NixOS/nix

fetchTree: use last-modified HTTP header where possible

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#9,067 opened on Sep 29, 2023

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featurefetchinggood first issue

Description

Is your feature request related to a problem? Please describe.

Currently fetchTree with type=tarball+http(s) gets lastModified from the mtime of the tarball contents. Some formats such as zip do not include this metadata, so lastModified ends up being incorrectly set to the current time.

type=file+http(s) does not set lastModified at all.

Describe the solution you'd like

Most webservers, when serving static files, will send a last-modified header set to the mtime of the served file. We could set lastModified to this value, or use it as fallback when mtime of contents is absent.

Describe alternatives you've considered

Do not set lastModified when mtime metadata is not present in archives. This should probably be done anyway when neither mtime nor last-modified is present.

Additional context

Priorities

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Contributor guide

Tech stack
cpp
Domain
backendcli
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++HTTP basicsNix source structure
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Investigate the fetchTree implementation in src/libfetchers/ (likely tarball.cc and file.cc). Look for how lastModified is currently set and where HTTP headers are available. Check if the HTTP response already passes headers; if not, modify the fetcher to parse the last modified header and use it as fallback when other mtime is absent. Consider edge cases where the header is missing or invalid.
fetchTree: use last-modified HTTP header where possible · NixOS/nix#9067 | Good First Issue