vapor: Collecting the request body sometimes hangs

Describe the bug

A route that .collects a request body hangs under certain conditions.

To Reproduce

Download the attached Vapor project hanging-collector.zip and unpack it. Then follow the instructions inreadme.md that’s found in the root of the project. I’ve copied most of the instructions here.

Prepare

1. Start the app:

$ swift run Run serve --port 7687

1. Upload the sample image:

$ curl -i -T ./sample.jpg -X PUT http://127.0.0.1:7687/hanger

This should work out ok: there’s a copy of sample.jpg in /tmp/pix/hanger.

Reproduce the hang

1. Start the app

$ swift run Run serve --port 7687

1. GET the image

curl -i http://127.0.0.1:7687/hanger

1. PUT the image

$ curl -i -T ./sample.jpg -X PUT http://127.0.0.1:7687/hanger

Often this will be enough. The vapor app has logged the PUT request but curl will now hang, and running lsof -i -nP will show the open connection:

$ lsof -i -nP
COMMAND     PID  USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
...
Run       22462 malte   12u  IPv4 0xd3a42b18da250499      0t0  TCP 127.0.0.1:7687 (LISTEN)
Run       22462 malte   13u  IPv4 0xd3a42b18da24e4d1      0t0  TCP 127.0.0.1:7687->127.0.0.1:55955 (ESTABLISHED)
curl      22503 malte    6u  IPv4 0xd3a42b18d947ef69      0t0  TCP 127.0.0.1:55955->127.0.0.1:7687 (ESTABLISHED)

Stopping the app now takes some time. After about 10 seconds the app quits with the following message:

[ ERROR ] Could not stop HTTP server: Abort.500: Server stop took too long.
ERROR: Cannot schedule tasks on an EventLoop that has already shut down. This will be upgraded to a forced crash in future SwiftNIO versions.

The hang is intermittent. I often have to retry from step 1 for the hang to occur. It’s important that the app is restarted!

Expected behavior

The PUT request should never hang.

Environment

• Vapor Framework version: 4.67.1
• Vapor Toolbox version: 18.6.0
• OS version: macOS 12.6.1 (21G217)

$ swift --version
swift-driver version: 1.62.15 Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51)
Target: arm64-apple-macosx12.0

I’m on an M2 MacBook Air running Xcode Version 14.1 (14B47b).