再议socket

再议socket

线程池

socket通道在内核中实际上只有一条，多个文件描述符指向同一个socket通道

本地套接字（类似于管道，两个进程的通信）

绑定是和磁盘文件绑定。

#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#define QLEN 10

/*
 * Create a server endpoint of a connection.
 * Returns fd if all OK, <0 on error.
 */
int serv_listen(const char *name)
{
    int fd, len, err, rval;
    struct sockaddr_un un;

    /* create a UNIX domain stream socket */
    if ((fd = socket(AF_UNIX, SOCK_STREAM, 0) < 0))
    return(-1);
    unlink(name);   /* in case it already exists */

    /* fill in socket address structure */
    memset(&un, 0, sizeof(un));
    un.sun_family = AF_UNIX;
    strcpy(un.sun_path, name);
    len = offsetof(struct sockaddr_un, sun_path) + strlen(name);

    /* bind the name to the descriptor */
    if (bind(fd, (struct sockaddr *)&un, len) < 0)
    {
    rval = -2;
    goto errout;
    }
    if (listen(fd, QLEN) < 0)
    {
    rval = -3;
    goto errout;
    }
    return(fd);

errout:
    err = errno;
    close(fd);
    errno = err;
    return(rval);
}
int serv_accept(int listenfd, uid_t *uidptr)
{
    int clifd, len, err, rval;
    struct sockaddr_un un;
    struct stat statbuf;
    
    len = sizeof(un);
    if ((clifd = accept(listenfd, (struct sockaddr *)&un, &len)) < 0)
    return(-1);    /* often errno=EINTR, if signal caught */

    /* obtain the client's uid from its calling address */
    len -= offsetof(struct sockaddr_un, sun_path);  /* len of pathname */
    un.sun_path[len] = '';    /* null terminate */

    if (stat(un.sun_path, &statbuf) < 0)
    {
    rval = -2;
    goto errout;
    }
    if (S_ISSOCK(statbuf.st_mode) == 0)
    {
    rval = -3;  /* not a socket */
    goto errout;
    }
    if (uidptr != NULL)
    *uidptr = statbuf.st_uid;   /* return uid of caller */
    unlink(un.sun_path);    /* we're done with pathname now */
    return(clifd);

errout:
    err = errno;
    close(clifd);
    errno = err;
    return(rval);
}
int main(void)
{
    int lfd, cfd, n, i;
    uid_t cuid;
    char buf[1024];

    lfd = serv_listen("foo.socket");
    if (lfd < 0)
    {
    switch (lfd)
    {
        case -3:perror("listen"); break;
        case -2:perror("bind"); break;
        case -1:perror("socket"); break;
    }
    exit(-1);
    }
    cfd = serv_accept(lfd, &cuid); 
    if (cfd < 0)
    {
    switch (cfd)
    {
        case -3:perror("not a socket"); break;
        case -2:perror("a bad filename"); break;
        case -1:perror("accept"); break;
    }
    exit(-1);
    }
    while (1)
    {
r_again:
    n = read(cfd, buf, 1024);
    if (n == -1)
    {
        if (errno == EINTR)
        goto r_again;
    }
    else if (n == 0)
    {
        printf("the other side has been closed.
");
        break;
    }
    for (i = 0; i < n; i++)
        buf[i] = toupper(buf[i]);
    write(cfd, buf, n);
    }
    close(cfd);
    close(lfd);
    return 0;
}

//客户端
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>

#define CLI_PATH "/var/tmp/"    /* +5 for pid = 14 chars */

/*
 * Create a client endpoint and connect to a server.
 * Returns fd if all OK, <0 on error.
 */
int cli_conn(const char *name)
{
    int fd, len, err, rval;
    struct sockaddr_un un;

    /* create a UNIX domain stream socket */
    if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
    return(-1);

    /* fill socket address structure with our address */
    memset(&un, 0, sizeof(un));
    un.sun_family = AF_UNIX;
    sprintf(un.sun_path, "%s%05d", CLI_PATH, getpid());
    len = offsetof(struct sockaddr_un, sun_path) + strlen(un.sun_path); 

    unlink(un.sun_path);    /* in case it already exists */
    if (bind(fd, (struct sockaddr *)&un, len) < 0)
    {
    rval = -2;
    goto errout;
    }

    /* fill socket address structure with server's address */
    memset(&un, 0, sizeof(un));
    un.sun_family = AF_UNIX;
    strcpy(un.sun_path, name);
    len = offsetof(struct sockaddr_un, sun_path) + strlen(name); 
    if (connect(fd, (struct sockaddr *)&un, len) < 0)
    {
    rval = -3;
    goto errout;
    }
    return(fd);

errout:
    err = errno;
    close(fd);
    errno = err;
    return(rval);
}
int main(void)
{
    int fd, n;
    char buf[1024];

    fd = cli_conn("foo.socket");
    if (fd < 0)
    {
    switch (fd)
    {
        case -3:perror("connect"); break;
        case -2:perror("bind"); break;
        case -1:perror("socket"); break;
    }
    exit(-1);
    }
    while (fgets(buf, sizeof(buf), stdin) != NULL)
    {
    write(fd, buf, strlen(buf));
    n = read(fd, buf, sizeof(buf));
    write(STDOUT_FILENO, buf, n);
    }
    close(fd);
    return 0;
}