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new 00c2778 Move readme to parent dir and add apicontroller proposal
00c2778 is described below
commit 00c2778a7e5fbeab1101bb25488d2ca91c2da9d7
Author: Carsten Ziegeler <[email protected]>
AuthorDate: Mon Nov 6 14:25:05 2017 +0100
Move readme to parent dir and add apicontroller proposal
---
featuremodel/apicontroller.md | 44 ++++++++++++++++++++++++++++++++++++
featuremodel/{feature => }/readme.md | 0
2 files changed, 44 insertions(+)
diff --git a/featuremodel/apicontroller.md b/featuremodel/apicontroller.md
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+# API Controller
+
+If you're assembling an application out of several features and provide this
application as a platform for customers to extend, an additional control of the
API provided by the platform is needed. The bundles within the features provide
all kinds of APIs but you might not want to expose all of these as extension
points but rather want to use some of it internally within your features.
+
+This is a proposal about how to add such additional metadata to the feature
model. An API controller at runtime enforces the rules.
+
+# Visibility of API
+
+A feature exports some api, however there are different types of clients of
the API:
+
+* Bundles shipped as part of the platform
+* 3rd party bundles based on the platform
+
+We can generalize this by saying that API is either globally visible (to every
client) or only visible to features within the same context. Usually this is
referred to as a "region": The platform spawns its own region and a customer
application has its own region, too. In theory there could be several customer
applications running in the same framework, and each application has its own
region.
+
+Without any further information, API is globally visible by default. However,
for platform features we want the opposite as we want to ensure that newly
added API is not world-wide visible by default. Therefore we'll add an
additional build time check (analyzer) that checks that each platform feature
has an api controller configuration as below.
+
+A feature can have an additional extension JSON named exports:
+
+ "exports" : {
+ "region" : "platform" // name of the region,
+ "global" : [
+ "org.apache.sling.resource.api.*"
+ ],
+ "local" : [
+ "org.apache.sling.commons.scheduler"
+ ]
+ }
+
+In the example above the feature declares:
+
+* The name of the region it belongs to (platform)
+* The list of packages it is exporting to everyone (Sling's resource API)
+* The additional list of packages it is exporting to features within the same
region (scheduler api)
+
+Of course the above mentioned packages need to be exported by some bundle
within the feature.
+
+If the exports extension is missing, it is assumed that all packages are
exported and that the feature runs in the global region.
+
+If the region information is missing, the global region is used. If the
packages list for global or local is missing, it is assumed to be all packages.
If none should be exported, an empty array needs to be specified.
+
+This model is intentionally kept simple and restricted to a feature being in
only a single region. In theory we could think of use cases where a feature is
shared across two (or more) regions, but not shared globally. However this gets
pretty complicated easily and therefore we suggest to make such features global.
+
+To support feature inheritance, a custom extension handler must be registered
which will merge the extension - if the inherited one and the target feature
use a different region, this is considered an error. If they have the same
region, the packages are merged. Of course the inheriting feature can remove
this extension before processing. In addition the extension handler must mark
each bundle with the region, otherwise this relationship gets lost later on
when the application is build.
diff --git a/featuremodel/feature/readme.md b/featuremodel/readme.md
similarity index 100%
rename from featuremodel/feature/readme.md
rename to featuremodel/readme.md
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