fluidattacks-core-git 0.56.0

use anyhow::{Context, Result};
use base64::Engine;
use std::process::Output;
use std::time::Duration;
use tokio::process::Command;

use super::aws;
use super::types::{CredentialKind, Credentials, LsRemoteResult, RemoteHead};
use crate::clone::https::HttpsAccess;
use crate::clone::reason::hide;
use crate::clone::ssh::{normalize_ssh_url, setup_ssh_env};

const LS_REMOTE_TIMEOUT_SECS: u64 = 20;

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

struct AwsRole {
    arn: String,
    external_id: String,
    via: Option<String>,
}

/// What a `git ls-remote` answered, read from its output or from its running
/// out of time. `SYMREF` is whether the output it reads is the one git prints
/// with `--symref`; the answer, not its caller, decides it, so an output is
/// never read by a parser meant for the other one.
trait Answer {
    const SYMREF: bool;

    fn timed_out() -> Self;
    fn read(output: &Output, secrets: &[&str]) -> Self;
}

impl Answer for LsRemoteResult {
    const SYMREF: bool = false;

    fn timed_out() -> Self {
        Self {
            commit: None,
            error: Some(LS_REMOTE_TIMEOUT_MESSAGE.to_owned()),
        }
    }

    fn read(output: &Output, secrets: &[&str]) -> Self {
        parse_ls_remote_output(output, secrets)
    }
}

impl Answer for RemoteHead {
    const SYMREF: bool = true;

    fn timed_out() -> Self {
        Self {
            branch: None,
            error: Some(LS_REMOTE_TIMEOUT_MESSAGE.to_owned()),
        }
    }

    fn read(output: &Output, secrets: &[&str]) -> Self {
        parse_symref_output(output, secrets)
    }
}

fn redirect_config(follow_redirects: bool) -> [String; 2] {
    [
        "-c".to_owned(),
        format!("http.followRedirects={follow_redirects}"),
    ]
}

fn ls_remote_args(url: &str, pattern: &str, symref: bool) -> Vec<String> {
    let mut args = vec!["ls-remote".to_owned()];
    if symref {
        args.push("--symref".to_owned());
    }
    args.extend(["--".to_owned(), url.to_owned(), pattern.to_owned()]);
    args
}

async fn run_ls_remote<A: Answer>(command: &mut Command, secrets: &[&str]) -> Result<A> {
    let Ok(output) = tokio::time::timeout(
        Duration::from_secs(LS_REMOTE_TIMEOUT_SECS),
        command.kill_on_drop(true).output(),
    )
    .await
    else {
        return Ok(A::timed_out());
    };

    Ok(A::read(&output.context("running git ls-remote")?, secrets))
}

pub async fn ls_remote(
    url: &str,
    branch: &str,
    credentials: Option<&Credentials>,
    follow_redirects: bool,
) -> Result<LsRemoteResult> {
    ask(url, branch, credentials, follow_redirects).await
}

/// 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, or
/// the credential could not be prepared.
pub async fn remote_head(
    url: &str,
    credentials: Option<&Credentials>,
    follow_redirects: bool,
) -> Result<RemoteHead> {
    ask(url, "HEAD", credentials, follow_redirects).await
}

async fn ask<A: Answer>(
    url: &str,
    pattern: &str,
    credentials: Option<&Credentials>,
    follow_redirects: bool,
) -> Result<A> {
    match credentials.map(|c| &c.kind) {
        Some(CredentialKind::Ssh { key }) => ls_remote_ssh(url, pattern, key).await,
        Some(CredentialKind::AwsRole {
            arn,
            external_id,
            via,
        }) => {
            let role = AwsRole {
                arn: arn.clone(),
                external_id: external_id.clone(),
                via: via.clone(),
            };
            ls_remote_codecommit(url, pattern, &role, follow_redirects).await
        }
        kind => {
            let access = HttpsAccess::new(url, kind)?;
            ls_remote_https(&access, pattern, follow_redirects).await
        }
    }
}

async fn ls_remote_ssh<A: Answer>(url: &str, pattern: &str, key_b64: &str) -> Result<A> {
    let key_data = base64::engine::general_purpose::STANDARD
        .decode(key_b64)
        .context("decoding SSH key")?;

    let key_file = tempfile::Builder::new()
        .prefix("melts-ssh-key-")
        .tempfile()
        .context("creating SSH key file")?;

    std::fs::write(key_file.path(), &key_data).context("writing SSH key")?;

    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        std::fs::set_permissions(key_file.path(), std::fs::Permissions::from_mode(0o400))
            .context("setting SSH key permissions")?;
    }

    let git_ssh_command = setup_ssh_env(key_file.path());
    let args = ls_remote_args(&normalize_ssh_url(url), pattern, A::SYMREF);

    let mut command = Command::new("git");
    command.args(&args).env("GIT_SSH_COMMAND", &git_ssh_command);
    run_ls_remote(&mut command, &[]).await
}

async fn ls_remote_https<A: Answer>(
    access: &HttpsAccess,
    pattern: &str,
    follow_redirects: bool,
) -> Result<A> {
    let mut args = vec!["-c".to_owned(), "http.sslVerify=false".to_owned()];
    args.extend(redirect_config(follow_redirects));
    args.extend(ls_remote_args(&access.url, pattern, A::SYMREF));

    let mut command = access.git();
    command.args(&args);
    run_ls_remote(&mut command, access.secret().as_slice()).await
}

async fn ls_remote_codecommit<A: Answer>(
    url: &str,
    pattern: &str,
    role: &AwsRole,
    follow_redirects: bool,
) -> Result<A> {
    let creds = aws::assume_role(&role.arn, &role.external_id, url, role.via.as_deref()).await?;

    let args = codecommit_ls_remote_args(url, pattern, A::SYMREF, follow_redirects);

    let mut command = Command::new("git");
    command
        .args(&args)
        .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);
    run_ls_remote(&mut command, &[]).await
}

