systemd A monkey with a typewriter Zbigniew Jędrzejewski-Szmek zbyszek@in.waw.pl 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. a SD_BUS_TYPE_ARRAY array determined by array type and size int, followed by array contents v SD_BUS_TYPE_VARIANT variant determined by the type argument signature string, followed by variant contents ( SD_BUS_TYPE_STRUCT_BEGIN array start determined by the nested types structure contents ) SD_BUS_TYPE_STRUCT_END array end { SD_BUS_TYPE_DICT_ENTRY_BEGIN dictionary entry start determined by the nested types dictionary 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_basic3 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. sd_bus_open_user() and other functions described here are available as a shared library, which can be compiled and linked to with the libelogind-bus pkg-config1 file. systemd1, sd-bus3, sd_bus_message_append_basic3, sd_bus_message_append_array3