sd_bus_message_append(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | TYPES STRING GRAMMAR | EXAMPLES | RETURN VALUE | NOTES | SEE ALSO | NOTES | COLOPHON

SD_BUS_MESSAGE_APPEND(3)  sd_bus_message_append SD_BUS_MESSAGE_APPEND(3)

NAME         top

       sd_bus_message_append, sd_bus_message_appendv - Attach fields to
       a D-Bus message based on a type string

SYNOPSIS         top

       #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         top

       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   │ int,        │
       │          │                              │                │ by array     │ followed by │
       │          │                              │                │ type and     │ array       │
       │          │                              │                │ size         │ contents    │
       ├──────────┼──────────────────────────────┼────────────────┼──────────────┼─────────────┤
       │"v"       │ SD_BUS_TYPE_VARIANT          │ variant        │ determined   │ signature   │
       │          │                              │                │ by the type  │ string,     │
       │          │                              │                │ argument     │ followed by │
       │          │                              │                │              │ variant     │
       │          │                              │                │              │ contents    │
       ├──────────┼──────────────────────────────┼────────────────┼──────────────┼─────────────┤
       │"("       │ SD_BUS_TYPE_STRUCT_BEGIN     │ array start    │ determined   │ structure   │
       ├──────────┼──────────────────────────────┼────────────────┤ by the       │ contents    │
       │")"       │ SD_BUS_TYPE_STRUCT_END       │ array end      │ nested types │             │
       ├──────────┼──────────────────────────────┼────────────────┼──────────────┼─────────────┤
       │"{"       │ SD_BUS_TYPE_DICT_ENTRY_BEGIN │ dictionary     │              │             │
       │          │                              │ entry start    │ determined   │ dictionary  │
       ├──────────┼──────────────────────────────┼────────────────┤ by the       │ contents    │
       │"}"       │ SD_BUS_TYPE_DICT_ENTRY_END   │ dictionary     │ nested 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         top

           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         top

       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         top

       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         top

       These APIs are implemented as a shared library, which can be
       compiled and linked to with the libsystemd pkg-config(1) file.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_message_append_basic(3),
       sd_bus_message_append_array(3), sd_bus_message_open_container(3)

NOTES         top

        1. D-Bus Specification
           http://dbus.freedesktop.org/doc/dbus-specification.html#type-system

COLOPHON         top

       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 page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 249                                     SD_BUS_MESSAGE_APPEND(3)

Pages that refer to this page: sd-bus(3)sd_bus_call(3)sd_bus_call_method(3)sd_bus_emit_signal(3)sd_bus_message_append_array(3)sd_bus_message_append_basic(3)sd_bus_message_append_strv(3)sd_bus_message_copy(3)sd_bus_message_open_container(3)sd_bus_message_read(3)sd_bus_message_verify_type(3)sd_bus_reply_method_return(3)sd_bus_set_property(3)