[INTERNAL] testRunner middleware: Use ETag caching

lib/middleware/testRunner.js

@@ -5,20 +5,43 @@ const path = require("path");
 const mime = require("mime-types");
 const parseurl = require("parseurl");
 const log = require("@ui5/logger").getLogger("server:middleware:testRunner");
+const etag = require("etag");
+const fresh = require("fresh");
 
 const testRunnerResourceRegEx = /\/test-resources\/sap\/ui\/qunit\/(testrunner\.(html|css)|TestRunner.js)$/;
 const resourceCache = {};
 
-function serveResource(res, resourcePath, resourceContent) {
+function isFresh(req, res) {
+	return fresh(req.headers, {
+		"etag": res.getHeader("ETag")
+	});
+}
+
+async function readResourceInfo(resourceName) {
+	const content = await readFile(path.join(__dirname, "testRunner", resourceName), {encoding: "utf8"});
+	return {
+		content,
+		etag: etag(content)
+	};
+}
+
+function serveResource(req, res, resourcePath, resourceInfo) {
 	const type = mime.lookup(resourcePath) || "application/octet-stream";
 	const charset = mime.charset(type);
 	const contentType = type + (charset ? "; charset=" + charset : "");
+	res.setHeader("Content-Type", contentType);
 
-	// resources served by this middleware do not change often
-	res.setHeader("Cache-Control", "public, max-age=1800");
+	// Enable ETag caching
+	res.setHeader("ETag", resourceInfo.etag);
 
-	res.setHeader("Content-Type", contentType);
-	res.end(resourceContent);
+	if (isFresh(req, res)) {
+		// client has a fresh copy of the resource
+		res.statusCode = 304;
+		res.end();
+		return;
+	}
+
+	res.end(resourceInfo.content);
 }
 
 /**
@@ -40,14 +63,14 @@ function createMiddleware({resources}) {
 				log.verbose(`Serving ${pathname}`);
 				let pResource;
 				if (!resourceCache[pathname]) {
-					pResource = readFile(path.join(__dirname, "testRunner", resourceName), {encoding: "utf8"});
+					pResource = readResourceInfo(resourceName);
 					resourceCache[pathname] = pResource;
 				} else {
 					pResource = resourceCache[pathname];
 				}
 
-				const resourceContent = await pResource;
-				serveResource(res, pathname, resourceContent);
+				const resourceInfo = await pResource;
+				serveResource(req, res, pathname, resourceInfo);
 			} else {
 				next();
 			}