jmap_base_client/ws/

mod.rs

//! WebSocket transport for JMAP (RFC 8887).
//!
//! Provides [`connect_ws`] which establishes a WebSocket connection and
//! returns a [`WsSession`] for sending and receiving frames.
//!
//! URL source: `Session::capabilities["urn:ietf:params:jmap:websocket"].url`
//! (the session document advertises the WebSocket endpoint).

use std::str::FromStr as _;
use std::sync::Arc;
use std::time::Duration;

use futures::SinkExt as _;
use futures::StreamExt as _;
use tokio_tungstenite::tungstenite::client::IntoClientRequest as _;
use tokio_tungstenite::tungstenite::protocol::WebSocketConfig;
use tokio_tungstenite::tungstenite::Message;

use crate::push::StateChange;

/// Wire frame sent from the client to the server over WebSocket (RFC 8887 §4.3.2).
///
/// Wraps a [`jmap_types::JmapRequest`] and injects the mandatory `@type: "Request"`
/// field (and optional `id`) in a single `serde_json::to_string` pass, avoiding
/// the `to_value` + mutation + `to_string` double-serialization that the naive
/// approach requires.
#[derive(serde::Serialize)]
struct WsRequestFrame<'a> {
    /// RFC 8887 §4.3.2 — every JMAP request frame MUST carry "@type": "Request".
    #[serde(rename = "@type")]
    ws_type: &'static str,
    /// Optional correlation ID echoed back in the server's Response frame.
    #[serde(skip_serializing_if = "Option::is_none")]
    id: Option<&'a str>,
    /// The JMAP request payload; flattened into the enclosing JSON object.
    #[serde(flatten)]
    inner: &'a jmap_types::JmapRequest,
}

/// Wire frame for RFC 8887 §4.3.5.2 `WebSocketPushEnable`.
///
/// `dataTypes` is `String[]|null` — always present, `null` meaning "all
/// supported data types" — so it is not skipped when `None`. `pushState`
/// is optional and omitted when `None`.
#[derive(serde::Serialize)]
struct WsPushEnableFrame<'a> {
    #[serde(rename = "@type")]
    ws_type: &'static str,
    #[serde(rename = "dataTypes")]
    data_types: Option<&'a [&'a str]>,
    #[serde(rename = "pushState", skip_serializing_if = "Option::is_none")]
    push_state: Option<&'a str>,
}

/// Wire text of an RFC 8887 §4.3.5.3 `WebSocketPushDisable` message; the
/// object has no property other than `@type`.
const WS_PUSH_DISABLE_FRAME: &str = r#"{"@type":"WebSocketPushDisable"}"#;

/// Maximum WebSocket message size (1 MiB), consistent with the SSE frame limit.
/// Prevents a misbehaving or hostile server from forcing the client to buffer
/// large messages over the event connection.
/// Default per-message / per-frame byte cap for WebSocket connections opened
/// via [`connect_ws`] (which does not take a limit parameter). Callers that
/// need a different cap should use [`connect_ws_with_limit`] or the
/// [`crate::JmapClient::connect_ws_session`] convenience method which
/// reads the `max_ws_message` field from `ClientConfig`. Default: 1 MiB.
pub const DEFAULT_WS_MAX_MESSAGE_BYTES: usize = 1 << 20;

