curl: 8.20 causes 100% CPU consumption in nheko

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Nixpkgs version

• Beta (26.05)

Describe the bug

A curl bug in 8.20 (curl/curl#21547) causes 100% CPU usage in nheko (Nheko-Reborn/nheko#2054), but also affects other packages (see curl bug report).

curl/curl@2a2104f was reported to fix the issue and would have to be cherry picked in nixpkgs.

Steps to reproduce

1. Upgrade NixOS beyond curlMinimal: 8.19.0 -> 8.20.0 #514706
2. Observe Constant 100% cpu usage Nheko-Reborn/nheko#2054 in nheko

Expected behaviour

Nheko does not consume a full core in a busy loop right from the start.

Screenshots

No response

Relevant log output

Additional context

No response

System metadata

• system: "x86_64-linux"
• host os: Linux 7.0.10, NixOS, 26.05 (Yarara), 26.05.20260528.ec942ba
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.34.7
• channels(root): "nixos"
• nixpkgs: /nix/store/lff22h6g4kvy848a7z8prfb0cgmy2hgy-source

Notify maintainers

@Scrumplex @balsoft @infinisil @pyrox0

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[Scrumplex]

See #522574

[rnhmjoj]

If you don't want to wait n weeks for staging to be merged and the channel to update:

  (self: super: {
      curl-fixed = super.curl.overrideAttrs (old: {
        doCheck = false;
        patches = [
          (self.writeText "fix-cpu-usage.patch" ''
            --- a/lib/multi.c
            +++ b/lib/multi.c
            @@ -2703,6 +2703,11 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
               Curl_uint32_bset_remove(&multi->dirty, data->mid);
             
               if(data == multi->admin) {
            +#ifdef ENABLE_WAKEUP
            +    /* Consume any pending wakeup signals before processing.
            +     * This is necessary for event based processing. See #21547 */
            +    (void)Curl_wakeup_consume(multi->wakeup_pair, TRUE);
            +#endif
             #ifdef USE_RESOLV_THREADED
                 Curl_async_thrdd_multi_process(multi);
             #endif
          '')
        ];
      });
      coeurl = super.coeurl.override { curl = self.curl-fixed; };
      nheko = super.nheko.override { curl = self.curl-fixed; };
  })

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The fix has landed in 26.05.