Fix: DateTimeParser trailing timezone designators & Timezone UTC offset cache invalidation

[kozemcak]

Hi all,

After we update poco to new version our applications tests start failing. We identified these issues and fix it. Some of the issues are little specific, so we are interesting what you say about that. Here are quick summary of our changes.

Thanks.

Summary

This MR contains two bug fixes for the Foundation library addressing datetime parsing and timezone handling regressions.

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Changes

1. fix(Foundation): DateTimeParser: allow trailing timezone designators

A strict trailing-garbage check introduced in commit 8410eb1a6 broke parsing of valid date strings with trailing timezone indicators not captured by the format string.

Affected scenarios:

• ASN.1 UTCTime strings (e.g. "230101120000Z") used by Poco::Crypto::X509Certificate::validFrom() and expiresOn() — caused certificate loading to fail
• ISO 8601 strings with fractional seconds and numeric UTC offsets (e.g. "2013-10-07 08:23:19.120-04:00") — triggered false SyntaxException

Fix: After skipping trailing whitespace, optionally consume fractional seconds and/or a trailing timezone designator before the trailing-garbage check.

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2. fix(Foundation): Timezone: invalidate utcOffset cache when /etc/localtime changes

The TZInfo UTC offset cache introduced in Poco commit 1850dc16 is only invalidated when the TZ environment variable changes. Since TZ is process-local, system timezone changes via /etc/localtime (symlink update) go undetected, causing Timezone::utcOffset() to return a stale value.

Fix: Extend cacheTZ()/tzChanged() to track the inode and mtime of /etc/localtime via stat(2). Cache is invalidated when either changes.

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Testing

• Verified ASN.1 UTCTime strings parse correctly
• Verified ISO 8601 strings with fractional seconds and UTC offsets parse correctly
• Verified utcOffset() reflects timezone changes after /etc/localtime is updated without modifying TZ

[matejk]

The ASN.1 UTCTime issue (X509Certificate::validFrom()/expiresOn()) is already fixed in #5263 by including the %Z specifier in the format strings on the caller side.

The other example "2013-10-07 08:23:19.120-04:00" is not a valid ISO 8601 datetime -- ISO 8601 requires the T separator between date and time (the 2019 revision removed the earlier allowance to omit it by mutual agreement). POCO's ISO8601_FORMAT correctly requires it.

The real issue is that %S stops at the fractional-second separator, leaving %z unable to reach the timezone. Rather than tolerating trailing garbage after parsing, a better fix is to make %S consume and discard optional fractional seconds:

case 'S':
    it = skipNonDigits(it, end);
    second = parseNumberN(dtStr, it, end, 2);
    if (it != end && (*it == '.' || *it == ','))
    {
        ++it;
        it = skipDigits(it, end);
    }
    break;

This way %z sees the timezone directly and the trailing-garbage check remains fully effective. Could you test this approach?

[kozemcak]

Hi matejk,

Thank you for the answer. Next week I will look at that and I will try your suggestion.