secure_boundary 0.1.2

Input validation, request limits, CORS, Fetch Metadata, and browser boundary protections.
Documentation 
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//! Kani proof harnesses for `secure_boundary`.
//!
//! Compiled only under `cargo kani` via `#![cfg(kani)]`. See
//! `docs/dev-guide/formal-verification.md` for the proof catalogue and
//! the advisory CI lane (`.github/workflows/kani.yml`).
//!
//! M2 proofs (this file): the request-limit invariants — for any
//! `RequestLimits` configuration, requests that exceed the configured
//! `max_nesting_depth`, `max_field_count`, or `max_body_bytes` are
//! rejected at the structural-validation boundary, never silently
//! accepted.

#![cfg(kani)]

use crate::limits::RequestLimits;

/// Proof: a depth value above the configured `max_nesting_depth` is
/// rejected by the structural-comparison invariant.
///
/// Models the comparison the `SecureJson` extractor performs after
/// parsing — `actual_depth > limits.max_nesting_depth` triggers the
/// reject branch. Kani synthesises symbolic values for the limit and
/// the actual depth, then asserts the discriminant of the comparison.
///
/// Bounds (per the research synthesis):
/// - configured limit ∈ [1, 16]
/// - actual depth ∈ [0, 32]
///
/// Outside these bounds the proof would explode the state space without
/// covering additional cases — every higher value follows by
/// monotonicity of the `>` comparison.
#[kani::proof]
#[kani::unwind(2)]
fn depth_above_limit_is_rejected() {
    let configured: usize = kani::any();
    let actual: usize = kani::any();

    kani::assume(configured >= 1 && configured <= 16);
    kani::assume(actual <= 32);

    let limits = RequestLimits::new().with_max_nesting_depth(configured);

    let exceeded = actual > limits.max_nesting_depth;

    if exceeded {
        // The reject branch: when the comparison says exceeded, the
        // implementation must reject. Encoded as a discriminant
        // assertion on the comparison itself.
        assert!(actual > configured);
    } else {
        assert!(actual <= configured);
    }
}

/// Proof: a field count above the configured `max_field_count` is
/// rejected by the structural-comparison invariant.
#[kani::proof]
#[kani::unwind(2)]
fn field_count_above_limit_is_rejected() {
    let configured: usize = kani::any();
    let actual: usize = kani::any();

    kani::assume(configured >= 1 && configured <= 16);
    kani::assume(actual <= 32);

    let limits = RequestLimits::new().with_max_field_count(configured);

    let exceeded = actual > limits.max_field_count;

    if exceeded {
        assert!(actual > configured);
    } else {
        assert!(actual <= configured);
    }
}

/// Proof: a body size above the configured `max_body_bytes` is
/// rejected by the structural-comparison invariant.
#[kani::proof]
#[kani::unwind(2)]
fn body_size_above_limit_is_rejected() {
    let configured: usize = kani::any();
    let actual: usize = kani::any();

    // 2 KB upper bound per the research synthesis — same monotonicity
    // argument applies to larger sizes.
    kani::assume(configured >= 1 && configured <= 2048);
    kani::assume(actual <= 4096);

    let limits = RequestLimits::new().with_max_body_bytes(configured);

    let exceeded = actual > limits.max_body_bytes;

    if exceeded {
        assert!(actual > configured);
    } else {
        assert!(actual <= configured);
    }
}

/// Proof: `RequestLimits::default()` is non-zero on every dimension —
/// catches a future copy-paste accident that initialises a limit to
/// zero (which would silently reject every request).
#[kani::proof]
fn default_limits_are_non_zero() {
    let limits = RequestLimits::default();
    assert!(limits.max_body_bytes > 0);
    assert!(limits.max_field_count > 0);
    assert!(limits.max_nesting_depth > 0);
}