`builtins.fetchTarball` fails with a large archive when url starts with `file://`

Describe the bug

Using builtins.fetchTarball with a url starting with file:// that references a file larger than 4 GiB results in nix crashing.

Note that I wasn't able to test this with the typical https:// url scheme, so it may have the same bug, but I suspect this bug only applies to file://.

Steps To Reproduce

1. Create a tar archive larger than 4 GiB For testing I used the following shell command to create the archive

$ dd if=/dev/urandom of=random.bin bs=64M count=64 iflag=fullblock && tar -cf random.tar random.bin

1. Use builtins.fetchTarball to fetch the archive

$ nix eval --expr "builtins.fetchTarball {url=\"file://$PWD/random.tar\"; sha256=\"\";}"

This hangs for a while and then fails. Here is the most relevant (and last) line of the output:

error: appending to git packfile index: failed to mmap. Could not write data: Cannot allocate memory (libgit2 error code = 2)

In this case, I'd expect nix to complain about a hash mismatch, but it doesn't.

Expected behavior

Nix to both extract the tarball to the store, and not crash.

Metadata

$ nix-env --version
nix-env (Nix) 2.34.8

Additional context

The bug didn't occur when I tried fetching an archive with a size of 2 GiB.

I have more than 8 GiB of memory available when nix crashes, so it shouldn't be running out of memory. The same goes for disk space.

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates
• reviewed the contributing guide

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