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    //! A `Source` for registry-based packages.
    //!
    //! # What's a Registry?
    //!
    //! [Registries] are central locations where packages can be uploaded to,
    //! discovered, and searched for. The purpose of a registry is to have a
    //! location that serves as permanent storage for versions of a crate over time.
    //!
    //! Compared to git sources (see [`GitSource`]), a registry provides many
    //! packages as well as many versions simultaneously. Git sources can also
    //! have commits deleted through rebasings where registries cannot have their
    //! versions deleted.
    //!
    //! In Cargo, [`RegistryData`] is an abstraction over each kind of actual
    //! registry, and [`RegistrySource`] connects those implementations to
    //! [`Source`] trait. Two prominent features these abstractions provide are
    //!
    //! * A way to query the metadata of a package from a registry. The metadata
    //!   comes from the index.
    //! * A way to download package contents (a.k.a source files) that are required
    //!   when building the package itself.
    //!
    //! We'll cover each functionality later.
    //!
    //! [Registries]: https://doc.rust-lang.org/nightly/cargo/reference/registries.html
    //! [`GitSource`]: super::GitSource
    //!
    //! # Different Kinds of Registries
    //!
    //! Cargo provides multiple kinds of registries. Each of them serves the index
    //! and package contents in a slightly different way. Namely,
    //!
    //! * [`LocalRegistry`] --- Serves the index and package contents entirely on
    //!   a local filesystem.
    //! * [`RemoteRegistry`] --- Serves the index ahead of time from a Git
    //!   repository, and package contents are downloaded as needed.
    //! * [`HttpRegistry`] --- Serves both the index and package contents on demand
    //!   over a HTTP-based registry API. This is the default starting from 1.70.0.
    //!
    //! Each registry has its own [`RegistryData`] implementation, and can be
    //! created from either [`RegistrySource::local`] or [`RegistrySource::remote`].
    //!
    //! [`LocalRegistry`]: local::LocalRegistry
    //! [`RemoteRegistry`]: remote::RemoteRegistry
    //! [`HttpRegistry`]: http_remote::HttpRegistry
    //!
    //! # The Index of a Registry
    //!
    //! One of the major difficulties with a registry is that hosting so many
    //! packages may quickly run into performance problems when dealing with
    //! dependency graphs. It's infeasible for cargo to download the entire contents
    //! of the registry just to resolve one package's dependencies, for example. As
    //! a result, cargo needs some efficient method of querying what packages are
    //! available on a registry, what versions are available, and what the
    //! dependencies for each version is.
    //!
    //! To solve the problem, a registry must provide an index of package metadata.
    //! The index of a registry is essentially an easily query-able version of the
    //! registry's database for a list of versions of a package as well as a list
    //! of dependencies for each version. The exact format of the index is
    //! described later.
    //!
    //! See the [`index`] module for topics about the management, parsing, caching,
    //! and versioning for the on-disk index.
    //!
    //! ## The Format of The Index
    //!
    //! The index is a store for the list of versions for all packages known, so its
    //! format on disk is optimized slightly to ensure that `ls registry` doesn't
    //! produce a list of all packages ever known. The index also wants to ensure
    //! that there's not a million files which may actually end up hitting
    //! filesystem limits at some point. To this end, a few decisions were made
    //! about the format of the registry:
    //!
    //! 1. Each crate will have one file corresponding to it. Each version for a
    //!    crate will just be a line in this file (see [`IndexPackage`] for its
    //!    representation).
    //! 2. There will be two tiers of directories for crate names, under which
    //!    crates corresponding to those tiers will be located.
    //!    (See [`cargo_util::registry::make_dep_path`] for the implementation of
    //!    this layout hierarchy.)
    //!
    //! As an example, this is an example hierarchy of an index:
    //!
    //! ```notrust
    //! .
    //! ├── 3
    //! │   └── u
    //! │       └── url
    //! ├── bz
    //! │   └── ip
    //! │       └── bzip2
    //! ├── config.json
    //! ├── en
    //! │   └── co
    //! │       └── encoding
    //! └── li
    //!     ├── bg
    //!     │   └── libgit2
    //!     └── nk
    //!         └── link-config
    //! ```
    //!
    //! The root of the index contains a `config.json` file with a few entries
    //! corresponding to the registry (see [`RegistryConfig`] below).
    //!
    //! Otherwise, there are three numbered directories (1, 2, 3) for crates with
    //! names 1, 2, and 3 characters in length. The 1/2 directories simply have the
    //! crate files underneath them, while the 3 directory is sharded by the first
    //! letter of the crate name.
    //!
    //! Otherwise the top-level directory contains many two-letter directory names,
    //! each of which has many sub-folders with two letters. At the end of all these
    //! are the actual crate files themselves.
    //!
    //! The purpose of this layout is to hopefully cut down on `ls` sizes as well as
    //! efficient lookup based on the crate name itself.
    //!
    //! See [The Cargo Book: Registry Index][registry-index] for the public
    //! interface on the index format.
    //!
    //! [registry-index]: https://doc.rust-lang.org/nightly/cargo/reference/registry-index.html
    //!
    //! ## The Index Files
    //!
    //! Each file in the index is the history of one crate over time. Each line in
    //! the file corresponds to one version of a crate, stored in JSON format (see
    //! the [`IndexPackage`] structure).
    //!
    //! As new versions are published, new lines are appended to this file. **The
    //! only modifications to this file that should happen over time are yanks of a
    //! particular version.**
    //!
    //! # Downloading Packages
    //!
    //! The purpose of the index was to provide an efficient method to resolve the
    //! dependency graph for a package. After resolution has been performed, we need
    //! to download the contents of packages so we can read the full manifest and
    //! build the source code.
    //!
    //! To accomplish this, [`RegistryData::download`] will "make" an HTTP request
    //! per-package requested to download tarballs into a local cache. These
    //! tarballs will then be unpacked into a destination folder.
    //!
    //! Note that because versions uploaded to the registry are frozen forever that
    //! the HTTP download and unpacking can all be skipped if the version has
    //! already been downloaded and unpacked. This caching allows us to only
    //! download a package when absolutely necessary.
    //!
    //! # Filesystem Hierarchy
    //!
    //! Overall, the `$HOME/.cargo` looks like this when talking about the registry
    //! (remote registries, specifically):
    //!
    //! ```notrust
    //! # A folder under which all registry metadata is hosted (similar to
    //! # $HOME/.cargo/git)
    //! $HOME/.cargo/registry/
    //!
    //!     # For each registry that cargo knows about (keyed by hostname + hash)
    //!     # there is a folder which is the checked out version of the index for
    //!     # the registry in this location. Note that this is done so cargo can
    //!     # support multiple registries simultaneously
    //!     index/
    //!         registry1-<hash>/
    //!         registry2-<hash>/
    //!         ...
    //!
    //!     # This folder is a cache for all downloaded tarballs (`.crate` file)
    //!     # from a registry. Once downloaded and verified, a tarball never changes.
    //!     cache/
    //!         registry1-<hash>/<pkg>-<version>.crate
    //!         ...
    //!
    //!     # Location in which all tarballs are unpacked. Each tarball is known to
    //!     # be frozen after downloading, so transitively this folder is also
    //!     # frozen once its unpacked (it's never unpacked again)
    //!     # CAVEAT: They are not read-only. See rust-lang/cargo#9455.
    //!     src/
    //!         registry1-<hash>/<pkg>-<version>/...
    //!         ...
    //! ```
    //!
    //! [`IndexPackage`]: index::IndexPackage