/// A parsed frame received from the JMAP WebSocket.
///
/// Marked `#[non_exhaustive]` because the spec may define additional
/// `@type` values in future revisions.
///
/// # `Debug` redaction
///
/// `WsFrame` has a hand-written [`std::fmt::Debug`] impl rather than
/// `#[derive(Debug)]` so the [`Unknown::raw`](WsFrame::Unknown) field is
/// printed as `[REDACTED]` instead of being serialised verbatim. See the
/// field doc on `Unknown.raw` for the credential-leak class this guards
/// against (bd:JMAP-6r7c.5). Use the structured accessors on the frame
/// itself, not `{:?}`, when you need the raw value.
#[non_exhaustive]
#[derive(Clone, PartialEq)]
pub enum WsFrame {
    /// RFC 8620 §7.1 StateChange — one or more object types have changed
    /// state; client must re-fetch the affected data types.
    StateChange(StateChange),
    /// RFC 8887 Response — reply to a JMAP request sent on this connection.
    ///
    /// The RFC 8887 §4.3.3 `requestId` lands in
    /// [`JmapResponse::extra`](jmap_types::JmapResponse::extra); read it
    /// with [`WsFrame::request_id`].
    Response(jmap_types::JmapResponse),
    /// RFC 8887 §4.3.4 RequestError — a request-level Problem Details
    /// object (RFC 8620 §3.6.1) answering a request sent on this connection.
    RequestError(WsRequestError),
    /// Unrecognized `@type` — silently ignored per forward-compatibility rules
    /// (RFC 8887 §4.3.1: clients SHOULD ignore unknown message types).
    ///
    /// Also produced when a known type (`"Response"`, `"RequestError"`, or
    /// `"StateChange"`) fails to deserialize — `type_name` will be that name
    /// in that case, which can signal server misbehavior or a schema version
    /// mismatch. Callers that log unknown frames should check for these names.
    Unknown {
        /// Value of the `@type` field. Either an unrecognized message type
        /// per RFC 8887 §4.3.1, or `"Response"` / `"RequestError"` /
        /// `"StateChange"` when a known type failed to deserialize into its
        /// typed variant.
        type_name: String,
        /// Raw JSON object as received from the server, preserved for
        /// forward-compatibility diagnostics.
        ///
        /// **DO NOT log this field verbatim.** Future or extension JMAP
        /// WebSocket message types may carry credential-grade material —
        /// push verification codes (RFC 8887 §7.2), federation handshake
        /// tokens, session-rotation challenges, etc. — and a malformed
        /// `Response` to a method like `PushSubscription/get` can echo a
        /// `verificationCode` back into this field.
        ///
        /// The enclosing `WsFrame` uses a hand-written `Debug` impl that
        /// renders this field as `[REDACTED]` to neutralise the natural
        /// `{:?}`-leaks-the-field failure mode (bd:JMAP-6r7c.5). For
        /// operator logs, prefer logging `type_name` only, or apply a
        /// project-specific redaction filter before passing `raw` to a
        /// logging sink. See bd:JMAP-sc1b.98.
        raw: serde_json::Value,
    },
}

impl WsFrame {
    /// The `requestId` correlating this frame with the `id` passed to
    /// [`WsSender::send_request`] (RFC 8887 §4.3.3, §4.3.4).
    ///
    /// Returns `None` for `StateChange` and `Unknown` frames, and for a
    /// `Response` or `RequestError` whose `requestId` is absent, `null`, or
    /// not a string. The server MUST echo the id when the request carried
    /// one, but sends `null` when it could not parse the request at all
    /// (RFC 8887 §4.4 `notJSON` example).
    pub fn request_id(&self) -> Option<&str> {
        match self {
            WsFrame::Response(r) => r.extra.get("requestId").and_then(serde_json::Value::as_str),
            WsFrame::RequestError(e) => e.request_id.as_deref(),
            WsFrame::StateChange(_) | WsFrame::Unknown { .. } => None,
        }
    }
}

/// A request-level error received over WebSocket (RFC 8887 §4.3.4).
///
/// An RFC 8620 §3.6.1 Problem Details object extended with
/// `"@type": "RequestError"` and `requestId`. The server sends one instead
/// of a `Response` when the whole request is rejected (not JSON, unknown
/// capability, limit exceeded, ...).
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub struct WsRequestError {
    /// `requestId`: the `id` of the request this error answers. `None` when
    /// the server sent `null` or omitted it.
    #[serde(rename = "requestId", default)]
    pub request_id: Option<String>,
    /// Problem Details `type` URI, e.g.
    /// `"urn:ietf:params:jmap:error:notJSON"` (RFC 8620 §3.6.1).
    #[serde(rename = "type")]
    pub problem_type: String,
    /// Problem Details `status`: the HTTP status code the error would carry
    /// over HTTP.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub status: Option<u16>,
    /// Problem Details `detail`: human-readable explanation.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub detail: Option<String>,
    /// `limit`: the name of the exceeded limit, present for
    /// `urn:ietf:params:jmap:error:limit` (RFC 8620 §3.6.1).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub limit: Option<String>,
    /// Remaining fields (`@type`, `title`, vendor extensions), preserved per
    /// the workspace extras-preservation policy.
    #[serde(flatten, default, skip_serializing_if = "serde_json::Map::is_empty")]
    pub extra: serde_json::Map<String, serde_json::Value>,
}

