hyper::Error(IncompleteMessage) on vercel dev

[platy]

I'm running the local dev server with vercel CLI version 37.14.0

I'm running tests against it and after handling quite a few requests, maybe 1000, the test requests will start to hang, with no response coming back from the vercel dev server. In the vercel dev server log I see:

Error: hyper_util::client::legacy::Error(SendRequest, hyper::Error(IncompleteMessage))

Once I've had one of these errors, they will become more frequent - suggesting that each failure is taking some resource away, like maybe I'm losing a thread in the tokio reactor. After I've had the first error, I can definitely get the error by making a single request at a time. But it might be that I've only triggered the first when it's been handling requests in parallel.

Subsequent errors could be:

Error: hyper_util::client::legacy::Error(SendRequest, hyper::Error(BodyWrite, Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }))

I've tried putting my whole handler into tokio::task::spawn_blocking as I worried that it's taking too long and preventing hyper from maintaining connections - but I'm still getting the issue