我正在尝试修改这两个程序。我想让 udpclient.c 能够接收消息并让 udpserver.c 将消息回显给客户端。我还希望在发送 udpclient 时间标签消息之前获得它们。接收到的消息应导致在客户端打印服务器的 IP 地址和往返时间 (RTT)。当我测试它时，客户端发送并且服务器接收但服务器不回显消息。我试图修改的地方是在“//添加”之后的每个程序的无限循环中
udpclient.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef WIN
#include <winsock.h>
#include <windows.h>
#endif
#ifndef WIN
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#endif
/* Here are some details of the sockaddr_in structure and the sockaddr structure
These declarations are copied from winsock.h
struct in_addr { this struct holds a 32 bit IP address
union {
struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
struct { u_short s_w1,s_w2; } S_un_w;
u_long S_addr;
} S_un;
#define s_addr S_un.S_addr
struct sockaddr_in { notice this structure is 16 bytes long
short sin_family;
u_short sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};
struct sockaddr { this generic address structure is 16 bytes long, too!
u_short sa_family;
char sa_data[14];
};
*/
/* we have to send on the same port the server is listening on */
#define PORT 20009
/* simple upd client */
int main()
{
#ifdef WIN
SOCKET sock;
#else
int sock;
#endif
int size;
int nbytes, flags;
int i;
char * cp;
#ifdef WIN
WSADATA wsaData;
int nCode;
#endif
char buffer[100];
char str_addr[20]; /* holds the chars of an IP address */
struct sockaddr_in target_pc, me;
/* magic call to initialize the network I/O code - only Microsoft requires this */
#ifdef WIN
if((nCode = WSAStartup(MAKEWORD(1,1), &wsaData)) != 0){
printf("Opps! WSA error %d\n",nCode);
return -1;
}
#endif
/* create a socket to send on */
sock = socket(PF_INET,SOCK_DGRAM,0);
if(sock < 0) {
printf("socket error = %d\n", sock);
return -1;
}
/* we fill in the address family and port, but we do not know the destination IP address yet */
target_pc.sin_family = PF_INET;
target_pc.sin_port = htons(PORT);
/* fill in my address and port */
me.sin_family = PF_INET;
me.sin_port = htons(0);
me.sin_addr.s_addr = htonl(INADDR_ANY);
i = bind(sock, (struct sockaddr *) &me, sizeof(me));
if( i < 0) {
printf("bind result: %d\n", i);
return -1;
}
nbytes = 99;
while(1){
printf("Enter the target IP address: ");
cp = fgets(str_addr,19,stdin);
/* remove the \n */
str_addr[strlen(str_addr)-1] = '\0';
/* the inet_addr function converts a string form of IP address to a 32 binary integer */
target_pc.sin_addr.s_addr = inet_addr(&str_addr[0]);
printf("Enter your message: ");
cp = fgets(buffer,99,stdin);
/* get the string length so we send exactly this many characters */
nbytes = strlen(buffer);
flags = 0;
size = sendto(sock, (char *) buffer, nbytes,flags,(struct sockaddr *)&target_pc,sizeof(target_pc));
printf("msg size = %d size = %d\n", nbytes, size);
//added
int addrlen = sizeof(target_pc);
size = recvfrom(sock, buffer, nbytes, flags, (struct sockaddr *)&target_pc,&addrlen);
if((size > 0) && (size < 99)){
buffer[size] = '\0'; //add the null byte so buffer now holds a string
i = puts((char *) buffer); // write this string to the display
}
}
#ifdef WIN
system("PAUSE");
#endif
return 0;
}
udpserver.c
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#ifdef WIN
#include <winsock.h>
#include <windows.h>
#endif
#ifndef WIN
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#endif
#define PORT 20009
/* simple upd server
this program receives short messages (<99 characters) from any IP address
and writes them to the display
be sure to use the linker line option "-l wsock32"
*/
int main()
{
/* first define a socket
a socket is an I/O port like a file descriptor
*/
#ifdef WIN
SOCKET sock; /* SOCKET is a typedef for a structure */
#else
int sock;
#endif
int size;
int nbytes, flags;
#ifdef WIN
int addrlen;
#else
socklen_t addrlen;
#endif
int i;
/* char loopback[20]="127.0.0.1"; */
#ifdef WIN
WSADATA wsaData; /* This is struct holds Windows required data */
int nCode;
#endif
char buffer[100];
struct sockaddr_in server; /* this holds my IP address and port info */
struct sockaddr_in from; /* this holds the same info for the sender of the packet
I received */
/* the call to WSAStartup is Windows magic */
#ifdef WIN
if((nCode = WSAStartup(MAKEWORD(1,1), &wsaData)) != 0){
printf("Opps! WSA error %d\n",nCode);
exit;
}
#endif
/* create a socket called sock. It is a datagram socket */
sock = socket(AF_INET,SOCK_DGRAM,0);
if(sock < 0){
printf("socket error = %d\n", sock);
return -1;
}
server.sin_family = AF_INET; /* initialize the server address family */
server.sin_addr.s_addr = htonl(INADDR_ANY); /* notice this struct within a struct */
/* printf("%x\n",server.sin_addr.s_addr); */
server.sin_port = htons(PORT);
/* associate the socket with the address structure - this is called binding */
i = bind(sock, (struct sockaddr *) &server, sizeof(server));
if( i < 0) {
printf("bind result: %d\n", i);
return -1;
} else
printf("Simple UDP server is ready!\n\n");
nbytes = 99; /* receive packets up to 99 bytes long */
flags = 0; /* must be zero or this will not work! */
while(1){
/* the recvfrom function is a read and the arguments are:
sock - the socket we are reading
buffer - array into which to read the data
nbytes - read up to this many bytes
flags - used for special purposes - not needed here
from - sockaddr struct to hold the IP address and port of the sender of the packet
addrlen - the size of the sockaddr struct written by this function
*/
addrlen = sizeof(from);
size = recvfrom(sock, buffer, nbytes, flags, (struct sockaddr *)&from,addrlen);
if((size > 0) && (size < 99)){
buffer[size] = '\0'; /* add the null byte so buffer now holds a string */
i = puts((char *) buffer); /* write this string to the display */
}
//added
sock = socket(PF_INET,SOCK_DGRAM,0);//
if(sock < 0) {//
printf("socket error = %d\n", sock);//
return -1;//
}//
sendto(sock, buffer, nbytes, flags, (struct sockaddr *)&from,addrlen); //
}
#ifdef WIN
system("PAUSE");
#endif
return 0;
}