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Commit ffeba906 authored by Neil Fuller's avatar Neil Fuller
Browse files

Clarify bogus NITZ correction logic / correction 

This change clarifies some logic used to correct for bogus
NITZ signals.

From looking at a frameworks/base commit
(df7bbfd7c28549742443bbf91200871c09e89299) from 2012
it is possible to better understand the original intent
of some NITZ correction logic due to a (since deleted)
comment.

The comments from the commit mentioned above has
been expanded on to reflect the latest code and reintroduced.

The original comment was:

// "(mZoneOffset == 0) && (mZoneDst == false) &&
//  (Arrays.binarySearch(GMT_COUNTRY_CODES, iso) < 0)"
// means that we received a NITZ string telling
// it is in GMT+0 w/ DST time zone
// BUT iso tells is NOT, e.g, a wrong NITZ reporting
// local time w/ 0 offset.

Since the recent commit d8ce8374, it has been possible
to tell the difference between "no NITZ data received" and
"offset from UTC is zero". The null case (i.e. when NITZ has
not been received) has been retained with the existing behavior
to avoid modifying the behavior at this time but it looks
(historically, but previously undetectably) incorrect and has
been commented.

There have been some small code-style improvements (addition
of braces and improved logging) made as part of changes to
the affected method.

Bug: 63743683
Bug: 69593701
Test: Boot device
Change-Id: I859c809ba004ff9f1996792e2f813ea081acb9f3
parent a3e776f0

src/java/com/android/internal/telephony/ServiceStateTracker.java

+54 −24
Original line number Diff line number Diff line
@@ -3180,9 +3180,9 @@ public class ServiceStateTracker extends Handler { 
    }



    private void fixTimeZone(String isoCountryCode) {

        TimeZone zone = null;

        // If the offset is (0, false) and the time zone property

        // is set, use the time zone property rather than GMT.

        // Capture the time zone property. This allows us to tell whether the device has a time zone

        // set. TimeZone.getDefault() returns a default zone (GMT) even when time zone is not

        // explicitly set making the system property a better indicator.

        final String zoneName = SystemProperties.get(TIMEZONE_PROPERTY);

        if (DBG) {

            log("fixTimeZone zoneName='" + zoneName
@@ -3190,6 +3190,7 @@ public class ServiceStateTracker extends Handler { 
                    + " iso-cc='" + isoCountryCode

                    + "' iso-cc-idx=" + Arrays.binarySearch(GMT_COUNTRY_CODES, isoCountryCode));

        }

        TimeZone zone;

        if ("".equals(isoCountryCode) && mNeedFixZoneAfterNitz) {

            // Country code not found.  This is likely a test network.

            // Get a TimeZone based only on the NITZ parameters (best guess).
@@ -3197,45 +3198,66 @@ public class ServiceStateTracker extends Handler { 
            // mNeedFixZoneAfterNitz is only set to true when mNitzData is set so there's no need to

            // check mNitzData == null.

            zone = NitzData.guessTimeZone(mNitzData);

            if (DBG) log("pollStateDone: using NITZ TimeZone");

        } else if ((mNitzData == null

                        || (mNitzData.getLocalOffsetMillis() == 0 && !mNitzData.isDst()))

                && (zoneName != null) && (zoneName.length() > 0)

            if (DBG) {

                log("pollStateDone: using NITZ information only:" + mNitzData);

            }

        } else if ((mNitzData == null || nitzOffsetMightBeBogus(mNitzData))

                && (zoneName != null && zoneName.length() > 0)

                && (Arrays.binarySearch(GMT_COUNTRY_CODES, isoCountryCode) < 0)) {

            // For NITZ string without time zone,

            // need adjust time to reflect default time zone setting



            // This case means that (1) the device received no NITZ signal yet or received an NITZ

            // signal that looks bogus due to having a zero offset from UTC, (2) the device has a

            // time zone set explicitly, and (3) the iso tells us the country is NOT one that uses a

