Does this work?

LightlessSyncServer/LightlessSyncStaticFilesServer/Services/CDNDownloadsService.cs

@@ -10,7 +10,8 @@ public class CDNDownloadsService
         Disabled,
         Unauthorized,
         NotFound,
-        Success
+        Success,
+        Downloading
     }
 
     public readonly record struct Result(ResultStatus Status, FileInfo? File);
@@ -53,4 +54,32 @@ public class CDNDownloadsService
 
         return new Result(ResultStatus.Success, fileInfo);
     }
+
+    public Result GetDownloadWithCacheCheck(string hash, long expiresUnixSeconds, string signature)
+    {
+        if (!_cdnDownloadUrlService.DirectDownloadsEnabled)
+        {
+            return new Result(ResultStatus.Disabled, null);
+        }
+
+        if (string.IsNullOrEmpty(signature) || string.IsNullOrEmpty(hash))
+        {
+            return new Result(ResultStatus.Unauthorized, null);
+        }
+
+        hash = hash.ToUpperInvariant();
+
+        if (!_cdnDownloadUrlService.TryValidateSignature(hash, expiresUnixSeconds, signature))
+        {
+            return new Result(ResultStatus.Unauthorized, null);
+        }
+
+        var fileInfo = _cachedFileProvider.TryGetLocalFileInfo(hash);
+        if (fileInfo == null)
+        {
+            return new Result(ResultStatus.Downloading, null);
+        }
+
+        return new Result(ResultStatus.Success, fileInfo);
+    }
 }