converting data to struct hostent from getaddrinfo()

Question

I am replacing old code to linux. I was using:

server_host = getipnodebyname(host.c_str(), AF_INET, 0, &err_num);

and

server_host = getipnodebyaddr(addr, sizeof(INET_ADDRSTRLEN), AF_INET, &err_num);

that it has to be replaced by the new getaddrinfo().

At moment I added:

struct addrinfo *p_addr = (struct addrinfo *) NULL;
struct addrinfo hints={0};                                          //Initialize the addrinfo hints
char addr[INET_ADDRSTRLEN]={0};
int result = 0;

memset(&hints, 0, sizeof(hints));

hints.ai_family = AF_INET;                                          //Request for IPV4 ADDRESSES ONLY

result = getaddrinfo(host.c_str(), NULL, &hints, &p_addr);

but I need to populate the gathered information in the hostent structure:

hostent     *server_host;

for compatibility with other code. I could use the gethostbyname() to get directly the hostent structure but I want avoid it. What do you suggest?

Answer 1

There is no C library function to convert an addrinfo into a hostent. You will have to construct the hostent yourself using the data from the addrinfo, eg:

#include <vector>

addrinfo hints = {0};
hints.ai_family = AF_INET;
hints.ai_flags = AI_CANONNAME;

addrinfo *p_addrs = NULL;

int result = getaddrinfo(host.c_str(), NULL, &hints, &p_addrs);
if (result != 0) ... // error handling...

std::vector<in_addr*> in_addrs;

for(addrinfo *p_addr = p_addrs; p_addr != NULL; p_addr = p_addr->ai_next) {
    in_addrs.push_back(&reinterpret_cast<sockaddr_in*>(p_addr->ai_addr)->sin_addr);
}
in_addrs.push_back(NULL);

hostent hst;
h.h_name = p_addrs->ai_canonname;
h.h_aliases = NULL;
h.h_addrtype = AF_INET;
h.h_length = sizeof(in_addr);
h.h_addr_list = reinterpret_cast<char**>(&in_addrs[0]/* or: in_addrs.data() */);

// use hst as needed ...

freeaddrinfo(p_addrs);