从ifaddrs结构分配IPv4地址给sockaddr_in结构

Question

我正在开发UDP服务器应用程序。
我希望将我的服务器套接字绑定到特定的接口(从配置文件中读取)。在本例中，eth0.
我使用getifaddrs读取当前网络接口的所有信息。
然后迭代链表作为返回的getifaddrs，并根据我想要的接口检查每个接口的名称。
一旦找到匹配，我计划从struct ifaddrs提取IPv4地址并将其分配给struct sockaddr_in对象。
目前我不确定如何通过struct ifaddrs->ifa_addr->sa_data到struct sockaddr_in.sin_addr.s_addr，或者这是我所遵循的正确/推荐的方法。

代码:

bool start_server(void)
{
struct sockaddr_in  server_address;
struct ifaddrs      *ifaddr;
int                 return_value;
try
{
this->sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (this->sock_fd < 0) 
{
//TODO : Log Error
return false;
}
// Initialize and configure struct sockaddr_in server_address
std::memset(&server_address, sizeof(sockaddr_in), 0); // Initialize struct sockaddr_in server_address to 0
server_address.sin_family = AF_INET;
server_address.sin_port = htons(6666); //We are using the port 6666
//Get IP address from the interface (eth0 currently) -> Interface name to be read from the configuration file
return_value = getifaddrs(&ifaddr);
if (return_value < 0) //On error, -1 is returned
{
//TODO : Log Error
return false;
}
for (struct ifaddrs *ifa; ifa != nullptr; ifa = ifaddr->ifa_next)//ifa stand for interface address
{
if (std::strcmp(ifa->ifa_name, "eth0") == 0) //We check the interface name in the linked Strings are exact match
{
if (ifa->ifa_addr == nullptr)
{
//TODO : Log Error - Selected interface doesn't have an assoiciated IP address
break; 
}
else
{
server_address.sin_addr.s_addr = inet_addr(ifa->ifa_addr->sa_data); //I am unsure will this work or if this is the right approach
break;
}
}
}
freeifaddrs(ifaddr); //Free up memeory allocated by getifaddrs. Prevents Memory Leaks
}

Answer 1

ifa_addr成员是指向struct sockaddr的指针。首先，您要通过检查sa_family是否设置为AF_INET来确保它是IPv4地址，如果是，您可以使用memcpy将其复制到struct sockadr_in。

for (struct ifaddrs *ifa = ifaddr; ifa != nullptr; ifa = ifaddr->ifa_next)
{
if (std::strcmp(ifa->ifa_name, "eth0") == 0)
{
if (ifa->ifa_addr == nullptr)
{
//TODO : Log Error - 
//Selected interface doesn't have an assoiciated IP address
break; 
}
else if (ifa->ifa_addr->sa_family == AF_INET)
{
memcpy(&server_address.sin_addr, ifa->ifa_addr, 
sizeof(server_address.sin_addr));
break;
}
}
}