recvmsg使用方法

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <netdb.h>
#include <pthread.h>
#include <sys/resource.h>
#include <sys/uio.h>

#define SA struct sockaddr
#define err(msg) perror(msg)

static int tcp_listen(const char *ip, int port)
{
        struct sockaddr_in addr;
        int fd;
        int on = 1;

        if ((fd = socket(PF_INET, SOCK_STREAM, 0)) == -1) {
                err("socket");
                goto out;
        }

        setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));

        memset(&addr, '\0', sizeof(addr));
        addr.sin_family = AF_INET;
        addr.sin_port = htons(port);
        if (inet_pton(AF_INET, ip, &addr.sin_addr) < 0) {
                err("inet_pton");
                goto err;
        }

        if (bind(fd, (SA *)&addr, sizeof(addr)) == -1) {
                err("bind");
                goto err;
        }
        if (listen(fd, 10) == -1) {
                err("listen");
                goto err;
        }

        return fd;
err:
        close(fd);
out:
        return -1;
}

static void handle_conn(int fd)
{
        struct msghdr msg;
        struct iovec iov[2], *piov;
        char buf0[5], buf1[10];
        ssize_t len;
        int i, dlen;

        memset(buf0, '\0', sizeof(buf0));
        memset(buf1, '\0', sizeof(buf1));
        iov[0].iov_base = buf0;
        iov[0].iov_len = 5;
        iov[1].iov_base = buf1;
        iov[1].iov_len = 10;

        memset(&msg, '\0', sizeof(msg));
        msg.msg_iov = iov;
        msg.msg_iovlen = 2;

        if ((len = recvmsg(fd, &msg, 0)) == -1) {
                err("recvmsg");
                return;
        }

        piov = iov;
        while (len > 0) {
                if (len <= piov->iov_len)
                        dlen = len;
                else
                        dlen = piov->iov_len;

                printf("dlen = %d\n", dlen);

                if (write(STDOUT_FILENO, piov->iov_base, dlen) == -1) {
                        err("write");
                        break;
                }

                piov++; /* f: pointer to next iov */
                len -= dlen;
        }
}

int main(void)
{
        int fd;

        if ((fd = tcp_listen("0.0.0.0", 8888)) == -1) {
                err("tcp_listen");
                goto out;
        }

        while (1) {
                int connfd = accept(fd, NULL, NULL);
                if (connfd == -1) {
                        err("accept");
                        break;
                }

                handle_conn(connfd);
                close(connfd);
        }
        close(fd);
        return 0;
out:
        return -1;
}