plecto-control 0.3.6

//! The chain dispatcher (ADR 000007): drive a request through the loaded filters in order,
//! honouring `decision` and applying `modified` edits; drive the response back in reverse.
//! Fail-closed — a trapped / timed-out filter (`RunError`) never falls through to upstream.

use std::sync::Arc;

use plecto_host::{
    Header, HttpRequest, HttpResponse, LoadedFilter, RequestBodyDecision, RequestDecision,
    RequestEdit, RequestTrace, ResponseDecision, ResponseEdit,
};

/// The result of driving a request through the chain.
pub enum ChainOutcome {
    /// Respond now without reaching upstream: a filter short-circuited, or the chain failed
    /// closed on a trap / deadline (the synthetic 5xx from `RunError::fail_closed_response`).
    Respond(HttpResponse),
    /// The chain passed: forward this (possibly edited) request upstream.
    Forward(HttpRequest),
}

/// The result of driving a buffered request body through the chain's `on-request-body` hooks
/// (ADR 000025).
pub enum RequestBodyOutcome {
    /// Respond now without reaching upstream: a body filter short-circuited, or the chain failed
    /// closed on a trap / deadline.
    Respond(HttpResponse),
    /// The chain passed: forward this (possibly transformed) body upstream.
    Forward(Vec<u8>),
}

/// The result of driving a response back through the chain (ADR 000073): the typed successor
/// of the old in-band "non-empty body means synthetic" signal.
pub enum ResponseOutcome {
    /// The chain passed: send the (possibly edited) status + headers and stream the upstream
    /// body through (its `body` is empty — header-only, ADR 000038).
    Forward(HttpResponse),
    /// Send this SYNTHESISED response instead of the upstream one (a filter's `replace`, or
    /// the chain failed closed on a trap / deadline) — the upstream stream is dropped unread.
    Respond(HttpResponse),
}

pub(crate) fn dispatch_request(
    chain: &[Arc<LoadedFilter>],
    mut request: HttpRequest,
    trace: &RequestTrace,
) -> ChainOutcome {
    for filter in chain {
        // `trace` parents each filter span (ADR 000009): the host times the call and emits the
        // span to its sink; we drive only the decision here.
        match filter.on_request(&request, trace) {
            Ok((RequestDecision::Continue, _logs)) => {}
            Ok((RequestDecision::Modified(edit), _logs)) => apply_request_edit(&mut request, edit),
            Ok((RequestDecision::ShortCircuit(response), _logs)) => {
                return ChainOutcome::Respond(response);
            }
            // fail-closed: a trapped / timed-out filter must not reach upstream.
            Err(err) => return ChainOutcome::Respond(err.fail_closed_response()),
        }
    }
    ChainOutcome::Forward(request)
}

/// Drive a buffered request body through the chain's `on-request-body` hooks in order (ADR 000025),
/// threading the possibly-transformed body from one filter to the next. A short-circuit (or a
/// fail-closed trap / deadline) stops the chain before upstream. The host already buffered the body;
/// this only sequences the decisions.
pub(crate) fn dispatch_request_body(
    chain: &[Arc<LoadedFilter>],
    mut body: Vec<u8>,
    trace: &RequestTrace,
) -> RequestBodyOutcome {
    for filter in chain {
        match filter.on_request_body(&body, trace) {
            Ok((RequestBodyDecision::Continue(next), _logs)) => body = next,
            Ok((RequestBodyDecision::ShortCircuit(response), _logs)) => {
                return RequestBodyOutcome::Respond(response);
            }
            // fail-closed: a trapped / timed-out body filter must not reach upstream.
            Err(err) => return RequestBodyOutcome::Respond(err.fail_closed_response()),
        }
    }
    RequestBodyOutcome::Forward(body)
}

pub(crate) fn dispatch_response(
    chain: &[Arc<LoadedFilter>],
    request: &HttpRequest,
    mut response: HttpResponse,
    trace: &RequestTrace,
) -> ResponseOutcome {
    // The response side runs the chain in reverse (CONTEXT: request/response are symmetric).
    // `request` is the as-forwarded snapshot every hook sees (ADR 000073). A `replace` stops
    // the chain and answers with the synthesised response — same terminal shape as the request
    // side's short-circuit and the fail-closed arm (and the general proxy-filter form: a local
    // response skips the remaining filters). The same `trace` as the request side, so request +
    // response spans share one trace (ADR 000009).
    for filter in chain.iter().rev() {
        match filter.on_response(request, &response, trace) {
            Ok((ResponseDecision::Continue, _logs)) => {}
            Ok((ResponseDecision::Modified(edit), _logs)) => {
                apply_response_edit(&mut response, edit)
            }
            Ok((ResponseDecision::Replace(replacement), _logs)) => {
                return ResponseOutcome::Respond(replacement);
            }
            Err(err) => return ResponseOutcome::Respond(err.fail_closed_response()),
        }
    }
    ResponseOutcome::Forward(response)
}

