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    1366

    //! Utilities for handling git repositories, mainly around
    //! authentication/cloning.

    use crate::core::{GitReference, Verbosity};
    use crate::sources::git::oxide;
    use crate::sources::git::oxide::cargo_config_to_gitoxide_overrides;
    use crate::util::errors::CargoResult;
    use crate::util::{human_readable_bytes, network, Config, IntoUrl, MetricsCounter, Progress};
    use anyhow::{anyhow, Context as _};
    use cargo_util::{paths, ProcessBuilder};
    use curl::easy::List;
    use git2::{self, ErrorClass, ObjectType, Oid};
    use log::{debug, info};
    use serde::ser;
    use serde::Serialize;
    use std::borrow::Cow;
    use std::fmt;
    use std::path::{Path, PathBuf};
    use std::process::Command;
    use std::str;
    use std::sync::atomic::{AtomicBool, Ordering};
    use std::time::{Duration, Instant};
    use url::Url;

    fn serialize_str<T, S>(t: &T, s: S) -> Result<S::Ok, S::Error>
    where
        T: fmt::Display,
        S: ser::Serializer,
    {
        s.collect_str(t)
    }

    pub struct GitShortID(git2::Buf);

    impl GitShortID {
        pub fn as_str(&self) -> &str {
            self.0.as_str().unwrap()
        }
    }

    /// `GitRemote` represents a remote repository. It gets cloned into a local
    /// `GitDatabase`.
    #[derive(PartialEq, Clone, Debug, Serialize)]
    pub struct GitRemote {
        #[serde(serialize_with = "serialize_str")]
        url: Url,
    }

    /// `GitDatabase` is a local clone of a remote repository's database. Multiple
    /// `GitCheckouts` can be cloned from this `GitDatabase`.
    #[derive(Serialize)]
    pub struct GitDatabase {
        remote: GitRemote,
        path: PathBuf,
        #[serde(skip_serializing)]
        repo: git2::Repository,
    }

    /// `GitCheckout` is a local checkout of a particular revision. Calling
    /// `clone_into` with a reference will resolve the reference into a revision,
    /// and return an `anyhow::Error` if no revision for that reference was found.
    #[derive(Serialize)]
    pub struct GitCheckout<'a> {
        database: &'a GitDatabase,
        location: PathBuf,
        #[serde(serialize_with = "serialize_str")]
        revision: git2::Oid,
        #[serde(skip_serializing)]
        repo: git2::Repository,
    }

    // Implementations

    impl GitRemote {
        pub fn new(url: &Url) -> GitRemote {
            GitRemote { url: url.clone() }
        }

        pub fn url(&self) -> &Url {
            &self.url
        }

        pub fn rev_for(&self, path: &Path, reference: &GitReference) -> CargoResult<git2::Oid> {
            reference.resolve(&self.db_at(path)?.repo)
        }

        pub fn checkout(
            &self,
            into: &Path,
            db: Option<GitDatabase>,
            reference: &GitReference,
            locked_rev: Option<git2::Oid>,
            cargo_config: &Config,
        ) -> CargoResult<(GitDatabase, git2::Oid)> {
            // If we have a previous instance of `GitDatabase` then fetch into that
            // if we can. If that can successfully load our revision then we've
            // populated the database with the latest version of `reference`, so
            // return that database and the rev we resolve to.
            if let Some(mut db) = db {
                fetch(&mut db.repo, self.url.as_str(), reference, cargo_config)
                    .context(format!("failed to fetch into: {}", into.display()))?;
                match locked_rev {
                    Some(rev) => {
                        if db.contains(rev) {
                            return Ok((db, rev));
                        }
                    }
                    None => {
                        if let Ok(rev) = reference.resolve(&db.repo) {
                            return Ok((db, rev));
                        }
                    }
                }
            }

            // Otherwise start from scratch to handle corrupt git repositories.
            // After our fetch (which is interpreted as a clone now) we do the same
            // resolution to figure out what we cloned.
            if into.exists() {
                paths::remove_dir_all(into)?;
            }
            paths::create_dir_all(into)?;
            let mut repo = init(into, true)?;
            fetch(&mut repo, self.url.as_str(), reference, cargo_config)
                .context(format!("failed to clone into: {}", into.display()))?;
            let rev = match locked_rev {
                Some(rev) => rev,
                None => reference.resolve(&repo)?,
            };

            Ok((
                GitDatabase {
                    remote: self.clone(),
                    path: into.to_path_buf(),
                    repo,
                },
                rev,
            ))
        }

        pub fn db_at(&self, db_path: &Path) -> CargoResult<GitDatabase> {
            let repo = git2::Repository::open(db_path)?;
            Ok(GitDatabase {
                remote: self.clone(),
                path: db_path.to_path_buf(),
                repo,
            })
        }
    }

    impl GitDatabase {
        pub fn copy_to(
            &self,
            rev: git2::Oid,
            dest: &Path,
            cargo_config: &Config,
            parent_remote_url: &Url,
        ) -> CargoResult<GitCheckout<'_>> {
            // If the existing checkout exists, and it is fresh, use it.
            // A non-fresh checkout can happen if the checkout operation was
            // interrupted. In that case, the checkout gets deleted and a new
            // clone is created.
            let checkout = match git2::Repository::open(dest)
                .ok()
                .map(|repo| GitCheckout::new(dest, self, rev, repo))
                .filter(|co| co.is_fresh())
            {
                Some(co) => co,
                None => GitCheckout::clone_into(dest, self, rev, cargo_config)?,
            };
            checkout.update_submodules(cargo_config, parent_remote_url)?;
            Ok(checkout)
        }

        pub fn to_short_id(&self, revision: git2::Oid) -> CargoResult<GitShortID> {
            let obj = self.repo.find_object(revision, None)?;
            Ok(GitShortID(obj.short_id()?))
        }

        pub fn contains(&self, oid: git2::Oid) -> bool {
            self.repo.revparse_single(&oid.to_string()).is_ok()
        }

        pub fn resolve(&self, r: &GitReference) -> CargoResult<git2::Oid> {
            r.resolve(&self.repo)
        }
    }

    impl GitReference {
        pub fn resolve(&self, repo: &git2::Repository) -> CargoResult<git2::Oid> {
            let id = match self {
                // Note that we resolve the named tag here in sync with where it's
                // fetched into via `fetch` below.
                GitReference::Tag(s) => (|| -> CargoResult<git2::Oid> {
                    let refname = format!("refs/remotes/origin/tags/{}", s);
                    let id = repo.refname_to_id(&refname)?;
                    let obj = repo.find_object(id, None)?;
                    let obj = obj.peel(ObjectType::Commit)?;
                    Ok(obj.id())
                })()
                .with_context(|| format!("failed to find tag `{}`", s))?,

