Introduction

I think today almost everyone is aware of the cache buster mechanism in UI5. In case you never heard about it or you have no clue what it does, it’s explained very well by SAP here

https://ui5.sap.com/#/topic/91f080966f4d1014b6dd926db0e91070

The cache buster mechanism enables UI5 applications to benefit from browser caching and still makes sure the browser bypasses the cache when a new version of the app is available.

Or how it’s explained in the documentation:

This cache buster concept adds a timestamp to the path of each file like “~20120716-0201~”. This allows the cache buster to update this file in the cache by changing the timestamp to access the file. For generating these timestamps and provide the paths, SAP has cache busting indexing mechanisms for Java, ABAP and embedded into BTP. But not for HANA XS or on any other system for serving OpenUI5 apps:

When you search for Cache Buster solutions on HANA XS and XSA, you might find some already.

In this blog I want to provide another solution to do this making use of the UI5 Tooling.

Enable Cachebuster in the app

Before explaining the solution, let’s enable cache buster in your OpenUI5 app. This needs to be activated in the bootstrap code in the index.html page like this.

<script
            id="sap-ui-bootstrap"
            src="https://openui5.hana.ondemand.com/resources/sap-ui-cachebuster/sap-ui-core.js"
            data-sap-ui-theme="sap_fiori_3"
            data-sap-ui-resourceroots='{"be.wl.cachebusterdemoapp": "./"}'
            data-sap-ui-compatVersion="edge"
            data-sap-ui-oninit="module:sap/ui/core/ComponentSupport"
            data-sap-ui-async="true"
	    data-sap-ui-preload="async"
            data-sap-ui-frameOptions="trusted"
	    data-sap-ui-appCacheBuster="./"
        ></script>

Maybe you don’t see the differences immediately so let’s focus on the parts that differs from the default bootstrap code.

First part is the “src” property, here we add “sap-ui-cachebuster” between “resources” and “sap-ui-core.js”:

src=https://openui5.hana.ondemand.com/resources/sap-ui-cachebuster/sap-ui-core.js

Second, the property “data-sap-ui-appCacheBuster=”./”” needs to be added to the bootstrap like this:

data-sap-ui-appCacheBuster=”./”

Test the App with CacheBuster locally

The CacheBuster mechanism can be tested locally by building the app with the task “generateCachebusterInfo” and run it from the “dist” folder.

Let’s Install “serve” to test the dist folder locally

npm i –save-dev serve

Add a start dist script to Package.json

“start:dist”:”serve dist”,

Run it:

npm run start:dist

Problem

Running the app from the dist folder will not work. With CacheBuster enabled, UI5 is adding the generated timestamp from the CacheBuster info file to the request url. This path does not exist in the “dist” folder.

This would be the exact same problem on an XSA server or none Fiori Launchpad environment. In other system you could solve this with a Java Servlet or PHP script. In the next step I will provide you an alternative.

Solution

As a solution for this problem, I created a Cachebuster indexing task for the UI5 tooling. This task will generate the CacheBuster info page, which contains all the files and their timestamp for the CacheBuster mechanism and use this CacheBuster info file to copy each file of the UI5 project to a folder with the generated timestamp. This will make sure that all request paths including timestamps generated by the CacheBuster mechanism can be resolved.

The UI5 tooling task is available on NPM:

https://www.npmjs.com/package/ui5-task-cachebuster-indexing

This makes it easy to consume, simply install the npm package:

npm install ui5-task-cachebuster-indexing –save-dev

Add as a UI5 dependency in the package.json

	"ui5": {
		"dependencies": [
			"ui5-task-cachebuster-indexing"
		]
	}

Make sure it run behinds the last possible step (eg generateVersionInfo) or after generateCachebusterInfo. The task generateCachebusterInfo is not required as this is included in this Cache Buster Indexing task as well.

Define the task ui5.yaml config as a custom builder task:

builder:
  customTasks:
  - name: ui5-task-cachebuster-indexing
    afterTask: generateCachebusterInfo

Build the app and you’ll see your productive app in the dist folder with a copy of each file in a folder with the related timestamp. The dist folder isn’t that beautiful anymore but it should only provide you a productive app. It doesn’t matter much what’s in it as long as it does the job 😊

Run test from dist folder again

Known limitations

The task “generateCacheBusterInfo” from the UI5 Tooling can be configured to work with hashes or timestamps. Like in this example: https://sap.github.io/ui5-tooling/pages/Configuration/#cachebuster

Currently this configuration is not taken into account in the custom task for Cache Buster Indexing. It’s not yet possible, or at least not that I know of, to access global config in a custom task.

Resources

This UI5 Tooling task is available on npm: https://www.npmjs.com/package/ui5-task-cachebuster-indexing

You can find the code of this package on GitHub: https://github.com/lemaiwo/ui5-task-cachebuster-indexing

The demo project is also available on GitHub: https://github.com/lemaiwo/cachebuster-demo-app

It is also listed in the UI5 Tooling Ecosystem Showcase: https://ui5-community.github.io/ui5-ecosystem-showcase/

Hope this will help you with any caching problems in your OpenUI5 project! 😉