NAME
sd_bus_message_read, sd_bus_message_readv, sd_bus_message_peek_type - Read a sequence of values from a messageSYNOPSIS
#include <systemd/sd-bus.h>
int
sd_bus_message_read(sd_bus_message *m,
const char *types, ...);
int
sd_bus_message_readv(sd_bus_message *m,
const char *types,
va_list ap);
int
sd_bus_message_peek_type(sd_bus_message *m,
char *type,
const char **contents);
DESCRIPTION
sd_bus_message_read() reads a sequence of fields from the D-Bus message object m and advances the read position in the message. The type string types describes the types of items expected in the message and the field arguments that follow. The type string may be NULL or empty, in which case nothing is read. The type string is composed of the elements described in sd_bus_message_append(3), i.e. basic and container types. It must contain zero or more single "complete types". The type string is NUL-terminated. For each type specified in the type string, one or more arguments need to be specified after the types parameter, in the same order. The arguments must be pointers to appropriate types (a pointer to int8_t for a "y" in the type string, a pointer to int32_t for an "i", a pointer to const char* for an "s", ...) which are set based on the values in the message. As an exception, in case of array and variant types, the first argument is an "input" argument that further specifies how the message should be read. See the table below for a complete list of allowed arguments and their types. Note that, if the basic type is a pointer (e.g., const char * in the case of a string), the argument is a pointer to a pointer, and also the pointer value that is written is only borrowed and the contents must be copied if they are to be used after the end of the message's lifetime. If the type is "h" (UNIX file descriptor), the descriptor is not duplicated by this call and the returned descriptor remains in possession of the message object, and needs to be duplicated by the caller in order to keep an open reference to it after the message object is freed. Each argument may also be NULL, in which case the value is read and ignored.Specifier | Constant | Description | Type of the first argument | Types of the subsequent arguments, if any |
"y" | SD_BUS_TYPE_BYTE | 8bit unsigned integer | uint8_t * | |
"b" | SD_BUS_TYPE_BOOLEAN | boolean | int * (NB: not bool *) | |
"n" | SD_BUS_TYPE_INT16 | 16bit signed integer | int16_t * | |
"q" | SD_BUS_TYPE_UINT16 | 16bit unsigned integer | uint16_t * | |
"i" | SD_BUS_TYPE_INT32 | 32bit signed integer | int32_t * | |
"u" | SD_BUS_TYPE_UINT32 | 32bit unsigned integer | uint32_t * | |
"x" | SD_BUS_TYPE_INT64 | 64bit signed integer | int64_t * | |
"t" | SD_BUS_TYPE_UINT64 | 64bit unsigned integer | uint64_t * | |
"d" | SD_BUS_TYPE_DOUBLE | IEEE 754 double precision floating-point | double * | |
"s" | SD_BUS_TYPE_STRING | UTF-8 string | const char ** | |
"o" | SD_BUS_TYPE_OBJECT_PATH | D-Bus object path string | const char ** | |
"g" | SD_BUS_TYPE_SIGNATURE | D-Bus signature string | const char ** | |
"h" | SD_BUS_TYPE_UNIX_FD | UNIX file descriptor | int * | |
"a" | SD_BUS_TYPE_ARRAY | array | int, which specifies the expected length n of the array | n sets of arguments appropriate for the array element type |
"v" | SD_BUS_TYPE_VARIANT | variant | signature string | arguments appropriate for the types specified by the signature |
"(" | SD_BUS_TYPE_STRUCT_BEGIN | array start | arguments appropriate for the structure elements | |
")" | SD_BUS_TYPE_STRUCT_END | array end | ||
"{" | SD_BUS_TYPE_DICT_ENTRY_BEGIN | dictionary entry start | arguments appropriate for the first type in the pair | arguments appropriate for the second type in the pair |
"}" | SD_BUS_TYPE_DICT_ENTRY_END | dictionary entry end |
RETURN VALUE
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: -EINVALSpecified type string is invalid or the
message parameter is NULL.
-ENXIO
The message does not contain the specified
type at current position.
-EBADMSG
The message cannot be parsed.
-EBUSY
When reading from a container, this error will
be returned if unread elements are left in the container.
NOTES
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.EXAMPLES
Read a single basic type (a 64-bit integer):sd_bus_message *m; int64_t x; sd_bus_message_read(m, "x", &x);
sd_bus_message *m; int x; /* Do not use C99 'bool' type here, it's typically smaller in memory and would cause memory corruption */ sd_bus_message_read(m, "b", &x);
uint8_t y; int16_t n; uint16_t q; int32_t i; uint32_t u; int32_t x; uint32_t t; double d; sd_bus_message_read(m, "ynqiuxtd", &y, &n, &q, &i, &u, &x, &t, &d);
const char *s, *p; sd_bus_message_read(m, "(so)", &s, &p);
const char *s; uint64_t *v; sd_bus_message_read(m, "v", "gt", &s, &v);
int i, j, k; const char *s, *t, *u; sd_bus_message_read(m, "a{is}", 3, &i, &s, &j, &t, &k, &u);
sd_bus_message *m; int fd, fd_copy; sd_bus_message_read(m, "h", &fd); fd_copy = fcntl(fd, FD_DUPFD_CLOEXEC, 3);
SEE ALSO
systemd(1), sd-bus(3), sd_bus_message_read_basic(3), sd_bus_message_skip(3), sd_bus_message_append(3), sd_bus_message_enter_container(3)systemd 252 |