下面是使用 Linux GCC 的 SCTP echo-server 程序的代码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sctp.h>
#include <sctp/syscalls.h>
#include <netdb.h>
#include <linux/signal.h>
#define PORT "5000" // the port users will be connecting to
#define BUFLEN 1024
/*
* Given an event notification, print out what it is.
*/
static void handle_event(void *buf)
{
char addrbuf[INET6_ADDRSTRLEN];
const char *ap;
struct sockaddr_in *sin;
struct sockaddr_in6 *sin6;
struct sctp_assoc_change *sac;
struct sctp_send_failed *ssf;
struct sctp_paddr_change *spc;
struct sctp_remote_error *sre;
union sctp_notification *snp = (union sctp_notification*)buf;
switch (snp->sn_header.sn_type) {
case SCTP_ASSOC_CHANGE:
sac = &snp->sn_assoc_change;
printf("^^^ assoc_change: state=%hu, error=%hu, instr=%hu "
"outstr=%hu\n", sac->sac_state, sac->sac_error,
sac->sac_inbound_streams, sac->sac_outbound_streams);
break;
case SCTP_SEND_FAILED:
ssf = &snp->sn_send_failed;
printf("^^^ sendfailed: len=%hu err=%d\n", ssf->ssf_length,
ssf->ssf_error);
break;
case SCTP_PEER_ADDR_CHANGE:
spc = &snp->sn_paddr_change;
if (spc->spc_aaddr.ss_family == AF_INET) {
sin = (struct sockaddr_in *)&spc->spc_aaddr;
ap = inet_ntop(AF_INET, &sin->sin_addr, addrbuf,
INET6_ADDRSTRLEN);
} else {
sin6 = (struct sockaddr_in6 *)&spc->spc_aaddr;
ap = inet_ntop(AF_INET6, &sin6->sin6_addr, addrbuf,
INET6_ADDRSTRLEN);
}
printf("^^^ intf_change: %s state=%d, error=%d\n", ap,
spc->spc_state, spc->spc_error);
break;
case SCTP_REMOTE_ERROR:
sre = &snp->sn_remote_error;
printf("^^^ remote_error: err=%hu len=%hu\n",
ntohs(sre->sre_error), ntohs(sre->sre_length));
break;
case SCTP_SHUTDOWN_EVENT:
printf("^^^ shutdown event\n");
break;
default:
printf("unknown type: %hu\n", snp->sn_header.sn_type);
break;
}
}
/*
* Receive a message from the network.
*/
static void* getmsg(int fd, struct msghdr *msg, void *buf, size_t *buflen,
ssize_t *nrp, size_t cmsglen)
{
ssize_t nr = 0;
struct iovec iov[1];
*nrp = 0;
iov->iov_base = buf;
msg->msg_iov = iov;
msg->msg_iovlen = 1;
/* Loop until a whole message is received. */
for (;;) {
msg->msg_flags = MSG_XPG4_2;
msg->msg_iov->iov_len = *buflen;
msg->msg_controllen = cmsglen;
nr += recvmsg(fd, msg, 0);
if (nr <= 0) {
/* EOF or error */
*nrp = nr;
return (NULL);
}
/* Whole message is received, return it. */
if (msg->msg_flags & MSG_EOR) {
*nrp = nr;
return (buf);
}
/* Maybe we need a bigger buffer, do realloc(). */
if (*buflen == nr) {
buf = realloc(buf, *buflen * 2);
if (buf == 0) {
fprintf(stderr, "out of memory\n");
exit(1);
}
*buflen *= 2;
}
/* Set the next read offset */
iov->iov_base = (char *)buf + nr;
iov->iov_len = *buflen - nr;
}
}
/*
* The echo server.