impl std::fmt::Debug for WsFrame {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            WsFrame::StateChange(sc) => f.debug_tuple("StateChange").field(sc).finish(),
            WsFrame::Response(r) => f.debug_tuple("Response").field(r).finish(),
            WsFrame::RequestError(e) => f.debug_tuple("RequestError").field(e).finish(),
            // `raw` may carry credential-grade material in failure modes
            // (see the field doc); render as a literal string so neither
            // `{:?}` nor `tracing::*` with `?frame` reveals the payload.
            WsFrame::Unknown { type_name, raw: _ } => f
                .debug_struct("Unknown")
                .field("type_name", type_name)
                .field("raw", &"[REDACTED]")
                .finish(),
        }
    }
}

type Inner =
    tokio_tungstenite::WebSocketStream<tokio_tungstenite::MaybeTlsStream<tokio::net::TcpStream>>;

/// Send half shared between [`WsSender`] and the keepalive in
/// [`WsReceiver`], which must be able to send Ping frames after a split.
type SharedSink = Arc<futures::lock::Mutex<futures::stream::SplitSink<Inner, Message>>>;

/// An established JMAP WebSocket session (RFC 8887).
///
/// Call [`next_frame`](WsSession::next_frame) in a loop to receive events.
/// Use [`send_request`](WsSession::send_request) to transmit JMAP requests.
///
/// The caller is responsible for reconnecting after the stream ends or returns
/// a transport error. Use exponential backoff.
///
/// # Drop and cancellation (bd:JMAP-6r7c.24)
///
/// `WsSession` may be dropped at any point — including from inside a
/// `tokio::select!` losing branch while [`next_frame`](WsSession::next_frame)
/// is awaiting. Dropping is always safe and always synchronous:
///
/// - **Partial frame state is discarded.** The split sink and stream halves
///   are owned by the session; dropping the session drops both halves and
///   any in-flight tungstenite buffering.
/// - **The underlying TCP / TLS connection is closed.** No `Close` frame is
///   sent — dropping skips the WebSocket close handshake. Callers that want
///   the server to see a clean shutdown should arrange to receive the
///   server's `Close` (which `next_frame` returns as `None`) before drop;
///   this crate does not currently expose an explicit client-initiated
///   `close()` method.
/// - **Resumption is the caller's job.** If you need to recover the
///   conversation state, you must either persist enough application-level
///   state to replay, or rely on the server's push-state replay protocol.
///   `WsSession` itself buffers nothing the caller can replay.
///
/// `next_frame` is cancel-safe in the sense that cancelling its future
/// (via `select!` or `drop`) does not corrupt subsequent calls to
/// `next_frame` on the same `WsSession` — but cancelling means giving up
/// on any partial frame that was being read; the next `next_frame` call
/// starts from the next complete message.
pub struct WsSession {
    sender: WsSender,
    receiver: WsReceiver,
}

/// Owning send-half of a WebSocket connection (bd:JMAP-6r7c.31).
///
/// Returned from [`WsSession::split`]. Holds the underlying tungstenite
/// sink and exposes the per-direction send methods that the unified
/// [`WsSession`] previously bundled with the receive half. Use with
/// [`WsReceiver`] in two-task topologies (one task in a `next_frame` loop,
/// one task occasionally sending requests) — the previous unified shape
/// required serialising send and receive through a single `&mut WsSession`
/// borrow, which made concurrent send-while-receiving impossible without a
/// `Mutex` that holds across `.await`.
pub struct WsSender {
    sink: SharedSink,
}

/// Owning receive-half of a WebSocket connection (bd:JMAP-6r7c.31).
///
/// Returned from [`WsSession::split`]. Holds the underlying tungstenite
/// stream and exposes [`next_frame`](WsReceiver::next_frame). See
/// [`WsSender`] for the companion type and the concurrency rationale.
pub struct WsReceiver {
    stream: futures::stream::SplitStream<Inner>,
    keepalive: Option<Keepalive>,
}

/// Client-side keepalive state, set by [`WsSession::enable_keepalive`].
///
/// Lives in the receiver (not on the stack of `next_frame`) so cancelling a
/// `next_frame` future does not reset the idle clock.
struct Keepalive {
    sink: SharedSink,
    interval: Duration,
    timeout: Duration,
    last_rx: tokio::time::Instant,
    ping_sent_at: Option<tokio::time::Instant>,
}

