fix: subdomain redirect for dir CIDs

Closes #7164

License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>


This commit was moved from ipfs/kubo@8290ec1

gateway/core/corehttp/gateway_handler.go

@@ -342,6 +342,16 @@ func (i *gatewayHandler) getOrHeadHandler(w http.ResponseWriter, r *http.Request
 		BackLink: backLink,
 		Hash:     hash,
 	}
+
+	// See statusResponseWriter.WriteHeader
+	// and https://github.com/ipfs/go-ipfs/issues/7164
+	// Note: this needs to occur before listingTemplate.Execute otherwise we get
+	// superfluous response.WriteHeader call from prometheus/client_golang
+	if w.Header().Get("Location") != "" {
+		w.WriteHeader(http.StatusMovedPermanently)
+		return
+	}
+
 	err = listingTemplate.Execute(w, tplData)
 	if err != nil {
 		internalWebError(w, err)