Linux 网络编程: echo Service

前言

大病初愈，感谢某人的陪伴，感谢王乐庆同学和赵攀同学的细心照顾。原以为过了第八周就不忙了，却没想到还有明天的党章考试。还是写代码比背党章有意思~趁着服务器还没过期，赶紧把 echo 完成了。关于错误提示和连接 socket 的代码就不贴出来了。

服务器配置

vi /etc/xinetd.d/echo

把

disable = yes

改成

disable = no

，类似 time 服务，如果没有写的权限，就要 chmod，然后重启 xinetd 服务。

service xinetd restart

Client

UDPecho.c

/* UDPecho.c - main */
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>

#define LINELEN     128

extern int  errno;

int UDPecho(const char *host, const char *service);
int connectUDP(const char *host, const char *service);
int errexit(const char *format, ...);

/*---------------------------------------------------------------------------
* main - UDP client for ECHO service
*---------------------------------------------------------------------------
*/
int main(int argc, char *argv[])
{
char    *host = "localhost";    /* host to use if none supplied */
char    *service = "echo";  /* default service name     */
int s, n;           /* socket descriptor, read count*/
char buf[LINELEN+1];
int outchars, inchars;

switch (argc) {
case 1:
host = "localhost";
break;
case 3:
service = argv[2];
/* FALL THROUGH */
case 2:
host = argv[1];
break;
default:
fprintf(stderr, "usage: UDPecho [host [port]]\n");
exit(1);
}
UDPecho(host, service);
exit(0);
}
/*---------------------------------------------------------------------------
* UDPecho - send input to ECHO service on specified host and print and reply
*---------------------------------------------------------------------------
*/
int UDPecho(const char *host, const char *service)
{
char buf[LINELEN+1];    /* buffer for one line of text */
int s, nchars;    /* socket descriptor, read count */

s = connectUDP(host, service);

while (fgets(buf, sizeof(buf), stdin)) {
//从命令行读入用户输入的字符
buf[LINELEN] = '\0';    /* insure null-terminated */
nchars = strlen(buf);
(void) write(s, buf, nchars);
//向网络中发送用户所输入的字符
memset(buf, 0, LINELEN);
if (read(s, buf, nchars) < 0) {
//从网络中读取服务器所返回的的字符
errexit("socket read failed: %s\n", strerror(errno));
}

fputs(buf, stdout);
}
}

编译运行

然后不使用 xinetd 的自带服务，自己写服务器端的程序：

Server

UDPechod.c

/* UDPechod.c - main */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <string.h>
#include <errno.h>

extern int  errno;
#define LINELEN     128

int UDPechod(const char *service);
int passiveUDP(const char *service);
int errexit(const char *format, ...);

/*------------------------------------------------------------------------
* main - Iterative UDP server for ECHO service
*------------------------------------------------------------------------
*/
int main(int argc, char *argv[])
{
char    *service = "echo";  /* service name or port number  */

switch (argc) {
case    1:
break;
case    2:
service = argv[1];
break;
default:
errexit("usage: UDPechod [port]\n");
}
UDPechod(service);
exit(0);
}

int UDPechod(const char *service)
{
struct sockaddr_in fsin;    /* the from address of a client */
unsigned int    alen;       /* from-address length      */
char    buf[LINELEN+1];         /* "input" buffer */
int sock;           /* server socket        */

sock = passiveUDP(service);

while (1) {
alen = sizeof(fsin);

if (recvfrom(sock, buf, sizeof(buf), 0, (struct sockaddr *)&fsin, &alen) < 0) {
//从已连接的 socket 中获取传递过来的信息
errexit("recvfrom: %s\n", strerror(errno));
}

(void) sendto(sock, &buf, sizeof(buf), 0, (struct sockaddr *)&fsin, sizeof(fsin));
//将信息返回
}
}

编译运行