прикрепляйте поля к сообщению D-Bus на основе строки типа (Attach fields to a D-Bus message based on a type string)
Описание (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
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.
