MM-22845: Added support for permalink previews. (#17796)

* MM-22845: Added support for permalink previews.

* MM-22845: Adds license to new file.

* MM-22845: Adds endpoint to retrieve multiple posts by id.

* MM-22845: Fix for deleted post.

* MM-22845: Adds config setting for permalink previews.

* MM-22845: Adds API test for new endpoint.

* MM-22845: Fix typo.

* MM-22845: Tests that post create or updated via App get the previewed_post prop.

* MM-22845: Tests for matching permalinks.

* MM-22845: Adds PreparePostForClient test for permalink previews.

* MM-22845: Embeds entire post in permalink metadata.

* MM-22845: Filter WS message payload of created and edited post based on permissions.

* MM-22845: Runs app layer generator.

* MM-22845: Lint check fix.

* MM-22845: Adds feature flag.

* MM-22845: Clones WS message.

* MM-22845: Removes knowledge of permalink from LinkMetadata table. Removes knowledge of user id from post embedding methods in favour of a 'sanitize' method/step.

* MM-22845: Handle nil post metadata.

* MM-22845: Switch to cloning post.

* MM-22845: Removes unused code.

* MM-22845: Refactor.

* MM-22845: Reverts whitespace change.

* MM-22845: Removes unnecessary code.

* MM-22845: Removes unnecessary function.

* MM-22845: Warn but don't error if permalinked referenced post or channel is not found.

* MM-22845: Fix for clone method.

* MM-22845: Fix for clone method.

* MM-22845: Updates translations.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/post_test.go

@@ -651,7 +651,7 @@ func TestDeletePostWithFileAttachments(t *testing.T) {
 	assert.Nil(t, err)
 
 	// Delete the post.
-	post, err = th.App.DeletePost(post.Id, userID)
+	_, err = th.App.DeletePost(post.Id, userID)
 	assert.Nil(t, err)
 
 	// Wait for the cleanup routine to finish.
@@ -755,6 +755,41 @@ func TestCreatePost(t *testing.T) {
 			th.AddPermissionToRole(model.PermissionUseChannelMentions.Id, model.ChannelAdminRoleId)
 		})
 	})
+
+	t.Run("Sets PostPropsPreviewedPost when a permalink is the first link", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+		th.AddUserToChannel(th.BasicUser, th.BasicChannel)
+
+		referencedPost := &model.Post{
+			ChannelId: th.BasicChannel.Id,
+			Message:   "hello world",
+			UserId:    th.BasicUser.Id,
+		}
+
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			*cfg.ServiceSettings.SiteURL = "http://mymattermost.com"
+		})
+
+		th.Context.Session().UserId = th.BasicUser.Id
+
+		referencedPost, err := th.App.CreatePost(th.Context, referencedPost, th.BasicChannel, false, false)
+		require.Nil(t, err)
+
+		permalink := fmt.Sprintf("%s/%s/pl/%s", *th.App.Config().ServiceSettings.SiteURL, th.BasicTeam.Name, referencedPost.Id)
+
+		channelForPreview := th.CreateChannel(th.BasicTeam)
+		previewPost := &model.Post{
+			ChannelId: channelForPreview.Id,
+			Message:   permalink,
+			UserId:    th.BasicUser.Id,
+		}
+
+		previewPost, err = th.App.CreatePost(th.Context, previewPost, channelForPreview, false, false)
+		require.Nil(t, err)
+
+		assert.Equal(t, previewPost.GetProps(), model.StringInterface{"previewed_post": referencedPost.Id})
+	})
 }
 
 func TestPatchPost(t *testing.T) {
@@ -1085,6 +1120,45 @@ func TestUpdatePost(t *testing.T) {
 		require.Nil(t, err)
 		assert.Equal(t, "![image]("+proxiedImageURL+")", rpost.Message)
 	})
+
+	t.Run("Sets PostPropsPreviewedPost when a post is updated to have a permalink as the first link", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+		th.AddUserToChannel(th.BasicUser, th.BasicChannel)
+
+		referencedPost := &model.Post{
+			ChannelId: th.BasicChannel.Id,
+			Message:   "hello world",
+			UserId:    th.BasicUser.Id,
+		}
+
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			*cfg.ServiceSettings.SiteURL = "http://mymattermost.com"
+		})
+
+		th.Context.Session().UserId = th.BasicUser.Id
+
+		referencedPost, err := th.App.CreatePost(th.Context, referencedPost, th.BasicChannel, false, false)
+		require.Nil(t, err)
+
+		permalink := fmt.Sprintf("%s/%s/pl/%s", *th.App.Config().ServiceSettings.SiteURL, th.BasicTeam.Name, referencedPost.Id)
+
+		channelForTestPost := th.CreateChannel(th.BasicTeam)
+		testPost := &model.Post{
+			ChannelId: channelForTestPost.Id,
+			Message:   "hello world",
+			UserId:    th.BasicUser.Id,
+		}
+
+		testPost, err = th.App.CreatePost(th.Context, testPost, channelForTestPost, false, false)
+		require.Nil(t, err)
+		assert.Equal(t, testPost.GetProps(), model.StringInterface{})
+
+		testPost.Message = permalink
+		testPost, err = th.App.UpdatePost(th.Context, testPost, false)
+		require.Nil(t, err)
+		assert.Equal(t, testPost.GetProps(), model.StringInterface{"previewed_post": referencedPost.Id})
+	})
 }
 
 func TestSearchPostsInTeamForUser(t *testing.T) {