fluidattacks_core_git/

remote.rs

use std::time::Duration;
use tokio::process::Command;

use super::aws::{self, AwsTempCreds};
use super::types::{CredentialKind, Credentials, LsRemoteResult, RemoteHead};
use crate::call::not_run;
use crate::clone::https::{public_pin, HttpsAccess};
use crate::clone::reason::hide;
use crate::clone::ssh::{drop_scp_scheme, SshKey, ONLY_SSH};
use crate::clone::{has_http_scheme, redirect_config};
use crate::errors::{
    GitCallError, HttpsAccessError, HttpsLsRemoteError, LsRemoteError, RemoteAccessError,
};

const LS_REMOTE_TIMEOUT: Duration = Duration::from_secs(20);

/// The message `roots/validations.py` matches on to raise `GitTimeoutError`.
const LS_REMOTE_TIMEOUT_MESSAGE: &str = "git ls-remote time out";

/// Which hosts an https ls-remote may reach.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Reach {
    Any,
    /// Only a host whose every address is reachable from outside, with git sent to
    /// those addresses alone, so a name that resolves elsewhere later is not followed.
    Public,
}

/// The refs a branch names, in the order `git clone --branch` tries them; git
/// matches any ref ending in `/<branch>`. `HEAD` is the line git lists as `HEAD`.
fn branch_refs(branch: &str) -> Vec<String> {
    if branch == "HEAD" {
        return vec!["HEAD".to_owned()];
    }
    vec![
        format!("refs/heads/{branch}"),
        format!("refs/tags/{branch}"),
    ]
}

fn ls_remote_args(url: &str, flags: &[&str], pattern: &str) -> Vec<String> {
    let mut args = vec!["ls-remote".to_owned()];
    args.extend(flags.iter().map(|&flag| flag.to_owned()));
    args.extend(["--".to_owned(), url.to_owned(), pattern.to_owned()]);
    args
}

/// What git listed; a refusal keeps the whole stderr, with `secrets` hidden.
async fn run_ls_remote(command: &mut Command, secrets: &[&str]) -> Result<String, GitCallError> {
    let Ok(output) =
        tokio::time::timeout(LS_REMOTE_TIMEOUT, command.kill_on_drop(true).output()).await
    else {
        return Err(GitCallError::TimedOut {
            command: "ls-remote",
            after: LS_REMOTE_TIMEOUT,
        });
    };

    let output = output.map_err(|source| not_run("ls-remote", source))?;
    if !output.status.success() {
        return Err(GitCallError::Refused {
            command: "ls-remote",
            status: output.status,
            stderr: hide(&String::from_utf8_lossy(&output.stderr), secrets),
        });
    }
    Ok(String::from_utf8_lossy(&output.stdout).into_owned())
}

/// A remote with its access prepared: the key written, the session assumed or the https access built.
enum Remote {
    Ssh { url: String, key: SshKey },
    CodeCommit { url: String, creds: AwsTempCreds },
    Https(HttpsAccess),
}

impl Remote {
    async fn connect(
        url: &str,
        credentials: Option<&Credentials>,
    ) -> Result<Self, RemoteAccessError> {
        Ok(match credentials.map(|c| &c.kind) {
            Some(CredentialKind::Ssh { key }) => Self::Ssh {
                url: drop_scp_scheme(url).to_owned(),
                key: SshKey::write(key)?,
            },
            Some(CredentialKind::AwsRole {
                arn,
                external_id,
                via,
            }) => Self::CodeCommit {
                url: url.to_owned(),
                creds: aws::assume_role(arn, external_id, url, via.as_deref()).await?,
            },
            kind => Self::Https(https_access(url, kind, None)?),
        })
    }

