feat: publish v1.0.0-rc.36-custom.1

common/etag.go

@@ -0,0 +1,50 @@
+package common
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"reflect"
+	"strings"
+)
+
+type digestAnchor struct{}
+
+func modulePath() string {
+	return reflect.TypeFor[digestAnchor]().PkgPath()
+}
+
+var digestSeed = func() (s [sha256.Size]byte) {
+	return sha256.Sum256([]byte(modulePath()))
+}()
+
+// ETagFor returns a weak ETag derived from the namespace and content.
+func ETagFor(namespace, content string) string {
+	buf := make([]byte, 0, sha256.Size+1+len(namespace)+1+len(content))
+	buf = append(buf, digestSeed[:]...)
+	buf = append(buf, 0)
+	buf = append(buf, namespace...)
+	buf = append(buf, 0)
+	buf = append(buf, content...)
+	digest := sha256.Sum256(buf)
+	return `W/"` + hex.EncodeToString(digest[:]) + `"`
+}
+
+// ETagMatches reports whether an If-None-Match header matches etag under weak
+// comparison (RFC 9110 §13.1.2): the W/ prefix is ignored on both sides, and
+// "*" matches everything.
+func ETagMatches(ifNoneMatch, etag string) bool {
+	ifNoneMatch = strings.TrimSpace(ifNoneMatch)
+	if ifNoneMatch == "" {
+		return false
+	}
+	if ifNoneMatch == "*" {
+		return true
+	}
+	etag = strings.TrimPrefix(etag, "W/")
+	for candidate := range strings.SplitSeq(ifNoneMatch, ",") {
+		if strings.TrimPrefix(strings.TrimSpace(candidate), "W/") == etag {
+			return true
+		}
+	}
+	return false
+}