                // Resolve the remote name since that's all we're configuring in
                // `fetch` below.
                GitReference::Branch(s) => {
                    let name = format!("origin/{}", s);
                    let b = repo
                        .find_branch(&name, git2::BranchType::Remote)
                        .with_context(|| format!("failed to find branch `{}`", s))?;
                    b.get()
                        .target()
                        .ok_or_else(|| anyhow::format_err!("branch `{}` did not have a target", s))?
                }

                // We'll be using the HEAD commit
                GitReference::DefaultBranch => {
                    let head_id = repo.refname_to_id("refs/remotes/origin/HEAD")?;
                    let head = repo.find_object(head_id, None)?;
                    head.peel(ObjectType::Commit)?.id()
                }

                GitReference::Rev(s) => {
                    let obj = repo.revparse_single(s)?;
                    match obj.as_tag() {
                        Some(tag) => tag.target_id(),
                        None => obj.id(),
                    }
                }
            };
            Ok(id)
        }
    }

    impl<'a> GitCheckout<'a> {
        fn new(
            path: &Path,
            database: &'a GitDatabase,
            revision: git2::Oid,
            repo: git2::Repository,
        ) -> GitCheckout<'a> {
            GitCheckout {
                location: path.to_path_buf(),
                database,
                revision,
                repo,
            }
        }

        fn clone_into(
            into: &Path,
            database: &'a GitDatabase,
            revision: git2::Oid,
            config: &Config,
        ) -> CargoResult<GitCheckout<'a>> {
            let dirname = into.parent().unwrap();
            paths::create_dir_all(&dirname)?;
            if into.exists() {
                paths::remove_dir_all(into)?;
            }

            // we're doing a local filesystem-to-filesystem clone so there should
            // be no need to respect global configuration options, so pass in
            // an empty instance of `git2::Config` below.
            let git_config = git2::Config::new()?;

            // Clone the repository, but make sure we use the "local" option in
            // libgit2 which will attempt to use hardlinks to set up the database.
            // This should speed up the clone operation quite a bit if it works.
            //
            // Note that we still use the same fetch options because while we don't
            // need authentication information we may want progress bars and such.
            let url = database.path.into_url()?;
            let mut repo = None;
            with_fetch_options(&git_config, url.as_str(), config, &mut |fopts| {
                let mut checkout = git2::build::CheckoutBuilder::new();
                checkout.dry_run(); // we'll do this below during a `reset`

                let r = git2::build::RepoBuilder::new()
                    // use hard links and/or copy the database, we're doing a
                    // filesystem clone so this'll speed things up quite a bit.
                    .clone_local(git2::build::CloneLocal::Local)
                    .with_checkout(checkout)
                    .fetch_options(fopts)
                    .clone(url.as_str(), into)?;
                repo = Some(r);
                Ok(())
            })?;
            let repo = repo.unwrap();

            let checkout = GitCheckout::new(into, database, revision, repo);
            checkout.reset(config)?;
            Ok(checkout)
        }

        fn is_fresh(&self) -> bool {
            match self.repo.revparse_single("HEAD") {
                Ok(ref head) if head.id() == self.revision => {
                    // See comments in reset() for why we check this
                    self.location.join(".cargo-ok").exists()
                }
                _ => false,
            }
        }

        fn reset(&self, config: &Config) -> CargoResult<()> {
            // If we're interrupted while performing this reset (e.g., we die because
            // of a signal) Cargo needs to be sure to try to check out this repo
            // again on the next go-round.
            //
            // To enable this we have a dummy file in our checkout, .cargo-ok, which
            // if present means that the repo has been successfully reset and is
            // ready to go. Hence if we start to do a reset, we make sure this file
            // *doesn't* exist, and then once we're done we create the file.
            let ok_file = self.location.join(".cargo-ok");
            let _ = paths::remove_file(&ok_file);
            info!("reset {} to {}", self.repo.path().display(), self.revision);

            // Ensure libgit2 won't mess with newlines when we vendor.
            if let Ok(mut git_config) = self.repo.config() {
                git_config.set_bool("core.autocrlf", false)?;
            }

            let object = self.repo.find_object(self.revision, None)?;
            reset(&self.repo, &object, config)?;
            paths::create(ok_file)?;
            Ok(())
        }

        fn update_submodules(&self, cargo_config: &Config, parent_remote_url: &Url) -> CargoResult<()> {
            return update_submodules(&self.repo, cargo_config, parent_remote_url);

            fn update_submodules(
                repo: &git2::Repository,
                cargo_config: &Config,
                parent_remote_url: &Url,
            ) -> CargoResult<()> {
                debug!("update submodules for: {:?}", repo.workdir().unwrap());

                for mut child in repo.submodules()? {
                    update_submodule(repo, &mut child, cargo_config, parent_remote_url).with_context(
                        || {
                            format!(
                                "failed to update submodule `{}`",
                                child.name().unwrap_or("")
                            )
                        },
                    )?;
                }
                Ok(())
            }

            fn update_submodule(
                parent: &git2::Repository,
                child: &mut git2::Submodule<'_>,
                cargo_config: &Config,
                parent_remote_url: &Url,
            ) -> CargoResult<()> {
                child.init(false)?;

                let child_url_str = child.url().ok_or_else(|| {
                    anyhow::format_err!("non-utf8 url for submodule {:?}?", child.path())
                })?;