    fn git(&self, follow_redirects: bool) -> RemoteGit<'_> {
        match self {
            Self::Ssh { url, key } => {
                let mut command = Command::new("git");
                command
                    .env("GIT_SSH_COMMAND", &key.command)
                    .env("GIT_ALLOW_PROTOCOL", ONLY_SSH);
                RemoteGit {
                    command,
                    url,
                    secrets: vec![],
                }
            }
            // git checks the certificate, since the helper always reaches AWS's own endpoint.
            Self::CodeCommit { url, creds } => {
                let mut command = Command::new("git");
                command
                    .args(redirect_config(follow_redirects))
                    .env("AWS_ACCESS_KEY_ID", &creds.access_key)
                    .env("AWS_SECRET_ACCESS_KEY", &creds.secret_key)
                    .env("AWS_SESSION_TOKEN", &creds.session_token)
                    .env("AWS_DEFAULT_REGION", &creds.region);
                RemoteGit {
                    command,
                    url,
                    secrets: vec![&creds.secret_key, &creds.session_token],
                }
            }
            Self::Https(access) => {
                let mut command = access.git();
                command
                    .args(["-c", "http.sslVerify=false"])
                    .args(redirect_config(follow_redirects));
                RemoteGit {
                    command,
                    url: access.url(),
                    secrets: access.secret().into_iter().collect(),
                }
            }
        }
    }
}

/// A git command for a remote, still waiting for its subcommand, with the
/// url to ask and the secrets to hide from what git says.
struct RemoteGit<'a> {
    command: Command,
    url: &'a str,
    secrets: Vec<&'a str>,
}

/// The commit `branch` names at `url`, empty when the remote has no such
/// branch or tag. `error` is what git said, with the credential hidden, when
/// the remote refused or did not answer in time.
pub async fn ls_remote(
    url: &str,
    branch: &str,
    credentials: Option<&Credentials>,
    follow_redirects: bool,
) -> Result<LsRemoteResult, LsRemoteError> {
    let remote = Remote::connect(url, credentials).await?;
    let listing = list_refs(&remote, &[], branch, follow_redirects).await;
    Ok(commit_answer(listing, branch)?)
}

/// `ls_remote` over https, and with `Reach::Public` the host is checked before anything
/// else: before the credential, and before git runs.
pub async fn https_ls_remote(
    url: &str,
    branch: &str,
    credential: Option<&CredentialKind>,
    follow_redirects: bool,
    reach: Reach,
) -> Result<LsRemoteResult, HttpsLsRemoteError> {
    let pin = match reach {
        Reach::Any => None,
        Reach::Public => Some(public_pin(url).await?),
    };
    let remote = Remote::Https(https_access(url, credential, pin)?);
    let listing = list_refs(&remote, &[], branch, follow_redirects).await;
    Ok(commit_answer(listing, branch)?)
}

fn commit_answer(
    listing: Result<String, GitCallError>,
    branch: &str,
) -> Result<LsRemoteResult, GitCallError> {
    match listing {
        Ok(listing) => Ok(LsRemoteResult {
            commit: Some(commit_of(&listing, branch)),
            error: None,
        }),
        Err(GitCallError::Refused { stderr, .. }) => Ok(LsRemoteResult {
            commit: None,
            error: Some(stderr),
        }),
        Err(GitCallError::TimedOut { .. }) => Ok(LsRemoteResult {
            commit: None,
            error: Some(LS_REMOTE_TIMEOUT_MESSAGE.to_owned()),
        }),
        Err(error) => Err(error),
    }
}

/// The branch the `HEAD` of the remote at `url` names, asked with the same
/// `credentials` and redirect policy a clone of `url` takes.
///
/// `branch` is the bare name, without `refs/heads/`. Neither field is set
/// when the remote names no branch: an empty repository, a detached `HEAD`,
/// or a server that does not advertise symbolic refs. `error` is what git
/// said, with the credential hidden, when the remote could not be asked or
/// did not answer in time. An `Err` means git could not be run at all, the
/// credential could not be prepared, or a url with no credential is not http.
pub async fn remote_head(
    url: &str,
    credentials: Option<&Credentials>,
    follow_redirects: bool,
) -> Result<RemoteHead, LsRemoteError> {
    let remote = Remote::connect(url, credentials).await?;
    let listing = list_refs(&remote, &["--symref"], "HEAD", follow_redirects).await;
    Ok(head_answer(listing)?)
}

fn head_answer(listing: Result<String, GitCallError>) -> Result<RemoteHead, GitCallError> {
    match listing {
        Ok(listing) => Ok(RemoteHead {
            branch: head_of(&listing),
            error: None,
        }),
        Err(GitCallError::Refused { stderr, .. }) => Ok(RemoteHead {
            branch: None,
            error: Some(stderr),
        }),
        Err(GitCallError::TimedOut { .. }) => Ok(RemoteHead {
            branch: None,
            error: Some(LS_REMOTE_TIMEOUT_MESSAGE.to_owned()),
        }),
        Err(error) => Err(error),
    }
}

