我想构建一个客户端 - 服务器模型，对于连接到服务器的任意数量的客户端，服务器应该发送广播消息。下面是我实现的代码，它没有抛出任何错误，但我看不到服务器和客户端之间发生的任何通信。请告诉我，代码中的问题在哪里。
我希望在客户端系统上看到从服务器传递的消息。
/************* UDP SERVER CODE *******************/
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[]){
int udpSocket, nBytes, buflen;
char buffer[1024];
char string[1024];
int portNum;
struct sockaddr_in serverAddr, clientAddr;
struct sockaddr_storage serverStorage;
socklen_t addr_size, client_addr_size;
int i;
/*Create UDP socket*/
udpSocket = socket(AF_INET, SOCK_DGRAM, 0);
portNum=atoi(argv[1]);
/*Configure settings in address struct*/
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(5000);
serverAddr.sin_addr.s_addr = inet_addr("192.168.1.117");
memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);
/*Bind socket with address struct*/
int bStatus=bind(udpSocket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));
if (bStatus < 0) {
printf("error binding on server's port number\n");
exit(1);
}
/*Initialize size variable to be used later on*/
addr_size = sizeof serverStorage;
memset(&clientAddr, 0, sizeof(clientAddr));
clientAddr.sin_family = AF_INET;
clientAddr.sin_port = htons(portNum); // this is where client is bound
clientAddr.sin_addr.s_addr = inet_addr("192.168.1.114");
while(1){
sprintf(buffer,"Hello Client");
buflen=strlen(buffer);
int bytesSent = sendto(udpSocket,buffer,buflen,0,(struct sockaddr *)&clientAddr, sizeof(clientAddr));
if (bytesSent < 0) {
printf("Error sending/ communicating with client\n");
exit(1);
}
printf("%s\n",buffer);
/*
// ****************************************************
memset(buffer, 0, 1024);
buflen=65536;
recvfrom(udpSocket,buffer,buflen,0,(struct sockaddr *)&serverStorage, &addr_size);
printf("Received from server: %s\n",buffer);
*/
}
return 0;
}
以下是客户端代码：
/************* UDP CLIENT CODE *******************/
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
int main(int argc, char *argv[]){
int clientSocket, portNum, nBytes, buflen;
char buffer[1024];
char string[1024];
struct sockaddr_in serverAddr,clientAddr;
socklen_t addr_size;
/*Create UDP socket*/
clientSocket = socket(AF_INET, SOCK_DGRAM, 0);
portNum = atoi(argv[1]);
/*Configure settings in address struct*/
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(portNum);
serverAddr.sin_addr.s_addr = inet_addr("192.168.1.117");
// memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);
memset(&serverAddr,0,sizeof(serverAddr));
// binding
bind(clientSocket, (struct sockaddr *) &clientAddr, sizeof(clientAddr));
/*Initialize size variable to be used later on*/
addr_size = sizeof serverAddr;
while(1){
memset(buffer, 0, 1024);
buflen=65536;
recvfrom(clientSocket,buffer,buflen,0,(struct sockaddr *)&serverAddr, &addr_size);
//recvfrom(clientSocket,buffer,buflen,0,NULL,NULL);
printf("Received from server: %s\n",buffer);
/*
//********************************************************************
sprintf(buffer,"Hello Client");
buflen=strlen(buffer);
sendto(clientSocket,buffer,buflen,0,(struct sockaddr *)&serverAddr,addr_size);
printf("%s\n",buffer);
*/
}
return 0;
}
答案 0 :(得分：0)
在高层次上，有一些事情需要解决。鉴于帖子中的代码有一个服务器，它启动与客户端的通信，需要修改行（以及相关代码）
在服务器端：
sendto(udpSocket,buffer,buflen,0,(struct sockaddr *)&serverStorage,addr_size);
基本上这里发生的是udpSocket绑定到serverAddr，我们正在尝试发送到serverStorage（倒数第二个参数）。这里的问题是serverStorage没有绑定任何东西。基本上sendto有源权但不是目的地。
在客户端：
recvfrom(clientSocket,buffer,buflen,0,(struct sockaddr *)&serverAddr, &addr_size);
clientSocket没有绑定任何东西，因此系统会选择一个随机端口来监听它。在recvfrom调用中，第二个参数捕获另一方的地址详细信息。在代码中，您已将其绑定到服务器的IP和端口，但它没有任何效果，因为它由recvfrom调用填充并返回。
为了让事情在这里工作是我建议的（你可以添加细节，但根据你发布的内容计算出骨架）
server_initiating_with_client.c
//...
