Can't add a file from stdin

[roberth]

Describe the bug

nix store add-file can't add a file from stdin.

Steps To Reproduce

$ echo hi | ./outputs/out/bin/nix store add-file /dev/stdin
error: ca hash mismatch importing path '/nix/store/c3cgy7lnh6ni2kqvsxqblyz2pzb2hl2a-stdin';
         specified: sha256:1r3v22qkypccqifzbww5lrn6hf1chi23m6zzkyvb8bvg457nxslq
         got:       sha256:0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73

It seems that it can add the empty file, but only the empty file

$ true | nix store add-file /dev/stdin
/nix/store/gzm5hrm4a70c5kard6v2792hpk07b1jy-stdin

Expected behavior

Print a store path.

Probably it needs to traverse the stream twice, which doesn't work for a pipe.
Three solutions

• write to temporary file first. This won't go out of memory, but can be expensive
• read everything into memory first.
• any of the above, but only when the fd doesn't allow seeking

Don't we have a Sink or Source that retains the contents in memory until it reaches a certain size and then writes it all to disk? If not, we should.

nix-env --version output

Happens with my system nix

$ nix-env --version
nix-env (Nix) 2.11.1

.. and also with a recently built master nix 2.14pre

Additional context

Priorities

Add 👍 to issues you find important.

[fricklerhandwerk]

Triaged in the Nix team meeting 2023-02-17:

• relevant for stabilsation as a global concern
• we may or may not want to support pipes
• have to make a design decision
• postponed, to be addressed together with other global issues

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-02-17-nix-team-meeting-minutes-33/25624/1