Provided by: libelogind-dev-doc_241.3-1+debian1_all bug

NAME

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

SYNOPSIS

       #include <elogind/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.

       The sd_bus_message_appendv() is equivalent to the 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
       ┌──────────┬──────────────────────────────┬──────────────────┬──────────────────┬──────────────────┐
       │SpecifierConstantDescriptionSizeExpected 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        │ 4 bytes          │ int              │
       │          │                              │ descriptor       │                  │                  │
       ├──────────┼──────────────────────────────┼──────────────────┼──────────────────┼──────────────────┤
       │"a"       │ SD_BUS_TYPE_ARRAY            │ array            │ determined by    │ int, followed by │
       │          │                              │                  │ array type and   │ array contents   │
       │          │                              │                  │ size             │                  │
       ├──────────┼──────────────────────────────┼──────────────────┼──────────────────┼──────────────────┤
       │"v"       │ SD_BUS_TYPE_VARIANT          │ variant          │ determined by    │ signature        │
       │          │                              │                  │ the type         │ string, followed │
       │          │                              │                  │ argument         │ by variant       │
       │          │                              │                  │                  │ contents         │
       ├──────────┼──────────────────────────────┼──────────────────┼──────────────────┼──────────────────┤
       │"("       │ SD_BUS_TYPE_STRUCT_BEGIN     │ array start      │ determined by    │ structure        │
       ├──────────┼──────────────────────────────┼──────────────────┤ the nested types │ contents         │
       │")"       │ SD_BUS_TYPE_STRUCT_END       │ array end        │                  │                  │
       ├──────────┼──────────────────────────────┼──────────────────┼──────────────────┼──────────────────┤
       │"{"       │ SD_BUS_TYPE_DICT_ENTRY_BEGIN │ dictionary entry │                  │                  │
       │          │                              │ start            │ determined by    │ dictionary       │
       ├──────────┼──────────────────────────────┼──────────────────┤ the nested types │ contents         │
       │"}"       │ SD_BUS_TYPE_DICT_ENTRY_END   │ dictionary 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 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 0 or a positive integer. On failure, these functions
       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 libelogind pkg-config(1) file.

SEE ALSO

       elogind(8),

       sd-bus(3), sd_bus_message_append_basic(3), sd_bus_message_append_array(3)

NOTES

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