/// The transport error [`WsReceiver::next_frame`] reports for a dead peer.
fn keepalive_timed_out(msg: &'static str) -> crate::error::ClientError {
    crate::error::ClientError::from_ws(tokio_tungstenite::tungstenite::Error::Io(
        std::io::Error::new(std::io::ErrorKind::TimedOut, msg),
    ))
}

/// Maximum number of consecutive non-Text non-Close non-Binary frames
/// (Ping, Pong, Frame, etc.) `next_frame` will silently skip in a single call.
///
/// Tungstenite handles ping/pong at the protocol layer, so seeing them at the
/// `Message` layer is unusual but legal — we skip them. A misbehaving or
/// hostile server that floods the stream with no-op frames could otherwise
/// starve a caller of `next_frame` indefinitely; this cap surfaces an
/// `UnexpectedResponse` error before that can happen. 64 is high enough that
/// a normal connection never trips it (typical SSE/WS streams interleave at
/// most a handful of pings between data frames) and low enough that the
/// caller doesn't wait long if a bad server is talking nonsense.
///
/// `Binary` frames are NOT counted here — they violate RFC 8887 §4.1 and
/// surface as `UnexpectedResponse` immediately on the first occurrence.
///
/// # Do not remove the cap (bd:JMAP-6r7c.17, originally bd:JMAP-6lsm.6)
///
/// A future contributor may suggest "tungstenite handles pings at the
/// protocol layer, just continue the loop silently for any non-text
/// non-close frame." That re-introduces the resource-exhaustion bug
/// bd:JMAP-6lsm.6 fixed. The cap is load-bearing for five reasons:
///
/// 1. **Starvation defense.** A hostile or misbehaving server can
///    flood the stream with no-op frames (Ping, Pong, Frame, future
///    variants) and starve a caller of `next_frame()` indefinitely.
///    The cap surfaces this as an error before the caller's outer
///    loop is starved.
/// 2. **Calibrated threshold.** 64 is high enough that a normal
///    connection never trips it. Lower numbers (e.g. 8) would
///    false-positive on networks with weak NAT keepalives where the
///    server sends frequent pings to keep the connection alive.
/// 3. **Binary frames are a separate guarantee.** They are NOT
///    subsumed by the cap — they violate RFC 8887 §4.1 and surface
///    immediately on first occurrence (see `classify_message`
///    `MessageDisposition::UnexpectedFrame` path). Removing the cap
///    does not affect Binary handling; the threats are different.
/// 4. **Unit-testable policy.** `classify_message` (free function,
///    not a method) is testable without a real WebSocket. The test
///    suite in this file exercises the classification explicitly so
///    a refactor that "just changes the loop" doesn't silently lose
///    the policy.
/// 5. **Pinned by tripwire test.**
///    `consecutive_skip_cap_matches_documented_value` asserts the
///    constant equals 64. A retune fails the test loudly so the
///    change is visible in CI, forcing a deliberate choice rather
///    than a silent regression.
///
/// Resist requests to "simplify" by removing the count.
const MAX_CONSECUTIVE_NON_TEXT_FRAMES: usize = 64;

/// Classify a single tungstenite [`Message`] into a [`MessageDisposition`]
/// that tells the [`WsSession::next_frame`] loop what to do with it.
///
/// Extracted as a free function so the policy is unit-testable without a
/// real WebSocket: see the inline test module. Pure function over the
/// message variant.
fn classify_message(msg: &Message) -> MessageDisposition {
    match msg {
        Message::Text(_) => MessageDisposition::Text,
        Message::Close(_) => MessageDisposition::Close,
        Message::Binary(_) => MessageDisposition::Binary,
        // Ping, Pong, Frame, and any future variants: skip, but count.
        _ => MessageDisposition::Skip,
    }
}