                // Skip the submodule if the config says not to update it.
                if child.update_strategy() == git2::SubmoduleUpdate::None {
                    cargo_config.shell().status(
                        "Skipping",
                        format!(
                            "git submodule `{}` due to update strategy in .gitmodules",
                            child_url_str
                        ),
                    )?;
                    return Ok(());
                }

                // Git only assumes a URL is a relative path if it starts with `./` or `../`.
                // See [`git submodule add`] documentation.
                //
                // [`git submodule add`]: https://git-scm.com/docs/git-submodule
                let url = if child_url_str.starts_with("./") || child_url_str.starts_with("../") {
                    let mut new_parent_remote_url = parent_remote_url.clone();

                    let mut new_path = Cow::from(parent_remote_url.path());
                    if !new_path.ends_with('/') {
                        new_path.to_mut().push('/');
                    }
                    new_parent_remote_url.set_path(&new_path);

                    match new_parent_remote_url.join(child_url_str) {
                        Ok(x) => x.to_string(),
                        Err(err) => Err(err).with_context(|| {
                            format!(
                                "failed to parse relative child submodule url `{}` using parent base url `{}`",
                                child_url_str, new_parent_remote_url
                            )
                        })?,
                    }
                } else {
                    child_url_str.to_string()
                };

                // A submodule which is listed in .gitmodules but not actually
                // checked out will not have a head id, so we should ignore it.
                let head = match child.head_id() {
                    Some(head) => head,
                    None => return Ok(()),
                };

                // If the submodule hasn't been checked out yet, we need to
                // clone it. If it has been checked out and the head is the same
                // as the submodule's head, then we can skip an update and keep
                // recursing.
                let head_and_repo = child.open().and_then(|repo| {
                    let target = repo.head()?.target();
                    Ok((target, repo))
                });
                let mut repo = match head_and_repo {
                    Ok((head, repo)) => {
                        if child.head_id() == head {
                            return update_submodules(&repo, cargo_config, parent_remote_url);
                        }
                        repo
                    }
                    Err(..) => {
                        let path = parent.workdir().unwrap().join(child.path());
                        let _ = paths::remove_dir_all(&path);
                        init(&path, false)?
                    }
                };
                // Fetch data from origin and reset to the head commit
                let reference = GitReference::Rev(head.to_string());
                cargo_config
                    .shell()
                    .status("Updating", format!("git submodule `{}`", url))?;
                fetch(&mut repo, &url, &reference, cargo_config).with_context(|| {
                    format!(
                        "failed to fetch submodule `{}` from {}",
                        child.name().unwrap_or(""),
                        url
                    )
                })?;

                let obj = repo.find_object(head, None)?;
                reset(&repo, &obj, cargo_config)?;
                update_submodules(&repo, cargo_config, parent_remote_url)
            }
        }
    }

    /// Prepare the authentication callbacks for cloning a git repository.
    ///
    /// The main purpose of this function is to construct the "authentication
    /// callback" which is used to clone a repository. This callback will attempt to
    /// find the right authentication on the system (without user input) and will
    /// guide libgit2 in doing so.
    ///
    /// The callback is provided `allowed` types of credentials, and we try to do as
    /// much as possible based on that:
    ///
    /// * Prioritize SSH keys from the local ssh agent as they're likely the most
    ///   reliable. The username here is prioritized from the credential
    ///   callback, then from whatever is configured in git itself, and finally
    ///   we fall back to the generic user of `git`.
    ///
    /// * If a username/password is allowed, then we fallback to git2-rs's
    ///   implementation of the credential helper. This is what is configured
    ///   with `credential.helper` in git, and is the interface for the macOS
    ///   keychain, for example.
    ///
    /// * After the above two have failed, we just kinda grapple attempting to
    ///   return *something*.
    ///
    /// If any form of authentication fails, libgit2 will repeatedly ask us for
    /// credentials until we give it a reason to not do so. To ensure we don't
    /// just sit here looping forever we keep track of authentications we've
    /// attempted and we don't try the same ones again.
    fn with_authentication<T, F>(
        cargo_config: &Config,
        url: &str,
        cfg: &git2::Config,
        mut f: F,
    ) -> CargoResult<T>
    where
        F: FnMut(&mut git2::Credentials<'_>) -> CargoResult<T>,
    {
        let mut cred_helper = git2::CredentialHelper::new(url);
        cred_helper.config(cfg);

        let mut ssh_username_requested = false;
        let mut cred_helper_bad = None;
        let mut ssh_agent_attempts = Vec::new();
        let mut any_attempts = false;
        let mut tried_sshkey = false;
        let mut url_attempt = None;

        let orig_url = url;
        let mut res = f(&mut |url, username, allowed| {
            any_attempts = true;
            if url != orig_url {
                url_attempt = Some(url.to_string());
            }
            // libgit2's "USERNAME" authentication actually means that it's just
            // asking us for a username to keep going. This is currently only really
            // used for SSH authentication and isn't really an authentication type.
            // The logic currently looks like:
            //
            //      let user = ...;
            //      if (user.is_null())
            //          user = callback(USERNAME, null, ...);
            //
            //      callback(SSH_KEY, user, ...)
            //
            // So if we're being called here then we know that (a) we're using ssh
            // authentication and (b) no username was specified in the URL that
            // we're trying to clone. We need to guess an appropriate username here,
            // but that may involve a few attempts. Unfortunately we can't switch
            // usernames during one authentication session with libgit2, so to
            // handle this we bail out of this authentication session after setting
            // the flag `ssh_username_requested`, and then we handle this below.
            if allowed.contains(git2::CredentialType::USERNAME) {
                debug_assert!(username.is_none());
                ssh_username_requested = true;
                return Err(git2::Error::from_str("gonna try usernames later"));
            }

