Function download 

pub async fn download(
    registry: &str,
    name: &str,
    version: &str,
    max_bytes: u64,
) -> Result<Vec<u8>, PackageError>

Downloads name at version from registry, refusing a tarball larger than max_bytes.

Errors

When the server does not fetch packages, the name or version is malformed, the registry does not have that version, the download is too large, or the registry cannot be reached.