MM-10702 Moving plugins to use hashicorp go-plugin. (#8978)

* Moving plugins to use hashicorp go-plugin.

* Tweaks from feedback.

app/plugin_key_value_store.go

@@ -0,0 +1,61 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package app
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+	"net/http"
+
+	"github.com/mattermost/mattermost-server/mlog"
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func getKeyHash(key string) string {
+	hash := sha256.New()
+	hash.Write([]byte(key))
+	return base64.StdEncoding.EncodeToString(hash.Sum(nil))
+}
+
+func (a *App) SetPluginKey(pluginId string, key string, value []byte) *model.AppError {
+	kv := &model.PluginKeyValue{
+		PluginId: pluginId,
+		Key:      getKeyHash(key),
+		Value:    value,
+	}
+
+	result := <-a.Srv.Store.Plugin().SaveOrUpdate(kv)
+
+	if result.Err != nil {
+		mlog.Error(result.Err.Error())
+	}
+
+	return result.Err
+}
+
+func (a *App) GetPluginKey(pluginId string, key string) ([]byte, *model.AppError) {
+	result := <-a.Srv.Store.Plugin().Get(pluginId, getKeyHash(key))
+
+	if result.Err != nil {
+		if result.Err.StatusCode == http.StatusNotFound {
+			return nil, nil
+		}
+		mlog.Error(result.Err.Error())
+		return nil, result.Err
+	}
+
+	kv := result.Data.(*model.PluginKeyValue)
+
+	return kv.Value, nil
+}
+
+func (a *App) DeletePluginKey(pluginId string, key string) *model.AppError {
+	result := <-a.Srv.Store.Plugin().Delete(pluginId, getKeyHash(key))
+
+	if result.Err != nil {
+		mlog.Error(result.Err.Error())
+	}
+
+	return result.Err
+}