            // An "SSH_KEY" authentication indicates that we need some sort of SSH
            // authentication. This can currently either come from the ssh-agent
            // process or from a raw in-memory SSH key. Cargo only supports using
            // ssh-agent currently.
            //
            // If we get called with this then the only way that should be possible
            // is if a username is specified in the URL itself (e.g., `username` is
            // Some), hence the unwrap() here. We try custom usernames down below.
            if allowed.contains(git2::CredentialType::SSH_KEY) && !tried_sshkey {
                // If ssh-agent authentication fails, libgit2 will keep
                // calling this callback asking for other authentication
                // methods to try. Make sure we only try ssh-agent once,
                // to avoid looping forever.
                tried_sshkey = true;
                let username = username.unwrap();
                debug_assert!(!ssh_username_requested);
                ssh_agent_attempts.push(username.to_string());
                return git2::Cred::ssh_key_from_agent(username);
            }

            // Sometimes libgit2 will ask for a username/password in plaintext. This
            // is where Cargo would have an interactive prompt if we supported it,
            // but we currently don't! Right now the only way we support fetching a
            // plaintext password is through the `credential.helper` support, so
            // fetch that here.
            //
            // If ssh-agent authentication fails, libgit2 will keep calling this
            // callback asking for other authentication methods to try. Check
            // cred_helper_bad to make sure we only try the git credential helper
            // once, to avoid looping forever.
            if allowed.contains(git2::CredentialType::USER_PASS_PLAINTEXT) && cred_helper_bad.is_none()
            {
                let r = git2::Cred::credential_helper(cfg, url, username);
                cred_helper_bad = Some(r.is_err());
                return r;
            }

            // I'm... not sure what the DEFAULT kind of authentication is, but seems
            // easy to support?
            if allowed.contains(git2::CredentialType::DEFAULT) {
                return git2::Cred::default();
            }

            // Whelp, we tried our best
            Err(git2::Error::from_str("no authentication methods succeeded"))
        });

        // Ok, so if it looks like we're going to be doing ssh authentication, we
        // want to try a few different usernames as one wasn't specified in the URL
        // for us to use. In order, we'll try:
        //
        // * A credential helper's username for this URL, if available.
        // * This account's username.
        // * "git"
        //
        // We have to restart the authentication session each time (due to
        // constraints in libssh2 I guess? maybe this is inherent to ssh?), so we
        // call our callback, `f`, in a loop here.
        if ssh_username_requested {
            debug_assert!(res.is_err());
            let mut attempts = vec![String::from("git")];
            if let Ok(s) = cargo_config
                .get_env("USER")
                .or_else(|_| cargo_config.get_env("USERNAME"))
            {
                attempts.push(s);
            }
            if let Some(ref s) = cred_helper.username {
                attempts.push(s.clone());
            }

            while let Some(s) = attempts.pop() {
                // We should get `USERNAME` first, where we just return our attempt,
                // and then after that we should get `SSH_KEY`. If the first attempt
                // fails we'll get called again, but we don't have another option so
                // we bail out.
                let mut attempts = 0;
                res = f(&mut |_url, username, allowed| {
                    if allowed.contains(git2::CredentialType::USERNAME) {
                        return git2::Cred::username(&s);
                    }
                    if allowed.contains(git2::CredentialType::SSH_KEY) {
                        debug_assert_eq!(Some(&s[..]), username);
                        attempts += 1;
                        if attempts == 1 {
                            ssh_agent_attempts.push(s.to_string());
                            return git2::Cred::ssh_key_from_agent(&s);
                        }
                    }
                    Err(git2::Error::from_str("no authentication methods succeeded"))
                });

                // If we made two attempts then that means:
                //
                // 1. A username was requested, we returned `s`.
                // 2. An ssh key was requested, we returned to look up `s` in the
                //    ssh agent.
                // 3. For whatever reason that lookup failed, so we were asked again
                //    for another mode of authentication.
                //
                // Essentially, if `attempts == 2` then in theory the only error was
                // that this username failed to authenticate (e.g., no other network
                // errors happened). Otherwise something else is funny so we bail
                // out.
                if attempts != 2 {
                    break;
                }
            }
        }
        let mut err = match res {
            Ok(e) => return Ok(e),
            Err(e) => e,
        };

        // In the case of an authentication failure (where we tried something) then
        // we try to give a more helpful error message about precisely what we
        // tried.
        if any_attempts {
            let mut msg = "failed to authenticate when downloading \
                           repository"
                .to_string();

            if let Some(attempt) = &url_attempt {
                if url != attempt {
                    msg.push_str(": ");
                    msg.push_str(attempt);
                }
            }
            msg.push('\n');
            if !ssh_agent_attempts.is_empty() {
                let names = ssh_agent_attempts
                    .iter()
                    .map(|s| format!("`{}`", s))
                    .collect::<Vec<_>>()
                    .join(", ");
                msg.push_str(&format!(
                    "\n* attempted ssh-agent authentication, but \
                     no usernames succeeded: {}",
                    names
                ));
            }
            if let Some(failed_cred_helper) = cred_helper_bad {
                if failed_cred_helper {
                    msg.push_str(
                        "\n* attempted to find username/password via \
                         git's `credential.helper` support, but failed",
                    );
                } else {
                    msg.push_str(
                        "\n* attempted to find username/password via \
                         `credential.helper`, but maybe the found \
                         credentials were incorrect",
                    );
                }
            }
            msg.push_str("\n\n");
            msg.push_str("if the git CLI succeeds then `net.git-fetch-with-cli` may help here\n");
            msg.push_str("https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli");
            err = err.context(msg);

        // Otherwise if we didn't even get to the authentication phase them we may
        // have failed to set up a connection, in these cases hint on the
        // `net.git-fetch-with-cli` configuration option.
        } else if let Some(e) = err.downcast_ref::<git2::Error>() {
            match e.class() {
                ErrorClass::Net
                | ErrorClass::Ssl
                | ErrorClass::Submodule
                | ErrorClass::FetchHead
                | ErrorClass::Ssh
                | ErrorClass::Http => {
                    let mut msg = "network failure seems to have happened\n".to_string();
                    msg.push_str(
                        "if a proxy or similar is necessary `net.git-fetch-with-cli` may help here\n",
                    );
                    msg.push_str(
                        "https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli",
                    );
                    err = err.context(msg);
                }
                ErrorClass::Callback => {
                    // This unwraps the git2 error. We're using the callback error
                    // specifically to convey errors from Rust land through the C
                    // callback interface. We don't need the `; class=Callback
                    // (26)` that gets tacked on to the git2 error message.
                    err = anyhow::format_err!("{}", e.message());
                }
                _ => {}
            }
        }

