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[worker] startCpuProfile can return invalid JSON for RegExp frames #67097
Description
Version
Node.js v25.9.0
Reproduction
import { Worker } from "node:worker_threads";
const source = [
'const re = new RegExp("^(\\\\d{6})");',
"function work() {",
" let matches = 0;",
" for (let i = 0; i < 30000; i++) if (re.test(String(i))) matches++;",
" return matches;",
"}",
"setInterval(work, 0);",
].join("\n");
const worker = new Worker(source, { eval: true });
await new Promise((resolve, reject) => {
worker.once("online", resolve);
worker.once("error", reject);
});
try {
const handle = await worker.startCpuProfile();
await new Promise((resolve) => setTimeout(resolve, 450));
const profileJson = await handle.stop();
JSON.parse(profileJson);
} finally {
await worker.terminate();
}
Actual result
The stop call returns a string, and JSON.parse throws SyntaxError: Bad escaped character in JSON. The malformed callFrame.functionName is RegExp: ^(\d{6}); its backslash is not escaped in the JSON string.
Expected result
The returned profile string should be valid JSON, or the API should return a structured profile object.
Control
For the same workload, an Inspector Profiler.stop response was an object and successfully round-tripped through JSON.stringify followed by JSON.parse.
Activity
shahinsamiur commentedon Oct 29, 2026
Hello, I would like to work on this problem. I will look into the reason why
worker.startCpuProfile()can produce invalid JSON because of backslashes in the RegExp frames, and try to work on a fix for this issue along with a regression test to make sure that the output is valid JSON.shahinsamiur commentedon Oct 29, 2026
The problem seems to be the serialization of CPU profile where some strings are written to JSON without escaping the special characters. In case the RegExp frame name contains a backslash, the JSON created may be invalid and cause an error
SyntaxErrorinJSON.parse().I have raised PR #67103 for the same where JSON string escaping will be added to
OutputStreamWriterfor function names, script URLs and deoptimization reasons along with a regression test for worker CPU profiles with RegExp frames.The objective here is to make sure that
worker.startCpuProfile()returns valid JSON.