Merge pull request ipfs/kubo#7330 from cloudflare/fix/dir-listing-con…

…tent-type

fix(gateway): ensure directory listings have Content-Type text/html

This commit was moved from ipfs/kubo@2380343

gateway/core/corehttp/gateway_handler.go

@@ -291,6 +291,18 @@ func (i *gatewayHandler) getOrHeadHandler(w http.ResponseWriter, r *http.Request
 		return
 	}
 
+	// 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
+	}
+
+	// A HTML directory index will be presented, be sure to set the correct
+	// type instead of relying on autodetection (which may fail).
+	w.Header().Set("Content-Type", "text/html")
 	if r.Method == http.MethodHead {
 		return
 	}
@@ -350,15 +362,6 @@ func (i *gatewayHandler) getOrHeadHandler(w http.ResponseWriter, r *http.Request
 		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)