[rami3l]

Closes #5188 via reusing the infrastructure provided by DownloadCfg for self-updates, which now handles various common concerns such as retrying and hash checking.

This patch adds a requirement for the release server to store rustup-init[.EXE].sha256 files as well, which our official server already ships today. By falling back to the old logic only when .sha256 returns 404, this design should be a good compromise between compatibility and convenience.

Concerns

• A proper fallback will need to be implemented when a 404 is returned while downloading the sha256, since this behavior is inconsistent across mirrors:
  • Official: https://static.rust-lang.org/rustup/archive/1.29.2/aarch64-pc-windows-msvc/rustup-init.exe.sha256 is available.
  • USTC: https://mirrors.ustc.edu.cn/rust-static/rustup/archive/1.29.2/aarch64-pc-windows-msvc/rustup-init.exe.sha256 is hidden but is downloadable.
  • TUNA: https://mirrors.tuna.tsinghua.edu.cn/rustup/rustup/archive/1.29.2/aarch64-pc-windows-msvc/rustup-init.exe.sha256 gives a 404.
  • ZJU: https://mirrors.zju.edu.cn/rustup/rustup/archive/1.29.2/aarch64-pc-windows-msvc/rustup-init.exe.sha256 gives a 404.
  • I don't think we should extend the fallback to any other cases than 404.
• The test fixture will need to be updated to include the sha256 files.
• A special test case will need to be created to explicitly omit the sha256 files.

[djc]

LGTM.

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[Copilot]

🟡 Changes recommended

A moderate active finding remains because malformed or truncated mirror hash responses can panic during self-update instead of returning a normal download error.

1 open issue

• Validate checksum response before slicing to avoid panics · New

What changed in this PR

This pull request routes rustup self-update downloads through DownloadCfg, adding checksum verification, resumable downloads, shared retry handling, and a 404-only fallback for mirrors without .sha256 files.

Changes:

• Added checksum-aware, retryable self-update downloads with compatibility fallback.
• Centralized retry configuration and download behavior in DownloadCfg.
• Updated test fixtures and self-update tests for checksum files and missing-checksum behavior.

Open review findings:

• Moderate (2 votes): Validate malformed or truncated .sha256 responses before slicing to avoid a panic.
• Moderate (1 vote): Add integration coverage for checksum-integrity failures.
• Moderate (1 vote): Add end-to-end coverage for resuming an interrupted self-update download.

File	Description
tests/​suite/​cli_self_upd.rs	Adds coverage for missing checksum files and clarifies self-update test names.
src/​test/​clitools.rs	Generates .sha256 files for self-update test fixtures.
src/​download/​mod.rs	Exposes DownloadError for checksum fallback handling.
src/​dist/​manifestation.rs	Reuses shared retry behavior for component downloads.
src/​dist/​download.rs	Adds shared retry configuration and retrying download support.
src/​cli/​self_update.rs	Uses checksum-based DownloadCfg downloads with retrying and a 404 compatibility fallback.

_{Review effort: Lite}

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