Eiffel on Cloud Events (#400)

* Add page for explaining Eiffel on Cloud Events

README.md

@@ -51,6 +51,7 @@ Visit [Eiffel Community](https://eiffel-community.github.io) to get started and
    1. [Activity Linking](./eiffel-syntax-and-usage/activity-linking.md)
    1. [Event Schemas](./eiffel-syntax-and-usage/event-schemas.md)
    1. [Event Categories](./eiffel-syntax-and-usage/event-categories.md)
+   1. [Eiffel and Cloud Events](./eiffel-syntax-and-usage/eiffel-and-cloud-events.md)
 1. The Eiffel Vocabulary
    1. [EiffelActivityTriggeredEvent (ActT)](./eiffel-vocabulary/EiffelActivityTriggeredEvent.md)
    1. [EiffelActivityCanceledEvent (ActC)](./eiffel-vocabulary/EiffelActivityCanceledEvent.md)

eiffel-syntax-and-usage/eiffel-and-cloud-events.md

@@ -0,0 +1,78 @@
+# Eiffel and Cloud Events
+
+This document describes using Eiffel on Cloud Events.
+Much inspiration is taken from the [CDEvents](https://cdevents.dev) and their idea on
+[cloud event binding](https://github.com/cdevents/spec/blob/main/cloudevents-binding.md).
+
+Eiffel as such does not care about the transportation of the events, and thus binding specific ideas reside in
+[Eiffel Sepia](https://eiffel-community.github.io/eiffel-sepia/). This document only covers the subject of binding
+Eiffel to Cloud Events.
+
+## Common
+
+Following how CDEvents has done it, we select the needed parameters from the `meta` field
+(CDEvents calls their meta-object `context`).
+
+Looking at the mandatory parameters from Cloud Events, we have to fill in:
+
+- `type` - Use the reverse DNS name `io.github.eiffel-community.<Eiffel type>` where:
+  - `io.github.eiffel-community` corresponds to the reverse DNS of our website
+  - `<Eiffel type>` - Use the value from `meta.type`
+- `source` - Cloud Events requires a *URI-reference*. Use `meta.source.uri` making this field mandatory when sending
+  Eiffel on top of Cloud Events.
+- `id` - Use the value from `meta.id`
+- `time` - Use the converted value from `meta.time`. Convert the unix timestamp to [RFC 3339](https://tools.ietf.org/html/rfc3339).
+- `dataschema` - (Optional) Use the value from `meta.schemaUri`.
+
+### Exemplification
+
+Given that we have an Eiffel event:
+
+```JSON
+{
+"meta": {
+    "type": "EiffelArtifactCreatedEvent",
+    "version": "4.0.0",
+    "time": 1720614264,
+    "id": "aaaaaaaa-bbbb-5ccc-8ddd-eeeeeeeeeee0",
+    "source": {
+        "uri": "https://ci.internal.myorg.org/ArtifactBuilder/info"
+    },
+    "schemaUri": "https://schemas.myorg.org/OurArtCEvent-1.0.json"
+},
+"data": {
+    "identity": "pkg:maven/com.mycompany.myproduct/[email protected]"
+},
+"links": []
+}
+```
+
+The cloud event in structured format would look like this (excluding `type`):
+
+```JSON
+{
+    "specversion": "1.0",
+    "type": "io.github.eiffel-community.EiffelArtifactCreatedEvent",    # Same as meta.type prefixed with our reverse DNS
+    "source": "https://ci.internal.myorg.org/ArtifactBuilder/info",     # Same as data.meta.source.uri
+    "id": "aaaaaaaa-bbbb-5ccc-8ddd-eeeeeeeeeee0",                       # Same as data.meta.id
+    "time": "2024-07-10T12:27:14+00:00",                                # NOTE: different format,
+    "dataschema": "https://schemas.myorg.org/OurArtCEvent-1.0.json",    # Same as data.meta.schemaUri (optional)
+    "datacontenttype": "application/json",
+    "data": {
+        "meta": {
+            "type": "EiffelArtifactCreatedEvent",
+            "version": "4.0.0",
+            "time": 1234567890,
+            "id": "aaaaaaaa-bbbb-5ccc-8ddd-eeeeeeeeeee0",
+            "source": {
+                "uri": "https://ci.internal.myorg.org/ArtifactBuilder/info"
+            },
+            "schemaUri": "https://schemas.myorg.org/OurArtCEvent-1.0.json"
+        },
+        "data": {
+            "identity": "pkg:maven/com.mycompany.myproduct/[email protected]"
+        },
+        "links": []
+    }
+}
+```