parlov-elicit 0.5.0

//! `CpAccept` -- content negotiation via unsupported `Accept` media type.
//!
//! Sends `Accept: application/x-parlov-nonexistent` on both baseline and probe.
//! Per RFC 9110 S12.5.1 a server MAY respond 406 when no representation matches.
//! A nonexistent resource returns 404, producing the differential.

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

use crate::context::ScanContext;
use crate::strategy::Strategy;
use crate::types::{ProbeSpec, RiskLevel, StrategyMetadata};
use crate::util::{build_pair, clone_headers_static};

static METADATA: StrategyMetadata = StrategyMetadata {
    strategy_id: "cp-accept",
    strategy_name: "Cache Probe: Accept negotiation",
    risk: RiskLevel::Safe,
};

static TECHNIQUE: Technique = Technique {
    id: "cp-accept",
    name: "Accept content negotiation probe",
    oracle_class: OracleClass::Existence,
    vector: Vector::CacheProbing,
    strength: NormativeStrength::May,
    normalization_weight: None,
    inverted_signal_weight: None,
    method_relevant: false,
    parser_relevant: false,
    applicability: always_applicable,
    contradiction_surface: SignalSurface::Status,
};

/// Elicits existence differentials via an unsupported `Accept` media type.
pub struct CpAccept;

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

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

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

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

    fn generate(&self, ctx: &ScanContext) -> Vec<ProbeSpec> {
        let mut specs = Vec::with_capacity(2);
        for method in [Method::GET, Method::HEAD] {
            let hdrs =
                clone_headers_static(&ctx.headers, "accept", "application/x-parlov-nonexistent");
            let pair = build_pair(
                ctx,
                method,
                hdrs.clone(),
                hdrs,
                None,
                METADATA.clone(),
                TECHNIQUE,
            );
            specs.push(ProbeSpec::Pair(pair));
        }
        specs
    }
}

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

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

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

    #[test]
    fn generates_probe_with_correct_header() {
        let specs = CpAccept.generate(&minimal_ctx());
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair variant")
        };
        assert_eq!(
            pair.probe.headers.get("accept").unwrap(),
            "application/x-parlov-nonexistent"
        );
    }

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

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