libdill: Structured Concurrency for C

NAME

udp_sendl - sends an UDP packet

SYNOPSIS

#include <libdill.h>

int udp_sendl(
    int s,
    const struct ipaddr* addr,
    struct iolist* first,
    struct iolist* last);

DESCRIPTION

UDP is an unreliable message-based protocol defined in RFC 768. The size of the message is limited. The protocol has no initial or terminal handshake. A single socket can be used to different destinations.

This function sends an UDP packet.

Given that UDP protocol is unreliable the function has no deadline. If packet cannot be sent it will be silently dropped.

This function accepts a linked list of I/O buffers instead of a single buffer. Argument first points to the first item in the list, last points to the last buffer in the list. The list represents a single, fragmented message, not a list of multiple messages. Structure iolist has the following members:

void *iol_base;          /* Pointer to the buffer. */
size_t iol_len;          /* Size of the buffer. */
struct iolist *iol_next; /* Next buffer in the list. */
int iol_rsvd;            /* Reserved. Must be set to zero. */

When receiving, iol_base equal to NULL means that iol_len bytes should be skipped.

The function returns EINVAL error in the case the list is malformed:

If last->iol_next is not NULL.
If first and last don't belong to the same list.
If there's a loop in the list.
If iol_rsvd of any item is non-zero.

The list (but not the buffers themselves) can be temporarily modified while the function is in progress. However, once the function returns the list is guaranteed to be the same as before the call.

s: Handle of the UDP socket.

addr: IP address to send the packet to. If set to NULL remote address specified in udp_open function will be used.

first: Pointer to the first item of a linked list of I/O buffers.

last: Pointer to the last item of a linked list of I/O buffers.

This function is not available if libdill is compiled with --disable-sockets option.

RETURN VALUE

In case of success the function returns 0. In case of error it returns -1 and sets errno to one of the values below.

ERRORS

EBADF: Invalid handle.
EINVAL: Invalid argument.
EMSGSIZE: The message is too long to fit into an UDP packet.
ENOTSUP: The handle does not support this operation.

EXAMPLE

struct ipaddr local;
ipaddr_local(&local, NULL, 5555, 0);
struct ipaddr remote;
ipaddr_remote(&remote, "server.example.org", 5555, 0, -1);
int s = udp_open(&local, &remote);
udp_send(s1, NULL, "ABC", 3);
char buf[2000];
ssize_t sz = udp_recv(s, NULL, buf, sizeof(buf), -1);
hclose(s);