iOS Code Snippet Resolve host to ip address (IPv4)

Add to B4XMainPage or any other module, at the end:

#if OBJC
@end
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
@interface AddressForHost : NSObject
@end
@implementation AddressForHost


- (NSString *)ipv4AddressForHost:(NSString *)hostName {
    struct addrinfo hints, *res = NULL;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET; 
    hints.ai_socktype = SOCK_STREAM;

    int err = getaddrinfo([hostName UTF8String], NULL, &hints, &res);
    if (err != 0) {
        NSLog(@"getaddrinfo error: %s", gai_strerror(err));
        return nil;
    }

    char ip[INET_ADDRSTRLEN];
    struct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;
    inet_ntop(AF_INET, &(ipv4->sin_addr), ip, sizeof(ip));
    freeaddrinfo(res);

    return [NSString stringWithUTF8String:ip];
}
#End If

Usage example:

Private Sub Button1_Click
    Dim no As NativeObject
    no = no.Initialize("AddressForHost").RunMethod("new", Null)
    Dim ip As String = no.RunMethod("ipv4AddressForHost:", Array("google.com")).AsString
    Log(ip)
End Sub

 

[BanditMrP]

Thanks

I've added that code, and will be able to test on Tuesday (Monday is a bank holiday in the UK).

I've also added an xui.msgboxasync to show the info.

It's a bit of a pain only being able to do this when on-site, but that's the only place it doesn't work!

 

[BanditMrP]

Out of interest, I've added to the code as shown in the snippet below. The code compiles and can be called. If I was in an IPv6 environment, would this show the resolved address if it was resolved as an IPv6 address?

#if OBJC
@end
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
@interface AddressForHost : NSObject
@end
@implementation AddressForHost


- (NSString *)ipv4AddressForHost:(NSString *)hostName {
    struct addrinfo hints, *res = NULL;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;

    int err = getaddrinfo([hostName UTF8String], NULL, &hints, &res);
    if (err != 0) {
        NSLog(@"getaddrinfo error: %s", gai_strerror(err));
        return nil;
    }

    char ip[INET_ADDRSTRLEN];
    struct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;
    inet_ntop(AF_INET, &(ipv4->sin_addr), ip, sizeof(ip));
    freeaddrinfo(res);

    return [NSString stringWithUTF8String:ip];
}
@end

@interface Address6ForHost : NSObject
@end
@implementation Address6ForHost

- (NSString *)ipv6AddressForHost:(NSString *)hostName {
    struct addrinfo hints, *res = NULL;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;

    int err = getaddrinfo([hostName UTF8String], NULL, &hints, &res);
    if (err != 0) {
        NSLog(@"getaddrinfo error: %s", gai_strerror(err));
        return nil;
    }

    char ip[INET_ADDRSTRLEN];
    struct sockaddr_in *ipv6 = (struct sockaddr_in *)res->ai_addr;
    inet_ntop(AF_INET, &(ipv6->sin_addr), ip, sizeof(ip));
    freeaddrinfo(res);

    return [NSString stringWithUTF8String:ip];
}
#End If

I've added the following to call the second implementation

Dim no As NativeObject
no = no.Initialize("Address6ForHost").RunMethod("new", Null)
Dim ip6 As String = no.RunMethod("ipv6AddressForHost:", Array("redacted.co.uk")).AsString
Log("IPv6: " & ip6)

 

[Erel]

What is the difference between the two code snippets?

 

[BanditMrP]

The difference is in the second half where I’m hoping to retrieve the IPv6 address instead of the IPv4 address

these lines

struct sockaddr_in *ipv6 = (struct sockaddr_in *)res->ai_addr;
    inet_ntop(AF_INET, &(ipv6->sin_addr), ip, sizeof(ip));

pure guesswork on my part, but trying to cover all possible reasons why this isn’t resolving internally, or where it is resolving to (in-app).

If its not doing what I wanted, is there a way to see the resolved IPv6 (if any)?

 

[Erel]

You just changed the variable name. It has no effect on the behavior.

Try to change AF_INET with AF_INET6 (two places).

 

[BanditMrP]

Oops - thank you - I’ll give that a try (told you I was guessing)!

Much appreciated.

 

[BanditMrP]

OK, I've changed the variables, and I can now see if the IPv6 address is resolved.

Many thanks. Roll on Tuesday when I'm on site again (the only place this app doesn't work) so I can see what's going on!

 

[BanditMrP]

Hmmm... So the URL is resolving through DNS to the correct IP Address, and as expected, isn't resolving an IPv6 address.

So for a change, it's not DNS!

Time to look at why the server can be accessed from a B4X App on Android, and not from the same B4X App on Apple - It's not even triggering anything in the IIS logs.

 

[BanditMrP]

I feel like a right idiot, but maybe this comment will help others.

In a B4X or B4i app:

• we are able to resolve DNS addresses internally to a local DNS server
• using a WebView we are able to load a "local" i.e. on the same LAN web site no issues (i.e. https://server01/index.html)
• using iHttpUtils2 we are able to query a web service

UNLESS - When we first run the App, and it asks for "Allow <appname> to discover devices on the local network" we click "Do Not Allow".

At which point:

• we are able to resolve DNS addresses internally to a local DNS server
• using a WebView we are able to load a "local" i.e. on the same LAN web site no issues (i.e. https://server01/index.html)
• using iHttpUtils2 we are NOT ABLE to query a web service (at least in my case!)

The solution to my ongoing problems with a B4X App not working when locally on-site sitting literally next to the server is that I habitually click "Do Not Allow" when asked if I want to allow an App to be able to find devices on the local network.

If ever there was time for a Homer Simpson "DOH!" this is it.

Thank you @Erel for your help with IP Address resolution etc., but the overall result is "It was me!"

 

[Erel]

This is important information. It is good that you found it and share it.