        Err(err)
    }

    fn reset(repo: &git2::Repository, obj: &git2::Object<'_>, config: &Config) -> CargoResult<()> {
        let mut pb = Progress::new("Checkout", config);
        let mut opts = git2::build::CheckoutBuilder::new();
        opts.progress(|_, cur, max| {
            drop(pb.tick(cur, max, ""));
        });
        debug!("doing reset");
        repo.reset(obj, git2::ResetType::Hard, Some(&mut opts))?;
        debug!("reset done");
        Ok(())
    }

    pub fn with_fetch_options(
        git_config: &git2::Config,
        url: &str,
        config: &Config,
        cb: &mut dyn FnMut(git2::FetchOptions<'_>) -> CargoResult<()>,
    ) -> CargoResult<()> {
        let mut progress = Progress::new("Fetch", config);
        let ssh_config = config.net_config()?.ssh.as_ref();
        let config_known_hosts = ssh_config.and_then(|ssh| ssh.known_hosts.as_ref());
        let diagnostic_home_config = config.diagnostic_home_config();
        network::retry::with_retry(config, || {
            with_authentication(config, url, git_config, |f| {
                let port = Url::parse(url).ok().and_then(|url| url.port());
                let mut last_update = Instant::now();
                let mut rcb = git2::RemoteCallbacks::new();
                // We choose `N=10` here to make a `300ms * 10slots ~= 3000ms`
                // sliding window for tracking the data transfer rate (in bytes/s).
                let mut counter = MetricsCounter::<10>::new(0, last_update);
                rcb.credentials(f);
                rcb.certificate_check(|cert, host| {
                    super::known_hosts::certificate_check(
                        config,
                        cert,
                        host,
                        port,
                        config_known_hosts,
                        &diagnostic_home_config,
                    )
                });
                rcb.transfer_progress(|stats| {
                    let indexed_deltas = stats.indexed_deltas();
                    let msg = if indexed_deltas > 0 {
                        // Resolving deltas.
                        format!(
                            ", ({}/{}) resolving deltas",
                            indexed_deltas,
                            stats.total_deltas()
                        )
                    } else {
                        // Receiving objects.
                        //
                        // # Caveat
                        //
                        // Progress bar relies on git2 calling `transfer_progress`
                        // to update its transfer rate, but we cannot guarantee a
                        // periodic call of that callback. Thus if we don't receive
                        // any data for, say, 10 seconds, the rate will get stuck
                        // and never go down to 0B/s.
                        // In the future, we need to find away to update the rate
                        // even when the callback is not called.
                        let now = Instant::now();
                        // Scrape a `received_bytes` to the counter every 300ms.
                        if now - last_update > Duration::from_millis(300) {
                            counter.add(stats.received_bytes(), now);
                            last_update = now;
                        }
                        let (rate, unit) = human_readable_bytes(counter.rate() as u64);
                        format!(", {:.2}{}/s", rate, unit)
                    };
                    progress
                        .tick(stats.indexed_objects(), stats.total_objects(), &msg)
                        .is_ok()
                });

                // Create a local anonymous remote in the repository to fetch the
                // url
                let mut opts = git2::FetchOptions::new();
                opts.remote_callbacks(rcb);
                cb(opts)
            })?;
            Ok(())
        })
    }

    pub fn fetch(
        repo: &mut git2::Repository,
        orig_url: &str,
        reference: &GitReference,
        config: &Config,
    ) -> CargoResult<()> {
        if config.frozen() {
            anyhow::bail!(
                "attempting to update a git repository, but --frozen \
                 was specified"
            )
        }
        if !config.network_allowed() {
            anyhow::bail!("can't update a git repository in the offline mode")
        }

        // If we're fetching from GitHub, attempt GitHub's special fast path for
        // testing if we've already got an up-to-date copy of the repository
        let oid_to_fetch = match github_fast_path(repo, orig_url, reference, config) {
            Ok(FastPathRev::UpToDate) => return Ok(()),
            Ok(FastPathRev::NeedsFetch(rev)) => Some(rev),
            Ok(FastPathRev::Indeterminate) => None,
            Err(e) => {
                debug!("failed to check github {:?}", e);
                None
            }
        };

        // We reuse repositories quite a lot, so before we go through and update the
        // repo check to see if it's a little too old and could benefit from a gc.
        // In theory this shouldn't be too expensive compared to the network
        // request we're about to issue.
        maybe_gc_repo(repo, config)?;

        clean_repo_temp_files(repo);

        // Translate the reference desired here into an actual list of refspecs
        // which need to get fetched. Additionally record if we're fetching tags.
        let mut refspecs = Vec::new();
        let mut tags = false;
        // The `+` symbol on the refspec means to allow a forced (fast-forward)
        // update which is needed if there is ever a force push that requires a
        // fast-forward.
        match reference {
            // For branches and tags we can fetch simply one reference and copy it
            // locally, no need to fetch other branches/tags.
            GitReference::Branch(b) => {
                refspecs.push(format!("+refs/heads/{0}:refs/remotes/origin/{0}", b));
            }
            GitReference::Tag(t) => {
                refspecs.push(format!("+refs/tags/{0}:refs/remotes/origin/tags/{0}", t));
            }

            GitReference::DefaultBranch => {
                refspecs.push(String::from("+HEAD:refs/remotes/origin/HEAD"));
            }

            GitReference::Rev(rev) => {
                if rev.starts_with("refs/") {
                    refspecs.push(format!("+{0}:{0}", rev));
                } else if let Some(oid_to_fetch) = oid_to_fetch {
                    refspecs.push(format!("+{0}:refs/commit/{0}", oid_to_fetch));
                } else {
                    // We don't know what the rev will point to. To handle this
                    // situation we fetch all branches and tags, and then we pray
                    // it's somewhere in there.
                    refspecs.push(String::from("+refs/heads/*:refs/remotes/origin/*"));
                    refspecs.push(String::from("+HEAD:refs/remotes/origin/HEAD"));
                    tags = true;
                }
            }
        }