async fn list_refs(
    remote: &Remote,
    flags: &[&str],
    pattern: &str,
    follow_redirects: bool,
) -> Result<String, GitCallError> {
    let mut git = remote.git(follow_redirects);
    git.command.args(ls_remote_args(git.url, flags, pattern));
    run_ls_remote(&mut git.command, &git.secrets).await
}

fn https_access(
    url: &str,
    credential: Option<&CredentialKind>,
    pin: Option<String>,
) -> Result<HttpsAccess, HttpsAccessError> {
    // git takes any url, an scp-like one over ssh with whatever keys this machine has.
    if credential.is_none() && !has_http_scheme(url) {
        return Err(HttpsAccessError::NotHttp);
    }
    let access = HttpsAccess::new(url, credential)?;
    Ok(match pin {
        Some(pin) => access.pinned(pin),
        None => access,
    })
}

/// The commit a `git ls-remote` listing gives `branch`; empty when it lists none.
fn commit_of(listing: &str, branch: &str) -> String {
    let listed = |wanted: &str| {
        listing.lines().find_map(|line| {
            let (commit, name) = line.split_once('\t')?;
            (name == wanted).then_some(commit)
        })
    };
    branch_refs(branch)
        .iter()
        .find_map(|wanted| listed(wanted))
        .unwrap_or_default()
        .to_owned()
}

/// The branch a `git ls-remote --symref` listing points `HEAD` at.
fn head_of(listing: &str) -> Option<String> {
    listing.lines().find_map(head_branch).map(str::to_owned)
}

/// The branch a `ref: <target>\tHEAD` line points `HEAD` at; none for any
/// other line, or for a target outside `refs/heads/`.
fn head_branch(line: &str) -> Option<&str> {
    let (target, name) = line.strip_prefix("ref: ")?.split_once('\t')?;
    if name != "HEAD" {
        return None;
    }
    target
        .strip_prefix("refs/heads/")
        .filter(|branch| !branch.is_empty())
}

#[cfg(test)]
mod tests {
    use std::io::{BufRead, BufReader, Write};
    use std::net::{TcpListener, TcpStream};
    use std::sync::{Arc, Mutex};

    use base64::Engine;

    use super::{
        commit_of, head_of, https_access, https_ls_remote, list_refs, ls_remote, ls_remote_args,
        redirect_config, remote_head, run_ls_remote, AwsTempCreds, Reach, Remote,
    };
    use crate::clone::https::HttpsAccess;
    use crate::errors::{
        GitCallError, HostError, HttpsAccessError, HttpsLsRemoteError, LsRemoteError,
    };
    use crate::types::{CredentialKind, Credentials};
    use tokio::process::Command;

    // The path asked for and the Authorization it carried.
    fn read_request(stream: &TcpStream) -> (String, Option<String>) {
        let mut path = String::new();
        let mut authorization = None;
        let mut reader = BufReader::new(stream);
        let mut line = String::new();
        while reader.read_line(&mut line).is_ok_and(|read| read > 0) {
            let header = line.trim_end();
            if header.is_empty() {
                break;
            }
            if path.is_empty() {
                header
                    .split(' ')
                    .nth(1)
                    .unwrap_or_default()
                    .clone_into(&mut path);
            }
            if let Some(value) = header.strip_prefix("Authorization: ") {
                authorization = Some(value.to_owned());
            }
            line.clear();
        }
        (path, authorization)
    }

    fn answer(redirect_to: Option<&str>, path: &str) -> String {
        redirect_to.map_or_else(
            || {
                "HTTP/1.1 401 Unauthorized\r\nWWW-Authenticate: Basic realm=\"x\"\r\n\
                 Content-Length: 0\r\nConnection: close\r\n\r\n"
                    .to_owned()
            },
            |host| {
                format!(
                    "HTTP/1.1 302 Found\r\nLocation: {host}{path}\r\n\
                     Content-Length: 0\r\nConnection: close\r\n\r\n"
                )
            },
        )
    }

