[performance] cache follow, follow request and block ID lists (#2027)

internal/cache/slice.go

@@ -0,0 +1,76 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// 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 cache
+
+import (
+	"codeberg.org/gruf/go-cache/v3/ttl"
+	"golang.org/x/exp/slices"
+)
+
+// SliceCache wraps a ttl.Cache to provide simple loader-callback
+// functions for fetching + caching slices of objects (e.g. IDs).
+type SliceCache[T any] struct {
+	*ttl.Cache[string, []T]
+}
+
+// Load will attempt to load an existing slice from the cache for the given key, else calling the provided load function and caching the result.
+func (c *SliceCache[T]) Load(key string, load func() ([]T, error)) ([]T, error) {
+	// Look for follow IDs list in cache under this key.
+	data, ok := c.Get(key)
+
+	if !ok {
+		var err error
+
+		// Not cached, load!
+		data, err = load()
+		if err != nil {
+			return nil, err
+		}
+
+		// Store the data.
+		c.Set(key, data)
+	}
+
+	// Return data clone for safety.
+	return slices.Clone(data), nil
+}
+
+// LoadRange is functionally the same as .Load(), but will pass the result through provided reslice function before returning a cloned result.
+func (c *SliceCache[T]) LoadRange(key string, load func() ([]T, error), reslice func([]T) []T) ([]T, error) {
+	// Look for follow IDs list in cache under this key.
+	data, ok := c.Get(key)
+
+	if !ok {
+		var err error
+
+		// Not cached, load!
+		data, err = load()
+		if err != nil {
+			return nil, err
+		}
+
+		// Store the data.
+		c.Set(key, data)
+	}
+
+	// Reslice to range.
+	slice := reslice(data)
+
+	// Return range clone for safety.
+	return slices.Clone(slice), nil
+}