*/
static void echo(int fd)
{
ssize_t nr;
struct sctp_sndrcvinfo *sri;
struct msghdr msg[1];
struct cmsghdr *cmsg;
char cbuf[sizeof (*cmsg) + sizeof (*sri)];
char *buf;
size_t buflen;
struct iovec iov[1];
size_t cmsglen = sizeof (*cmsg) + sizeof (*sri);
/* Allocate the initial data buffer */
buflen = BUFLEN;
if ((buf = (char*)malloc(BUFLEN)) == NULL) {
fprintf(stderr, "out of memory\n");
exit(1);
}
/* Set up the msghdr structure for receiving */
memset(msg, 0, sizeof (*msg));
msg->msg_control = cbuf;
msg->msg_controllen = cmsglen;
msg->msg_flags = 0;
cmsg = (struct cmsghdr *)cbuf;
sri = (struct sctp_sndrcvinfo *)(cmsg + 1);
/* Wait for something to echo */
while ((buf =(char*)getmsg(fd, msg, buf, &buflen, &nr, cmsglen)) != NULL) {
/* Intercept notifications here */
if (msg->msg_flags & MSG_NOTIFICATION) {
handle_event(buf);
continue;
}
iov->iov_base = buf;
msg->msg_iov = iov;
msg->msg_iovlen = 1;
iov->iov_len = nr;
msg->msg_control = cbuf;
msg->msg_controllen = sizeof (*cmsg) + sizeof (*sri);
write(0, buf, nr);
/* Echo it back */
msg->msg_flags = MSG_XPG4_2;
if (sendmsg(fd, msg, 0) < 0) {
perror("sendmsg");
exit(1);
}
}
if (nr < 0) {
perror("recvmsg");
}
close(fd);
}
int
main(void)
{
int lfd;
int cfd;
int onoff = 1;
struct sockaddr_in sin;
struct sctp_event_subscribe events;
struct sctp_initmsg initmsg;
if ((lfd = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP)) == -1) {
perror("socket");
exit(1);
}
sin.sin_family = AF_INET;
sin.sin_port = htons(5000);
sin.sin_addr.s_addr = INADDR_ANY;
if((sctp_bindx(lfd,(struct sockaddr*)&sin,1,SCTP_BINDX_ADD_ADDR))<0 ){
close(lfd);
perror("bind");
exit(1);
}
if (listen(lfd, 1) == -1) {
perror("listen");
exit(1);
}else{
printf("Server listening on port 5000.....");
}
/* Events to be notified for */
(void) memset(&events, 0, sizeof (events));
events.sctp_data_io_event = 1;
events.sctp_association_event = 1;
events.sctp_send_failure_event = 1;
events.sctp_address_event = 1;
events.sctp_peer_error_event = 1;
events.sctp_shutdown_event = 1;
/* Wait for new associations */
for (;;) {
if ((cfd = accept(lfd, NULL, 0)) == -1) {
perror("accept");
exit(1);
}
/* Enable ancillary data */
if (setsockopt(cfd, IPPROTO_SCTP, SCTP_EVENTS, &events,
sizeof (events)) < 0) {
perror("setsockopt SCTP_EVENTS");
exit(1);
}
/* Echo back any and all data */
echo(cfd);
}
}
代码编译时，编译器会发出有关字节排序函数（htons、htonl、ntohs、ntonl）的警告消息：
-*- mode: compilation; default-directory: "/usr/lib/gcc/x86_64-linux-gnu/4.7.3/include/" -*-
Compilation started at Wed Jan 15 09:48:12
gcc sctp_es.c
sctp_es.c: In function ‘handle_event’:
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c:63:13: warning: ‘force’ attribute directive ignored [-Wattributes]
sctp_es.c: In function ‘main’:
sctp_es.c:203:5: warning: ‘force’ attribute directive ignored [-Wattributes]
Compilation finished at Wed Jan 15 09:48:12
那么这里的问题似乎是什么？我用这 4 个函数创建了一个额外的标题，并将其作为标题添加到标题中，但这并不能解决问题。