git push with http/2 sometimes hangs with "17 bytes stray data"

Question

I'm using git-http-backend behind apache and some, but not all, users are saying that git push hangs for them. After enabling GIT_TRACE=1 GIT_CURL_VERBOSE=1, we see that they are using http/2 and there is a suspicious line that says

17 bytes stray data read before trying h2 connection

When I ask them to force http/1.1, the problem goes away. Wireshark doesn't seem to help since the data is encrypted and I'm out of ideas on how to debug this issue. Any ideas on how to proceed would be very helpful!

Why would there be stray data with http/2 and is there anything I can do to debug this issue?

Answer 1

You must have seen this, which recommends:

git config --local http.version HTTP/1.1

But it also mention "an HTTP/2 issue of some kind with some versions of curl or git"

Try and see if updating curl/git on the server side, and Git on the client side would be enough.