RFR: 8231640: (prop) Canonical property storage [v21]

Alan Bateman alanb at openjdk.java.net
Wed Sep 22 10:08:05 UTC 2021

On Sat, 18 Sep 2021 03:52:17 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:
>   Roger's suggestion to reword the implSpec text

src/java.base/share/classes/java/lang/System.java line 766:

> 764:      * <tr><th scope="row">{@systemProperty java.properties.date}</th>
> 765:      *     <td>Text for the comment that must replace the default date comment
> 766:      *     written out by {@code Properties.store()} methods <em>(optional)</em> </td></tr>

To date, the table in getProperties has listed the supported system properties that the runtime makes available to applications. It hasn't historically listed the many other standard properties that can be set on the command line. So I'm sure about adding this one to the table as it opens the door to expanding the table to all the other system properties that are documented elsewhere in the API docs. Note that javadoc creates a table of system properties from usages of `@systemProperty` so there is already a more complete table in the javadoc build.


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

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