOPSIS
#include <systemd/sd-bus.h>
int sd_bus_message_append(sd_bus_message *m, const char *types, ...);
int sd_bus_message_appendv(sd_bus_message *m, const char *types,
va_list ap);
DESCRIPTION
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.
sd_bus_message_appendv() is equivalent to sd_bus_message_append(),
except that it is called with a "va_list" instead of a variable number
of arguments. This function does not call the va_end() macro. Because
it invokes the va_arg() macro, the value of ap is undefined after the
call.
For further details on the D-Bus type system, please consult the D-Bus
Specification[1].
Table 1. Item type specifiers
+----------+------------------------------+----------------+---------------+---------------+
|Specifier | Constant | Description | Size | Expected C |
| | | | | Type |
+----------+------------------------------+----------------+---------------+---------------+
|"y" | SD_BUS_TYPE_BYTE | unsigned | 1 byte | uint8_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"b" | SD_BUS_TYPE_BOOLEAN | boolean | 4 bytes | int |
+----------+------------------------------+----------------+---------------+---------------+
|"n" | SD_BUS_TYPE_INT16 | signed | 2 bytes | int16_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"q" | SD_BUS_TYPE_UINT16 | unsigned | 2 bytes | uint16_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"i" | SD_BUS_TYPE_INT32 | signed | 4 bytes | int32_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"u" | SD_BUS_TYPE_UINT32 | unsigned | 4 bytes | uint32_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"x" | SD_BUS_TYPE_INT64 | signed | 8 bytes | int64_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"t" | SD_BUS_TYPE_UINT64 | unsigned | 8 bytes | uint64_t |
| | | integer | | |
+----------+------------------------------+----------------+---------------+---------------+
|"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 | 4 bytes | int |
| | | descriptor | | |
+----------+------------------------------+----------------+---------------+---------------+
|"a" | SD_BUS_TYPE_ARRAY | array | determined by | int, followed |
| | | | array type | by array |
| | | | and size | contents |
+----------+------------------------------+----------------+---------------+---------------+
|"v" | SD_BUS_TYPE_VARIANT | variant | determined by | signature |
| | | | the type | string, |
| | | | argument | followed by |
| | | | | variant |
| | | | | contents |
+----------+------------------------------+----------------+---------------+---------------+
|"(" | SD_BUS_TYPE_STRUCT_BEGIN | array start | determined by | structure |
+----------+------------------------------+----------------+ the nested | contents |
|")" | SD_BUS_TYPE_STRUCT_END | array end | types | |
+----------+------------------------------+----------------+---------------+---------------+
|"{" | SD_BUS_TYPE_DICT_ENTRY_BEGIN | dictionary | | |
| | | entry start | determined by | dictionary |
+----------+------------------------------+----------------+ the nested | contents |
|"}" | SD_BUS_TYPE_DICT_ENTRY_END | dictionary | types | |
| | | entry end | | |
+----------+------------------------------+----------------+---------------+---------------+
For types "s" and "g" (unicode string or signature), the pointer may be
NULL, which is equivalent to an empty string. For "h" (UNIX file
descriptor), the descriptor is duplicated by this call and the passed
descriptor stays in possession of the caller. See
sd_bus_message_append_basic(3) for the precise interpretation of those
and other types.
TYPES STRING GRAMMAR
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 "}"
EXAMPLES
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);
RETURN VALUE
On success, these functions return a non-negative integer. On failure,
they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
Specified parameter is invalid.
-EPERM
Message has been sealed.
-ESTALE
Message is in invalid state.
-ENXIO
Message cannot be appended to.
-ENOMEM
Memory allocation failed.
NOTES
These APIs are implemented 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), sd_bus_message_append_basic(3),
sd_bus_message_append_array(3), sd_bus_message_open_container(3)
NOTES
1. D-Bus Specification
https://dbus.freedesktop.org/doc/dbus-specification.html#type-system
systemd 252 SD_BUS_MESSAGE_APPEND(3)
Czas wygenerowania: 0.00173 sek.
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