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NAME | SYNOPSIS | DESCRIPTION | TYPES STRING GRAMMAR | EXAMPLES | RETURN VALUE | ERRORS | NOTES | SEE ALSO | NOTES | COLOPHON |
SD_BUS_MESSAGE_APPEND(3) sd_bus_message_append SD_BUS_MESSAGE_APPEND(3)
sd_bus_message_append, sd_bus_message_appendv - 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, ...);
int sd_bus_message_appendv(sd_bus_message *m, const char *types,
va_list ap);
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.
The sd_bus_message_appendv() is equivalent to the function
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. See
sd_bus_message_append_basic(3) for the precise interpretation of
those and other types.
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, these functions return 0 or a positive integer. On
failure, these functions return a negative errno-style error code.
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.
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.
systemd(1), sd-bus(3), sd_bus_message_append_basic(3),
sd_bus_message_append_array(3)
1. D-Bus Specification
http://dbus.freedesktop.org/doc/dbus-specification.html#type-system
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
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⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
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COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SD_BUS_MESSAGE_APPEND(3)
Pages that refer to this page: sd-bus(3), sd_bus_message_append_array(3), sd_bus_message_append_basic(3), sd_bus_message_append_strv(3), systemd.directives(7), systemd.index(7)