    // A host that sends every request to `redirect_to` when given one, and
    // otherwise turns it down; it keeps the Authorization each request carried.
    fn serve(redirect_to: Option<String>) -> (String, Arc<Mutex<Vec<Option<String>>>>) {
        let listener = TcpListener::bind("127.0.0.1:0").expect("bind");
        let port = listener.local_addr().expect("addr").port();
        let seen = Arc::new(Mutex::new(Vec::new()));
        let record = Arc::clone(&seen);
        std::thread::spawn(move || {
            for stream in listener.incoming().flatten() {
                let (path, authorization) = read_request(&stream);
                record.lock().expect("lock").push(authorization);
                let answer = answer(redirect_to.as_deref(), &path);
                let _ = (&stream).write_all(answer.as_bytes());
            }
        });
        (format!("http://127.0.0.1:{port}"), seen)
    }

    fn token(token: &str) -> Credentials {
        Credentials {
            kind: CredentialKind::Token {
                token: token.to_owned(),
                is_pat: false,
                oauth_type: String::new(),
            },
        }
    }

    fn pat(token: &str) -> Credentials {
        Credentials {
            kind: CredentialKind::Token {
                token: token.to_owned(),
                is_pat: true,
                oauth_type: String::new(),
            },
        }
    }

    // A git that writes `stderr` and exits with `code`.
    fn refusing(stderr: &str, code: i32) -> Command {
        let mut command = Command::new("sh");
        command.args([
            "-c",
            &format!("printf '%s' \"$0\" >&2; exit {code}"),
            stderr,
        ]);
        command
    }

    #[test]
    fn redirects_are_forbidden_explicitly_and_not_left_to_the_git_default() {
        assert_eq!(
            redirect_config(false),
            ["-c".to_owned(), "http.followRedirects=false".to_owned()]
        );
        assert_eq!(
            redirect_config(true),
            ["-c".to_owned(), "http.followRedirects=true".to_owned()]
        );
    }

    #[test]
    fn a_branch_missing_from_the_remote_is_an_empty_commit_and_not_a_missing_one() {
        assert_eq!(commit_of("", "main"), "");
    }

    #[test]
    fn a_branch_is_read_by_its_full_name_and_before_a_tag_of_the_same_name() {
        for (said, commit) in [
            (
                "aaa\trefs/heads/feature/main\nbbb\trefs/heads/main\n",
                "bbb",
            ),
            ("ttt\trefs/tags/main\nbbb\trefs/heads/main\n", "bbb"),
            ("ttt\trefs/tags/main\n", "ttt"),
            ("aaa\trefs/heads/feature/main\n", ""),
        ] {
            assert_eq!(commit_of(said, "main"), commit, "{said:?}");
        }
    }

    #[test]
    fn head_is_read_only_from_the_line_git_lists_as_head() {
        for (said, commit) in [
            ("aaa\tHEAD\nbbb\trefs/heads/HEAD\n", "aaa"),
            ("bbb\trefs/heads/HEAD\nccc\trefs/remotes/origin/HEAD\n", ""),
        ] {
            assert_eq!(commit_of(said, "HEAD"), commit, "{said:?}");
        }
    }

    #[tokio::test]
    async fn a_refusal_keeps_the_whole_stderr_with_the_credential_hidden() {
        let said = "remote: token tok123 is not valid\nfatal: Authentication failed\n";

        let refused = run_ls_remote(&mut refusing(said, 128), &["tok123"]).await;

        let Err(GitCallError::Refused { stderr, .. }) = refused else {
            panic!("{refused:?}");
        };
        assert_eq!(
            stderr,
            "remote: token [REDACTED] is not valid\nfatal: Authentication failed\n"
        );
    }

    #[tokio::test]
    async fn a_token_reaches_its_host_and_stays_out_of_the_error() {
        for (credentials, login) in [
            (token("Zm9v+YmFy"), "Zm9v+YmFy:"),
            (pat("Zm9v+YmFy"), "pat:Zm9v+YmFy"),
        ] {
            let (host, seen) = serve(None);
            let result = ls_remote(
                &format!("{host}/org/repo.git"),
                "main",
                Some(&credentials),
                false,
            )
            .await
            .unwrap();

            let sent = base64::engine::general_purpose::STANDARD.encode(login);
            assert!(seen
                .lock()
                .unwrap()
                .contains(&Some(format!("Basic {sent}"))));
            let error = result.error.unwrap();
            assert!(error.contains("Authentication failed"), "{error}");
            assert!(!error.contains("Zm9v"), "{error}");
        }
    }

