[feature] Cleanup unattached local media (#680)

* add localUnattached db function

* add parseOlderThan util function

* add pruneunusedlocalattachments to media manager

* add unusedlocal pruning to schedule + admin call

* set number of days to keep as a const

* fix test

internal/media/pruneunusedlocal.go

@@ -0,0 +1,86 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package media
+
+import (
+	"context"
+	"fmt"
+
+	"codeberg.org/gruf/go-store/storage"
+	"github.com/sirupsen/logrus"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+func (m *manager) PruneUnusedLocalAttachments(ctx context.Context) (int, error) {
+	var totalPruned int
+	var maxID string
+	var attachments []*gtsmodel.MediaAttachment
+	var err error
+
+	olderThan, err := parseOlderThan(UnusedLocalAttachmentCacheDays)
+	if err != nil {
+		return totalPruned, fmt.Errorf("PruneUnusedLocalAttachments: error parsing olderThanDays %d: %s", UnusedLocalAttachmentCacheDays, err)
+	}
+	logrus.Infof("PruneUnusedLocalAttachments: pruning unused local attachments older than %s", olderThan)
+
+	// select 20 attachments at a time and prune them
+	for attachments, err = m.db.GetLocalUnattachedOlderThan(ctx, olderThan, maxID, selectPruneLimit); err == nil && len(attachments) != 0; attachments, err = m.db.GetLocalUnattachedOlderThan(ctx, olderThan, maxID, selectPruneLimit) {
+		// use the id of the last attachment in the slice as the next 'maxID' value
+		l := len(attachments)
+		maxID = attachments[l-1].ID
+		logrus.Tracef("PruneUnusedLocalAttachments: got %d unused local attachments older than %s with maxID < %s", l, olderThan, maxID)
+
+		for _, attachment := range attachments {
+			if err := m.pruneOneLocal(ctx, attachment); err != nil {
+				return totalPruned, err
+			}
+			totalPruned++
+		}
+	}
+
+	// make sure we don't have a real error when we leave the loop
+	if err != nil && err != db.ErrNoEntries {
+		return totalPruned, err
+	}
+
+	logrus.Infof("PruneUnusedLocalAttachments: finished pruning: pruned %d entries", totalPruned)
+	return totalPruned, nil
+}
+
+func (m *manager) pruneOneLocal(ctx context.Context, attachment *gtsmodel.MediaAttachment) error {
+	if attachment.File.Path != "" {
+		// delete the full size attachment from storage
+		logrus.Tracef("pruneOneLocal: deleting %s", attachment.File.Path)
+		if err := m.storage.Delete(attachment.File.Path); err != nil && err != storage.ErrNotFound {
+			return err
+		}
+	}
+
+	if attachment.Thumbnail.Path != "" {
+		// delete the thumbnail from storage
+		logrus.Tracef("pruneOneLocal: deleting %s", attachment.Thumbnail.Path)
+		if err := m.storage.Delete(attachment.Thumbnail.Path); err != nil && err != storage.ErrNotFound {
+			return err
+		}
+	}
+
+	// delete the attachment completely
+	return m.db.DeleteByID(ctx, attachment.ID, attachment)
+}