    use std::collections::HashSet;
    use std::fs;
    use std::fs::{File, OpenOptions};
    use std::io;
    use std::io::Read;
    use std::io::Write;
    use std::path::{Path, PathBuf};
    use std::task::{ready, Poll};

    use anyhow::Context as _;
    use cargo_util::paths::{self, exclude_from_backups_and_indexing};
    use flate2::read::GzDecoder;
    use serde::Deserialize;
    use serde::Serialize;
    use tar::Archive;
    use tracing::debug;

    use crate::core::dependency::Dependency;
    use crate::core::global_cache_tracker;
    use crate::core::{Package, PackageId, SourceId};
    use crate::sources::source::MaybePackage;
    use crate::sources::source::QueryKind;
    use crate::sources::source::Source;
    use crate::sources::PathSource;
    use crate::util::cache_lock::CacheLockMode;
    use crate::util::hex;
    use crate::util::interning::InternedString;
    use crate::util::network::PollExt;
    use crate::util::{restricted_names, CargoResult, Config, Filesystem, LimitErrorReader};

    /// The `.cargo-ok` file is used to track if the source is already unpacked.
    /// See [`RegistrySource::unpack_package`] for more.
    ///
    /// Not to be confused with `.cargo-ok` file in git sources.
    const PACKAGE_SOURCE_LOCK: &str = ".cargo-ok";

    pub const CRATES_IO_INDEX: &str = "https://github.com/rust-lang/crates.io-index";
    pub const CRATES_IO_HTTP_INDEX: &str = "sparse+https://index.crates.io/";
    pub const CRATES_IO_REGISTRY: &str = "crates-io";
    pub const CRATES_IO_DOMAIN: &str = "crates.io";

    /// The content inside `.cargo-ok`.
    /// See [`RegistrySource::unpack_package`] for more.
    #[derive(Deserialize, Serialize)]
    struct LockMetadata {
        /// The version of `.cargo-ok` file
        v: u32,
    }

