Add support for customizing Astral mirror URLs

Summary

Hello!

Following the introduction of an Astral mirror which is used to fetch Ruff release metadata, Ruff, CPython and uv itself, I was wondering whether it could be made possible to customize these URLs.

In isolated environments, access to github.com or releases.astral.sh might not permitted, and it is currently impossible to proxy requests to proxy repositories or internal mirrors. Thus, it is impossible to download Ruff using uv, uv cannot update itself, and the uv version must be provided explicitly when installing uv using its standalone installer.

I believe that adding support for customizing the base URL of the Astral mirror could solve these issues.

I know that the updater does not fetch uv release metadata and uv archives from an Astral mirror yet, but I believe that this is already on Astral's roadmap.

Design-wise, I believe that adding configuration support using a single environment variable would be enough.

Example

Considering that UV_ASTRAL_MIRROR_URL could be set to customize the base URL of the Astral mirror, it could be used as such:

$ curl https://github.com/
curl: (6) Could not resolve host: github.com
$ curl https://releases.astral.sh/
curl: (6) Could not resolve host: releases.astral.sh
$ export UV_ASTRAL_MIRROR_URL="https://nexus.example.com/repository/releases.astral.sh"
$ uv python install 3.14  # uv fetches CPython from the proxy repository.
$ uv format  # uv fetches Ruff release metadata and Ruff from the proxy repository.
$ uv self update # The updater fetches uv release metadata and uv from the proxy repository.

Some extra context:

Current status of what's fetched from the mirror and what isn't is tracked under Fetch release assets from releases.astral.sh first #18503
You can customize UV_DOWNLOAD_URL when fetching uv using the standalone installer scripts, in which case the mirror won't be used
There's also UV_INSTALLER_GITHUB_BASE_URL which apparently uv self update also respects
For Python downloads there's this setting that already controls the mirror URL, but I don't think there's an environment variable
Fetching of Ruff isn't configurable at all at the moment

Some extra context:

* Current status of what's fetched from the mirror and what isn't is tracked under [Fetch release assets from `releases.astral.sh` first #18503](https://github.com/astral-sh/uv/issues/18503)

* You can customize [`UV_DOWNLOAD_URL`](https://docs.astral.sh/uv/reference/environment/#uv_download_url) when fetching uv using the standalone installer scripts, in which case the mirror won't be used

* There's also [`UV_INSTALLER_GITHUB_BASE_URL`](https://docs.astral.sh/uv/reference/environment/#uv_installer_github_base_url) which apparently `uv self update` also respects

* For Python downloads there's [this setting](https://docs.astral.sh/uv/reference/settings/#python-install-mirror) that already controls the mirror URL, but I don't think there's an environment variable

* Fetching of Ruff isn't configurable at all at the moment

Thank you for the quick answer!

UV_DOWNLOAD_URL and UV_PYTHON_INSTALL_MIRROR can be used to make it possible to install uv and CPython, but it remains impossible to run updates. UV_INSTALLER_GITHUB_BASE_URL cannot be used in environments without access to GitHub or GitHub Enterprise as the updater uses the GitHub REST API to fetch release metadata.

Because UV_DOWNLOAD_URL includes the version to install and because there is no solution to make uv self update work in isolated environments, uv needs to be reinstalled regularly to keep up-to-date.

I believe that #9134 (Sonatype Nexus Repository) and #16519 (JFrog Artifactory) are related and would be solved with the resolution of the current issue.

Congrats on completing #18503! It makes it easier to install the latest versions of uv. Now that everything (?) has been migrated to releases.astral.sh, do you believe that such configuration could be implemented?

An unmentioned issue with GitHub-related environment variables is that any path is stripped and only the domain name is kept. This makes sense but it makes it impossible to use with proxy repositories.

Yeah I think this is a reasonable feature to implement.

That would effectively resolve these: #9134 #16519 #17255 #15970

Add Astral mirror URL override (astral-sh#19206)

Thank you for your work on this, the new env var is very useful !

Would it be possible for the install script to support it as well ? It contains

if [ -n "${UV_DOWNLOAD_URL:-}" ]; then
    ARTIFACT_DOWNLOAD_URLS="$UV_DOWNLOAD_URL"
elif [ -n "${INSTALLER_DOWNLOAD_URL:-}" ]; then
    ARTIFACT_DOWNLOAD_URLS="$INSTALLER_DOWNLOAD_URL"
elif [ -n "${UV_INSTALLER_GHE_BASE_URL:-}" ]; then
    INSTALLER_BASE_URL="$UV_INSTALLER_GHE_BASE_URL"
    ARTIFACT_DOWNLOAD_URLS="${INSTALLER_BASE_URL}/astral-sh/uv/releases/download/0.11.14"
elif [ -n "${UV_INSTALLER_GITHUB_BASE_URL:-}" ]; then
    INSTALLER_BASE_URL="$UV_INSTALLER_GITHUB_BASE_URL"
    ARTIFACT_DOWNLOAD_URLS="${INSTALLER_BASE_URL}/astral-sh/uv/releases/download/0.11.14"
else
    ARTIFACT_DOWNLOAD_URLS="https://releases.astral.sh/github/uv/releases/download/0.11.14 https://github.com/astral-sh/uv/releases/download/0.11.14"
fi

So there is no path to installing the latest version from a mirror

something in that vein:

ARTIFACT_DOWNLOAD_URLS="${UV_ASTRAL_MIRROR_URL:-https://releases.astral.sh}/github/uv/releases/download/0.11.14 https://github.com/astral-sh/uv/releases/download/0.11.14"

would allow that

I don't fully understand why the existing env vars aren't enough for the standalone installer. Keep in mind that an installer is always tied to a particular version (the hashes of that version's binaries are embedded within the script).

Right, let me start by clarifying this is purely for convenience

I'm trying to give our users installation instructions similar to curl -LsSf https://astral.sh/uv/install.sh | sh, in an environment where astral.sh can't be reached directly. The goal is "install the latest version without knowing what the latest version number is".

The latest installer is available at https://releases.astral.sh/installers/uv/latest/uv-installer.sh, which is mirrored at https://our-mirror.our-company.com/installers/uv/latest/uv-installer.sh

But there is currently no variable we can set to make the installer pull the uv binaries for the latest version from our mirror - we need to either:

specify ARTIFACT_DOWNLOAD_URLS with the full URL, including the version (so this is no longer "whatever the latest version is"
use sed or similar to replace https://releases.astral.sh with https://our-mirror.our-company.com, which seems a bit brittle

So reading ARTIFACT_DOWNLOAD_URLS would allow us to go from:

curl -LsSf https://our-mirror.our-company.com/installers/uv/latest/uv-installer.sh | sed 's#https://releases.astral.sh#hhttps://our-mirror.our-company.com/astral#g' | sh

to

curl -LsSf https://our-mirror.our-company.com/installers/uv/latest/uv-installer.sh  | sh

This is a bit of an edge case, but might be worth considering for consistency with UV_INSTALLER_GITHUB_BASE_URL / UV_INSTALLER_GHE_BASE_URL (both allow setting a base URL without specifying the version, but rely on the github releases API)

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Add support for customizing Astral mirror URLs #18525

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