    #[tokio::test]
    async fn a_redirect_to_another_host_carries_no_credential() {
        for credentials in [token("tok123"), pat("tok123")] {
            let (other, other_seen) = serve(None);
            let other = other.replace("127.0.0.1", "localhost");
            let (host, _) = serve(Some(other));
            let result = ls_remote(
                &format!("{host}/org/repo.git"),
                "main",
                Some(&credentials),
                true,
            )
            .await
            .unwrap();

            assert!(result.error.is_some());
            let other_seen = other_seen.lock().unwrap().clone();
            assert!(!other_seen.is_empty());
            assert!(other_seen.iter().all(Option::is_none), "{other_seen:?}");
        }
    }

    #[tokio::test]
    async fn a_helper_the_caller_configured_never_sees_the_credential() {
        let (host, _) = serve(None);
        let calls = tempfile::NamedTempFile::new().unwrap();
        let access =
            HttpsAccess::new(&format!("{host}/org/repo.git"), Some(&token("tok123").kind)).unwrap();
        let mut command = access.git();
        command
            .env(
                "GIT_CONFIG_PARAMETERS",
                format!(
                    "'credential.helper'='!f() {{ echo $1 >> {}; }}; f'",
                    calls.path().display()
                ),
            )
            .args(["ls-remote", "--", access.url(), "main"]);
        let refused = run_ls_remote(&mut command, access.secret().as_slice()).await;

        assert!(
            matches!(refused, Err(GitCallError::Refused { .. })),
            "{refused:?}"
        );

        assert_eq!(std::fs::read_to_string(calls.path()).unwrap(), "");
    }

    fn session() -> AwsTempCreds {
        AwsTempCreds {
            access_key: "an-access-key".to_owned(),
            secret_key: "a-secret-key".to_owned(),
            session_token: "a-token".to_owned(),
            region: "us-east-1".to_owned(),
        }
    }

    #[test]
    fn a_codecommit_url_lets_git_check_the_certificate() {
        let remote = Remote::CodeCommit {
            url: "codecommit::us-east-1://repo".to_owned(),
            creds: session(),
        };

        let git = remote.git(false);

        assert!(!git
            .command
            .as_std()
            .get_args()
            .any(|arg| arg == "http.sslVerify=false"));
    }

    #[tokio::test]
    async fn a_codecommit_ls_remote_keeps_the_session_out_of_what_git_says() {
        let tmp = tempfile::tempdir().unwrap();
        // git names the repository it could not find, so the url carries the session into stderr.
        let url = format!("{}/a-secret-key/a-token", tmp.path().display());
        let remote = Remote::CodeCommit {
            url,
            creds: session(),
        };

        let answer = list_refs(&remote, &[], "main", false).await;

        let Err(GitCallError::Refused { stderr, .. }) = answer else {
            panic!("{answer:?}");
        };
        assert!(stderr.contains("[REDACTED]/[REDACTED]"), "{stderr}");
    }

    #[test]
    fn symbolic_refs_are_asked_for_only_when_wanted_and_before_the_url() {
        assert_eq!(
            ls_remote_args("https://h/r", &["--symref"], "HEAD"),
            ["ls-remote", "--symref", "--", "https://h/r", "HEAD"]
        );
        assert_eq!(
            ls_remote_args("https://h/r", &[], "main"),
            ["ls-remote", "--", "https://h/r", "main"]
        );
    }

    // A repository at a local path whose HEAD names `branch`, with `commits`
    // commits on it; git reaches a path the way it reaches a public remote.
    fn repository(branch: &str, commits: usize) -> tempfile::TempDir {
        let dir = tempfile::tempdir().unwrap();
        let git = |args: &[&str]| {
            let status = std::process::Command::new("git")
                .arg("-C")
                .arg(dir.path())
                .args(["-c", "user.name=t", "-c", "user.email=t@example.com"])
                .args(args)
                .output()
                .unwrap()
                .status;
            assert!(status.success(), "git {args:?}");
        };
        git(&["init", "--quiet", "--initial-branch", branch]);
        for _ in 0..commits {
            git(&["commit", "--quiet", "--allow-empty", "--message", "c"]);
        }
        dir
    }

