100% CPU usage after HTTPS fetch requests in node:http server (SSL connection pooling bug) #25430
Description
What version of Bun is running?
1.3.4
What platform is your computer?
Darwin 25.1.0 arm64 arm
What steps can reproduce the bug?
When using node:http to create an HTTP server that makes outbound HTTPS fetch() requests, CPU usage spikes to 100% and stays there indefinitely after requests complete.
Root cause: SSL socket connection pooling causes pooled sockets to continuously report as "readable" to the event loop (kevent64/epoll), even when there's no application data. This results in busy-polling.
Affected versions: Bun 1.3.4 (likely affects earlier versions too)
Platform: macOS (darwin), likely also Linux
Impact: Production servers become unresponsive, high resource usage, potential crashes.
// cpu-bug-repro.js
// Run with: bun cpu-bug-repro.js
// Then in another terminal: curl http://localhost:3456/
// Watch CPU: top -pid $(pgrep -f cpu-bug-repro)
const http = require("node:http");
const server = http.createServer(async (req, res) => {
console.log(`${new Date().toISOString()} - ${req.method} ${req.url}`);
if (req.url === "/") {
// Make HTTPS fetch requests - triggers SSL connection pooling
const results = await Promise.all([
fetch("https://jsonplaceholder.typicode.com/posts/1").then(r => r.json()).catch(() => ({})),
fetch("https://jsonplaceholder.typicode.com/posts/2").then(r => r.json()).catch(() => ({})),
fetch("https://jsonplaceholder.typicode.com/users/1").then(r => r.json()).catch(() => ({})),
fetch("https://api.github.com/repos/oven-sh/bun", {
headers: { "User-Agent": "bun-test" }
}).then(r => r.json()).catch(() => ({})),
]);
res.writeHead(200, { "Content-Type": "application/json" });
res.end(JSON.stringify({ fetched: results.length }));
} else {
res.writeHead(404);
res.end();
}
});
server.listen(3456, () => {
console.log(`
=======================================================
Bun 100% CPU Bug Reproduction
=======================================================
Server: http://localhost:3456
Bun version: ${Bun.version}
Steps:
1. curl http://localhost:3456/
2. Watch CPU: top -pid $(pgrep -f cpu-bug-repro)
Expected: CPU returns to ~0% after request
Actual: CPU stays at 100% indefinitely
=======================================================
`);
});
then on another terminal
bun cpu-bug-repro.js
for i in {1..10}; do curl -s http://localhost:3456/ & done; wait
Watch the CPU stays at 100%
What is the expected behavior?
CPU should go back to idle 0%
What do you see instead?
CPU stays at 100%
Additional information
No response