    /// A [`Source`] implementation for a local or a remote registry.
    ///
    /// This contains common functionality that is shared between each registry
    /// kind, with the registry-specific logic implemented as part of the
    /// [`RegistryData`] trait referenced via the `ops` field.
    ///
    /// For general concepts of registries, see the [module-level documentation](crate::sources::registry).
    pub struct RegistrySource<'cfg> {
        /// A unique name of the source (typically used as the directory name
        /// where its cached content is stored).
        name: InternedString,
        /// The unique identifier of this source.
        source_id: SourceId,
        /// The path where crate files are extracted (`$CARGO_HOME/registry/src/$REG-HASH`).
        src_path: Filesystem,
        /// Local reference to [`Config`] for convenience.
        config: &'cfg Config,
        /// Abstraction for interfacing to the different registry kinds.
        ops: Box<dyn RegistryData + 'cfg>,
        /// Interface for managing the on-disk index.
        index: index::RegistryIndex<'cfg>,
        /// A set of packages that should be allowed to be used, even if they are
        /// yanked.
        ///
        /// This is populated from the entries in `Cargo.lock` to ensure that
        /// `cargo update somepkg` won't unlock yanked entries in `Cargo.lock`.
        /// Otherwise, the resolver would think that those entries no longer
        /// exist, and it would trigger updates to unrelated packages.
        yanked_whitelist: HashSet<PackageId>,
    }

    /// The [`config.json`] file stored in the index.
    ///
    /// The config file may look like:
    ///
    /// ```json
    /// {
    ///     "dl": "https://example.com/api/{crate}/{version}/download",
    ///     "api": "https://example.com/api",
    ///     "auth-required": false             # unstable feature (RFC 3139)
    /// }
    /// ```
    ///
    /// [`config.json`]: https://doc.rust-lang.org/nightly/cargo/reference/registry-index.html#index-configuration
    #[derive(Deserialize, Debug, Clone)]
    #[serde(rename_all = "kebab-case")]
    pub struct RegistryConfig {
        /// Download endpoint for all crates.
        ///
        /// The string is a template which will generate the download URL for the
        /// tarball of a specific version of a crate. The substrings `{crate}` and
        /// `{version}` will be replaced with the crate's name and version
        /// respectively.  The substring `{prefix}` will be replaced with the
        /// crate's prefix directory name, and the substring `{lowerprefix}` will
        /// be replaced with the crate's prefix directory name converted to
        /// lowercase. The substring `{sha256-checksum}` will be replaced with the
        /// crate's sha256 checksum.
        ///
        /// For backwards compatibility, if the string does not contain any
        /// markers (`{crate}`, `{version}`, `{prefix}`, or `{lowerprefix}`), it
        /// will be extended with `/{crate}/{version}/download` to
        /// support registries like crates.io which were created before the
        /// templating setup was created.
        ///
        /// For more on the template of the download URL, see [Index Configuration](
        /// https://doc.rust-lang.org/nightly/cargo/reference/registry-index.html#index-configuration).
        pub dl: String,

        /// API endpoint for the registry. This is what's actually hit to perform
        /// operations like yanks, owner modifications, publish new crates, etc.
        /// If this is None, the registry does not support API commands.
        pub api: Option<String>,

        /// Whether all operations require authentication. See [RFC 3139].
        ///
        /// [RFC 3139]: https://rust-lang.github.io/rfcs/3139-cargo-alternative-registry-auth.html
        #[serde(default)]
        pub auth_required: bool,
    }

    /// Result from loading data from a registry.
    pub enum LoadResponse {
        /// The cache is valid. The cached data should be used.
        CacheValid,

        /// The cache is out of date. Returned data should be used.
        Data {
            raw_data: Vec<u8>,
            /// Version of this data to determine whether it is out of date.
            index_version: Option<String>,
        },

        /// The requested crate was found.
        NotFound,
    }

    /// An abstract interface to handle both a local and remote registry.
    ///
    /// This allows [`RegistrySource`] to abstractly handle each registry kind.
    ///
    /// For general concepts of registries, see the [module-level documentation](crate::sources::registry).
    pub trait RegistryData {
        /// Performs initialization for the registry.
        ///
        /// This should be safe to call multiple times, the implementation is
        /// expected to not do any work if it is already prepared.
        fn prepare(&self) -> CargoResult<()>;

        /// Returns the path to the index.
        ///
        /// Note that different registries store the index in different formats
        /// (remote = git, http & local = files).
        fn index_path(&self) -> &Filesystem;