/// Decision a `next_frame` loop iteration takes after looking at one
/// [`Message`]. See [`classify_message`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum MessageDisposition {
    /// Text frame: hand to `parse_ws_frame` and return its result.
    Text,
    /// Close frame: end the stream by returning `None`.
    Close,
    /// Binary frame: violates RFC 8887 §4.1; surface as
    /// `UnexpectedResponse` immediately on the first occurrence.
    Binary,
    /// Ping / Pong / Frame / future variants: silently skip and continue
    /// the loop, subject to [`MAX_CONSECUTIVE_NON_TEXT_FRAMES`].
    Skip,
}

impl WsReceiver {
    /// Receive the next parsed frame from the server.
    ///
    /// Returns `None` when the server has cleanly closed the connection.
    /// Returns `Some(Err(...))` on parse failure, transport error, RFC 8887
    /// §4.1 violation (Binary frame), or starvation cap (more than 64
    /// consecutive Ping/Pong/Frame messages — see the private
    /// `MAX_CONSECUTIVE_NON_TEXT_FRAMES` constant for the exact value).
    /// After a transport error the connection is broken and `next_frame`
    /// must not be called again. After an `UnexpectedResponse` error the
    /// underlying stream is still healthy — the caller may choose to
    /// ignore it and retry, or to disconnect.
    ///
    /// With keepalive enabled ([`WsSession::enable_keepalive`]) this call
    /// also sends the Ping frames, so keep a `next_frame` loop running; a
    /// dead peer surfaces as a transport error whose
    /// [`WebSocketError::is_io`](crate::error::WebSocketError::is_io) is
    /// `true`.
    pub async fn next_frame(&mut self) -> Option<Result<WsFrame, crate::error::ClientError>> {
        let mut consecutive_skips = 0usize;
        loop {
            let next = match self.keepalive.as_mut() {
                None => self.stream.next().await,
                Some(ka) => {
                    let deadline = match ka.ping_sent_at {
                        Some(sent) => sent + ka.timeout,
                        None => ka.last_rx + ka.interval,
                    };
                    match tokio::time::timeout_at(deadline, self.stream.next()).await {
                        Ok(next) => {
                            // Any inbound message, not only a Pong, proves
                            // the peer is alive.
                            ka.last_rx = tokio::time::Instant::now();
                            ka.ping_sent_at = None;
                            next
                        }
                        Err(_elapsed) if ka.ping_sent_at.is_some() => {
                            return Some(Err(keepalive_timed_out(
                                "WebSocket keepalive: no traffic from server after Ping",
                            )));
                        }
                        Err(_elapsed) => {
                            // Bounded: a WsSender blocked on a dead peer's
                            // full send buffer holds the sink lock, and an
                            // unbounded wait here would never time out.
                            let sent = tokio::time::timeout(ka.timeout, async {
                                ka.sink
                                    .lock()
                                    .await
                                    .send(Message::Ping(Vec::new().into()))
                                    .await
                            })
                            .await;
                            match sent {
                                Ok(Ok(())) => {}
                                Ok(Err(e)) => {
                                    return Some(Err(crate::error::ClientError::from_ws(e)))
                                }
                                Err(_elapsed) => {
                                    return Some(Err(keepalive_timed_out(
                                        "WebSocket keepalive: could not send Ping in time",
                                    )))
                                }
                            }
                            ka.ping_sent_at = Some(tokio::time::Instant::now());
                            // The Pong we just solicited is not server
                            // misbehaviour: restart the flood count so an
                            // idle connection never trips the cap. At most
                            // one reset per interval keeps the flood
                            // defence intact.
                            consecutive_skips = 0;
                            continue;
                        }
                    }
                }
            };
            let msg = match next? {
                Ok(m) => m,
                Err(e) => return Some(Err(crate::error::ClientError::from_ws(e))),
            };
            match classify_message(&msg) {
                MessageDisposition::Text => {
                    let Message::Text(text) = msg else {
                        // Unreachable: classify_message returned Text only for
                        // Message::Text. Defensive in case the variant grows.
                        return Some(Err(crate::error::ClientError::UnexpectedResponse(
                            "WebSocket: classify_message returned Text for non-Text variant".into(),
                        )));
                    };
                    return Some(parse_ws_frame(&text));
                }
                MessageDisposition::Close => return None,
                MessageDisposition::Binary => {
                    // RFC 8887 §4.1: JMAP only uses text frames. Surface the
                    // violation; underlying stream is still healthy so the
                    // caller can choose to retry next_frame if it wants.
                    return Some(Err(crate::error::ClientError::UnexpectedResponse(
                        "WebSocket: server sent Binary frame; RFC 8887 §4.1 mandates text frames"
                            .into(),
                    )));
                }
                MessageDisposition::Skip => {
                    consecutive_skips = consecutive_skips.saturating_add(1);
                    if consecutive_skips > MAX_CONSECUTIVE_NON_TEXT_FRAMES {
                        return Some(Err(crate::error::ClientError::UnexpectedResponse(
                            format!(
                                "WebSocket: exceeded {MAX_CONSECUTIVE_NON_TEXT_FRAMES} consecutive non-text frames; possible server misbehaviour"
                            ),
                        )));
                    }
                }
            }
        }
    }
}

