amiss-bootstrap 0.1.0

use std::process::{Child, ExitStatus};
use std::time::{Duration, Instant};

use amiss_wire::digest::hj;
use amiss_wire::json::{Value, canonical, parse};
use amiss_wire::report::PAYLOAD_SCHEMA;

/// The exact acceptance defect, most specific first in evaluation order. The
/// trusted wrapper publishes success only when acceptance returns no defect.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum AcceptanceDefect {
    /// The bytes are not one parsable envelope with the expected members.
    Shape,
    /// The bytes are not exactly `JCS(envelope) || LF`.
    Noncanonical,
    /// The payload-only digest does not recompute.
    PayloadDigest,
    /// The engine digest differs from the binary the wrapper validated.
    Engine,
    /// The evaluated base identity differs from the one requested.
    BaseIdentity,
    /// The evaluated candidate identity differs from the one requested.
    CandidateIdentity,
    /// The completeness flag disagrees with the exit class.
    Completeness,
    /// The finding count differs from the findings array length.
    FindingCount,
}

/// What the wrapper expects the accepted envelope to carry: the digest of the
/// binary it validated and launched, and the identities it asked that binary
/// to evaluate. A wrapper can only hold an engine to what it knows it
/// requested.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Expectations {
    pub engine_digest: String,
    pub base_commit: String,
    pub candidate_commit: Option<String>,
}

fn member<'value>(value: &'value Value, key: &str) -> Option<&'value Value> {
    match value {
        Value::Object(members) => members
            .iter()
            .find(|(name, _)| name == key)
            .map(|(_, member)| member),
        Value::Null | Value::Bool(_) | Value::Integer(_) | Value::String(_) | Value::Array(_) => {
            None
        }
    }
}

fn text<'value>(value: &'value Value, key: &str) -> Option<&'value str> {
    match member(value, key) {
        Some(Value::String(text)) => Some(text),
        _ => None,
    }
}

/// The acceptance law: the wire is exactly `JCS(envelope) || LF`, the
/// payload-only digest recomputes, the engine digest equals the validated
/// binary's, the evaluated identities equal the ones requested, the
/// completeness flag agrees with the exit class, and the finding count equals
/// the findings array length. Text printed before a crash is never
/// interpreted as a result. Success returns the envelope's exit class, so the
/// wrapper can hold the engine process to it.
///
/// # Errors
///
/// The first applicable defect in the order above.
pub fn accept(wire: &[u8], expectations: &Expectations) -> Result<i64, AcceptanceDefect> {
    let trimmed = wire
        .strip_suffix(b"\n")
        .ok_or(AcceptanceDefect::Noncanonical)?;
    let envelope = parse(trimmed).map_err(|_defect| AcceptanceDefect::Shape)?;
    if canonical(&envelope) != trimmed {
        return Err(AcceptanceDefect::Noncanonical);
    }
    let payload = member(&envelope, "payload").ok_or(AcceptanceDefect::Shape)?;
    let recorded = text(&envelope, "payload_digest").ok_or(AcceptanceDefect::Shape)?;
    if hj(PAYLOAD_SCHEMA, payload).to_string() != recorded {
        return Err(AcceptanceDefect::PayloadDigest);
    }
    let engine_row = member(payload, "engine").ok_or(AcceptanceDefect::Shape)?;
    if text(engine_row, "engine_digest") != Some(expectations.engine_digest.as_str()) {
        return Err(AcceptanceDefect::Engine);
    }
    let evaluation = member(payload, "evaluation").ok_or(AcceptanceDefect::Shape)?;
    let resolved = text(evaluation, "status") != Some("unavailable");
    if resolved {
        let base = member(evaluation, "base").ok_or(AcceptanceDefect::Shape)?;
        if text(base, "commit_oid") != Some(expectations.base_commit.as_str()) {
            return Err(AcceptanceDefect::BaseIdentity);
        }
        let candidate = member(evaluation, "candidate").ok_or(AcceptanceDefect::Shape)?;
        if let (Some(expected), Some("git-commit")) = (
            expectations.candidate_commit.as_deref(),
            text(candidate, "kind"),
        ) && text(candidate, "commit_oid") != Some(expected)
        {
            return Err(AcceptanceDefect::CandidateIdentity);
        }
    }
    let result = member(payload, "result").ok_or(AcceptanceDefect::Shape)?;
    let exit_code = match member(result, "exit_code") {
        Some(Value::Integer(code)) => *code,
        _ => return Err(AcceptanceDefect::Shape),
    };
    let complete = member(result, "complete") == Some(&Value::Bool(true));
    if complete != (exit_code == 0 || exit_code == 1) {
        return Err(AcceptanceDefect::Completeness);
    }
    let count = match member(result, "finding_count") {
        Some(Value::Integer(count)) => *count,
        _ => return Err(AcceptanceDefect::Shape),
    };
    let findings = match member(payload, "findings") {
        Some(Value::Array(rows)) => rows.len(),
        _ => return Err(AcceptanceDefect::Shape),
    };
    if i64::try_from(findings).map_err(|_defect| AcceptanceDefect::Shape)? != count {
        return Err(AcceptanceDefect::FindingCount);
    }
    Ok(exit_code)
}