    // The file `path` names under `git_dir`, as an http answer; a 404 when there is none.
    fn file_answer(git_dir: &std::path::Path, path: &str) -> Vec<u8> {
        let file = path.split('?').next().unwrap_or_default();
        let Ok(body) = std::fs::read(git_dir.join(file.trim_start_matches('/'))) else {
            return b"HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\nConnection: close\r\n\r\n"
                .to_vec();
        };
        let head = format!(
            "HTTP/1.1 200 OK\r\nContent-Length: {}\r\nConnection: close\r\n\r\n",
            body.len()
        );
        [head.into_bytes(), body].concat()
    }

    // The files of `repository`'s .git, the way git's dumb http reads them; refs
    // made after this call stay unseen.
    fn serve_repository(repository: &std::path::Path) -> String {
        let git_dir = repository.join(".git");
        let updated = std::process::Command::new("git")
            .arg("-C")
            .arg(&git_dir)
            .arg("update-server-info")
            .status()
            .unwrap();
        assert!(updated.success());
        let listener = TcpListener::bind("127.0.0.1:0").expect("bind");
        let port = listener.local_addr().expect("addr").port();
        std::thread::spawn(move || {
            for stream in listener.incoming().flatten() {
                let (path, _) = read_request(&stream);
                let _ = (&stream).write_all(&file_answer(&git_dir, &path));
            }
        });
        format!("http://127.0.0.1:{port}/")
    }

    #[test]
    fn the_branch_head_names_is_read_without_its_prefix() {
        assert_eq!(
            head_of("ref: refs/heads/release/2.0\tHEAD\nabc123\tHEAD\n").as_deref(),
            Some("release/2.0")
        );
    }

    #[test]
    fn a_head_that_names_no_branch_is_no_branch() {
        for said in [
            "",
            "abc123\tHEAD\n",
            "ref: refs/tags/v1\tHEAD\n",
            "ref: refs/heads/\tHEAD\n",
            "ref: refs/heads/main\trefs/remotes/origin/HEAD\n",
        ] {
            assert!(head_of(said).is_none(), "{said:?}");
        }
    }

    #[tokio::test]
    async fn a_remote_answers_the_branch_its_head_names() {
        let remote = repository("trunk", 1);
        let url = serve_repository(remote.path());

        let result = remote_head(&url, None, false).await.unwrap();

        assert_eq!(result.branch.as_deref(), Some("trunk"));
        assert!(result.error.is_none());
    }

    #[tokio::test]
    async fn an_empty_remote_names_no_branch() {
        let remote = repository("trunk", 0);
        let url = serve_repository(remote.path());

        let result = remote_head(&url, None, false).await.unwrap();

        assert!(result.branch.is_none());
        assert!(result.error.is_none());
    }

    #[tokio::test]
    async fn a_branch_is_not_found_by_a_ref_that_only_ends_in_its_name() {
        let remote = repository("trunk", 1);
        let moved = std::process::Command::new("git")
            .arg("-C")
            .arg(remote.path())
            .args(["update-ref", "refs/heads/feature/dev", "trunk"])
            .status()
            .unwrap();
        assert!(moved.success());
        let url = serve_repository(remote.path());

        let found = ls_remote(&url, "trunk", None, false).await.unwrap();
        let missing = ls_remote(&url, "dev", None, false).await.unwrap();

        assert_eq!(found.commit.unwrap().len(), 40);
        assert_eq!(missing.commit.as_deref(), Some(""));
    }

    #[tokio::test]
    async fn only_a_public_reach_refuses_a_local_host() {
        let remote = repository("trunk", 1);
        let url = serve_repository(remote.path());

        let public = https_ls_remote(&url, "trunk", None, false, Reach::Public).await;
        let any = https_ls_remote(&url, "trunk", None, false, Reach::Any)
            .await
            .unwrap();

        assert!(
            matches!(public, Err(HttpsLsRemoteError::Host(HostError::Local(_)))),
            "{public:?}"
        );
        assert_eq!(any.commit.unwrap().len(), 40);
    }