/// The `git ls-remote` arguments for a `codecommit::` url. git checks the
/// certificate, since the helper always reaches AWS's own endpoint.
fn codecommit_ls_remote_args(
    url: &str,
    pattern: &str,
    symref: bool,
    follow_redirects: bool,
) -> Vec<String> {
    let mut args = redirect_config(follow_redirects).to_vec();
    args.extend(ls_remote_args(url, pattern, symref));
    args
}

fn parse_ls_remote_output(output: &Output, secrets: &[&str]) -> LsRemoteResult {
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        return LsRemoteResult {
            commit: None,
            error: Some(hide(&stderr, secrets)),
        };
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    let commit = stdout
        .lines()
        .next()
        .and_then(|line| line.split('\t').next())
        .unwrap_or_default()
        .trim()
        .to_owned();

    LsRemoteResult {
        commit: Some(commit),
        error: None,
    }
}

fn parse_symref_output(output: &Output, secrets: &[&str]) -> RemoteHead {
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        return RemoteHead {
            branch: None,
            error: Some(hide(&stderr, secrets)),
        };
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    RemoteHead {
        branch: stdout.lines().find_map(head_branch).map(str::to_owned),
        error: None,
    }
}

/// 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::{
        codecommit_ls_remote_args, ls_remote, ls_remote_args, parse_ls_remote_output,
        parse_symref_output, redirect_config, remote_head, run_ls_remote,
    };
    use crate::clone::https::HttpsAccess;
    use crate::types::{CredentialKind, Credentials, LsRemoteResult};

    // 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(),
            },
        }
    }

    fn output(code: i32, stdout: &str, stderr: &str) -> std::process::Output {
        use std::os::unix::process::ExitStatusExt;
        std::process::Output {
            status: std::process::ExitStatus::from_raw(code << 8),
            stdout: stdout.as_bytes().to_vec(),
            stderr: stderr.as_bytes().to_vec(),
        }
    }

    #[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() {
        let result = parse_ls_remote_output(&output(0, "", ""), &[]);
        assert_eq!(result.commit, Some(String::new()));
        assert!(result.error.is_none());
    }

    #[test]
    fn the_first_ref_is_the_commit() {
        let result = parse_ls_remote_output(
            &output(0, "abc123\trefs/heads/main\ndef456\trefs/heads/other\n", ""),
            &[],
        );
        assert_eq!(result.commit.as_deref(), Some("abc123"));
    }

    #[test]
    fn a_failure_reports_the_stderr_and_no_commit() {
        let result = parse_ls_remote_output(&output(128, "", "fatal: repository not found"), &[]);
        assert!(result.commit.is_none());
        assert_eq!(result.error.as_deref(), Some("fatal: repository not found"));
    }

    #[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"]);
        run_ls_remote::<LsRemoteResult>(&mut command, access.secret().as_slice())
            .await
            .unwrap();

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

    #[test]
    fn a_failure_hides_the_credential_a_server_echoes() {
        let said = "remote: token tok123 is not valid\nfatal: Authentication failed\n";
        let result = parse_ls_remote_output(&output(128, "", said), &["tok123"]);
        assert_eq!(
            result.error.as_deref(),
            Some("remote: token [REDACTED] is not valid\nfatal: Authentication failed\n")
        );
    }

    #[test]
    fn a_codecommit_url_lets_git_check_the_certificate() {
        for symref in [false, true] {
            let args =
                codecommit_ls_remote_args("codecommit::us-east-1://repo", "main", symref, false);
            assert!(!args.contains(&"http.sslVerify=false".to_owned()));
        }
    }

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

    #[test]
    fn the_branch_head_names_is_read_without_its_prefix() {
        let result = parse_symref_output(
            &output(0, "ref: refs/heads/release/2.0\tHEAD\nabc123\tHEAD\n", ""),
            &[],
        );
        assert_eq!(result.branch.as_deref(), Some("release/2.0"));
        assert!(result.error.is_none());
    }

    #[test]
    fn a_head_that_names_no_branch_is_no_branch_and_no_error() {
        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",
        ] {
            let result = parse_symref_output(&output(0, said, ""), &[]);
            assert!(result.branch.is_none(), "{said:?}");
            assert!(result.error.is_none(), "{said:?}");
        }
    }

    #[test]
    fn a_failed_head_read_reports_the_stderr_with_the_credential_hidden() {
        let said = "remote: token tok123 is not valid\nfatal: Authentication failed\n";
        let result = parse_symref_output(&output(128, "", said), &["tok123"]);
        assert!(result.branch.is_none());
        assert_eq!(
            result.error.as_deref(),
            Some("remote: token [REDACTED] is not valid\nfatal: Authentication failed\n")
        );
    }

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

        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 = remote.path().to_str().unwrap();

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

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

    #[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:?}");
        }
    }
}