        // Unfortunately `libgit2` is notably lacking in the realm of authentication
        // when compared to the `git` command line. As a result, allow an escape
        // hatch for users that would prefer to use `git`-the-CLI for fetching
        // repositories instead of `libgit2`-the-library. This should make more
        // flavors of authentication possible while also still giving us all the
        // speed and portability of using `libgit2`.
        if let Some(true) = config.net_config()?.git_fetch_with_cli {
            return fetch_with_cli(repo, orig_url, &refspecs, tags, config);
        }
        if config
            .cli_unstable()
            .gitoxide
            .map_or(false, |git| git.fetch)
        {
            let git2_repo = repo;
            let config_overrides = cargo_config_to_gitoxide_overrides(config)?;
            let repo_reinitialized = AtomicBool::default();
            let res = oxide::with_retry_and_progress(
                &git2_repo.path().to_owned(),
                config,
                &|repo_path,
                  should_interrupt,
                  mut progress,
                  url_for_authentication: &mut dyn FnMut(&gix::bstr::BStr)| {
                    // The `fetch` operation here may fail spuriously due to a corrupt
                    // repository. It could also fail, however, for a whole slew of other
                    // reasons (aka network related reasons). We want Cargo to automatically
                    // recover from corrupt repositories, but we don't want Cargo to stomp
                    // over other legitimate errors.
                    //
                    // Consequently we save off the error of the `fetch` operation and if it
                    // looks like a "corrupt repo" error then we blow away the repo and try
                    // again. If it looks like any other kind of error, or if we've already
                    // blown away the repository, then we want to return the error as-is.
                    loop {
                        let res = oxide::open_repo(
                            repo_path,
                            config_overrides.clone(),
                            oxide::OpenMode::ForFetch,
                        )
                        .map_err(crate::sources::git::fetch::Error::from)
                        .and_then(|repo| {
                            debug!("initiating fetch of {:?} from {}", refspecs, orig_url);
                            let url_for_authentication = &mut *url_for_authentication;
                            let remote = repo
                                .remote_at(orig_url)?
                                .with_fetch_tags(if tags {
                                    gix::remote::fetch::Tags::All
                                } else {
                                    gix::remote::fetch::Tags::Included
                                })
                                .with_refspecs(
                                    refspecs.iter().map(|s| s.as_str()),
                                    gix::remote::Direction::Fetch,
                                )
                                .map_err(crate::sources::git::fetch::Error::Other)?;
                            let url = remote
                                .url(gix::remote::Direction::Fetch)
                                .expect("set at init")
                                .to_owned();
                            let connection =
                                remote.connect(gix::remote::Direction::Fetch, &mut progress)?;
                            let mut authenticate = connection.configured_credentials(url)?;
                            let connection = connection.with_credentials(
                                move |action: gix::protocol::credentials::helper::Action| {
                                    if let Some(url) = action
                                        .context()
                                        .and_then(|ctx| ctx.url.as_ref().filter(|url| *url != orig_url))
                                    {
                                        url_for_authentication(url.as_ref());
                                    }
                                    authenticate(action)
                                },
                            );
                            let outcome = connection
                                .prepare_fetch(gix::remote::ref_map::Options::default())?
                                .receive(should_interrupt)?;
                            Ok(outcome)
                        });
                        let err = match res {
                            Ok(_) => break,
                            Err(e) => e,
                        };
                        debug!("fetch failed: {}", err);

                        if !repo_reinitialized.load(Ordering::Relaxed)
                            // We check for errors that could occour if the configuration, refs or odb files are corrupted.
                            // We don't check for errors related to writing as `gitoxide` is expected to create missing leading
                            // folder before writing files into it, or else not even open a directory as git repository (which is
                            // also handled here).
                            && err.is_corrupted()
                        {
                            repo_reinitialized.store(true, Ordering::Relaxed);
                            debug!(
                                "looks like this is a corrupt repository, reinitializing \
                         and trying again"
                            );
                            if oxide::reinitialize(repo_path).is_ok() {
                                continue;
                            }
                        }

                        return Err(err.into());
                    }
                    Ok(())
                },
            );
            if repo_reinitialized.load(Ordering::Relaxed) {
                *git2_repo = git2::Repository::open(git2_repo.path())?;
            }
            res
        } else {
            debug!("doing a fetch for {}", orig_url);
            let git_config = git2::Config::open_default()?;
            with_fetch_options(&git_config, orig_url, config, &mut |mut opts| {
                if tags {
                    opts.download_tags(git2::AutotagOption::All);
                }
                // The `fetch` operation here may fail spuriously due to a corrupt
                // repository. It could also fail, however, for a whole slew of other
                // reasons (aka network related reasons). We want Cargo to automatically
                // recover from corrupt repositories, but we don't want Cargo to stomp
                // over other legitimate errors.
                //
                // Consequently we save off the error of the `fetch` operation and if it
                // looks like a "corrupt repo" error then we blow away the repo and try
                // again. If it looks like any other kind of error, or if we've already
                // blown away the repository, then we want to return the error as-is.
                let mut repo_reinitialized = false;
                loop {
                    debug!("initiating fetch of {:?} from {}", refspecs, orig_url);
                    let res = repo
                        .remote_anonymous(orig_url)?
                        .fetch(&refspecs, Some(&mut opts), None);
                    let err = match res {
                        Ok(()) => break,
                        Err(e) => e,
                    };
                    debug!("fetch failed: {}", err);

                    if !repo_reinitialized
                        && matches!(err.class(), ErrorClass::Reference | ErrorClass::Odb)
                    {
                        repo_reinitialized = true;
                        debug!(
                            "looks like this is a corrupt repository, reinitializing \
                         and trying again"
                        );
                        if reinitialize(repo).is_ok() {
                            continue;
                        }
                    }

                    return Err(err.into());
                }
                Ok(())
            })
        }
    }