    #[tokio::test]
    async fn a_pinned_access_sends_git_to_the_pinned_address() {
        let remote = repository("trunk", 1);
        let served = serve_repository(remote.path());
        let port = served.trim_end_matches('/').rsplit(':').next().unwrap();
        let url = format!("http://pinned.invalid:{port}/");
        let pin = Some(format!("pinned.invalid:{port}:127.0.0.1"));

        let pinned = Remote::Https(https_access(&url, None, pin).unwrap());
        let listing = list_refs(&pinned, &[], "trunk", false).await.unwrap();

        assert!(listing.ends_with("\trefs/heads/trunk\n"), "{listing:?}");
    }

    #[tokio::test]
    async fn without_a_credential_a_url_that_is_not_http_never_runs_git() {
        let remote = repository("trunk", 1);
        let path = remote.path().to_str().unwrap();

        for url in [
            path,
            "httpx://127.0.0.1/repo.git",
            "http:127.0.0.1/repo.git",
        ] {
            let answer = ls_remote(url, "trunk", None, false).await;

            assert!(
                matches!(
                    answer,
                    Err(LsRemoteError::Access(HttpsAccessError::NotHttp))
                ),
                "{url}: {answer:?}"
            );
        }
    }

    #[tokio::test]
    async fn a_head_read_that_cannot_ask_says_why_as_before() {
        // clones logs this text when it cannot read the default branch.
        let error = remote_head("git@example.com:org/repo.git", None, false)
            .await
            .unwrap_err();

        assert_eq!(error.to_string(), "expected an http or https url");
    }

    #[tokio::test]
    async fn an_ssh_ls_remote_with_a_nul_in_the_branch_never_runs_git() {
        let key = Credentials {
            kind: CredentialKind::Ssh {
                key: base64::engine::general_purpose::STANDARD.encode("not a real key"),
            },
        };

        let nul = ls_remote("git@example.com:org/repo.git", "ma\0in", Some(&key), false).await;

        assert!(matches!(
            nul,
            Err(LsRemoteError::Git(GitCallError::NullByte {
                command: "ls-remote"
            }))
        ));
    }

    #[tokio::test]
    async fn a_key_reads_no_head_from_a_url_that_is_not_ssh() {
        let remote = repository("trunk", 1);
        let url = remote.path().to_str().unwrap();
        let key = Credentials {
            kind: CredentialKind::Ssh {
                key: base64::engine::general_purpose::STANDARD.encode("not a real key"),
            },
        };

        let result = remote_head(url, Some(&key), false).await.unwrap();

        assert!(result.branch.is_none());
        assert!(result.error.is_some());
    }

    #[tokio::test]
    async fn a_head_read_takes_the_token_to_its_host_and_out_of_the_error() {
        for (credentials, login) in [
            (token("Zm9v+YmFy"), "Zm9v+YmFy:"),
            (pat("Zm9v+YmFy"), "pat:Zm9v+YmFy"),
        ] {
            let (host, seen) = serve(None);
            let result = remote_head(&format!("{host}/org/repo.git"), Some(&credentials), false)
                .await
                .unwrap();

            let sent = base64::engine::general_purpose::STANDARD.encode(login);
            assert!(seen
                .lock()
                .unwrap()
                .contains(&Some(format!("Basic {sent}"))));
            assert!(result.branch.is_none());
            let error = result.error.unwrap();
            assert!(error.contains("Authentication failed"), "{error}");
            assert!(!error.contains("Zm9v"), "{error}");
        }
    }

    #[tokio::test]
    async fn a_head_read_redirected_to_another_host_carries_no_credential() {
        for credentials in [token("tok123"), pat("tok123")] {
            let (other, other_seen) = serve(None);
            let other = other.replace("127.0.0.1", "localhost");
            let (host, _) = serve(Some(other));
            let result = remote_head(&format!("{host}/org/repo.git"), Some(&credentials), true)
                .await
                .unwrap();

            assert!(result.error.is_some());
            let other_seen = other_seen.lock().unwrap().clone();
            assert!(!other_seen.is_empty());
            assert!(other_seen.iter().all(Option::is_none), "{other_seen:?}");
        }
    }
}