Tests relying on reqwest::Client may fail with "dispatch task is gone: runtime dropped the dispatch task"

[rami3l]

Verification

• I searched for recent similar issues at https://github.com/rust-lang/rustup/issues?q=is%3Aissue+is%3Aopen%2Cclosed and found no duplicates.
• I am on the latest version of Rustup according to https://github.com/rust-lang/rustup/tags and am still able to reproduce my issue.

Problem

This is causing irregular failures for different CI platforms:

• Linux
  • https://github.com/rust-lang/rustup/actions/runs/9303236385/job/25605096671
  • https://github.com/rust-lang/rustup/actions/runs/9354772182/job/25748366479
  • https://github.com/rust-lang/rustup/actions/runs/9337787790/job/25700115067
  • https://github.com/rust-lang/rustup/actions/runs/9343224087/job/25712479916
• Windows
  • https://github.com/rust-lang/rustup/actions/runs/9335696949/job/25695378538

The error message here is identical (although the exact test that failed might differ):

running 395 tests
...
test suite::cli_exact::check_updates_with_update ... FAILED
error: could not download file from 'https://static.rust-lang.org/rustup/release-stable.toml' to '/tmp/rustup-updateD58GcC/release-stable.toml': failed to make network request: error sending request for url (https://static.rust-lang.org/rustup/release-stable.toml): client error (SendRequest): dispatch task is gone: runtime dropped the dispatch task

Notes

Possibly related to hyperium/hyper#2312, Azure/azure-sdk-for-rust#1550 or fussybeaver/bollard#387 (comment).

I'm pretty sure that #3367 has caused this.

[rami3l]

According to the error message format and my IDE searching the current codebase, this is a RustupError::DownloadingFile. This kind error message can only be emitted from here:

rustup/src/utils/utils.rs

Lines 154 to 190 in 6d43761

	pub(crate) async fn download_file_with_resume(
	url: &Url,
	path: &Path,
	hasher: Option<&mut Sha256>,
	resume_from_partial: bool,
	notify_handler: &dyn Fn(Notification<'_>),
	) -> Result<()> {
	use download::DownloadError as DEK;
	match download_file_(url, path, hasher, resume_from_partial, notify_handler).await {
	Ok(_) => Ok(()),
	Err(e) => {
	if e.downcast_ref::<std::io::Error>().is_some() {
	return Err(e);
	}
	let is_client_error = match e.downcast_ref::<DEK>() {
	// Specifically treat the bad partial range error as not our
	// fault in case it was something odd which happened.
	Some(DEK::HttpStatus(416)) => false,
	Some(DEK::HttpStatus(400..=499)) | Some(DEK::FileNotFound) => true,
	_ => false,
	};
	Err(e).with_context(|| {
	if is_client_error {
	RustupError::DownloadNotExists {
	url: url.clone(),
	path: path.to_path_buf(),
	}
	} else {
	RustupError::DownloadingFile {
	url: url.clone(),
	path: path.to_path_buf(),
	}
	}
	})
	}
	}
	}