/// Apply a request rewrite: remove the named headers, then set (replace-or-add) the given
/// ones. Header names match case-insensitively (HTTP semantics).
fn apply_request_edit(request: &mut HttpRequest, edit: RequestEdit) {
    remove_headers(&mut request.headers, &edit.remove_headers);
    set_headers(&mut request.headers, edit.set_headers);
}

fn apply_response_edit(response: &mut HttpResponse, edit: ResponseEdit) {
    if let Some(status) = edit.set_status {
        response.status = status;
    }
    remove_headers(&mut response.headers, &edit.remove_headers);
    set_headers(&mut response.headers, edit.set_headers);
}

fn remove_headers(headers: &mut Vec<Header>, names: &[String]) {
    for name in names {
        headers.retain(|h| !h.name.eq_ignore_ascii_case(name));
    }
}

fn set_headers(headers: &mut Vec<Header>, set: Vec<Header>) {
    for header in set {
        // Repeatable headers (Set-Cookie) APPEND: each field line is independent, so collapsing
        // them on `set` would drop all but the last cookie (review f000005 P3#7). Every other
        // header REPLACES — the semantics a filter relies on to AUTHORITATIVELY overwrite a value
        // (e.g. a spoofed `x-authenticated-user`), so this carve-out is for repeatables only.
        if !is_repeatable(&header.name) {
            headers.retain(|existing| !existing.name.eq_ignore_ascii_case(&header.name));
        }
        headers.push(header);
    }
}

/// Headers that may legitimately appear multiple times and must not be collapsed by `set`.
/// `Set-Cookie` is the canonical case (RFC 6265: one cookie per field line).
fn is_repeatable(name: &str) -> bool {
    name.eq_ignore_ascii_case("set-cookie")
}

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

    fn h(name: &str, value: &str) -> Header {
        Header {
            name: name.to_string(),
            value: value.as_bytes().to_vec(),
        }
    }

    #[test]
    fn request_edit_sets_replaces_and_removes_case_insensitively() {
        let mut request = HttpRequest {
            method: "GET".to_string(),
            path: "/".to_string(),
            authority: "a".to_string(),
            scheme: "https".to_string(),
            headers: vec![h("X-Keep", "1"), h("X-Drop", "old"), h("X-Replace", "old")],
        };
        apply_request_edit(
            &mut request,
            RequestEdit {
                set_headers: vec![h("x-replace", "new"), h("X-Add", "1")],
                remove_headers: vec!["x-drop".to_string()],
            },
        );

        assert!(
            !request
                .headers
                .iter()
                .any(|x| x.name.eq_ignore_ascii_case("x-drop")),
            "removed header gone"
        );
        let replaced: Vec<_> = request
            .headers
            .iter()
            .filter(|x| x.name.eq_ignore_ascii_case("x-replace"))
            .collect();
        assert_eq!(replaced.len(), 1, "set replaces, not duplicates");
        assert_eq!(replaced[0].value.as_slice(), b"new");
        assert!(
            request
                .headers
                .iter()
                .any(|x| x.name.eq_ignore_ascii_case("x-add"))
        );
        assert!(request.headers.iter().any(|x| x.name == "X-Keep"));
    }

    #[test]
    fn response_edit_sets_status_and_headers() {
        let mut response = HttpResponse {
            status: 200,
            headers: vec![h("X-Old", "1")],
            body: vec![],
        };
        apply_response_edit(
            &mut response,
            ResponseEdit {
                set_status: Some(503),
                set_headers: vec![h("X-New", "1")],
                remove_headers: vec!["x-old".to_string()],
            },
        );

        assert_eq!(response.status, 503);
        assert!(response.headers.iter().any(|x| x.name == "X-New"));
        assert!(
            !response
                .headers
                .iter()
                .any(|x| x.name.eq_ignore_ascii_case("x-old"))
        );
    }

    #[test]
    fn response_edit_appends_repeatable_set_cookie_but_replaces_others() {
        // review f000005 P3#7: two Set-Cookie in one edit must BOTH survive (append), not collapse
        // to the last — otherwise a filter setting a session + a flag cookie silently loses one.
        // A non-repeatable header still replaces (the `set replaces` contract is unchanged for it).
        let mut response = HttpResponse {
            status: 200,
            headers: vec![h("x-keep", "1")],
            body: vec![],
        };
        apply_response_edit(
            &mut response,
            ResponseEdit {
                set_status: None,
                set_headers: vec![
                    h("set-cookie", "session=abc"),
                    h("set-cookie", "flag=1"),
                    h("x-keep", "2"),
                ],
                remove_headers: vec![],
            },
        );

        let cookies: Vec<&str> = response
            .headers
            .iter()
            .filter(|x| x.name.eq_ignore_ascii_case("set-cookie"))
            .map(|x| std::str::from_utf8(&x.value).expect("utf-8"))
            .collect();
        assert_eq!(
            cookies,
            vec!["session=abc", "flag=1"],
            "both Set-Cookie field lines must survive (append, not collapse)"
        );
        let keep: Vec<&Header> = response
            .headers
            .iter()
            .filter(|x| x.name.eq_ignore_ascii_case("x-keep"))
            .collect();
        assert_eq!(keep.len(), 1, "a non-repeatable header still replaces");
        assert_eq!(keep[0].value.as_slice(), b"2");
    }
}