    fn fetch_with_cli(
        repo: &mut git2::Repository,
        url: &str,
        refspecs: &[String],
        tags: bool,
        config: &Config,
    ) -> CargoResult<()> {
        let mut cmd = ProcessBuilder::new("git");
        cmd.arg("fetch");
        if tags {
            cmd.arg("--tags");
        }
        match config.shell().verbosity() {
            Verbosity::Normal => {}
            Verbosity::Verbose => {
                cmd.arg("--verbose");
            }
            Verbosity::Quiet => {
                cmd.arg("--quiet");
            }
        }
        cmd.arg("--force") // handle force pushes
            .arg("--update-head-ok") // see discussion in #2078
            .arg(url)
            .args(refspecs)
            // If cargo is run by git (for example, the `exec` command in `git
            // rebase`), the GIT_DIR is set by git and will point to the wrong
            // location (this takes precedence over the cwd). Make sure this is
            // unset so git will look at cwd for the repo.
            .env_remove("GIT_DIR")
            // The reset of these may not be necessary, but I'm including them
            // just to be extra paranoid and avoid any issues.
            .env_remove("GIT_WORK_TREE")
            .env_remove("GIT_INDEX_FILE")
            .env_remove("GIT_OBJECT_DIRECTORY")
            .env_remove("GIT_ALTERNATE_OBJECT_DIRECTORIES")
            .cwd(repo.path());
        config
            .shell()
            .verbose(|s| s.status("Running", &cmd.to_string()))?;
        cmd.exec()?;
        Ok(())
    }

    /// Cargo has a bunch of long-lived git repositories in its global cache and
    /// some, like the index, are updated very frequently. Right now each update
    /// creates a new "pack file" inside the git database, and over time this can
    /// cause bad performance and bad current behavior in libgit2.
    ///
    /// One pathological use case today is where libgit2 opens hundreds of file
    /// descriptors, getting us dangerously close to blowing out the OS limits of
    /// how many fds we can have open. This is detailed in #4403.
    ///
    /// To try to combat this problem we attempt a `git gc` here. Note, though, that
    /// we may not even have `git` installed on the system! As a result we
    /// opportunistically try a `git gc` when the pack directory looks too big, and
    /// failing that we just blow away the repository and start over.
    fn maybe_gc_repo(repo: &mut git2::Repository, config: &Config) -> CargoResult<()> {
        // Here we arbitrarily declare that if you have more than 100 files in your
        // `pack` folder that we need to do a gc.
        let entries = match repo.path().join("objects/pack").read_dir() {
            Ok(e) => e.count(),
            Err(_) => {
                debug!("skipping gc as pack dir appears gone");
                return Ok(());
            }
        };
        let max = config
            .get_env("__CARGO_PACKFILE_LIMIT")
            .ok()
            .and_then(|s| s.parse::<usize>().ok())
            .unwrap_or(100);
        if entries < max {
            debug!("skipping gc as there's only {} pack files", entries);
            return Ok(());
        }

        // First up, try a literal `git gc` by shelling out to git. This is pretty
        // likely to fail though as we may not have `git` installed. Note that
        // libgit2 doesn't currently implement the gc operation, so there's no
        // equivalent there.
        match Command::new("git")
            .arg("gc")
            .current_dir(repo.path())
            .output()
        {
            Ok(out) => {
                debug!(
                    "git-gc status: {}\n\nstdout ---\n{}\nstderr ---\n{}",
                    out.status,
                    String::from_utf8_lossy(&out.stdout),
                    String::from_utf8_lossy(&out.stderr)
                );
                if out.status.success() {
                    let new = git2::Repository::open(repo.path())?;
                    *repo = new;
                    return Ok(());
                }
            }
            Err(e) => debug!("git-gc failed to spawn: {}", e),
        }

        // Alright all else failed, let's start over.
        reinitialize(repo)
    }

    /// Removes temporary files left from previous activity.
    ///
    /// If libgit2 is interrupted while indexing pack files, it will leave behind
    /// some temporary files that it doesn't clean up. These can be quite large in
    /// size, so this tries to clean things up.
    ///
    /// This intentionally ignores errors. This is only an opportunistic cleaning,
    /// and we don't really care if there are issues (there's unlikely anything
    /// that can be done).
    ///
    /// The git CLI has similar behavior (its temp files look like
    /// `objects/pack/tmp_pack_9kUSA8`). Those files are normally deleted via `git
    /// prune` which is run by `git gc`. However, it doesn't know about libgit2's
    /// filenames, so they never get cleaned up.
    fn clean_repo_temp_files(repo: &git2::Repository) {
        let path = repo.path().join("objects/pack/pack_git2_*");
        let pattern = match path.to_str() {
            Some(p) => p,
            None => {
                log::warn!("cannot convert {path:?} to a string");
                return;
            }
        };
        let paths = match glob::glob(pattern) {
            Ok(paths) => paths,
            Err(_) => return,
        };
        for path in paths {
            if let Ok(path) = path {
                match paths::remove_file(&path) {
                    Ok(_) => log::debug!("removed stale temp git file {path:?}"),
                    Err(e) => log::warn!("failed to remove {path:?} while cleaning temp files: {e}"),
                }
            }
        }
    }

    fn reinitialize(repo: &mut git2::Repository) -> CargoResult<()> {
        // Here we want to drop the current repository object pointed to by `repo`,
        // so we initialize temporary repository in a sub-folder, blow away the
        // existing git folder, and then recreate the git repo. Finally we blow away
        // the `tmp` folder we allocated.
        let path = repo.path().to_path_buf();
        debug!("reinitializing git repo at {:?}", path);
        let tmp = path.join("tmp");
        let bare = !repo.path().ends_with(".git");
        *repo = init(&tmp, false)?;
        for entry in path.read_dir()? {
            let entry = entry?;
            if entry.file_name().to_str() == Some("tmp") {
                continue;
            }
            let path = entry.path();
            drop(paths::remove_file(&path).or_else(|_| paths::remove_dir_all(&path)));
        }
        *repo = init(&path, bare)?;
        paths::remove_dir_all(&tmp)?;
        Ok(())
    }