        /// Loads the JSON for a specific named package from the index.
        ///
        /// * `root` is the root path to the index.
        /// * `path` is the relative path to the package to load (like `ca/rg/cargo`).
        /// * `index_version` is the version of the requested crate data currently
        ///    in cache. This is useful for checking if a local cache is outdated.
        fn load(
            &mut self,
            root: &Path,
            path: &Path,
            index_version: Option<&str>,
        ) -> Poll<CargoResult<LoadResponse>>;

        /// Loads the `config.json` file and returns it.
        ///
        /// Local registries don't have a config, and return `None`.
        fn config(&mut self) -> Poll<CargoResult<Option<RegistryConfig>>>;

        /// Invalidates locally cached data.
        fn invalidate_cache(&mut self);

        /// If quiet, the source should not display any progress or status messages.
        fn set_quiet(&mut self, quiet: bool);

        /// Is the local cached data up-to-date?
        fn is_updated(&self) -> bool;

        /// Prepare to start downloading a `.crate` file.
        ///
        /// Despite the name, this doesn't actually download anything. If the
        /// `.crate` is already downloaded, then it returns [`MaybeLock::Ready`].
        /// If it hasn't been downloaded, then it returns [`MaybeLock::Download`]
        /// which contains the URL to download. The [`crate::core::package::Downloads`]
        /// system handles the actual download process. After downloading, it
        /// calls [`Self::finish_download`] to save the downloaded file.
        ///
        /// `checksum` is currently only used by local registries to verify the
        /// file contents (because local registries never actually download
        /// anything). Remote registries will validate the checksum in
        /// `finish_download`. For already downloaded `.crate` files, it does not
        /// validate the checksum, assuming the filesystem does not suffer from
        /// corruption or manipulation.
        fn download(&mut self, pkg: PackageId, checksum: &str) -> CargoResult<MaybeLock>;

        /// Finish a download by saving a `.crate` file to disk.
        ///
        /// After [`crate::core::package::Downloads`] has finished a download,
        /// it will call this to save the `.crate` file. This is only relevant
        /// for remote registries. This should validate the checksum and save
        /// the given data to the on-disk cache.
        ///
        /// Returns a [`File`] handle to the `.crate` file, positioned at the start.
        fn finish_download(&mut self, pkg: PackageId, checksum: &str, data: &[u8])
            -> CargoResult<File>;

        /// Returns whether or not the `.crate` file is already downloaded.
        fn is_crate_downloaded(&self, _pkg: PackageId) -> bool {
            true
        }

        /// Validates that the global package cache lock is held.
        ///
        /// Given the [`Filesystem`], this will make sure that the package cache
        /// lock is held. If not, it will panic. See
        /// [`Config::acquire_package_cache_lock`] for acquiring the global lock.
        ///
        /// Returns the [`Path`] to the [`Filesystem`].
        fn assert_index_locked<'a>(&self, path: &'a Filesystem) -> &'a Path;

        /// Block until all outstanding Poll::Pending requests are Poll::Ready.
        fn block_until_ready(&mut self) -> CargoResult<()>;
    }

    /// The status of [`RegistryData::download`] which indicates if a `.crate`
    /// file has already been downloaded, or if not then the URL to download.
    pub enum MaybeLock {
        /// The `.crate` file is already downloaded. [`File`] is a handle to the
        /// opened `.crate` file on the filesystem.
        Ready(File),
        /// The `.crate` file is not downloaded, here's the URL to download it from.
        ///
        /// `descriptor` is just a text string to display to the user of what is
        /// being downloaded.
        Download {
            url: String,
            descriptor: String,
            authorization: Option<String>,
        },
    }

    mod download;
    mod http_remote;
    mod index;
    pub use index::IndexSummary;
    mod local;
    mod remote;

    /// Generates a unique name for [`SourceId`] to have a unique path to put their
    /// index files.
    fn short_name(id: SourceId, is_shallow: bool) -> String {
        // CAUTION: This should not change between versions. If you change how
        // this is computed, it will orphan previously cached data, forcing the
        // cache to be rebuilt and potentially wasting significant disk space. If
        // you change it, be cautious of the impact. See `test_cratesio_hash` for
        // a similar discussion.
        let hash = hex::short_hash(&id);
        let ident = id.url().host_str().unwrap_or("").to_string();
        let mut name = format!("{}-{}", ident, hash);
        if is_shallow {
            name.push_str("-shallow");
        }
        name
    }

    impl<'cfg> RegistrySource<'cfg> {
        /// Creates a [`Source`] of a "remote" registry.
        /// It could be either an HTTP-based [`http_remote::HttpRegistry`] or
        /// a Git-based [`remote::RemoteRegistry`].
        ///
        /// * `yanked_whitelist` --- Packages allowed to be used, even if they are yanked.
        pub fn remote(
            source_id: SourceId,
            yanked_whitelist: &HashSet<PackageId>,
            config: &'cfg Config,
        ) -> CargoResult<RegistrySource<'cfg>> {
            assert!(source_id.is_remote_registry());
            let name = short_name(
                source_id,
                config
                    .cli_unstable()
                    .git
                    .map_or(false, |features| features.shallow_index)
                    && !source_id.is_sparse(),
            );
            let ops = if source_id.is_sparse() {
                Box::new(http_remote::HttpRegistry::new(source_id, config, &name)?) as Box<_>
            } else {
                Box::new(remote::RemoteRegistry::new(source_id, config, &name)) as Box<_>
            };

