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Colitu VPN
@colitu.com

Our Hysteria2 connections died about 60 seconds into every upload speed test. DNS kept working, web traffic didn't. The cause was a QUIC flow-control stall in the Hysteria server. We fixed it with about 37 lines of Go. 🧵

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Colitu VPN
@colitu.com

A speed-test server stops reading its upload but keeps the connection open. The unread data fills the connection's 20 MB flow-control window, so no stream can send anymore, not even new requests. UDP isn't flow-controlled, so everything looked healthy.

Colitu VPN
@colitu.com

The fix: if a write to the target makes no progress for 10 s, close it and release the window. Lab: the official server never recovers, the patched one in 7.8 s. On a phone: 4 speed tests over 160 s, no stall. Live on our servers, no app update needed.

Colitu VPN
@colitu.com

We sent it upstream with an integration test: github.com/HyNetworks/hysteria/pull/1703 github.com/XTLS/Xray-core/issues/7169 Full report: lab.colitu.com/research/hysteria2-stall-after-upload #QUIC #golang #opensource

github.comfix(core/server): close TCP targets that stop accepting data by colituvpn · Pull Request #1703 · HyNetworks/hysteriaFixes #1702 Problem A TCP target that stops reading but keeps its connection open blocks the copy from the stream into it. The stream's unread data keeps occupying the connection-level flow-con...