RFR: 8231640: (prop) Canonical property storage [v11]

[Jaikiran Pai]

On Sun, 12 Sep 2021 14:03:42 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> The commit in this PR implements the proposal for enhancement that was discussed in the core-libs-dev mailing list recently[1], for https://bugs.openjdk.java.net/browse/JDK-8231640
>> 
>> At a high level - the `store()` APIs in `Properties` have been modified to now look for the `SOURCE_DATE_EPOCH` environment variable[2]. If that env variable is set, then instead of writing out the current date time as a date comment, the `store()` APIs instead will use the value set for this env variable to parse it to a `Date` and write out the string form of such a date. The implementation here uses the `d MMM yyyy HH:mm:ss 'GMT'` date format and `Locale.ROOT` to format and write out such a date. This should provide reproducibility whenever the `SOURCE_DATE_EPOCH` is set. Furthermore, intentionally, no changes in the date format of the "current date" have been done.
>> 
>> These  modified `store()` APIs work in the presence of the `SecurityManager` too. The caller is expected to have a read permission on the `SOURCE_DATE_EPOCH` environment variable. If the caller doesn't have that permission, then the implementation of these `store()` APIs will write out the "current date" and will ignore any value that has been set for the `SOURCE_DATE_EPOCH` env variable. This should allow for backward compatibility of existing applications, where, when they run under a `SecurityManager` and perhaps with an existing restrictive policy file, the presence of `SOURCE_DATE_EPOCH` shouldn't impact their calls to the `store()` APIs.
>> 
>> The modified `store()` APIs will also ignore any value for `SOURCE_DATE_EPOCH` that  cannot be parsed to an `long` value. In such cases, the `store()` APIs will write out the "current date" and ignore the value set for this environment variable. No exceptions will be thrown for such invalid values. This is an additional backward compatibility precaution to prevent any rogue value for `SOURCE_DATE_EPOCH` from breaking applications.
>> 
>> An additional change in the implementation of these `store()` APIs and unrelated to the date comment, is that these APIs will now write out the property keys in a deterministic order. The keys will be written out in the natural ordering as specified by `java.lang.String#compareTo()` API.
>> 
>> The combination of the ordering of the property keys when written out and the usage of `SOURCE_DATE_EPOCH` environment value to determine the date comment should together allow for reproducibility of the output generated by these `store()` APIs.
>> 
>> New jtreg test classes have been introduced to verify these changes. The primary focus of `PropertiesStoreTest` is the ordering aspects of the property keys that are written out. On the other hand `StoreReproducibilityTest` focuses on the reproducibility of the output generated by these APIs.  The `StoreReproducibilityTest` runs these tests both in the presence and absence of `SecurityManager`. Plus, in the presence of SecurityManager, it tests both the scenarios where the caller is granted the requisite permission and in other case not granted that permission.
>> 
>> These new tests and existing tests under `test/jdk/java/util/Properties/` pass with these changes.
>> 
>> [1] https://mail.openjdk.java.net/pipermail/core-libs-dev/2021-August/080758.html
>> [2] https://reproducible-builds.org/specs/source-date-epoch/
>
> Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update javadoc based on Stuart's inputs

Thinking more about this, given that there's now willingless to allow this system property to allow empty comments or even free form text and do away with backward compatibilty concerns that this will no longer  be representing a date comment, I would like to propose something else. Let's take a small step back though. I think we all agree that the text of the default date comment isn't what is contentious. Instead, it's the presence of that comment itself. So instead of trying to allow users to feed some different text into this comment, why not just allow them to say whether or not they want this comment? In other words, why not consider the  value of java.util.Properties.storeDate be either "true" or "false" and consider it a boolean system property? That should avoid all these complexities.

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PR: https://git.openjdk.java.net/jdk/pull/5372