parlov-elicit 0.5.0

//! `CpIfUnmodifiedSince` -- precondition via `If-Unmodified-Since`.
//!
//! Sends `If-Unmodified-Since: Mon, 01 Jan 1990 00:00:00 GMT` on both sides.
//! Per RFC 9110 S13.1.4 a server SHOULD respond 412 when the resource has been
//! modified after the given date. A nonexistent resource returns 404.

use http::{HeaderMap, Method};
use parlov_core::{
    always_applicable, NormativeStrength, OracleClass, ResponseClass, SignalSurface, Technique,
    Vector,
};

use crate::chain::{Consumer, Producer, ProducerOutput, ProducerOutputKind};
use crate::context::ScanContext;
use crate::strategy::Strategy;
use crate::types::{ProbeSpec, RiskLevel, StrategyMetadata};
use crate::util::{build_pair, clone_headers_static, try_clone_headers_with};

/// Distant past date that guarantees precondition failure on any existing resource.
const DISTANT_PAST: &str = "Mon, 01 Jan 1990 00:00:00 GMT";

static METADATA: StrategyMetadata = StrategyMetadata {
    strategy_id: "cp-if-unmodified-since",
    strategy_name: "Cache Probe: If-Unmodified-Since",
    risk: RiskLevel::Safe,
};

static TECHNIQUE: Technique = Technique {
    id: "cp-if-unmodified-since",
    name: "If-Unmodified-Since precondition check",
    oracle_class: OracleClass::Existence,
    vector: Vector::CacheProbing,
    strength: NormativeStrength::Should,
    normalization_weight: None,
    inverted_signal_weight: None,
    method_relevant: false,
    parser_relevant: false,
    applicability: always_applicable,
    contradiction_surface: SignalSurface::Status,
};

/// Extracts a `Last-Modified` date from 2xx responses for `If-Unmodified-Since` chaining.
pub(super) struct CpIfUnmodifiedSinceProducer;

impl Producer for CpIfUnmodifiedSinceProducer {
    /// Admits 2xx — `Last-Modified` only meaningful on success.
    fn admits(&self, class: ResponseClass) -> bool {
        matches!(class, ResponseClass::Success)
    }

    fn extract(&self, _class: ResponseClass, headers: &HeaderMap) -> Option<ProducerOutput> {
        let raw = headers.get(http::header::LAST_MODIFIED)?.to_str().ok()?;
        Some(ProducerOutput::LastModified(raw.to_owned()))
    }
}

/// Converts a `LastModified` output into an `If-Unmodified-Since` chained probe spec.
pub(super) struct CpIfUnmodifiedSinceConsumer;

impl Consumer for CpIfUnmodifiedSinceConsumer {
    fn needs(&self) -> ProducerOutputKind {
        ProducerOutputKind::LastModified
    }

    fn generate(&self, ctx: &ScanContext, output: &ProducerOutput) -> Vec<ProbeSpec> {
        let ProducerOutput::LastModified(date) = output else {
            return vec![];
        };
        let Some(hdrs) = try_clone_headers_with(&ctx.headers, "if-unmodified-since", date) else {
            return vec![];
        };
        let pair = build_pair(
            ctx,
            Method::GET,
            hdrs.clone(),
            hdrs,
            None,
            METADATA.clone(),
            TECHNIQUE,
        );
        vec![ProbeSpec::Pair(pair)]
    }
}

/// Elicits existence differentials via `If-Unmodified-Since` with a distant-past date.
pub struct CpIfUnmodifiedSince;

impl Strategy for CpIfUnmodifiedSince {
    fn metadata(&self) -> &'static StrategyMetadata {
        &METADATA
    }

    fn technique_def(&self) -> &'static Technique {
        &TECHNIQUE
    }

    fn methods(&self) -> &[Method] {
        &[Method::GET]
    }

    fn is_applicable(&self, _ctx: &ScanContext) -> bool {
        true
    }

    fn generate(&self, ctx: &ScanContext) -> Vec<ProbeSpec> {
        let hdrs = clone_headers_static(&ctx.headers, "if-unmodified-since", DISTANT_PAST);
        let pair = build_pair(
            ctx,
            Method::GET,
            hdrs.clone(),
            hdrs,
            None,
            METADATA.clone(),
            TECHNIQUE,
        );
        vec![ProbeSpec::Pair(pair)]
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test_utils::minimal_ctx;

    #[test]
    fn generates_correct_technique_vector() {
        let specs = CpIfUnmodifiedSince.generate(&minimal_ctx());
        assert_eq!(specs[0].technique().vector, Vector::CacheProbing);
    }

    #[test]
    fn generates_correct_technique_strength() {
        let specs = CpIfUnmodifiedSince.generate(&minimal_ctx());
        assert_eq!(specs[0].technique().strength, NormativeStrength::Should);
    }

    #[test]
    fn generates_probe_with_correct_header() {
        let specs = CpIfUnmodifiedSince.generate(&minimal_ctx());
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair variant")
        };
        assert_eq!(
            pair.probe.headers.get("if-unmodified-since").unwrap(),
            DISTANT_PAST
        );
    }

    #[test]
    fn is_always_applicable() {
        assert!(CpIfUnmodifiedSince.is_applicable(&minimal_ctx()));
    }

    #[test]
    fn risk_is_safe() {
        assert_eq!(CpIfUnmodifiedSince.risk(), RiskLevel::Safe);
    }
}