fix(storage): COS 资源下载 - 公开 CDN 模式使用附件响应头 (#718)

backend/internal/storage/objects.go

@@ -248,6 +248,28 @@ func SignedOriginObjectDownloadURL(setting Settings, objectKey string, expiresAt
 	return signedOriginObjectURL(setting, objectKey, objectURLSigning{ExpiresAt: expiresAt, ContentDisposition: disposition})
 }
 
+// PublicCDNObjectDownloadURL returns a public CDN URL that asks the object
+// storage origin to emit an attachment response. The query parameter keeps
+// ordinary display URLs inline while allowing a browser to download this one
+// without routing object bytes through the application server.
+//
+// Public CDN deployments must preserve response-content-disposition when
+// forwarding requests to the object store.
+func PublicCDNObjectDownloadURL(setting Settings, objectKey string, fileName string) (string, error) {
+	value, err := OssCDNObjectURL(setting.CDNBaseURL, objectKey)
+	if err != nil {
+		return "", err
+	}
+	parsed, err := url.Parse(value)
+	if err != nil {
+		return "", err
+	}
+	query := parsed.Query()
+	query.Set("response-content-disposition", objectDownloadContentDisposition(fileName, objectKey))
+	parsed.RawQuery = query.Encode()
+	return parsed.String(), nil
+}
+
 func objectDownloadContentDisposition(fileName string, objectKey string) string {
 	name := strings.TrimSpace(fileName)
 	name = strings.ReplaceAll(name, "\\", "_")