parlov-elicit 0.5.0

//! `EmptyBodyElicitation` -- probes with a minimal empty JSON object body.
//!
//! Sends `{}` as the body on both baseline and probe requests with
//! `Content-Type: application/json`. The oracle signal is the server returning
//! 422 for an existing resource versus 404 for a nonexistent one.

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

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

static METADATA: StrategyMetadata = StrategyMetadata {
    strategy_id: "empty-body-elicit",
    strategy_name: "Empty Body Elicitation",
    risk: RiskLevel::MethodDestructive,
};

/// Confirms the parser/validator inspected the empty body.
/// `Strong` for 400, 415, or 422 (parser/validator response). `Weak` otherwise.
fn empty_body_applicable(baseline: &ResponseSurface, probe: &ResponseSurface) -> Applicability {
    let is_strong = |s: u16| matches!(s, 400 | 415 | 422);
    if is_strong(baseline.status.as_u16()) || is_strong(probe.status.as_u16()) {
        return Applicability::Strong;
    }
    Applicability::Weak
}

static TECHNIQUE: Technique = Technique {
    id: "empty-body",
    name: "Empty JSON body validation probe",
    oracle_class: OracleClass::Existence,
    vector: Vector::StatusCodeDiff,
    strength: NormativeStrength::May,
    normalization_weight: Some(0.05),
    inverted_signal_weight: None,
    method_relevant: false,
    parser_relevant: true,
    applicability: empty_body_applicable,
    contradiction_surface: SignalSurface::Status,
};

/// Elicits existence differentials by sending a minimal empty JSON body to mutating methods.
pub struct EmptyBodyElicitation;

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

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

    fn methods(&self) -> &[Method] {
        &[Method::POST, Method::PUT, Method::PATCH]
    }

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

    fn generate(&self, ctx: &ScanContext) -> Vec<ProbeSpec> {
        let body = Some(json_body(&[]));
        let mut specs = Vec::with_capacity(3);
        for method in [Method::POST, Method::PUT, Method::PATCH] {
            let headers = clone_headers_static(&ctx.headers, "content-type", "application/json");
            let pair = build_pair(
                ctx,
                method,
                headers.clone(),
                headers,
                body.clone(),
                METADATA.clone(),
                TECHNIQUE,
            );
            specs.push(ProbeSpec::Pair(pair));
        }
        specs
    }
}

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

    #[test]
    fn risk_is_method_destructive() {
        assert_eq!(EmptyBodyElicitation.risk(), RiskLevel::MethodDestructive);
    }

    #[test]
    fn generate_returns_three_items() {
        assert_eq!(
            EmptyBodyElicitation
                .generate(&ctx_method_destructive())
                .len(),
            3
        );
    }

    #[test]
    fn both_have_application_json_content_type() {
        let specs = EmptyBodyElicitation.generate(&ctx_method_destructive());
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair")
        };
        assert_eq!(
            pair.baseline.headers.get("content-type").unwrap(),
            "application/json"
        );
        assert_eq!(
            pair.probe.headers.get("content-type").unwrap(),
            "application/json"
        );
    }

    #[test]
    fn both_body_is_empty_json_object() {
        let specs = EmptyBodyElicitation.generate(&ctx_method_destructive());
        let ProbeSpec::Pair(pair) = &specs[0] else {
            panic!("expected Pair")
        };
        assert_eq!(pair.baseline.body.as_deref().unwrap(), b"{}");
        assert_eq!(pair.probe.body.as_deref().unwrap(), b"{}");
    }

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

    #[test]
    fn normalization_weight_is_0_05() {
        assert_eq!(TECHNIQUE.normalization_weight, Some(0.05));
    }

    #[test]
    fn inverted_signal_weight_is_none() {
        assert_eq!(TECHNIQUE.inverted_signal_weight, None);
    }
}