1 files changed, 105 insertions, 0 deletions
diff --git a/internal/cache/headerfilter/filter.go b/internal/cache/headerfilter/filter.go
new file mode 100644
index 000000000..96b6e757f
--- /dev/null
+++ b/internal/cache/headerfilter/filter.go
@@ -0,0 +1,105 @@
+// 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 headerfilter
+
+import (
+	"fmt"
+	"net/http"
+	"sync/atomic"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/headerfilter"
+)
+
+// Cache provides a means of caching headerfilter.Filters in
+// memory to reduce load on an underlying storage mechanism.
+type Cache struct {
+	// current cached header filters slice.
+	ptr atomic.Pointer[headerfilter.Filters]
+}
+
+// RegularMatch performs .RegularMatch() on cached headerfilter.Filters, loading using callback if necessary.
+func (c *Cache) RegularMatch(h http.Header, load func() ([]*gtsmodel.HeaderFilter, error)) (string, string, error) {
+	// Load ptr value.
+	ptr := c.ptr.Load()
+
+	if ptr == nil {
+		// Cache is not hydrated.
+		// Load filters from callback.
+		filters, err := loadFilters(load)
+		if err != nil {
+			return "", "", err
+		}
+
+		// Store the new
+		// header filters.
+		ptr = &filters
+		c.ptr.Store(ptr)
+	}
+
+	// Deref and perform match.
+	return ptr.RegularMatch(h)
+}
+
+// InverseMatch performs .InverseMatch() on cached headerfilter.Filters, loading using callback if necessary.
+func (c *Cache) InverseMatch(h http.Header, load func() ([]*gtsmodel.HeaderFilter, error)) (string, string, error) {
+	// Load ptr value.
+	ptr := c.ptr.Load()
+
+	if ptr == nil {
+		// Cache is not hydrated.
+		// Load filters from callback.
+		filters, err := loadFilters(load)
+		if err != nil {
+			return "", "", err
+		}
+
+		// Store the new
+		// header filters.
+		ptr = &filters
+		c.ptr.Store(ptr)
+	}
+
+	// Deref and perform match.
+	return ptr.InverseMatch(h)
+}
+
+// Clear will drop the currently loaded filters,
+// triggering a reload on next call to ._Match().
+func (c *Cache) Clear() { c.ptr.Store(nil) }
+
+// loadFilters will load filters from given load callback, creating and parsing raw filters.
+func loadFilters(load func() ([]*gtsmodel.HeaderFilter, error)) (headerfilter.Filters, error) {
+	// Load filters from callback.
+	hdrFilters, err := load()
+	if err != nil {
+		return nil, fmt.Errorf("error reloading cache: %w", err)
+	}
+
+	// Allocate new header filter slice to store expressions.
+	filters := make(headerfilter.Filters, 0, len(hdrFilters))
+
+	// Add all raw expression to filter slice.
+	for _, filter := range hdrFilters {
+		if err := filters.Append(filter.Header, filter.Regex); err != nil {
+			return nil, fmt.Errorf("error appending exprs: %w", err)
+		}
+	}
+
+	return filters, nil
+}