feat: generic event source (#895)

* feat: added generic event source

* feat: updated types for generic eventsource

* fix: remove site folder

* fix: added eventsource in eventing

* fix: added logic to auto-connect for generic eventsource

* fix: added logic to auto-connect for generic eventsource

* chore: updated mkdocs for generic eventsource

* fix: typo

* fix: logging in minio

* fix: conn closing condition

* chore: generic es logging

.gitignore

@@ -9,4 +9,5 @@ hack/**/debug
 debug.test
 *.iml
 .coverage
-*.out
+*.out
+site/

docs/eventsources/deployment-strategies.md

@@ -44,6 +44,7 @@ EventSource object, defaults to 1.
 - Redis
 - Resource
 - Calendar
+- Generic
 
 ### Replicas Of Recreate Types
 

docs/eventsources/generic.md

@@ -0,0 +1,82 @@
+# Generic EventSource
+
+Generic eventsource extends Argo-Events eventsources via a simple gRPC contract. This is specifically useful when you want to onboard a custom eventsource implementation.
+
+## Contract
+
+In order to qualify as generic eventsource, the eventsource server needs to implement following gRPC contract,
+
+        syntax = "proto3";
+        
+        package generic;
+        
+        service Eventing {
+            rpc StartEventSource(EventSource) returns (stream Event);
+        }
+        
+        message EventSource {
+            // The event source name.
+            string name = 1;
+            // The event source configuration value.
+            bytes config = 2;
+        }
+        
+        /**
+        * Represents an event
+        */
+        message Event {
+            // The event source name.
+            string name = 1;
+            // The event payload.
+            bytes payload = 2;
+        }
+
+The proto file is available [here](https://github.com/argoproj/argo-events/blob/master/eventsources/sources/generic/generic.proto).
+
+## Architecture
+
+<br/>
+<br/>
+
+![arch](../assets/generic-eventsource.png)
+
+<br/>
+
+Consider a generic eventsource,
+
+        apiVersion: argoproj.io/v1alpha1
+        kind: EventSource
+        metadata:
+          name: generic
+        spec:
+          generic:
+            example:
+              insecure: true
+              url: "generic-event-source-server.argo-events.svc:8080"
+              config: |-
+                key1: value1
+                key2: value2
+
+The values placed under `config` field follows a free-form style and Argo-Events eventsource client is not 
+opinionated about them. Although, it is expected that the eventsource server implemented by the user is able to parse the configuration. 
+
+## Flow
+
+1. The eventsource client connects to the server via the `url` defined under eventsource `spec` and sends over the configuration defined
+under `config` over an RPC call.
+
+2. The eventsource server then parses the configuration and connects to any external source if required to consume the events.
+The eventsource server can produce events without connecting to any external source, e.g. a special implementation of calendar events.
+
+3. The events from eventsource server are streamed back to the client.
+
+4. Client then writes the events to the eventbus which are read by the sensor to trigger the workflows.
+
+## Connection Strategy
+
+The eventsource client performs indefinite retries to connect to the eventsource server and receives events over a stream upon successful
+connection. This also applies when the eventsource server goes down.
+
+## Deployment Strategy
+
+The deployment strategy for the generic eventsource is `Recreate`. More info is available [here](../eventsources/deployment-strategies.md).

eventsources/eventing.go

@@ -18,6 +18,7 @@ import (
 	"github.com/argoproj/argo-events/eventsources/sources/emitter"
 	"github.com/argoproj/argo-events/eventsources/sources/file"
 	"github.com/argoproj/argo-events/eventsources/sources/gcppubsub"
+	"github.com/argoproj/argo-events/eventsources/sources/generic"
 	"github.com/argoproj/argo-events/eventsources/sources/github"
 	"github.com/argoproj/argo-events/eventsources/sources/gitlab"
 	"github.com/argoproj/argo-events/eventsources/sources/hdfs"
@@ -223,6 +224,13 @@ func GetEventingServers(eventSource *v1alpha1.EventSource) map[apicommon.EventSo
 		}
 		result[apicommon.PulsarEvent] = servers
 	}
+	if len(eventSource.Spec.Generic) != 0 {
+		servers := []EventingServer{}
+		for k, v := range eventSource.Spec.Generic {
+			servers = append(servers, &generic.EventListener{EventSourceName: eventSource.Name, EventName: k, GenericEventSource: v})
+		}
+		result[apicommon.GenericEvent] = servers
+	}
 	return result
 }