metrics: add stream api for system info

src/routes/system.js

@@ -9,6 +9,7 @@ exports = module.exports = {
     getLogs,
     getLogStream,
     getMetrics,
+    getMetricStream,
     getBlockDevices,
     getCpus,
 };
@@ -130,6 +131,30 @@ async function getMetrics(req, res, next) {
     next(new HttpSuccess(200, result));
 }
 
+async function getMetricStream(req, res, next) {
+    if (req.headers.accept !== 'text/event-stream') return next(new HttpError(400, 'This API call requires EventStream'));
+
+    const [error, metricStream] = await safe(metrics.getSystemStream());
+    if (error) return next(BoxError.toHttpError(error));
+
+    res.writeHead(200, {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache',
+        'Connection': 'keep-alive',
+        'X-Accel-Buffering': 'no', // disable nginx buffering
+        'Access-Control-Allow-Origin': '*'
+    });
+    res.write('retry: 3000\n');
+    res.on('close', () => metricStream.destroy());
+    metricStream.on('data', function (data) {
+        const obj = JSON.parse(data);
+        const sse = `data: ${JSON.stringify(obj)}\n\n`;
+        res.write(sse);
+    });
+    metricStream.on('end', res.end.bind(res));
+    metricStream.on('error', res.end.bind(res, null));
+}
+
 async function getBlockDevices(req, res, next) {
     const [error, devices] = await safe(system.getBlockDevices());
     if (error) return next(new HttpError(500, error));