第 60 章 Sockets: 服务器设计 (Sockets: Server Design)

// 摘自《The Linux Programming Interface》 第 60 章 Listing 60-2 (UDP echo, iterative)
#include <syslog.h>
#include "id_echo.h"
#include "become_daemon.h"
int main(int argc, char *argv[]) {
    int sfd;
    ssize_t numRead;
    socklen_t addrlen, len;
    struct sockaddr_storage claddr;
    char buf[BUF_SIZE];
    char addrStr[IS_ADDR_STR_LEN];

    if (becomeDaemon(0) == -1) errExit("becomeDaemon");
    sfd = inetBind(SERVICE, SOCK_DGRAM, &addrlen);
    if (sfd == -1) { syslog(LOG_ERR, "..."); exit(EXIT_FAILURE); }

    for (;;) {
        len = sizeof(struct sockaddr_storage);
        numRead = recvfrom(sfd, buf, BUF_SIZE, 0,
                           (struct sockaddr *) &claddr, &len);
        if (numRead == -1) errExit("recvfrom");
        if (sendto(sfd, buf, numRead, 0,
                   (struct sockaddr *) &claddr, len) != numRead)
            syslog(LOG_WARNING, "Error echoing response to %s (%s)",
                   inetAddressStr(...), strerror(errno));
    }
}

// 摘自《The Linux Programming Interface》 第 60 章 Listing 60-4
#include <signal.h>
#include <syslog.h>
#include <sys/wait.h>
#include "become_daemon.h"
#include "inet_sockets.h"
#include "tlpi_hdr.h"
#define SERVICE "echo"
#define BUF_SIZE 4096

static void grimReaper(int sig) {
    int savedErrno = errno;
    while (waitpid(-1, NULL, WNOHANG) > 0) continue;
    errno = savedErrno;
}

static void handleRequest(int cfd) {
    char buf[BUF_SIZE]; ssize_t numRead;
    while ((numRead = read(cfd, buf, BUF_SIZE)) > 0)
        if (write(cfd, buf, numRead) != numRead) { syslog(...); exit(EXIT_FAILURE); }
    if (numRead == -1) { syslog(...); exit(EXIT_FAILURE); }
}

int main(int argc, char *argv[]) {
    int lfd, cfd;
    struct sigaction sa;

    if (becomeDaemon(0) == -1) errExit("becomeDaemon");

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = grimReaper;
    if (sigaction(SIGCHLD, &sa, NULL) == -1) ...

    lfd = inetListen(SERVICE, 10, NULL);
    if (lfd == -1) ...

    for (;;) {
        cfd = accept(lfd, NULL, NULL);
        if (cfd == -1) { syslog(LOG_ERR, "accept fail"); exit(EXIT_FAILURE); }
        switch (fork()) {
        case -1: syslog(LOG_ERR, "fork"); close(cfd); break;  /* try next */
        case 0:  close(lfd); handleRequest(cfd); _exit(EXIT_SUCCESS);
        default: close(cfd); break;  /* loop to accept next */
        }
    }
}

# service  socket-type  protocol  flags    user   server-program  args
echo        stream        tcp      nowait   root   internal
echo        dgram         udp      wait     root   internal
ftp         stream        tcp      nowait   root   /usr/sbin/tcpd   in.ftpd
telnet      stream        tcp      nowait   root   /usr/sbin/tcpd   in.telnetd

// 摘自《The Linux Programming Interface》 第 60 章 Listing 60-6
#include <syslog.h>
#include "tlpi_hdr.h"
#define BUF_SIZE 4096
int main(int argc, char *argv[]) {
    char buf[BUF_SIZE]; ssize_t numRead;
    while ((numRead = read(STDIN_FILENO, buf, BUF_SIZE)) > 0) {
        if (write(STDOUT_FILENO, buf, numRead) != numRead) {
            syslog(LOG_ERR, "write failed: %s", strerror(errno));
            exit(EXIT_FAILURE);
        }
    }
    if (numRead == -1) { syslog(...); exit(EXIT_FAILURE); }
    exit(EXIT_SUCCESS);
}