1 files changed, 61 insertions, 0 deletions
diff --git a/internal/web/etag.go b/internal/web/etag.go
new file mode 100644
index 000000000..37c1cb423
--- /dev/null
+++ b/internal/web/etag.go
@@ -0,0 +1,61 @@
+/*
+   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 web
+
+import (
+	// nolint:gosec
+	"crypto/sha1"
+	"encoding/hex"
+	"io"
+	"time"
+
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+
+	"codeberg.org/gruf/go-cache/v2"
+)
+
+func newETagCache() cache.Cache[string, eTagCacheEntry] {
+	eTagCache := cache.New[string, eTagCacheEntry]()
+	eTagCache.SetTTL(time.Hour, false)
+	if !eTagCache.Start(time.Minute) {
+		log.Panic("could not start eTagCache")
+	}
+	return eTagCache
+}
+
+type eTagCacheEntry struct {
+	eTag         string
+	lastModified time.Time
+}
+
+// generateEtag generates a strong (byte-for-byte) etag using
+// the entirety of the provided reader.
+func generateEtag(r io.Reader) (string, error) {
+	// nolint:gosec
+	hash := sha1.New()
+
+	if _, err := io.Copy(hash, r); err != nil {
+		return "", err
+	}
+
+	b := make([]byte, 0, sha1.Size)
+	b = hash.Sum(b)
+
+	return `"` + hex.EncodeToString(b) + `"`, nil
+}