Linux 网络编程: daytime Service

前言

如果你这段时间过得很舒服，那就证明你荒废以一段时间。如果你这段时间过得很辛苦，那么恭喜，你又进步了。最近入党的事情忙得焦头烂额，博客也拖了好久没写，主要也是因为要装 xinetd 服务一直没装好，Mac 上也无法编译多个文件，于是我还特意租了一个月服务器。OK，现在来实现客户端链接主机，从主机获取时间。

Error

errexit.c

/* errexit.c - errexit */
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

/*------------------------------------------------------------------------
 * errexit - print an error message and exit
 *------------------------------------------------------------------------
 */
int errexit(const char *format, ...)
{
	va_list	args;

	va_start(args, format);
	vfprintf(stderr, format, args);
	va_end(args);
	exit(1);
}

errno.h

/* Error constants.  Linux specific version.
   Copyright (C) 1996, 1997, 1998, 1999 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifdef _ERRNO_H

# undef EDOM
# undef EILSEQ
# undef ERANGE
# include <linux/errno.h>

/* Linux has no ENOTSUP error code.  */
# define ENOTSUP EOPNOTSUPP

/* Linux also had no ECANCELED error code.  Since it is not used here
   we define it to an invalid value.  */
# ifndef ECANCELED
#  define ECANCELED	125
# endif

# ifndef __ASSEMBLER__
/* Function to get address of global `errno' variable.  */
extern int *__errno_location (void) __THROW __attribute__ ((__const__));

#  if !defined _LIBC || defined _LIBC_REENTRANT
/* When using threads, errno is a per-thread value.  */
#   define errno (*__errno_location ())
#  endif
# endif /* !__ASSEMBLER__ */
#endif /* _ERRNO_H */

#if !defined _ERRNO_H && defined __need_Emath
/* This is ugly but the kernel header is not clean enough.  We must
   define only the values EDOM, EILSEQ and ERANGE in case __need_Emath is
   defined.  */
# define EDOM	33	/* Math argument out of domain of function.  */
# define EILSEQ	84	/* Illegal byte sequence.  */
# define ERANGE	34	/* Math result not representable.  */
#endif /* !_ERRNO_H && __need_Emath */

Server

passivesock.c

/* passivesock.c - passivesock */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
extern int	errno;

int	errexit(const char *format, ...);

unsigned short	portbase = 0;	/* port base, for non-root servers	*/

/*------------------------------------------------------------------------
 * passivesock - allocate & bind a server socket using TCP or UDP
 *------------------------------------------------------------------------
 */
int passivesock(const char *service, const char *transport, int qlen)
/*
 * Arguments:
 *      service   - service associated with the desired port
 *      transport - transport protocol to use ("tcp" or "udp")
 *      qlen      - maximum server request queue length
 */
{
	struct servent	*pse;	/* pointer to service information entry	*/
	struct protoent *ppe;	/* pointer to protocol information entry*/
	struct sockaddr_in sin;	/* an Internet endpoint address		*/
	int	s, type;	/* socket descriptor and socket type	*/

	memset(&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_addr.s_addr = INADDR_ANY;

    /* Map service name to port number */
	if ( pse = getservbyname(service, transport) )
		sin.sin_port = htons(ntohs((unsigned short)pse->s_port)
			+ portbase);
	else if ((sin.sin_port=htons((unsigned short)atoi(service))) == 0)
		errexit("can't get \"%s\" service entry\n", service);

    /* Map protocol name to protocol number */
	if ( (ppe = getprotobyname(transport)) == 0)
		errexit("can't get \"%s\" protocol entry\n", transport);

    /* Use protocol to choose a socket type */
	if (strcmp(transport, "udp") == 0)
		type = SOCK_DGRAM;
	else
		type = SOCK_STREAM;

    /* Allocate a socket */
	s = socket(PF_INET, type, ppe->p_proto);
	if (s < 0)
		errexit("can't create socket: %s\n", strerror(errno));

