git-http-backend errors under IIS

git-http-backend errors under IIS

[forums]

I’m getting errors trying to execute simple git clone from IIS-hosted
git-http-backend to a local folder.

Setup:
Host: fresh install of x64 Windows Server 2022 Standard on i7-11700K @
3.60GHz with 32GB RAM & 2x 1TB SSD drives, named ‘zeus’, IIS version 10.0.
Host has the latest 64-bit git version 2.46.0.windows.1
Client: either the same machine or Hyper-V VM on the same box with 1 Virtual
CPU & 4GB of RAM running Windows 10 Enterprise LTSC 21H2. VM has 64-bit git
version 2.37.0.windows.1

IIS is configured with dedicated ‘git’ website running on port 80 with its
own app pool and local ‘git’ user as identity. There’re no other sites on
that port and I stopped the rest of the sites anyway. The site has Anonymous
authentication disabled and Basic Authentication enabled with CGI
Impersonation ‘True’

Test git repository myproject.git was initialized from command window in the
host folder pointed to by IIS ‘git’ website using command:
git init --bare myproject.git using git version 2.46.0

Test case 1:
git clone http://zeus/myproject.git executed from the host command window
using test user credentials results in error:
>fatal: http://zeus/myproject.git/info/refs not valid: could not determine
hash algorithm; is this a git repository?<

Please note the path myproject.git/info/refs doesn’t even exist in the repo,
the folder myproject.git/info/ contains single file ‘exclude’ and nothing
else. 

Test case 2:
git clone http://zeus/myproject.git executed from the VM command window
using test user credentials results in error:
>fatal: unable to access 'http://zeus/myproject.git/': Header without colon<

If I execute the above commands with host Administrator credentials they
both succeed with correct warning (the repo was just initialized):
>warning: You appear to have cloned an empty repository.<

So far the issue sounds like some permissions problem, especially taking
into account when I tried to make test user member of the host
Administrators group both commands worked after iisreset.
Unfortunately I was unable to figure out what permission(s) are missing, the
user clearly passes authentication step and executes git-http-backend.exe as
I had different error when it was unable to.

What is really odd if I downgrade git version on the host to 2.44.0 then
everything starts working as expected for the test user as well even after I
removed it from Administrators group and performed iisreset, the rest was
the same:  the site / permissions / etc

I actually started from version 2.37.0 thinking may be it would make a
difference as I recalled the similar set up was working under 2.37.0 and to
my great surprise it worked indeed. Then I decided to ‘upgrade’ the version
and 2.44.0 was the latest one that worked from the versions I tried. I
believe I also tried 2.45.2 and it gave the same errors as 2.46.0 so I left
it at 2.44.0. I didn’t try any other version between 2.44.0 and 2.45.2.

Since this issue misleadingly looks like ‘permission’ one and the error
messages are really odd and it cost me a day to troubleshoot I decided to
publish it here to possibly spare someone major headache.

Please let me know if I’m missing something obvious or if it’s indeed a bug
that very well may be specific to my environment which triggers some racing
condition in the code. 
If there’s an interest in tracing this problem further I can easily
reproduce it as the system is not used for Production. The Portable version
2.46.0 has the same problem so switching back and forth between versions is
really simple, I just replace content of the git folder with another
version.

Thanks,
Michael.