RFR: 8315487: Security Providers Filter [v19]

[Sean Mullan]

On Wed, 8 Jan 2025 16:50:01 GMT, Martin Balao <mbalao at openjdk.org> wrote:

>> In addition to the goals, scope, motivation, specification and requirement notes in [JDK-8315487](https://bugs.openjdk.org/browse/JDK-8315487), we would like to describe the most relevant decisions taken during the implementation of this enhancement. These notes are organized by feature, may encompass more than one file or code segment, and are aimed to provide a high-level view of this PR.
>> 
>> ## ProvidersFilter
>> 
>> ### Filter construction (parser)
>> 
>> The providers filter is constructed from a string value, taken from either a system or a security property with name "jdk.security.providers.filter". This process occurs at sun.security.jca.ProvidersFilter class —simply referred as ProvidersFilter onward— static initialization. Thus, changes to the filter's overridable property are not effective afterwards and no assumptions should be made regarding when this class gets initialized.
>> 
>> The filter's string value is processed with a custom parser of order 'n', being 'n' the number of characters. The parser, represented by the ProvidersFilter.Parser class, can be characterized as a Deterministic Finite Automaton (DFA). The ProvidersFilter.Parser::parse method is the starting point to get characters from the filter's string value and generate state transitions in the parser's internal state-machine. See ProvidersFilter.Parser::nextState for more details about the parser's states and both valid and invalid transitions. The ParsingState enum defines valid parser states and Transition the reasons to move between states. If a filter string cannot be parsed, a ProvidersFilter.ParserException exception is thrown, and turned into an unchecked IllegalArgumentException in the ProvidersFilter.Filter constructor.
>> 
>> While we analyzed —and even tried, at early stages of the development— the use of regular expressions for filter parsing, we discarded the approach in order to get maximum performance, support a more advanced syntax and have flexibility for further extensions in the future.
>> 
>> ### Filter (structure and behavior)
>> 
>> A filter is represented by the ProvidersFilter.Filter class. It consists of an ordered list of rules, returned by the parser, that represents filter patterns from left to right (see the filter syntax for reference). At the end of this list, a match-all and deny rule is added for default behavior. When a service is evaluated against the filter, each filter rule is checked in the ProvidersFilter.Filter::apply method. The rule makes an all...
>
> Martin Balao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Copyright date update.
>   
>   Co-authored-by: Martin Balao Alonso <mbalao at redhat.com>
>   Co-authored-by: Francisco Ferrari Bihurriet <fferrari at redhat.com>

I have been starting to review the code, and am initially reviewing this with respect to how it complies with the current API specification.
 
All of the JCA API `getInstance` methods that do not have a provider argument have text like the following:

> This method traverses the list of registered security Providers, starting with the most preferred Provider. A new `<service>` object encapsulating the `<service>Spi` implementation from the first provider that supports the specified algorithm is returned.

However, the providers filter can be configured to prevent that object from being returned. I think this is an important difference in behavior that it should be documented as an implementation note. My initial suggestion is something like the following:

"The JDK Reference Implementation additionally uses the `jdk.security.providers.filter` system and security property to determine which services are enabled. A provider whose <service> algorithm is not enabled will not be selected."

I think similar text will need to be added in the `Provider` API, but I need to review those changes more closely first.

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PR Comment: https://git.openjdk.org/jdk/pull/15539#issuecomment-2611086422