    /* Bind the socket */
	if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
		errexit("can't bind to %s port: %s\n", service,
			strerror(errno));
	if (type == SOCK_STREAM && listen(s, qlen) < 0)
		errexit("can't listen on %s port: %s\n", service,
			strerror(errno));
	return s;
}

passiveTCP.c

/* passiveTCP.c - passiveTCP */

int	passivesock(const char *service, const char *transport,
		int qlen);

/*------------------------------------------------------------------------
 * passiveTCP - create a passive socket for use in a TCP server
 *------------------------------------------------------------------------
 */
int passiveTCP(const char *service, int qlen)
/*
 * Arguments:
 *      service - service associated with the desired port
 *      qlen    - maximum server request queue length
 */
{
	return passivesock(service, "tcp", qlen);
}

TCPdaytimed.c

/* TCPdaytimed.c - main */
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
extern int	errno;
int		errexit(const char *format, ...);
void		TCPdaytimed(int fd);
int		passiveTCP(const char *service, int qlen);

#define QLEN	32

/*------------------------------------------------------------------------
 * main - Iterative TCP server for DAYTIME service
 *------------------------------------------------------------------------
 */
int main(int argc, char *argv[])
{
	struct	sockaddr_in fsin;	/* the from address of a client	*/
	char	*service = "daytime";	/* service name or port number	*/
	int	msock, ssock;		/* master & slave sockets	*/
	unsigned int	alen;		/* from-address length		*/

	switch (argc) {
	case	1:
		break;
	case	2:
		service = argv[1];
		break;
	default:
		errexit("usage: TCPdaytimed [port]\n");
	}

	msock = passiveTCP(service, QLEN);

	while (1) {
		alen = sizeof(fsin);
		ssock = accept(msock, (struct sockaddr *)&fsin, &alen);
		if (ssock < 0)
			errexit("accept failed: %s\n", strerror(errno));
		TCPdaytimed(ssock);
		(void) close(ssock);
	}
}

/*------------------------------------------------------------------------
 * TCPdaytimed - do TCP DAYTIME protocol
 *------------------------------------------------------------------------
 */
void TCPdaytimed(int fd)
{
	char	*pts;			/* pointer to time string	*/
	time_t	now;			/* current time			*/
	char	*ctime();

	(void) time(&now);
	pts = ctime(&now);
	(void) write(fd, pts, strlen(pts));
}

客户端链接服务器时，服务器获取时间然后将获取到的秒数通过 ctime() 函数转换成标准格式返回给客户端。

Client

connectsock.c

/* connectsock.c - connectsock */
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>

#ifndef	INADDR_NONE
#define	INADDR_NONE	0xffffffff
#endif	/* INADDR_NONE */

extern int	errno;

int	errexit(const char *format, ...);

/*------------------------------------------------------------------------
 * connectsock - allocate & connect a socket using TCP or UDP
 *------------------------------------------------------------------------
 */
int connectsock(const char *host, const char *service, const char *transport )
/*
 * Arguments:
 *      host      - name of host to which connection is desired
 *      service   - service associated with the desired port
 *      transport - name of transport protocol to use ("tcp" or "udp")
 */
{
	struct hostent	*phe;	/* pointer to host information entry	*/
	struct servent	*pse;	/* pointer to service information entry	*/
	struct protoent *ppe;	/* pointer to protocol information entry*/
	struct sockaddr_in sin;	/* an Internet endpoint address		*/
	int	s, type;	/* socket descriptor and socket type	*/

	memset(&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;

    /* Map service name to port number */
	if ( pse = getservbyname(service, transport) )
		sin.sin_port = pse->s_port;
	else if ((sin.sin_port=htons((unsigned short)atoi(service))) == 0)
		errexit("can't get \"%s\" service entry\n", service);

    /* Map host name to IP address, allowing for dotted decimal */
	if ( phe = gethostbyname(host) )
		memcpy(&sin.sin_addr, phe->h_addr, phe->h_length);
	else if ( (sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE )
		errexit("can't get \"%s\" host entry\n", host);

    /* Map transport protocol name to protocol number */
	if ( (ppe = getprotobyname(transport)) == 0)
		errexit("can't get \"%s\" protocol entry\n", transport);