impl WsSender {
    /// Send a raw text frame over the WebSocket connection.
    ///
    /// Used by extension crates to send non-JMAP frames (e.g., JMAP Chat
    /// ephemeral stream control messages).
    pub async fn send_text(&mut self, text: String) -> Result<(), crate::error::ClientError> {
        self.sink
            .lock()
            .await
            .send(Message::Text(text.into()))
            .await
            .map_err(crate::error::ClientError::from_ws)
    }

    /// Send a JMAP request over the WebSocket connection.
    ///
    /// Serializes `req` and injects `"@type": "Request"` into the outgoing
    /// JSON object as required by RFC 8887 §4.3.2.  The optional `id` is
    /// echoed back in the corresponding `Response` frame, enabling out-of-order
    /// correlation.
    ///
    /// # Errors
    ///
    /// Returns `ClientError::Serialize` if `req` cannot be serialized, or
    /// `ClientError::WebSocket` on a transport failure.
    pub async fn send_request(
        &mut self,
        req: &jmap_types::JmapRequest,
        id: Option<&str>,
    ) -> Result<(), crate::error::ClientError> {
        // Wrap req in WsRequestFrame to inject @type and optional id in one
        // serialization pass (no intermediate serde_json::Value allocation).
        let frame = WsRequestFrame {
            ws_type: "Request",
            id,
            inner: req,
        };
        let text =
            serde_json::to_string(&frame).map_err(crate::error::ClientError::from_serialize)?;
        self.send_text(text).await
    }

    /// Enable push notifications on this connection (RFC 8887 §4.3.5.2).
    ///
    /// Sends a `WebSocketPushEnable` object. `data_types` limits pushes to
    /// the named types (`["Mailbox", "Email"]`); `None` sends
    /// `"dataTypes": null`, which asks for every supported type.
    /// `push_state` is the last `pushState` seen on a previous connection,
    /// from which the server SHOULD replay missed changes; read it from
    /// the `"pushState"` entry of [`StateChange::extra`].
    ///
    /// Only meaningful when the session's WebSocket capability advertises
    /// `supportsPush: true` (RFC 8887 §4.3.5).
    ///
    /// # Errors
    ///
    /// Returns `ClientError::WebSocket` on a transport failure.
    pub async fn send_push_enable(
        &mut self,
        data_types: Option<&[&str]>,
        push_state: Option<&str>,
    ) -> Result<(), crate::error::ClientError> {
        let frame = WsPushEnableFrame {
            ws_type: "WebSocketPushEnable",
            data_types,
            push_state,
        };
        let text =
            serde_json::to_string(&frame).map_err(crate::error::ClientError::from_serialize)?;
        self.send_text(text).await
    }

    /// Disable push notifications on this connection (RFC 8887 §4.3.5.3)
    /// by sending a `WebSocketPushDisable` object.
    ///
    /// # Errors
    ///
    /// Returns `ClientError::WebSocket` on a transport failure.
    pub async fn send_push_disable(&mut self) -> Result<(), crate::error::ClientError> {
        self.send_text(WS_PUSH_DISABLE_FRAME.to_owned()).await
    }
}

impl WsSession {
    /// Receive the next parsed frame from the server.
    ///
    /// Delegates to [`WsReceiver::next_frame`]. Use this unified handle when
    /// a single task drives both send and receive; for the
    /// receive-loop-in-a-separate-task topology, call [`split`](Self::split)
    /// to get owned [`WsReceiver`] / [`WsSender`] halves.
    pub async fn next_frame(&mut self) -> Option<Result<WsFrame, crate::error::ClientError>> {
        self.receiver.next_frame().await
    }

    /// Send a raw text frame over the WebSocket connection.
    ///
    /// Delegates to [`WsSender::send_text`].
    pub async fn send_text(&mut self, text: String) -> Result<(), crate::error::ClientError> {
        self.sender.send_text(text).await
    }