            Ok(RegistrySource::new(
                source_id,
                config,
                &name,
                ops,
                yanked_whitelist,
            ))
        }

        /// Creates a [`Source`] of a local registry, with [`local::LocalRegistry`] under the hood.
        ///
        /// * `path` --- The root path of a local registry on the file system.
        /// * `yanked_whitelist` --- Packages allowed to be used, even if they are yanked.
        pub fn local(
            source_id: SourceId,
            path: &Path,
            yanked_whitelist: &HashSet<PackageId>,
            config: &'cfg Config,
        ) -> RegistrySource<'cfg> {
            let name = short_name(source_id, false);
            let ops = local::LocalRegistry::new(path, config, &name);
            RegistrySource::new(source_id, config, &name, Box::new(ops), yanked_whitelist)
        }

        /// Creates a source of a registry. This is a inner helper function.
        ///
        /// * `name` --- Name of a path segment which may affect where `.crate`
        ///   tarballs, the registry index and cache are stored. Expect to be unique.
        /// * `ops` --- The underlying [`RegistryData`] type.
        /// * `yanked_whitelist` --- Packages allowed to be used, even if they are yanked.
        fn new(
            source_id: SourceId,
            config: &'cfg Config,
            name: &str,
            ops: Box<dyn RegistryData + 'cfg>,
            yanked_whitelist: &HashSet<PackageId>,
        ) -> RegistrySource<'cfg> {
            RegistrySource {
                name: name.into(),
                src_path: config.registry_source_path().join(name),
                config,
                source_id,
                index: index::RegistryIndex::new(source_id, ops.index_path(), config),
                yanked_whitelist: yanked_whitelist.clone(),
                ops,
            }
        }

        /// Decode the [configuration](RegistryConfig) stored within the registry.
        ///
        /// This requires that the index has been at least checked out.
        pub fn config(&mut self) -> Poll<CargoResult<Option<RegistryConfig>>> {
            self.ops.config()
        }