    fn init(path: &Path, bare: bool) -> CargoResult<git2::Repository> {
        let mut opts = git2::RepositoryInitOptions::new();
        // Skip anything related to templates, they just call all sorts of issues as
        // we really don't want to use them yet they insist on being used. See #6240
        // for an example issue that comes up.
        opts.external_template(false);
        opts.bare(bare);
        Ok(git2::Repository::init_opts(&path, &opts)?)
    }

    enum FastPathRev {
        /// The local rev (determined by `reference.resolve(repo)`) is already up to
        /// date with what this rev resolves to on GitHub's server.
        UpToDate,
        /// The following SHA must be fetched in order for the local rev to become
        /// up to date.
        NeedsFetch(Oid),
        /// Don't know whether local rev is up to date. We'll fetch _all_ branches
        /// and tags from the server and see what happens.
        Indeterminate,
    }

    /// Updating the index is done pretty regularly so we want it to be as fast as
    /// possible. For registries hosted on GitHub (like the crates.io index) there's
    /// a fast path available to use [1] to tell us that there's no updates to be
    /// made.
    ///
    /// This function will attempt to hit that fast path and verify that the `oid`
    /// is actually the current branch of the repository.
    ///
    /// [1]: https://developer.github.com/v3/repos/commits/#get-the-sha-1-of-a-commit-reference
    ///
    /// Note that this function should never cause an actual failure because it's
    /// just a fast path. As a result all errors are ignored in this function and we
    /// just return a `bool`. Any real errors will be reported through the normal
    /// update path above.
    fn github_fast_path(
        repo: &mut git2::Repository,
        url: &str,
        reference: &GitReference,
        config: &Config,
    ) -> CargoResult<FastPathRev> {
        let url = Url::parse(url)?;
        if !is_github(&url) {
            return Ok(FastPathRev::Indeterminate);
        }

        let local_object = reference.resolve(repo).ok();

        let github_branch_name = match reference {
            GitReference::Branch(branch) => branch,
            GitReference::Tag(tag) => tag,
            GitReference::DefaultBranch => "HEAD",
            GitReference::Rev(rev) => {
                if rev.starts_with("refs/") {
                    rev
                } else if looks_like_commit_hash(rev) {
                    // `revparse_single` (used by `resolve`) is the only way to turn
                    // short hash -> long hash, but it also parses other things,
                    // like branch and tag names, which might coincidentally be
                    // valid hex.
                    //
                    // We only return early if `rev` is a prefix of the object found
                    // by `revparse_single`. Don't bother talking to GitHub in that
                    // case, since commit hashes are permanent. If a commit with the
                    // requested hash is already present in the local clone, its
                    // contents must be the same as what is on the server for that
                    // hash.
                    //
                    // If `rev` is not found locally by `revparse_single`, we'll
                    // need GitHub to resolve it and get a hash. If `rev` is found
                    // but is not a short hash of the found object, it's probably a
                    // branch and we also need to get a hash from GitHub, in case
                    // the branch has moved.
                    if let Some(local_object) = local_object {
                        if is_short_hash_of(rev, local_object) {
                            return Ok(FastPathRev::UpToDate);
                        }
                    }
                    rev
                } else {
                    debug!("can't use github fast path with `rev = \"{}\"`", rev);
                    return Ok(FastPathRev::Indeterminate);
                }
            }
        };

        // This expects GitHub urls in the form `github.com/user/repo` and nothing
        // else
        let mut pieces = url
            .path_segments()
            .ok_or_else(|| anyhow!("no path segments on url"))?;
        let username = pieces
            .next()
            .ok_or_else(|| anyhow!("couldn't find username"))?;
        let repository = pieces
            .next()
            .ok_or_else(|| anyhow!("couldn't find repository name"))?;
        if pieces.next().is_some() {
            anyhow::bail!("too many segments on URL");
        }

        // Trim off the `.git` from the repository, if present, since that's
        // optional for GitHub and won't work when we try to use the API as well.
        let repository = repository.strip_suffix(".git").unwrap_or(repository);

        let url = format!(
            "https://api.github.com/repos/{}/{}/commits/{}",
            username, repository, github_branch_name,
        );
        let mut handle = config.http()?.borrow_mut();
        debug!("attempting GitHub fast path for {}", url);
        handle.get(true)?;
        handle.url(&url)?;
        handle.useragent("cargo")?;
        handle.http_headers({
            let mut headers = List::new();
            headers.append("Accept: application/vnd.github.3.sha")?;
            if let Some(local_object) = local_object {
                headers.append(&format!("If-None-Match: \"{}\"", local_object))?;
            }
            headers
        })?;

        let mut response_body = Vec::new();
        let mut transfer = handle.transfer();
        transfer.write_function(|data| {
            response_body.extend_from_slice(data);
            Ok(data.len())
        })?;
        transfer.perform()?;
        drop(transfer); // end borrow of handle so that response_code can be called

        let response_code = handle.response_code()?;
        if response_code == 304 {
            Ok(FastPathRev::UpToDate)
        } else if response_code == 200 {
            let oid_to_fetch = str::from_utf8(&response_body)?.parse::<Oid>()?;
            Ok(FastPathRev::NeedsFetch(oid_to_fetch))
        } else {
            // Usually response_code == 404 if the repository does not exist, and
            // response_code == 422 if exists but GitHub is unable to resolve the
            // requested rev.
            Ok(FastPathRev::Indeterminate)
        }
    }

    fn is_github(url: &Url) -> bool {
        url.host_str() == Some("github.com")
    }

    fn looks_like_commit_hash(rev: &str) -> bool {
        rev.len() >= 7 && rev.chars().all(|ch| ch.is_ascii_hexdigit())
    }

    fn is_short_hash_of(rev: &str, oid: Oid) -> bool {
        let long_hash = oid.to_string();
        match long_hash.get(..rev.len()) {
            Some(truncated_long_hash) => truncated_long_hash.eq_ignore_ascii_case(rev),
            None => false,
        }
    }