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
", service);
/* Map protocol name to protocol number */
if ( (ppe = getprotobyname(transport)) == 0)
errexit("can't get "%s" protocol entry
", 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
", strerror(errno));
/* Bind the socket */
if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
errexit("can't bind to %s port: %s
", service,
strerror(errno));
if (type == SOCK_STREAM && listen(s, qlen) < 0)
errexit("can't listen on %s port: %s
", 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]
");
}
msock = passiveTCP(service, QLEN);
while (1) {
alen = sizeof(fsin);
ssock = accept(msock, (struct sockaddr *)&fsin, &alen);
if (ssock < 0)
errexit("accept failed: %s
", 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
", 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
", host);
/* Map transport protocol name to protocol number */
if ( (ppe = getprotobyname(transport)) == 0)
errexit("can't get "%s" protocol entry
", 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
", strerror(errno));
/* Connect the socket */
if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
errexit("can't connect to %s.%s: %s
", 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~
");
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] = ' '; /* ensure null-terminated */
strptime(buf, "%a %b %d %H:%M:%S %Y", &time1);
printf("time in localhost is ");
(void) fputs( buf, stdout );
}
while( (n = read(s2, buf, LINELEN)) > 0) {
buf[n] = ' '; /* ensure null-terminated */
strptime(buf, "%a %b %d %H:%M:%S %Y", &time2);
printf("time in %s is ", 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.
", 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：