    /// Send a JMAP request over the WebSocket connection.
    ///
    /// Delegates to [`WsSender::send_request`].
    pub async fn send_request(
        &mut self,
        req: &jmap_types::JmapRequest,
        id: Option<&str>,
    ) -> Result<(), crate::error::ClientError> {
        self.sender.send_request(req, id).await
    }

    /// Enable push notifications on this connection.
    ///
    /// Delegates to [`WsSender::send_push_enable`].
    pub async fn send_push_enable(
        &mut self,
        data_types: Option<&[&str]>,
        push_state: Option<&str>,
    ) -> Result<(), crate::error::ClientError> {
        self.sender.send_push_enable(data_types, push_state).await
    }

    /// Disable push notifications on this connection.
    ///
    /// Delegates to [`WsSender::send_push_disable`].
    pub async fn send_push_disable(&mut self) -> Result<(), crate::error::ClientError> {
        self.sender.send_push_disable().await
    }

    /// Turn on client-side keepalive (RFC 6455 §5.5.2 Ping).
    ///
    /// When no message has arrived from the server for `interval`,
    /// [`next_frame`](WsReceiver::next_frame) sends a Ping. If nothing at
    /// all (Pong or any other message) arrives within `timeout` of that
    /// Ping, `next_frame` returns a transport error (`is_io() == true`,
    /// timed out) and the connection should be treated as dead.
    ///
    /// Pings are sent from inside `next_frame`, so a receive loop must be
    /// running for keepalive to work. Call this before
    /// [`split`](Self::split); the receive half keeps the setting. Off by
    /// default.
    ///
    /// # Errors
    ///
    /// Returns `ClientError::InvalidArgument` if `interval` or `timeout` is
    /// zero.
    pub fn enable_keepalive(
        &mut self,
        interval: Duration,
        timeout: Duration,
    ) -> Result<(), crate::error::ClientError> {
        if interval.is_zero() || timeout.is_zero() {
            return Err(crate::error::ClientError::InvalidArgument(
                "enable_keepalive: interval and timeout must be > 0".to_owned(),
            ));
        }
        self.receiver.keepalive = Some(Keepalive {
            sink: Arc::clone(&self.sender.sink),
            interval,
            timeout,
            last_rx: tokio::time::Instant::now(),
            ping_sent_at: None,
        });
        Ok(())
    }

    /// Consume the session and return its owned send and receive halves
    /// (bd:JMAP-6r7c.31).
    ///
    /// Use this when a caller needs to drive the receive loop and the
    /// send path concurrently — typically from two `tokio::spawn`-ed
    /// tasks, one running a `while let Some(...) = receiver.next_frame()
    /// .await` loop and one occasionally sending requests via
    /// `sender.send_request(...)`. The unified `WsSession` API requires
    /// `&mut self` for both directions and therefore cannot service them
    /// concurrently; `split` is the explicit opt-in.
    ///
    /// The two halves are independent owners of their tungstenite
    /// sub-streams. Dropping one half does not close the connection until
    /// the other half is also dropped (tungstenite's `WebSocketStream`
    /// only initiates the close handshake when both halves are gone). To
    /// initiate a clean shutdown from a split session, drop the sender
    /// after sending a final request and read from the receiver until it
    /// returns `None`.
    pub fn split(self) -> (WsSender, WsReceiver) {
        let WsSession { sender, receiver } = self;
        (sender, receiver)
    }
}

/// Parse a raw WebSocket text frame into a `WsFrame`.
///
/// Two passes over `text`:
///
/// 1. Parse to [`serde_json::Value`] to extract `@type` (and to keep a
///    structured fallback alive for the Unknown branch).
/// 2. For the typed branches (`StateChange`, `Response`), call
///    [`serde_json::from_str`] directly against the original `text`.
///
/// The previous shape `let raw = val.clone(); from_value::<T>(val)` paid a
/// deep Value clone on every successful frame even though `raw` was thrown
/// away. For 1-MiB-cap WS messages on a hot push path, the clone allocates
/// a HashMap per `Value::Object` and a `String` per `Value::String` and
/// dropped them moments later. Two text parses are cheaper for typical
/// payload shapes than one parse + one deep Value clone, and the borrow
/// checker no longer needs ownership tricks (bd:JMAP-6lsm.11).
fn parse_ws_frame(text: &str) -> Result<WsFrame, crate::error::ClientError> {
    let val: serde_json::Value =
        serde_json::from_str(text).map_err(crate::error::ClientError::from_parse)?;

