C语言 UDP - sendto() 中的错误:协议不支持的地址系列

Question

以下代码是使用 UDP 套接字的编程示例。

有 3 个.c源文件(Client_UDP.c、Server_UDP.c和Message_UDP.c(和 1 个.h头文件 (Prototype.h(。

我希望服务器和客户端仅通过Message_UDP中的函数相互通信。

事件的过程似乎是这样的：

1. 客户端向服务器发送第一个数据包/消息。
2. 服务器从客户端接收数据包。
3. 服务器尝试发送响应包，但显示错误："Error in sendto(): Address family not supported by protocol"。

有谁知道为什么？ 我该如何解决这个问题？

Client_UDP.c

#include <stdio.h>      
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "Prototype.h"
int main(int argc, char * argv[]) {
int fd_socket;
struct sockaddr_in server;      
socklen_t length_server = sizeof (server);
fd_socket = socket(AF_INET, SOCK_DGRAM, 0);
Error_A(fd_socket, "Error in socket()");
server.sin_port = htons(8888);
server.sin_family = AF_INET;
server.sin_addr.s_addr = inet_addr("127.0.0.1");
// send packet to server
function_SEND(fd_socket, server, length_server, "CLIENT");
// receive packet from server
function_RECEIVE(fd_socket, server, length_server, "CLIENT");
close(fd_socket);
return EXIT_SUCCESS;
}

Server_UDP.c

#include <stdio.h>      
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "Prototype.h"
int main(int argc, char * argv[]) {
int fd_socket;
int rv; // return value
struct sockaddr_in server;
struct sockaddr_in client;
socklen_t length_server = sizeof (server);
socklen_t length_client = sizeof (client);
fd_socket = socket(AF_INET, SOCK_DGRAM, 0);
Error_A(fd_socket, "Errore in socket()");
server.sin_port = htons(8888);
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
rv = bind(fd_socket, (struct sockaddr *) &server, length_server);
Error_A(rv, "Error in bind()");
// receive packet from client
function_RECEIVE(fd_socket, client, length_client, "SERVER");
// send packet to client
function_SEND(fd_socket, client, length_client, "SERVER");
close(fd_socket);
return EXIT_SUCCESS;
}

Message_UDP.c

#include <stdio.h>      
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "Prototype.h"
void Error_A(int return_value, char *error_message) {
if (return_value < 0) {
perror(error_message);
exit(EXIT_FAILURE);
}
}
void function_SEND(int fd_socket, struct sockaddr_in host, int length_host, char *sender) {
int rv; // return value
char packet[100] = "PACKET";
// send packet
rv = sendto(fd_socket, packet, 100, 0, (struct sockaddr *) &host, length_host);
Error_A(rv, "Error in sendto()");
printf("<%s> -- package sent: <%s> n", sender, packet);
}
void function_RECEIVE(int fd_socket, struct sockaddr_in host, int length_host, char* receiver) {
int rv; // return value
char packet[100] = "";
// receive packet
rv = recvfrom(fd_socket, packet, 100, 0, (struct sockaddr *) &host, &length_host);
Error_A(rv, "Errore in recvfrom()");
printf("<%s> -- packet received: <%s> n", receiver, packet);
}

原型.h

void Error_A(int return_value, char *error_message);
void function_SEND(int fd_socket, struct sockaddr_in host, int length_host, char *sender);
void function_RECEIVE(int fd_socket, struct sockaddr_in host, int length_host, char* receiver);

这是客户端输出：

客户端 -- 发送的包：数据包

这是服务器输出：

服务器 -- 收到的包：数据包

sendto(( 中的错误：协议不支持地址族

Answer 1

我可能错过了一些明显的东西。这是我注意到的。在 Server_UDP.c 中，客户端没有初始化。 我在客户端sockaddr_in看到声明结构;，但没有赋值。在这里，我假设客户端将被分配相同的端口号和环回 IP 地址，如下所示

client.sin_port = 8888;
client.sin_family = AF_INET;
client.sin_addr.s_addr = inet_addr("127.0.0.1");

这可能是服务器发送失败的原因

Answer 2

我在Prototype.h中添加了这个结构：

struct Host {
struct sockaddr_in host;
socklen_t length_host;
} host_return;
void Error_A(int return_value, char *error_message);
void function_SEND(int fd_socket, struct sockaddr_in host, int length_host, char *sender);
struct Host function_RECEIVE(int fd_socket, struct sockaddr_in host, int length_host, char* receiver);

用这个更改Message_UDP.c中的function_RECEIVE((：

struct Host function_RECEIVE(int fd_socket, struct sockaddr_in host, int length_host, char* receiver) {
int rv; // return value
char packet[100] = "";
// receive packet
rv = recvfrom(fd_socket, packet, 100, 0, (struct sockaddr *) &host, &length_host);
Error_A(rv, "Errore in recvfrom()");
printf("%s -- packet received: %s n", receiver, packet);
host_return.host = host;
host_return.length_host = length_host;
return host_return;
}

Server_UDP.c中的代码是这样写的：

// receive packet from client
host_return = function_RECEIVE(fd_socket, client, length_client, "SERVER");

// send packet to client
function_SEND(fd_socket, host_return.host, host_return.length_host,"SERVER");

而不是

// receive packet from client
function_RECEIVE(fd_socket, client, length_client, "SERVER");
// send packet to client
function_SEND(fd_socket, client, length_client, "SERVER");

它似乎有效，因为输出是(但我希望我没有运气(：

客户端 -- 发送的数据包：数据包

客户端 -- 收到的数据包：数据包

服务器：

服务器 -- 接收的数据包：数据包

服务器 -- 发送的数据包：数据包