        /// Unpacks a downloaded package into a location where it's ready to be
        /// compiled.
        ///
        /// No action is taken if the source looks like it's already unpacked.
        ///
        /// # History of interruption detection with `.cargo-ok` file
        ///
        /// Cargo has always included a `.cargo-ok` file ([`PACKAGE_SOURCE_LOCK`])
        /// to detect if extraction was interrupted, but it was originally empty.
        ///
        /// In 1.34, Cargo was changed to create the `.cargo-ok` file before it
        /// started extraction to implement fine-grained locking. After it was
        /// finished extracting, it wrote two bytes to indicate it was complete.
        /// It would use the length check to detect if it was possibly interrupted.
        ///
        /// In 1.36, Cargo changed to not use fine-grained locking, and instead used
        /// a global lock. The use of `.cargo-ok` was no longer needed for locking
        /// purposes, but was kept to detect when extraction was interrupted.
        ///
        /// In 1.49, Cargo changed to not create the `.cargo-ok` file before it
        /// started extraction to deal with `.crate` files that inexplicably had
        /// a `.cargo-ok` file in them.
        ///
        /// In 1.64, Cargo changed to detect `.crate` files with `.cargo-ok` files
        /// in them in response to [CVE-2022-36113], which dealt with malicious
        /// `.crate` files making `.cargo-ok` a symlink causing cargo to write "ok"
        /// to any arbitrary file on the filesystem it has permission to.
        ///
        /// In 1.71, `.cargo-ok` changed to contain a JSON `{ v: 1 }` to indicate
        /// the version of it. A failure of parsing will result in a heavy-hammer
        /// approach that unpacks the `.crate` file again. This is in response to a
        /// security issue that the unpacking didn't respect umask on Unix systems.
        ///
        /// This is all a long-winded way of explaining the circumstances that might
        /// cause a directory to contain a `.cargo-ok` file that is empty or
        /// otherwise corrupted. Either this was extracted by a version of Rust
        /// before 1.34, in which case everything should be fine. However, an empty
        /// file created by versions 1.36 to 1.49 indicates that the extraction was
        /// interrupted and that we need to start again.
        ///
        /// Another possibility is that the filesystem is simply corrupted, in
        /// which case deleting the directory might be the safe thing to do. That
        /// is probably unlikely, though.
        ///
        /// To be safe, we deletes the directory and starts over again if an empty
        /// `.cargo-ok` file is found.
        ///
        /// [CVE-2022-36113]: https://blog.rust-lang.org/2022/09/14/cargo-cves.html#arbitrary-file-corruption-cve-2022-36113
        fn unpack_package(&self, pkg: PackageId, tarball: &File) -> CargoResult<PathBuf> {
            let package_dir = format!("{}-{}", pkg.name(), pkg.version());
            let dst = self.src_path.join(&package_dir);
            let path = dst.join(PACKAGE_SOURCE_LOCK);
            let path = self
                .config
                .assert_package_cache_locked(CacheLockMode::DownloadExclusive, &path);
            let unpack_dir = path.parent().unwrap();
            match fs::read_to_string(path) {
                Ok(ok) => match serde_json::from_str::<LockMetadata>(&ok) {
                    Ok(lock_meta) if lock_meta.v == 1 => {
                        self.config
                            .deferred_global_last_use()?
                            .mark_registry_src_used(global_cache_tracker::RegistrySrc {
                                encoded_registry_name: self.name,
                                package_dir: package_dir.into(),
                                size: None,
                            });
                        return Ok(unpack_dir.to_path_buf());
                    }
                    _ => {
                        if ok == "ok" {
                            tracing::debug!("old `ok` content found, clearing cache");
                        } else {
                            tracing::warn!("unrecognized .cargo-ok content, clearing cache: {ok}");
                        }
                        // See comment of `unpack_package` about why removing all stuff.
                        paths::remove_dir_all(dst.as_path_unlocked())?;
                    }
                },
                Err(e) if e.kind() == io::ErrorKind::NotFound => {}
                Err(e) => anyhow::bail!("unable to read .cargo-ok file at {path:?}: {e}"),
            }
            dst.create_dir()?;
            let mut tar = {
                let size_limit = max_unpack_size(self.config, tarball.metadata()?.len());
                let gz = GzDecoder::new(tarball);
                let gz = LimitErrorReader::new(gz, size_limit);
                let mut tar = Archive::new(gz);
                set_mask(&mut tar);
                tar
            };
            let mut bytes_written = 0;
            let prefix = unpack_dir.file_name().unwrap();
            let parent = unpack_dir.parent().unwrap();
            for entry in tar.entries()? {
                let mut entry = entry.with_context(|| "failed to iterate over archive")?;
                let entry_path = entry
                    .path()
                    .with_context(|| "failed to read entry path")?
                    .into_owned();

                // We're going to unpack this tarball into the global source
                // directory, but we want to make sure that it doesn't accidentally
                // (or maliciously) overwrite source code from other crates. Cargo
                // itself should never generate a tarball that hits this error, and
                // crates.io should also block uploads with these sorts of tarballs,
                // but be extra sure by adding a check here as well.
                if !entry_path.starts_with(prefix) {
                    anyhow::bail!(
                        "invalid tarball downloaded, contains \
                         a file at {:?} which isn't under {:?}",
                        entry_path,
                        prefix
                    )
                }
                // Prevent unpacking the lockfile from the crate itself.
                if entry_path
                    .file_name()
                    .map_or(false, |p| p == PACKAGE_SOURCE_LOCK)
                {
                    continue;
                }
                // Unpacking failed
                bytes_written += entry.size();
                let mut result = entry.unpack_in(parent).map_err(anyhow::Error::from);
                if cfg!(windows) && restricted_names::is_windows_reserved_path(&entry_path) {
                    result = result.with_context(|| {
                        format!(
                            "`{}` appears to contain a reserved Windows path, \
                            it cannot be extracted on Windows",
                            entry_path.display()
                        )
                    });
                }
                result
                    .with_context(|| format!("failed to unpack entry at `{}`", entry_path.display()))?;
            }

            // Now that we've finished unpacking, create and write to the lock file to indicate that
            // unpacking was successful.
            let mut ok = OpenOptions::new()
                .create_new(true)
                .read(true)
                .write(true)
                .open(&path)
                .with_context(|| format!("failed to open `{}`", path.display()))?;

            let lock_meta = LockMetadata { v: 1 };
            write!(ok, "{}", serde_json::to_string(&lock_meta).unwrap())?;

            self.config
                .deferred_global_last_use()?
                .mark_registry_src_used(global_cache_tracker::RegistrySrc {
                    encoded_registry_name: self.name,
                    package_dir: package_dir.into(),
                    size: Some(bytes_written),
                });

