[External] : Re: How to open a package from a module in the boot layer to a module in another layer?

[Alex Buckley]

You can split your application so that a small loader module goes in the 
boot layer, while the bulk of the application (CORE module, API module, 
etc) lives in a child layer. That child layer becomes the parent for the 
plugins' layers. You are already resolving plugin modules (and their 
dependencies, such as Gson) in the context of their own layers, so no 
change there.

Exposing the boot layer's controller would allow arbitrary code to 
export JDK packages without the use of --add-exports on the command 
line. That's a non-starter, as discussed in "Integrity by Default" 
(https://openjdk.org/jeps/8305968#Restrictions-on-standard-unsafe-APIs).

Alex

On 1/13/2025 12:58 PM, Code Ranger wrote:
> Alex, thank you for your suggestion.
> 
> Putting application in its own layer
> 1) is technically impossible, because the "CORE module" creates child 
> layers, including the child layer you are talking about,
> 2) gives nothing, because it doesn't solve the main problem when child 
> layer require adding directives to boot layer modules.
> 
> Best regards, CR
> 
> On 1/13/25 22:51, Alex Buckley wrote:
>> Mike/Code Ranger, the obvious suggestion is to put your application 
>> (including the "CORE module") in its own layer, rather than the boot 
>> layer.
>>
>> Alex
>>
>> On 1/13/2025 1:46 AM, Code Ranger wrote:
>>> Hello, Alan
>>>
>>> Thank you for your suggestions, help, and time. I truly appreciate 
>>> and am deeply grateful for them.
>>>
>>> However, I’m afraid I failed to convey the most crucial point. 
>>> Therefore, I decided to illustrate it graphically. I believe 
>>> everything will become clear now.
>>>
>>> Please, see https://urldefense.com/v3/__https://ibb.co/bLTzp0n__;!! 
>>> ACWV5N9M2RV99hQ! 
>>> LnYA2Im1AFI5I96HdRK8cKttxczpYE2hMPXX9jrASNBXjyB7Um4AQQe5nSLytW1VWQYs7Wx_p4gvO2F6QrwcLVh6G0MYwg$
>>> If you have any questions, I’m ready to answer them, as I’ve already 
>>> mentioned, this matter is extremely important to me.
>>>
>>>
>>> On 1/13/25 09:54, Alan Bateman wrote:
>>>> On 12/01/2025 09:12, Code Ranger wrote:
>>>>> 1. I see that JDK-8347283 was closed with your comment. I don't 
>>>>> agree with you decision, but I can be wrong. Let me explain, why I 
>>>>> think that is wrong using this concrete example.
>>>>>
>>>>> Boot layer has jdk modules and main application modules. The CORE 
>>>>> module of the application creates plugins with child layers. No one 
>>>>> in the world can know what plugins will be created and used when 
>>>>> the main application starts. Now, somewhere in the future, the 
>>>>> module A from plugin X will require module B from boot layer to 
>>>>> open its package to module A. I believe, that the only solution to 
>>>>> do it is to provide the controller of the boot layer.
>>>>>
>>>>> 2. Now, I tried to do apiModule.addOpens in CORE module. I got:
>>>>>
>>>>> java.lang.IllegalCallerException: com.foo.api.packagename is not 
>>>>> open to module com.foo.core
>>>>>     at java.base/java.lang.Module.addOpens(Module.java:918) ~[?:?]
>>>>>
>>>>>
>>>>> Therefore, as far as I understand, for the solution you are 
>>>>> suggesting to work, the packagename package of the API module must 
>>>>> be opened to the Core module. But the main problem, as I've said 
>>>>> above - no one knows in advance which packages of which modules 
>>>>> from the boot layer will need to be opened/exported, etc., to the 
>>>>> plugins that will be created by users and deployed dynamically.
>>>>
>>>> Your second mail reveals a bit more but it's not clear if your issue 
>>>> is one of these scenarios:
>>>>
>>>> 1. A serialization library that is incompatible with strong 
>>>> encapsulation. If so, that's a different discussion.
>>>>
>>>> 2. The API and CORE modules have some interesting internals that the 
>>>> authors of these modules have chosen not to export. The author of a 
>>>> plugin doesn't agree. As you've found, this can only be facilitated 
>>>> with cooperation from code in CORE. It may additionally require CLI 
>>>> option if API won't open its packages to CORE. This means running 
>>>> with --add-opens API/com.foo.api=CORE so that CORE can open API's 
>>>> package to the plugin module in the child layer.
>>>>
>>>> 3. A badly behaved plugin that depends on the internals of standard 
>>>> or JDK modules. This would be whack-a-mole and require a combination 
>>>> of CLI options and code in CORE to open java.* and jdk.* packages to 
>>>> the offending code in the plugin.
>>>>
>>>> -Alan
>>>>
>>>>
>>>
>>
>