snapshot of https://github.com/mattermost/mattermost.git (master, 2026-09-16; blobs > 131072B omitted)

server/channels/app/post_file_change.go

@@ -0,0 +1,70 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package app
+
+import (
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/request"
+	"github.com/mattermost/mattermost/server/public/utils"
+)
+
+func (a *App) processPostFileChanges(rctx request.CTX, newPost, oldPost *model.Post, updatePostOptions *model.UpdatePostOptions) (model.StringArray, *model.AppError) {
+	newFileIDs := model.RemoveDuplicateStrings(newPost.FileIds)
+	oldFileIDs := model.RemoveDuplicateStrings(oldPost.FileIds)
+
+	addedFileIDs, removedFileIDs, unchangedFileIDs := utils.FindExclusives(newFileIDs, oldFileIDs)
+
+	if len(addedFileIDs) > 0 {
+		if updatePostOptions != nil && updatePostOptions.IsRestorePost {
+			err := a.Srv().Store().FileInfo().RestoreForPostByIds(rctx, newPost.Id, addedFileIDs)
+			if err != nil {
+				return nil, model.NewAppError("app.processPostFileChanges", "app.file_info.undelete_for_post_ids.app_error", map[string]any{"post_id": newPost.Id}, "", 0).Wrap(err)
+			}
+		} else {
+			a.attachNewFilesToPost(rctx, newPost, addedFileIDs, unchangedFileIDs)
+		}
+	}
+
+	if len(removedFileIDs) > 0 {
+		if appErr := a.detachFilesFromPost(rctx, newPost.Id, removedFileIDs); appErr != nil {
+			return nil, appErr
+		}
+	}
+
+	filesChanged := len(addedFileIDs) > 0 || len(removedFileIDs) > 0
+	if filesChanged {
+		// if files were modified, invalidate the file metadata cache for the post
+		// so that the updated file metadata can be returned.
+		a.Srv().Store().FileInfo().InvalidateFileInfosForPostCache(newPost.Id, false)
+	}
+
+	return newPost.FileIds, nil
+}
+
+func (a *App) attachNewFilesToPost(rctx request.CTX, post *model.Post, addedFileIDs, unchangedFileIDs []string) {
+	// for newly added files, we need to attach them to the post
+
+	// intentionally using UserID from session instead of post.UserID
+	// to support admin attaching files in someone else's post.
+	// Admins can edit other's posts, including message, removing existing files,
+	// and attaching new files.
+	// When an admin uploads new files, they are associated with their user ID. So, when attaching
+	// these file to a post, we need to search for their FileInfo entry
+	// by the admin's user ID and not the post author's user ID.
+	userId := rctx.Session().UserId
+	attachedFileIDs := a.attachFileIDsToPost(rctx, post.Id, post.ChannelId, userId, addedFileIDs)
+	if len(attachedFileIDs) != len(addedFileIDs) {
+		// if not all files could be attached, the final list of files
+		// is those that could be attached + the existing, unchanged files
+		post.FileIds = append(attachedFileIDs, unchangedFileIDs...)
+	}
+}
+
+func (a *App) detachFilesFromPost(rctx request.CTX, postId string, removedFileIDs []string) *model.AppError {
+	if err := a.Srv().Store().FileInfo().DeleteForPostByIds(rctx, postId, removedFileIDs); err != nil {
+		return model.NewAppError("app.detachFilesFromPost", "app.file_info.delete_for_post_ids.app_error", map[string]any{"post_id": postId}, "", 0).Wrap(err)
+	}
+
+	return nil
+}