MM-10249 Adding plugin ability to intercept posts before they reach the DB. (#8791)

* Adding plugin ability to intercept posts before they reach the DB.

* s/envoked/invoked/

plugin/hooks.go

@@ -36,4 +36,37 @@ type Hooks interface {
 	// ExecuteCommand executes a command that has been previously registered via the RegisterCommand
 	// API.
 	ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError)
+
+	// MessageWillBePosted is invoked when a message is posted by a user before it is commited
+	// to the database. If you also want to act on edited posts, see MessageWillBeUpdated.
+	// Return values should be the modified post or nil if rejected and an explanation for the user.
+	//
+	// If you don't need to modify or reject posts, use MessageHasBeenPosted instead.
+	//
+	// Note that this method will be called for posts created by plugins, including the plugin that
+	// created the post.
+	MessageWillBePosted(post *model.Post) (*model.Post, string)
+
+	// MessageWillBeUpdated is invoked when a message is updated by a user before it is commited
+	// to the database. If you also want to act on new posts, see MessageWillBePosted.
+	// Return values should be the modified post or nil if rejected and an explanation for the user.
+	// On rejection, the post will be kept in its previous state.
+	//
+	// If you don't need to modify or rejected updated posts, use MessageHasBeenUpdated instead.
+	//
+	// Note that this method will be called for posts updated by plugins, including the plugin that
+	// updated the post.
+	MessageWillBeUpdated(newPost, oldPost *model.Post) (*model.Post, string)
+
+	// MessageHasBeenPosted is invoked after the message has been commited to the databse.
+	// If you need to modify or reject the post, see MessageWillBePosted
+	// Note that this method will be called for posts created by plugins, including the plugin that
+	// created the post.
+	MessageHasBeenPosted(post *model.Post)
+
+	// MessageHasBeenUpdated is invoked after a message is updated and has been updated in the databse.
+	// If you need to modify or reject the post, see MessageWillBeUpdated
+	// Note that this method will be called for posts created by plugins, including the plugin that
+	// created the post.
+	MessageHasBeenUpdated(newPost, oldPost *model.Post)
 }