Crash when using libcurl with new hyper + rustls backend

Hi, Curl added a new TLS backend that is written in Rust recently. If you are using Mac, you can install it by running "brew install --HEAD meterup/safe/curl", or view the specific compilation flags I passed to curl, here: https://github.com/meterup/homebrew-safe/blob/main/Formula/curl.rb

If you are on Linux, you can use these instructions to build libcurl with rustls: https://github.com/abetterinternet/crustls/wiki/Building-curl-with-crustls-and-Hyper

When I compile Git using this curl, I get a segfault when running "git fetch https://go.googlesource.com/tools"

* thread #1, queue = 'com.apple.main-thread', stop reason =
EXC_BAD_ACCESS (code=1, address=0x8)
  * frame #0: 0x00000001000e2b58 git-remote-https`strbuf_grow + 16
    frame #1: 0x00000001000e3020 git-remote-https`strbuf_add + 27
    frame #2: 0x00000001000076d5 git-remote-https`fwrite_buffer + 27
    frame #3: 0x00000001002ebfba libcurl.4.dylib`Curl_hyper_stream + 594
    frame #4: 0x000000010032fdf8 libcurl.4.dylib`Curl_readwrite + 203
    frame #5: 0x0000000100319a80 libcurl.4.dylib`multi_runsingle + 2113
    frame #6: 0x00000001003191c6 libcurl.4.dylib`curl_multi_perform + 113
    frame #7: 0x00000001000094cb git-remote-https`step_active_slots + 25
    frame #8: 0x0000000100009532 git-remote-https`run_active_slot + 67
    frame #9: 0x00000001000097fd git-remote-https`run_one_slot + 41
    frame #10: 0x000000010000bb06 git-remote-https`http_request + 1630
    frame #11: 0x00000001000099b7 git-remote-https`http_request_reauth + 34
    frame #12: 0x0000000100006131 git-remote-https`discover_refs + 625
    frame #13: 0x00000001000053fc git-remote-https`cmd_main + 4484
    frame #14: 0x000000010000ce55 git-remote-https`main + 130
    frame #15: 0x00007fff699fbcc9 libdyld.dylib`start + 1
    frame #16: 0x00007fff699fbcc9 libdyld.dylib`start + 1

I had previously reported this issue to curl here, which includes a number of useful pieces of information including the contents of each register at the time of the crash. https://github.com/curl/curl/issues/6619

The latest comment on that issue suggests git may not be setting curl flags appropriately, which is why I am raising an issue here. I'm not great at C programming and have not been able to sort out what's going on myself, unfortunately.

Here's some more information about my git installation:

[System Info] git version: git version 2.30.1 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Darwin 19.6.0 Darwin Kernel Version 19.6.0: Tue Jan 12 22:13:05 PST 2021; root:xnu-6153.141.16~1/RELEASE_X86_64 x86_64 compiler info: clang: 12.0.0 (clang-1200.0.32.28) libc info: no libc information available $SHELL (typically, interactive shell): /usr/local/bin/zsh

Hope this helps, Kevin

On Tue, 23 Feb 2021, Kevin Burke wrote:

The hyper backend in curl is still considered experimental and it doesn't even pass all curl's own tests yet. Before it does that, I'm not sure it is constructive to bring problems to libcurl users like git since if the problems can't be produced with the built-in libcurl HTTP code, they seem likely to rather be libcurl internal problems.