            // zero offset. This is interpreted as being NITZ incorrectly reporting a local time and

            // not a UTC time. The zone is left as the current device's zone setting, and the time

            // may be adjusted by assuming the current zone setting is correct.

            zone = TimeZone.getDefault();



            // Note that mNeedFixZoneAfterNitz => (implies) { mNitzData != null }. Therefore, if

            // mNitzData == null, mNeedFixZoneAfterNitz cannot be true. The code in this section

            // therefore means that when mNitzData == null (and the country is one that doesn't use

            // a zero UTC offset) the device will retain the existing time zone setting and not try

            // to derive one from the isoCountryCode.

            if (mNeedFixZoneAfterNitz) {

                long ctm = System.currentTimeMillis();

                long tzOffset = zone.getOffset(ctm);

                if (DBG) {

                    log("fixTimeZone: tzOffset=" + tzOffset +

                            " ltod=" + TimeUtils.logTimeOfDay(ctm));

                    log("fixTimeZone: tzOffset=" + tzOffset

                            + " ltod=" + TimeUtils.logTimeOfDay(ctm));

                }

                if (getAutoTime()) {

                    long adj = ctm - tzOffset;

                    if (DBG) log("fixTimeZone: adj ltod=" + TimeUtils.logTimeOfDay(adj));

                    if (DBG) {

                        log("fixTimeZone: adj ltod=" + TimeUtils.logTimeOfDay(adj));

                    }

                    setAndBroadcastNetworkSetTime(adj);

                } else {

                    // Adjust the saved NITZ time to account for tzOffset.

                    mSavedTime = mSavedTime - tzOffset;

                    if (DBG) log("fixTimeZone: adj mSavedTime=" + mSavedTime);

                    if (DBG) {

                        log("fixTimeZone: adj mSavedTime=" + mSavedTime);

                    }

                }

            if (DBG) log("fixTimeZone: using default TimeZone");

        } else {

            if (mNitzData == null) {

                // This behavior is unusual but consistent with historical behavior when it wasn't

                // possible to detect whether a previous NITZ signal had been saved.

            }

            if (DBG) {

                log("fixTimeZone: using default TimeZone");

            }

        } else if (mNitzData == null) {

            // The use of 1/1/1970 UTC is unusual but consistent with historical behavior when

            // it wasn't possible to detect whether a previous NITZ signal had been saved.

            zone = TimeUtils.getTimeZone(0 /* offset */, false /* dst */, 0 /* when */,

                    isoCountryCode);

            if (DBG) {

                log("fixTimeZone: No cached NITZ data available, using only country code."

                        + " zone=" + zone);

            }

        } else {

            zone = TimeUtils.getTimeZone(mNitzData.getLocalOffsetMillis(), mNitzData.isDst(),

                    mNitzData.getCurrentTimeInMillis(), isoCountryCode);

            if (DBG) {

                log("fixTimeZone: using getTimeZone(off, dst, time, iso)");

            }

            if (DBG) log("fixTimeZone: using getTimeZone(off, dst, time, iso)");

        }



        final String tmpLog = "fixTimeZone zoneName=" + zoneName + " mNitzData=" + mNitzData

                + " iso-cc=" + isoCountryCode + " mNeedFixZoneAfterNitz="

                + mNeedFixZoneAfterNitz + " zone=" + (zone != null ? zone.getID() : "NULL");
@@ -3257,6 +3279,14 @@ public class ServiceStateTracker extends Handler { 
        mNeedFixZoneAfterNitz = false;

    }



    /**

     * Returns {@code true} if the NITZ data looks like it might be incomplete or bogus, i.e. it has

     * a zero offset from UTC with either no DST information available or a zero DST offset.

     */

    private static boolean nitzOffsetMightBeBogus(NitzData nitzData) {

        return nitzData.getLocalOffsetMillis() == 0 && !nitzData.isDst();

    }



    /**

     * Check if GPRS got registered while voice is registered.

     *