UDP sockets

QUIC runs over UDP, and wired talks to the kernel directly instead of through libc. This page binds two sockets on 127.0.0.1 and sends hello from one to the other.

Code

main.c

#define WIRED_MAIN
#include "wired.h"

int wired_main(int argc, char** argv) {
  (void)argc;
  (void)argv;
  static const u8 lo[4] = {127, 0, 0, 1};
  sockaddr        a, b, from;
  wired_udp_addr(&a, 14512, lo);
  wired_udp_addr(&b, 14513, lo);

  i64 sa = wired_udp_socket();
  i64 sb = wired_udp_socket();
  if (wired_udp_bind(sa, &a) < 0 || wired_udp_bind(sb, &b) < 0) return 1;

  /* a -> b, then b reads it along with the sender's address. */
  wired_udp_send(sa, &b, wired_span_cstr("hello"));
  u8  buf[64];
  i64 n = wired_udp_recvfrom(sb, wired_mspan_of(buf, sizeof buf - 1), &from);
  if (n < 0) return 1;
  buf[n] = 0;

  u16 port =
      (u16)((from.port_be >> 8) | (from.port_be << 8)); /* to host order */
  wired_dprintf(
      2, "recv %llu bytes: %s from %llu\n", (u64)n, (const char*)buf,
      (u64)port);

  wired_udp_close(sa);
  wired_udp_close(sb);
  return 0;
}

Output

$ ./quic-udp
recv 5 bytes: hello from 14512

How it works

• wired_udp_addr(&sa, port, octets) builds an address; IPv4 octets become a v4-mapped IPv6 address, because every socket is dual-stack.
• wired_udp_socket opens a socket, wired_udp_bind binds it. Both return a negative errno on failure.
• wired_udp_send(fd, &dst, span) sends one datagram; wired_udp_recvfrom(fd, buf, &src) receives one and fills in the sender.
• sockaddr.port_be is in network byte order; swap it to print it.
• wired_udp_close releases the socket.