Add plugin context sharing types (#127)

* Add plugin context sharing types

* Add more docs & explanation for interface functions

pkg/plugin/context_sharing_types.go

@@ -0,0 +1,54 @@
+// Copyright © 2023 The Knative Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package plugin
+
+// Manifest represents plugin metadata
+type Manifest struct {
+	// Path to external plugin binary. Always empty for inlined plugins.
+	Path string `json:"path,omitempty"`
+
+	// Plugin declares its own manifest to be included in Context Sharing feature
+	HasManifest bool `json:"hasManifest"`
+
+	// ProducesContextDataKeys is a list of keys for the ContextData that
+	// a plugin can produce. Nil or an empty list declares that this
+	// plugin is not ContextDataProducer
+	ProducesContextDataKeys []string `json:"producesKeys,omitempty"`
+
+	// ConsumesContextDataKeys is a list of keys from a ContextData that a
+	// plugin is interested in to consume. Nil or an empty list declares
+	// that this plugin is not a ContextDataConsumer
+	ConsumesContextDataKeys []string `json:"consumesKeys,omitempty"`
+}
+
+// PluginWithManifest represents extended plugin support for Manifest and Context Sharing feature
+type PluginWithManifest interface {
+	// Plugin original interface wrapper
+	Plugin
+
+	// GetManifest returns a metadata descriptor of plugin
+	GetManifest() *Manifest
+
+	// GetContextData returns a map structure that is used to share common context data from plugin
+	GetContextData() map[string]string
+
+	// ExecuteWithContextData an extended version of plugin.Execute command to allow injection and use of ContextData.
+	// This is a map[string]string structure to share common value service name between kn and plugins.
+	ExecuteWithContextData(ctx map[string]string, args []string) error
+	// Alternative impl: use of native context.Context as a data structure.
+	// We decided to use plain map, because Context can't be extended to external plugins anyway.
+	// Another encode to JSON is required to pass it. We might reconsider that in future development iterations.
+
+}