            Ok(unpack_dir.to_path_buf())
        }

        /// Turns the downloaded `.crate` tarball file into a [`Package`].
        ///
        /// This unconditionally sets checksum for the returned package, so it
        /// should only be called after doing integrity check. That is to say,
        /// you need to call either [`RegistryData::download`] or
        /// [`RegistryData::finish_download`] before calling this method.
        fn get_pkg(&mut self, package: PackageId, path: &File) -> CargoResult<Package> {
            let path = self
                .unpack_package(package, path)
                .with_context(|| format!("failed to unpack package `{}`", package))?;
            let mut src = PathSource::new(&path, self.source_id, self.config);
            src.update()?;
            let mut pkg = match src.download(package)? {
                MaybePackage::Ready(pkg) => pkg,
                MaybePackage::Download { .. } => unreachable!(),
            };

            // After we've loaded the package configure its summary's `checksum`
            // field with the checksum we know for this `PackageId`.
            let cksum = self
                .index
                .hash(package, &mut *self.ops)
                .expect("a downloaded dep now pending!?")
                .expect("summary not found");
            pkg.manifest_mut()
                .summary_mut()
                .set_checksum(cksum.to_string());

            Ok(pkg)
        }
    }

    impl<'cfg> Source for RegistrySource<'cfg> {
        fn query(
            &mut self,
            dep: &Dependency,
            kind: QueryKind,
            f: &mut dyn FnMut(IndexSummary),
        ) -> Poll<CargoResult<()>> {
            let mut req = dep.version_req().clone();

            // Handle `cargo update --precise` here.
            if let Some((_, requested)) = self
                .source_id
                .precise_registry_version(dep.package_name().as_str())
                .filter(|(c, _)| req.matches(c))
            {
                req.update_precise(&requested);
            }

            // If this is a locked dependency, then it came from a lock file and in
            // theory the registry is known to contain this version. If, however, we
            // come back with no summaries, then our registry may need to be
            // updated, so we fall back to performing a lazy update.
            if kind == QueryKind::Exact && req.is_locked() && !self.ops.is_updated() {
                debug!("attempting query without update");
                let mut called = false;
                ready!(self
                    .index
                    .query_inner(dep.package_name(), &req, &mut *self.ops, &mut |s| {
                        if dep.matches(s.as_summary()) {
                            // We are looking for a package from a lock file so we do not care about yank
                            called = true;
                            f(s);
                        }
                    },))?;
                if called {
                    Poll::Ready(Ok(()))
                } else {
                    debug!("falling back to an update");
                    self.invalidate_cache();
                    Poll::Pending
                }
            } else {
                let mut called = false;
                ready!(self
                    .index
                    .query_inner(dep.package_name(), &req, &mut *self.ops, &mut |s| {
                        let matched = match kind {
                            QueryKind::Exact => dep.matches(s.as_summary()),
                            QueryKind::Fuzzy => true,
                        };
                        // Next filter out all yanked packages. Some yanked packages may
                        // leak through if they're in a whitelist (aka if they were
                        // previously in `Cargo.lock`
                        if matched
                            && (!s.is_yanked() || self.yanked_whitelist.contains(&s.package_id()))
                        {
                            f(s);
                            called = true;
                        }
                    }))?;
                if called {
                    return Poll::Ready(Ok(()));
                }
                let mut any_pending = false;
                if kind == QueryKind::Fuzzy {
                    // Attempt to handle misspellings by searching for a chain of related
                    // names to the original name. The resolver will later
                    // reject any candidates that have the wrong name, and with this it'll
                    // along the way produce helpful "did you mean?" suggestions.
                    // For now we only try the canonical lysing `-` to `_` and vice versa.
                    // More advanced fuzzy searching become in the future.
                    for name_permutation in [
                        dep.package_name().replace('-', "_"),
                        dep.package_name().replace('_', "-"),
                    ] {
                        let name_permutation = InternedString::new(&name_permutation);
                        if name_permutation == dep.package_name() {
                            continue;
                        }
                        any_pending |= self
                            .index
                            .query_inner(name_permutation, &req, &mut *self.ops, f)?
                            .is_pending();
                    }
                }
                if any_pending {
                    Poll::Pending
                } else {
                    Poll::Ready(Ok(()))
                }
            }
        }

        fn supports_checksums(&self) -> bool {
            true
        }

        fn requires_precise(&self) -> bool {
            false
        }

        fn source_id(&self) -> SourceId {
            self.source_id
        }

        fn invalidate_cache(&mut self) {
            self.index.clear_summaries_cache();
            self.ops.invalidate_cache();
        }

        fn set_quiet(&mut self, quiet: bool) {
            self.ops.set_quiet(quiet);
        }

        fn download(&mut self, package: PackageId) -> CargoResult<MaybePackage> {
            let hash = loop {
                match self.index.hash(package, &mut *self.ops)? {
                    Poll::Pending => self.block_until_ready()?,
                    Poll::Ready(hash) => break hash,
                }
            };
            match self.ops.download(package, hash)? {
                MaybeLock::Ready(file) => self.get_pkg(package, &file).map(MaybePackage::Ready),
                MaybeLock::Download {
                    url,
                    descriptor,
                    authorization,
                } => Ok(MaybePackage::Download {
                    url,
                    descriptor,
                    authorization,
                }),
            }
        }

