Unable to load `/temp/manifests.js` on https

Question

On my SharePoint 2016 on-premise development site workbench, to load my SPFx webpart in the config\server.json I have set the "https": false. My development site loads on http and in my browser console I can see request is sent to http://localhost:4321/temp/manifests.js, it successfully resolved and I can add my webpart to the page to test it.

If I set "https": true in config\server.json request is made to https://localhost:4321/temp/manifests.js (notice https). But the request returns error as

GET https://localhost:4321/temp/manifests.js net::ERR_SSL_PROTOCOL_ERROR
Failed to load debug manifests: Error: Error loading https://localhost:4321/temp/manifests.js
    XHR error loading https://localhost:4321/temp/manifests.js
GET http://localhost:4321/temp/manifests.js net::ERR_INVALID_HTTP_RESPONSE
Uncaught (in promise) Error: Error loading http://localhost:4321/temp/manifests.js
    XHR error loading http://localhost:4321/temp/manifests.js
    at XMLHttpRequest.o (eval at <anonymous> (sp-webpart-workbench-assembly_en-us_1c43756ae201421249073388e4dea068.js:1171), <anonymous>:4:14084)

and the page shows:

Your web part will not appear in the toolbox. Please make sure "gulp serve" is running in a web part project. Please refresh the page once "gulp serve" is running.

When I try to run the webpart on my SharePoint Online workbench with either "https": true OR "https": false set in config\server.json, I am unable to load the webpart with same error as above.

I have deleted the <homedir>/.gcb-serve-data directory and run the gulp trust-dev-cert again, but it has't worked.

How can I load /temp/manifests.js on https?

Answer 1

Finally figured out what was the problem.

1. Before doing gulp serve run the command set NODE_NO_HTTP2=1. This will allow the manifestes.js file to be served over https.
2. Before opening the SharePoint Online workbench, access the URL https://localhost:4321/temp/manifests.js from your browser. It may give you warning that it is not really secure, continue anyway. Now open the SharePoint Online workbench.