/// The watchdog outcome for one spawned engine process.
#[derive(Debug)]
pub enum Supervised {
    /// The engine exited on its own within the ceiling.
    Completed(ExitStatus),
    /// The ceiling passed; the engine was killed and reaped. A killed engine
    /// yields no accepted envelope.
    Killed,
}

/// The operational wall-time watchdog: polls the engine until it exits or the
/// ceiling passes, then kills and reaps it. The kill can never produce a
/// partial result whose presence depends on runner speed; the caller fails the
/// run without an envelope.
///
/// # Errors
///
/// Only `try_wait` failures; kill and reap errors after a timeout are
/// deliberately ignored because the outcome is already `Killed`.
pub fn supervise(child: &mut Child, ceiling: Duration) -> std::io::Result<Supervised> {
    let start = Instant::now();
    loop {
        if let Some(status) = child.try_wait()? {
            return Ok(Supervised::Completed(status));
        }
        if start.elapsed() >= ceiling {
            let _signalled = child.kill();
            let _reaped = child.wait();
            return Ok(Supervised::Killed);
        }
        std::thread::sleep(Duration::from_millis(25));
    }
}

/// Why a run produced no accepted result. Every one of these is a failed
/// required check, and none of them publishes an envelope: a report the
/// wrapper cannot accept is not a report.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Defect {
    /// The engine outlived the wall ceiling and was killed.
    Killed,
    /// The engine died on a signal and carries no exit code.
    Signalled,
    /// The engine wrote more than the wire ceiling admits.
    Oversize,
    /// The engine's own exit code disagrees with the exit class it reported.
    ExitMismatch,
    /// The envelope failed the acceptance law.
    Acceptance(AcceptanceDefect),
}

/// The settlement law, over what the wrapper can observe of a finished engine:
/// its exit code and its complete stdout. An accepted envelope returns the
/// exit class the wrapper then exits with, and which the engine's own process
/// exit code must already equal. Nothing else is publishable.
///
/// # Errors
///
/// The defect that refused the result.
pub fn settle(
    outcome: &Supervised,
    stdout: &[u8],
    expectations: &Expectations,
) -> Result<i64, Defect> {
    let status = match *outcome {
        Supervised::Killed => return Err(Defect::Killed),
        Supervised::Completed(status) => status,
    };
    if u64::try_from(stdout.len()).unwrap_or(u64::MAX) > amiss_wire::report::MACHINE_JSON_BYTES {
        return Err(Defect::Oversize);
    }
    let code = status.code().ok_or(Defect::Signalled)?;
    let class = accept(stdout, expectations).map_err(Defect::Acceptance)?;
    if i64::from(code) != class {
        return Err(Defect::ExitMismatch);
    }
    Ok(class)
}