(feature) New MessagesWillBeConsumed Server Plugin Hook (#23305)

* feature: implemented basic MessageWillBeConsumed hook and applied on GetSinglePost method.

* use hook in get methods

* chore: refactored hook usage and created utils functions to apply hook

* bugfix: single post not updating

* chore: adjusted hook to return post

* chore: reverted some uneeded  changes

* chore: updated hook to accept slice of posts

* bugfix: slice filled with niil values

* chore: MessageWillBeConsumed ranamed to MessagesWillBeConsumed

* Update plugin/hooks.go

Co-authored-by: Jesse Hallam <jesse@thehallams.ca>

* Add feature flag

* Update min version

* update tests to account for feature flag

* fix linting issues

---------

Co-authored-by: Matej Topolovac <>
Co-authored-by: mtopolovac <43346061+mtopolovac@users.noreply.github.com>
Co-authored-by: Jesse Hallam <jesse@thehallams.ca>
Co-authored-by: Kevin Hsieh <kevinh@qrypt.com>
Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

server/channels/app/plugin_hooks_test.go

@@ -1550,3 +1550,82 @@ func TestHookNotificationWillBePushed(t *testing.T) {
 		})
 	}
 }
+
+func TestHookMessagesWillBeConsumed(t *testing.T) {
+	setupPlugin := func(t *testing.T, th *TestHelper) {
+		var mockAPI plugintest.API
+		mockAPI.On("LoadPluginConfiguration", mock.Anything).Return(nil)
+		mockAPI.On("LogDebug", "message").Return(nil)
+
+		tearDown, _, _ := SetAppEnvironmentWithPlugins(t, []string{`
+			package main
+
+			import (
+				"github.com/mattermost/mattermost/server/public/plugin"
+				"github.com/mattermost/mattermost/server/public/model"
+			)
+
+			type MyPlugin struct {
+				plugin.MattermostPlugin
+			}
+
+			func (p *MyPlugin) MessagesWillBeConsumed(posts []*model.Post) []*model.Post {
+				for _, post := range posts {
+					post.Message = "mwbc_plugin:" + post.Message
+				}
+				return posts
+			}
+
+			func main() {
+				plugin.ClientMain(&MyPlugin{})
+			}
+		`}, th.App, func(*model.Manifest) plugin.API { return &mockAPI })
+		t.Cleanup(tearDown)
+	}
+
+	t.Run("feature flag disabled", func(t *testing.T) {
+		os.Setenv("MM_FEATUREFLAGS_CONSUMEPOSTHOOK", "false")
+		defer os.Unsetenv("MM_FEATUREFLAGS_CONSUMEPOSTHOOK")
+
+		th := Setup(t).InitBasic()
+		t.Cleanup(th.TearDown)
+
+		setupPlugin(t, th)
+
+		newPost := &model.Post{
+			UserId:    th.BasicUser.Id,
+			ChannelId: th.BasicChannel.Id,
+			Message:   "message",
+			CreateAt:  model.GetMillis() - 10000,
+		}
+		_, err := th.App.CreatePost(th.Context, newPost, th.BasicChannel, false, true)
+		require.Nil(t, err)
+
+		post, err := th.App.GetSinglePost(newPost.Id, true)
+		require.Nil(t, err)
+		assert.Equal(t, "message", post.Message)
+	})
+
+	t.Run("feature flag enabled", func(t *testing.T) {
+		os.Setenv("MM_FEATUREFLAGS_CONSUMEPOSTHOOK", "true")
+		defer os.Unsetenv("MM_FEATUREFLAGS_CONSUMEPOSTHOOK")
+
+		th := Setup(t).InitBasic()
+		t.Cleanup(th.TearDown)
+
+		setupPlugin(t, th)
+
+		newPost := &model.Post{
+			UserId:    th.BasicUser.Id,
+			ChannelId: th.BasicChannel.Id,
+			Message:   "message",
+			CreateAt:  model.GetMillis() - 10000,
+		}
+		_, err := th.App.CreatePost(th.Context, newPost, th.BasicChannel, false, true)
+		require.Nil(t, err)
+
+		post, err := th.App.GetSinglePost(newPost.Id, true)
+		require.Nil(t, err)
+		assert.Equal(t, "mwbc_plugin:message", post.Message)
+	})
+}