int udpSocket, nBytes, buflen;
char buffer[1024];
int portNum;
struct sockaddr_in serverAddr, clientAddr;
struct sockaddr_storage serverStorage;
socklen_t addr_size, client_addr_size;
/*Create UDP socket*/
udpSocket = socket(AF_INET, SOCK_DGRAM, 0);
portNum=atoi(argv[1]);
/*Configure settings in address struct*/
memset(&serverAddr, 0, sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(5000); // Making sure server has a unique port number
serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
/*Bind socket with address struct*/
int bStatus = bind(udpSocket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));
if (bStatus < 0) {
printf("error binding on server's port number\n");
exit(1);
}
/*Initialize size variable to be used later on*/
addr_size = sizeof serverStorage;
/* Because server is initiating the communication here one needs to set the
* clientAddr and needs to know the port number of the client
*/
memset(&clientAddr, 0, sizeof(clientAddr));
clientAddr.sin_family = AF_INET;
clientAddr.sin_port = htons(portNum);
clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);
while(1){
sprintf(buffer,"Hello Client");
buflen=strlen(buffer);
int bytesSent = sendto(udpSocket,buffer,buflen, 0,
(struct sockaddr *)&clientAddr,
sizeof(clientAddr));
if (bytesSent < 0) {
printf("Error sending/ communicating with client\n");
exit(1);
}
printf("Done sending %s\n", buffer);
sleep(1);
}
..
在客户端，沿着这些方向的东西
//..
int clientSocket, portNum, nBytes, buflen;
char buffer[1024];
struct sockaddr_in serverAddr;
struct sockaddr_in clientAddr;
socklen_t addr_size;
/*Create UDP socket*/
clientSocket = socket(PF_INET, SOCK_DGRAM, 0);
portNum = atoi(argv[1]);
/*Configure settings in address struct*/
memset(&clientAddr, 0, sizeof(clientAddr));
clientAddr.sin_family = AF_INET;
clientAddr.sin_port = htons(portNum);
clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);
memset(&serverAddr, 0, sizeof(serverAddr));
/*Bind on client side as well because you are specifically sending something over
* to the client. Usually the server will know where to talk back to the client
* but in your example because of the reversed semantics this will be needed
*/
bind(clientSocket, (struct sockaddr *) &clientAddr, sizeof(clientAddr));
/*Initialize size variable to be used later on*/
addr_size = sizeof serverAddr;
while(1){
memset(buffer, 0, 1024);
buflen=65536;
recvfrom(clientSocket,buffer,buflen,0,(struct sockaddr *)&serverAddr, &addr_size);
printf("Received from server: %s\n",buffer);
sleep(1);
}
return 0;
如果您将通信从客户端转发到服务器，则可以简化代码，从而消除客户端上固定端口号的需要。
答案 1 :(得分：-1)
只需对其进行一些更改。将套接字长度预定义的（socklen_t *）结构分配给类型转换长度
n = recvfrom(sockfd, (char *)buffer, MAXLINE,MSG_WAITALL, (struct sockaddr *) &servaddr, (socklen_t*)&len);
socklen_t *将长度转换为套接字长度。 在客户端和服务器端都进行这些更改