[SOLVED] Proxy EventSource (SSE) connections through NodeJS to a localhost backend

Proxy EventSource (SSE) connections through NodeJS to a localhost backend

I have an issue with EventSource connections through node-http-proxy v1.18.1. The connections work in development, from create-react-app, proxy: , but when deploying to production, the connection fails with the following browser (chromium) error:

EventSource's response has a MIME type ("text/html") that is not "text/event-stream". Aborting the connection.

The portion of my server.js that creates the proxy is:

const httpProxy = require('http-proxy');

var app = express();
var apiProxy = httpProxy.createProxyServer({secure: false});

app.use(express.static(root));
app.use(compression());

/* proxy api calls over to port 9047 */
app.all('/api/*', (req, res) => {
   apiProxy.web(req,res, { target: 'https://localhost:9047' });
});

and the HTML document that React/NodeJS appears to be returning to the browser instead of the EventStream data is:

<!doctype html>
<html lang="en">
    <head>
        <meta charset="utf-8"/>
        <link rel="icon" href="/icons/favicon.ico"/>
        <meta name="viewport" content="width=device-width,initial-scale=1"/>
        <meta name="theme-color" content="#000000"/>
        <meta name="description" content="Web site created using create-react-app"/>
        <link rel="apple-touch-icon" href="/icons/threaded_icon_57x57.png"/>
        <link rel="manifest" href="/manifest.json"/>
        <title>My App</title>
        <script defer="defer" src="/static/js/main.8ebfafc7.js"></script>
        <link href="/static/css/main.8c23b3de.css" rel="stylesheet">
    </head>
    <body>
        <noscript>You need to enable JavaScript to run this app.</noscript>
        <div id="root"></div>
    </body>
</html>

I have also tried using the http-proxy-middleware library, which wraps the node-http-proxy module. Same exact results.

The backend server (springboot) on localhost does not appear to be receiving the call. It appears to be not proxying correctly within NodeJS/Express.

I am 100% sure that my backend (springboot) server is returning the correct response type because it works in dev, and it works in production using a non-React/non-express client. Any suggestions?

Solution

The root issue had to do with the URL path for the event stream registration being different than the pattern matched in the express .all() call.