Using getaddrinfo to resolve an IPv4 address literal

#include <sys/socket.h>

#include <netdb.h>

#include <arpa/inet.h>

#include <err.h>



void joyTcpGenericConnect()

{

struct addrinfo hints, *res, *res0;

int error, s;



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

hints.ai_family = PF_UNSPEC;

hints.ai_socktype = SOCK_STREAM;

// hints.ai_flags = AI_DEFAULT;

error = getaddrinfo("42.62.27.212", "6478", &hints, &res0);

if (error) {

printf("%s", gai_strerror(error));

}



s = -1;

for (res = res0; res; res = res->ai_next) {

s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

if (s < 0) {

continue;

}

printf("ai_flags:%d ai_family:%d ai_socktype:%d ai_protocol:%d ai_addrlen:%d ai_canonname:%s\n"

, res->ai_flags

, res->ai_family

, res->ai_socktype

, res->ai_protocol

, res->ai_addrlen

, res->ai_canonname == NULL ? "" : res->ai_canonname);



printf("sa_len:%d sa_family:%d sa_data:%d-%d-%d-%d-%d-%d-%d-%d-%d-%d-%d-%d-%d-%d"

, res->ai_addr->sa_len

, res->ai_addr->sa_family

, res->ai_addr->sa_data[0]

, res->ai_addr->sa_data[1]

, res->ai_addr->sa_data[2]

, res->ai_addr->sa_data[3]

, res->ai_addr->sa_data[4]

, res->ai_addr->sa_data[5]

, res->ai_addr->sa_data[6]

, res->ai_addr->sa_data[7]

, res->ai_addr->sa_data[8]

, res->ai_addr->sa_data[9]

, res->ai_addr->sa_data[10]

, res->ai_addr->sa_data[11]

, res->ai_addr->sa_data[12]

, res->ai_addr->sa_data[13]);


if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {

printf("connect failed!");

close(s);

s = -1;

continue;

}



printf("connect success!")

break; / okay we got one */

}

freeaddrinfo(res0);

}



when i test in ipv4 network : console output:


> ai_flags:0 ai_family:2 ai_socktype:1 ai_protocol:6 ai_addrlen:16 ai_canonname:

> sa_len:16 sa_family:2 sa_data:25-78-42-62-47--44-0-0-0-0-0-0-0-0

> connect success!


when i test in ipv6 nat64 network: Test for IPv6 DNS64/NAT64 Compatibility Regularly



1. // hints.ai_flags = AI_DEFAULT; console output:

> ai_flags:0 ai_family:30 ai_socktype:1 ai_protocol:6 ai_addrlen:28 ai_canonname:

> sa_len:28 sa_family:30 sa_data:0-0-0-0-0-0-0-100--1--101-0-0-0-0

> connect failed!

> ai_flags:0 ai_family:2 ai_socktype:1 ai_protocol:6 ai_addrlen:16 ai_canonname:

> sa_len:16 sa_family:2 sa_data:0-0-42-62-47--44-0-0-0-0-0-0-0-0

> connect failed!


2. set hints.ai_flags = AI_DEFAULT; console output:

> ai_flags:0 ai_family:30 ai_socktype:1 ai_protocol:6 ai_addrlen:28 ai_canonname:

> sa_len:28 sa_family:30 sa_data:0-0-0-0-0-0-0-100--1--101-0-0-0-0

> connect failed!


the different between ipv4 network and ipv6 network is


sa_data:25-78-42-62-47--44-0-0-0-0-0-0-0-0 in ipv4 network

sa_data:0-0-42-62-47--44-0-0-0-0-0-0-0-0 in ipv6 network !


What's wrong with my code？？

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micromatrix
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Replies

IP: "42.62.27.212", PORT: "6478"

The corrent address is 25-78-42-62-47--44-0-0-0-0-0-0-0-0

PORT: 6478 = 25 * 256 + 78

Posted by
micromatrix
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In general I’ve had good success with IPv6 address synthesis but the issue you’re seeing is definitely a bug (r. 26365575). 

getaddrinfo
does the right thing if you pass in a service name, as shown by the sample code (Listing 10-1) in the Networking Overview: 
error = getaddrinfo(ipv4_str, "http", &hints, &res0);

but fails if you pass in a numeric port:

error = getaddrinfo(ipv4_str, "80", &hints, &res0);

As you’ve discovered, the port comes back as 0, which is definitely wrong.

If you’re connecting to a well-known port the workaround is easy:

  1. on your Mac, open 

    /etc/services
    and find the service name that corresponds to that port

  2. pass that name in as a string to 

    getaddrinfo

If you’re connecting to a port that’s not well known, things get trickier. The obvious workaround is to post-process the results of 

getaddrinfo
to set the port if 
getaddrinfo
has not done so. Pasted in below is a drop-in replacement that does just that.

Please try this out and let us know how you get along.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
static int getaddrinfo_compat(
    const char * hostname,
    const char * servname,
    const struct addrinfo * hints,
    struct addrinfo ** res
) {
    int    err;
    int    numericPort;

    // If we're given a service name and it's a numeric string, set `numericPort` to that,
    // otherwise it ends up as 0.

    numericPort = servname != NULL ? atoi(servname) : 0;

    // Call `getaddrinfo` with our input parameters.

    err = getaddrinfo(hostname, servname, hints, res);

    // Post-process the results of `getaddrinfo` to work around <rdar://problem/26365575>.

    if ( (err == 0) && (numericPort != 0) ) {
        for (const struct addrinfo * addr = *res; addr != NULL; addr = addr->ai_next) {
            in_port_t *    portPtr;

            switch (addr->ai_family) {
                case AF_INET: {
                    portPtr = &((struct sockaddr_in *) addr->ai_addr)->sin_port;
                } break;
                case AF_INET6: {
                    portPtr = &((struct sockaddr_in6 *) addr->ai_addr)->sin6_port;
                } break;
                default: {
                    portPtr = NULL;
                } break;
            }
            if ( (portPtr != NULL) && (*portPtr == 0) ) {
                *portPtr = htons(numericPort);
            }
        }
    }
    return err;
}
Posted by
eskimo
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it works fine , 3Q !

Posted by
micromatrix
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