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Based on @trinity-1686a's patch: https://github.com/Plume-org/Plume/issues/786#issuecomment-647170325

src/template_utils.rs

@@ -63,7 +63,10 @@ impl<'r> Responder<'r> for Ructe {
         let etag = format!("{:x}", hasher.finish());
         if r.headers()
             .get("If-None-Match")
-            .any(|s| s[1..s.len() - 1] == etag)
+            // This check matches both weak and strong ETags
+            // NGINX (and maybe other software) sometimes sends ETags with a
+            // "W/" prefix, that we ignore here
+            .any(|s| s[1..s.len() - 1] == etag || s[3..s.len() - 1] == etag)
         {
             Response::build()
                 .status(Status::NotModified)