Occasional error Using InetAddress.getByName()

Question

In my application, I use InetAddress.getByName() quite a bit to convert strings like "192.168.1.56" to InetAddress objects -- mainly because it seems to me to be a good idea to store IP addresses as IP addresses rather than as strings. Up til now, I would have sworn it was pretty foolproof too, but today I discovered a bug. This does not work:

InetAddress ia = InetAddress.getByName ("192.168.1.056");

It would appear that my Android thinks THAT string is a host name, and so it's trying to look it up (which isn't possible, because it's not on a "real" network). Is this something I can work around -- meaning is there a way to insist to getByName that this is an IP address, not a hostname? Or do I need to build method to purge leading zeroes out of IP address strings?? Or is there an Apache utility buried somewhere that might do a better job of this??

What's the error you get? Additionally, some implementations will handle leading zeros as an octal value, which won't be what you want. Not sure about this one. — FatalError, Nov 07 '14 at 15:45
Check this question and answers: http://stackoverflow.com/questions/9556978/how-come-inetaddress-getbyname1-2-is-valid-ip-address — Anas Alkhatib, Nov 07 '14 at 15:49
The error I'm getting is NetworkOnMainThread -- which leads me to believe the software is treating the string as a hostname and going out the network to try to resolve it -- which is both impossible and not the right thing to do. Sorry about the incomplete post. — Rich, Nov 07 '14 at 15:52
Anas: I did, but that doesn't seem to be germane to this issue. My address string has 4 numbers in it, and is separately verified to actually BE and IP address (using a java.util.regex.Pattern). — Rich, Nov 07 '14 at 15:55

score 0 · Answer 1 · answered Nov 08 '14 at 04:52

0

Why not try getByAddress (byte[] ipAddress)? This method seems more suitable for your needs.

answered Nov 08 '14 at 04:52

Roberto Betancourt

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I'm using my code to parse an IP address string provided by the user in a Dialog EditText. Apparently, one of my users found a new and interesting way to screw things up. I'm trying to trap the error without resorting to toasting an Invalid Address Error and doing nothing. – Rich Nov 10 '14 at 15:27

score 0 · Accepted Answer · answered Nov 10 '14 at 15:36

It may be that a Regex-wizard could have found a way to fix the IP address string directly, but I don't know how to do that. However, there is something called the Apache SubnetUtils library which is native to Android. SubnetUtils doesn't have a cow over an IP address string with a leading zero in it. My code looks like this:

public static InetAddress addrFromStr (String addr)
{
    InetAddress ia = null;
    SubnetUtils su = new SubnetUtils (addr + "/8");

    try
    {
        ia = InetAddress.getByName (su.getInfo().getAddress());
    }
    catch (UnknownHostException e)
    { }

    return ia;
}

Basically, I create a SubnetUtils object and then ask it for the IP address -- which is now stripped of any numerical strangeness that InetAddress.getByName() apparently can't handle. (The "/8" business is the CIDR notation subnet mask, and the only thing I can say about it is don't use "/0").

Occasional error Using InetAddress.getByName()

2 Answers2