    /* Use protocol to choose a socket type */
	if (strcmp(transport, "udp") == 0)
		type = SOCK_DGRAM;
	else
		type = SOCK_STREAM;

    /* Allocate a socket */
	s = socket(PF_INET, type, ppe->p_proto);
	if (s < 0)
		errexit("can't create socket: %s\n", strerror(errno));

    /* Connect the socket */
	if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
		errexit("can't connect to %s.%s: %s\n", host, service,
			strerror(errno));
	return s;
}

connectTCP.c

/* connectTCP.c - connectTCP */

int	connectsock(const char *host, const char *service,
		const char *transport);

/*------------------------------------------------------------------------
 * connectTCP - connect to a specified TCP service on a specified host
 *------------------------------------------------------------------------
 */
int connectTCP(const char *host, const char *service )
/*
 * Arguments:
 *      host    - name of host to which connection is desired
 *      service - service associated with the desired port
 */
{
	return connectsock( host, service, "tcp");
}

TCPdaytime.c

/* TCPdaytime.c - TCPdaytime, main */
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdio.h>
#include <time.h>

extern int      errno;

int     TCPdaytime(const char *host, const char *service);
int     errexit(const char *format, ...);
int     connectTCP(const char *host, const char *service);

#define LINELEN         128

/*------------------------------------------------------------------------
 * main - TCP client for DAYTIME service
 *------------------------------------------------------------------------
 */
int main(int argc, char *argv[])
{
        char    *host1 = "localhost";    /* host to use if none supplied */
        char    *host2 = "localhost";    /* host to use if none supplied */

        switch (argc) {
        case 1:
                host1 = "localhost";
                host2 = "localhost";
                break;
        case 2:
                host2 = argv[1];
                break;
        default:
                fprintf(stderr, "The number of parameter is to much! Just need the other host~\n");
                exit(1);
        }
        TCPdaytime(host1, host2);
        exit(0);
}

/*------------------------------------------------------------------------
 * TCPdaytime - invoke Daytime on specified host and print results
 *------------------------------------------------------------------------
 */
int TCPdaytime(const char *host1, const char *host2)
{
    char    buf[LINELEN+1];         /* buffer for one line of text  */
    int     s1, s2, n;              /* socket, read count           */
    struct  tm time1, time2;
    long    second1, second2;

    s1 = connectTCP(host1, "daytime");
    s2 = connectTCP(host2, "daytime");

    while( (n = read(s1, buf, LINELEN)) > 0) {
        buf[n] = '\0';          /* ensure null-terminated       */
        strptime(buf, "%a %b %d %H:%M:%S %Y", &time1);
        printf("time in localhost is\t");
        (void) fputs( buf, stdout );
    }

    while( (n = read(s2, buf, LINELEN)) > 0) {
        buf[n] = '\0';          /* ensure null-terminated       */
        strptime(buf, "%a %b %d %H:%M:%S %Y", &time2);
        printf("time in %s is\t", host2);
        (void) fputs( buf, stdout );
        /*stdout是一个文件指针,C己经在头文件中定义好的了，可以直接使用，把它
          赋给另一个文件指针。只是方便操作输出，比如传给一个函数等等。这时函数
          的输出就不是输出到文件，而是传进来的stdout文件指针，即标准输出。*/
    }

    second1 = mktime(&time1);
    second2 = mktime(&time2);

    printf("time difference is %d seconds.\n", abs(second1-second2));

    return 0;
}

默认连接的两个主机都是 localhost ，如果输入主机地址，则同时连接 localhost 和目标主机，获取到两台主机的时间。为了比较两台主机之间的时间差，一开始我想着服务器直接返回秒数，但是要转换成字符串才能返回就放弃了。通过 strptime()按照特定时间格式将字符串转换为时间类型，然后通过 mktime()将时间转换为自1970年1月1日以来持续时间的秒数，这样就可以进行运算了。

编译运行

编译运行 server：

将 server 上传到服务器：

连接服务器开启服务：

开启客户端，分别只连接 localhost 和同时连接两台服务器：