        fn finish_download(&mut self, package: PackageId, data: Vec<u8>) -> CargoResult<Package> {
            let hash = loop {
                match self.index.hash(package, &mut *self.ops)? {
                    Poll::Pending => self.block_until_ready()?,
                    Poll::Ready(hash) => break hash,
                }
            };
            let file = self.ops.finish_download(package, hash, &data)?;
            self.get_pkg(package, &file)
        }

        fn fingerprint(&self, pkg: &Package) -> CargoResult<String> {
            Ok(pkg.package_id().version().to_string())
        }

        fn describe(&self) -> String {
            self.source_id.display_index()
        }

        fn add_to_yanked_whitelist(&mut self, pkgs: &[PackageId]) {
            self.yanked_whitelist.extend(pkgs);
        }

        fn is_yanked(&mut self, pkg: PackageId) -> Poll<CargoResult<bool>> {
            self.index.is_yanked(pkg, &mut *self.ops)
        }

        fn block_until_ready(&mut self) -> CargoResult<()> {
            // Before starting to work on the registry, make sure that
            // `<cargo_home>/registry` is marked as excluded from indexing and
            // backups. Older versions of Cargo didn't do this, so we do it here
            // regardless of whether `<cargo_home>` exists.
            //
            // This does not use `create_dir_all_excluded_from_backups_atomic` for
            // the same reason: we want to exclude it even if the directory already
            // exists.
            //
            // IO errors in creating and marking it are ignored, e.g. in case we're on a
            // read-only filesystem.
            let registry_base = self.config.registry_base_path();
            let _ = registry_base.create_dir();
            exclude_from_backups_and_indexing(&registry_base.into_path_unlocked());

            self.ops.block_until_ready()
        }
    }

    impl RegistryConfig {
        /// File name of [`RegistryConfig`].
        const NAME: &'static str = "config.json";
    }

    /// Get the maximum upack size that Cargo permits
    /// based on a given `size` of your compressed file.
    ///
    /// Returns the larger one between `size * max compression ratio`
    /// and a fixed max unpacked size.
    ///
    /// In reality, the compression ratio usually falls in the range of 2:1 to 10:1.
    /// We choose 20:1 to cover almost all possible cases hopefully.
    /// Any ratio higher than this is considered as a zip bomb.
    ///
    /// In the future we might want to introduce a configurable size.
    ///
    /// Some of the real world data from common compression algorithms:
    ///
    /// * <https://www.zlib.net/zlib_tech.html>
    /// * <https://cran.r-project.org/web/packages/brotli/vignettes/brotli-2015-09-22.pdf>
    /// * <https://blog.cloudflare.com/results-experimenting-brotli/>
    /// * <https://tukaani.org/lzma/benchmarks.html>
    fn max_unpack_size(config: &Config, size: u64) -> u64 {
        const SIZE_VAR: &str = "__CARGO_TEST_MAX_UNPACK_SIZE";
        const RATIO_VAR: &str = "__CARGO_TEST_MAX_UNPACK_RATIO";
        const MAX_UNPACK_SIZE: u64 = 512 * 1024 * 1024; // 512 MiB
        const MAX_COMPRESSION_RATIO: usize = 20; // 20:1

        let max_unpack_size = if cfg!(debug_assertions) && config.get_env(SIZE_VAR).is_ok() {
            // For integration test only.
            config
                .get_env(SIZE_VAR)
                .unwrap()
                .parse()
                .expect("a max unpack size in bytes")
        } else {
            MAX_UNPACK_SIZE
        };
        let max_compression_ratio = if cfg!(debug_assertions) && config.get_env(RATIO_VAR).is_ok() {
            // For integration test only.
            config
                .get_env(RATIO_VAR)
                .unwrap()
                .parse()
                .expect("a max compression ratio in bytes")
        } else {
            MAX_COMPRESSION_RATIO
        };

        u64::max(max_unpack_size, size * max_compression_ratio as u64)
    }

    /// Set the current [`umask`] value for the given tarball. No-op on non-Unix
    /// platforms.
    ///
    /// On Windows, tar only looks at user permissions and tries to set the "read
    /// only" attribute, so no-op as well.
    ///
    /// [`umask`]: https://man7.org/linux/man-pages/man2/umask.2.html
    #[allow(unused_variables)]
    fn set_mask<R: Read>(tar: &mut Archive<R>) {
        #[cfg(unix)]
        tar.set_mask(crate::util::get_umask());
    }