8 November 2009

I know I wrote about Android already today, but there is another thing that concerns me right now. I am owner of an Android-based phone (an HTC Dream) and recently switched my mobile network provider. The problem is that my new provider is a virtual provider and as such there is no real network of that provider. Now Android has a feature to turn off broadband connections when in roaming mode, which itself is a great idea and can save you from paying quite a lot of money when the phone connects to 3G abroad, but this feature also turns off broadband connections when roaming locally. All this is being discussed in bug report #3499. After noticing this problem I became curious on how Android detects that it is roaming and I found the GsmServiceStateTracker.isRoamingBetweenOperators method to be responsible for that magic, but soon noticed that the method is not only inefficient, but also doesn t work as intended. This is hardly related to the bug mentioned above, but let s have a look at the code in question:

/**
* Set roaming state when gsmRoaming is true and, if operator mcc is the
* same as sim mcc, ons is different from spn
* @param gsmRoaming TS 27.007 7.2 CREG registered roaming
* @param s ServiceState hold current ons
* @return true for roaming state set
*/
    private
    boolean isRoamingBetweenOperators(boolean gsmRoaming, ServiceState s)  
        String spn = SystemProperties.get(PROPERTY_ICC_OPERATOR_ALPHA, "empty");
        String onsl = s.getOperatorAlphaLong();
        String onss = s.getOperatorAlphaShort();
        boolean equalsOnsl = onsl != null && spn.equals(onsl);
        boolean equalsOnss = onss != null && spn.equals(onss);
        String simNumeric = SystemProperties.get(PROPERTY_ICC_OPERATOR_NUMERIC, "");
        String operatorNumeric = s.getOperatorNumeric();
        boolean equalsMcc = true;
        try  
            equalsMcc = simNumeric.substring(0, 3).
                    equals(operatorNumeric.substring(0, 3));
          catch (Exception e) 
         
        return gsmRoaming && !(equalsMcc && (equalsOnsl   equalsOnss));
     

Okay, let me summarize what this piece of code does wrong, at least from my understanding:

• It takes both the network operator alphanumeric identifier and alphanumeric long identifier and compares both to the alphanumeric identifier coming from the SIM card, whilst
• it could simply use the network and SIM card numeric identifiers and compare those, which should be a lot cheaper than comparing those strings
• Then it takes the first three characters/digits of the numeric identifiers (which indicate the country) and compares those

Now in my case my SIM card doesn t seem to provide the phone with a alphanumeric identifier, so the first two comparisons always fail for obvious reasons and, looking at the inline-if in the last line of that method my phone will always indicate that I am in roaming mode, even when I am not. The problem is not only the logic which seems to be wrong, but I rather see the inefficient comparisons used there to be a major problem in embedded systems like mobile phones. This is the first piece of Android code I have had a look at, but if all other code is as ugly and inefficient as these few lines Android really needs some major fixes. Related to this I have reported bug #4590 and forked the git repository in question over at github, to fix this method, should be a matter of 5 minutes.