parlov-elicit 0.5.0

//! `CpRangeUnsatisfiable` -- unsatisfiable byte-range request.
//!
//! Sends `Range: bytes=99999999-99999999` on both baseline and probe. Per
//! RFC 9110 S14.1.1 a server SHOULD respond 416 when the range cannot be
//! satisfied. A nonexistent resource returns 404, producing the differential.
//!
//! Also exports `CpRangeUnsatisfiableConsumer`, a phase 2 consumer that uses
//! the `ContentRangeSize` produced by `CpRangeSizeProducer` (defined in the
//! sibling `range_satisfiable` module) to generate beyond-end range probes.

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

use crate::chain::{Consumer, 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};

static METADATA: StrategyMetadata = StrategyMetadata {
    strategy_id: "cp-range-unsatisfiable",
    strategy_name: "Cache Probe: Range (unsatisfiable)",
    risk: RiskLevel::Safe,
};

static TECHNIQUE: Technique = Technique {
    id: "cp-range-unsatisfiable",
    name: "Unsatisfiable byte-range request",
    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,
};

/// Converts `ContentRangeSize` into unsatisfiable range probe specs.
///
/// Generates two `Range` headers that point beyond the resource end:
/// `bytes=size-size` (single beyond-end byte) and `bytes=(size+1)-` (open-ended).
/// Uses `CpRangeSizeProducer` from the sibling `range_satisfiable` module.
pub(super) struct CpRangeUnsatisfiableConsumer;

impl Consumer for CpRangeUnsatisfiableConsumer {
    fn needs(&self) -> ProducerOutputKind {
        ProducerOutputKind::ContentRangeSize
    }

    fn generate(&self, ctx: &ScanContext, output: &ProducerOutput) -> Vec<ProbeSpec> {
        let ProducerOutput::ContentRangeSize(size) = output else {
            return vec![];
        };
        let beyond = format!("bytes={size}-{size}");
        let open = format!("bytes={}-", size.saturating_add(1));
        let mut specs = Vec::with_capacity(2);
        for range_val in [beyond, open] {
            let Some(hdrs) = try_clone_headers_with(&ctx.headers, "range", &range_val) else {
                continue;
            };
            let pair = build_pair(
                ctx,
                Method::GET,
                hdrs.clone(),
                hdrs,
                None,
                METADATA.clone(),
                TECHNIQUE,
            );
            specs.push(ProbeSpec::Pair(pair));
        }
        specs
    }
}

/// Elicits existence differentials via an unsatisfiable `Range` header.
pub struct CpRangeUnsatisfiable;

impl Strategy for CpRangeUnsatisfiable {
    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, "range", "bytes=99999999-99999999");
        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::chain::ProducerOutput;
    use crate::test_utils::minimal_ctx;

    // --- CpRangeUnsatisfiable strategy tests ---

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

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

    #[test]
    fn generates_probe_with_correct_header() {
        let specs = CpRangeUnsatisfiable.generate(&minimal_ctx());
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair variant")
        };
        assert_eq!(
            pair.probe.headers.get("range").unwrap(),
            "bytes=99999999-99999999"
        );
    }

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

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

    // --- CpRangeUnsatisfiableConsumer tests ---

    #[test]
    fn unsatisfiable_consumer_needs_content_range_size() {
        assert_eq!(
            CpRangeUnsatisfiableConsumer.needs(),
            ProducerOutputKind::ContentRangeSize
        );
    }

    #[test]
    fn unsatisfiable_consumer_generates_two_specs_from_size() {
        let ctx = minimal_ctx();
        let out = ProducerOutput::ContentRangeSize(4096);
        let specs = CpRangeUnsatisfiableConsumer.generate(&ctx, &out);
        assert_eq!(
            specs.len(),
            2,
            "expected exactly 2 specs; got {}",
            specs.len()
        );
    }

    #[test]
    fn unsatisfiable_consumer_probe_has_beyond_end_range() {
        let ctx = minimal_ctx();
        let out = ProducerOutput::ContentRangeSize(4096);
        let specs = CpRangeUnsatisfiableConsumer.generate(&ctx, &out);
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair")
        };
        assert_eq!(
            pair.probe.headers.get("range").unwrap(),
            "bytes=4096-4096",
            "first spec must be beyond-end single byte"
        );
    }

    #[test]
    fn unsatisfiable_consumer_probe_has_open_ended_range() {
        let ctx = minimal_ctx();
        let out = ProducerOutput::ContentRangeSize(4096);
        let specs = CpRangeUnsatisfiableConsumer.generate(&ctx, &out);
        let ProbeSpec::Pair(pair) = &specs[1] else {
            panic!("expected Pair")
        };
        assert_eq!(
            pair.probe.headers.get("range").unwrap(),
            "bytes=4097-",
            "second spec must be open-ended beyond-end"
        );
    }
}