    let type_name = val
        .get("@type")
        .and_then(|v| v.as_str())
        .unwrap_or("<no @type>")
        .to_owned();

    match type_name.as_str() {
        // A malformed StateChange is degraded to Unknown rather than a
        // transport error. A single bad server frame must not kill the
        // entire WebSocket connection; only tungstenite transport errors
        // warrant a reconnect. The `val` we already parsed is the Unknown
        // payload — no clone needed.
        "StateChange" => match serde_json::from_str::<StateChange>(text) {
            Ok(sc) => Ok(WsFrame::StateChange(sc)),
            Err(_) => Ok(WsFrame::Unknown {
                type_name,
                raw: val,
            }),
        },
        // Same degradation policy for malformed Response frames.
        "Response" => match serde_json::from_str::<jmap_types::JmapResponse>(text) {
            Ok(r) => Ok(WsFrame::Response(r)),
            Err(_) => Ok(WsFrame::Unknown {
                type_name,
                raw: val,
            }),
        },
        "RequestError" => match serde_json::from_str::<WsRequestError>(text) {
            Ok(e) => Ok(WsFrame::RequestError(e)),
            Err(_) => Ok(WsFrame::Unknown {
                type_name,
                raw: val,
            }),
        },
        _ => Ok(WsFrame::Unknown {
            type_name,
            raw: val,
        }),
    }
}

/// Open a JMAP WebSocket connection (RFC 8887).
///
/// `ws_url` must come from the session document's WebSocket capability URL
/// (a `wss://` endpoint in production; `ws://` is accepted in tests).
///
/// `auth_header` is an optional `(header-name, header-value)` pair injected
/// into the WebSocket upgrade request. Pass `None` when the server does not
/// require authentication headers on the WebSocket handshake.
///
/// Returns `ClientError::InvalidArgument` if the URL scheme is not
/// `ws://` or `wss://`, preventing accidental use with untrusted URLs.
///
/// The returned [`WsSession`] provides [`WsSession::next_frame`] for receiving
/// events. The caller is responsible for reconnecting after disconnect with
/// exponential backoff.
///
/// Uses [`DEFAULT_WS_MAX_MESSAGE_BYTES`] as the per-message / per-frame cap.
/// Callers that need a different cap should use [`connect_ws_with_limit`] or
/// [`crate::JmapClient::connect_ws_session`] (which reads `ClientConfig::max_ws_message`).
///
/// # Security
///
/// The `auth_header` value is a credential and must not be logged or
/// echoed back to other systems. Treat it with the same care as a
/// [`crate::auth::BearerAuth`] token.
pub async fn connect_ws(
    ws_url: &str,
    auth_header: Option<crate::auth::AuthHeader<'_>>,
) -> Result<WsSession, crate::error::ClientError> {
    connect_ws_with_limit(ws_url, auth_header, DEFAULT_WS_MAX_MESSAGE_BYTES).await
}

/// Establish a WebSocket connection with an explicit per-message / per-frame
/// byte cap.
///
/// Same contract as [`connect_ws`] but lets the caller pin the
/// `max_message_size` / `max_frame_size` config passed to tungstenite.
/// Useful when the JMAP server is known to send larger pushes than the
/// 1 MiB default (e.g. some Mailbox/changes push payloads on accounts with
/// many mailboxes can exceed 1 MiB).
///
/// `max_message_bytes` MUST be > 0; tungstenite treats `Some(0)` as
/// "no message of any size is acceptable" which is a misconfiguration trap.
/// We surface `ClientError::InvalidArgument` instead.
///
/// # Security
///
/// The `auth_header` value is a credential and must not be logged or
/// echoed back to other systems. Treat it with the same care as a
/// [`crate::auth::BearerAuth`] token. The `ClientError::InvalidArgument`
/// values produced for malformed auth header names or values are
/// constructed without the original bytes, but callers should still
/// avoid printing or storing the `auth_header` they passed in.
pub async fn connect_ws_with_limit(
    ws_url: &str,
    auth_header: Option<crate::auth::AuthHeader<'_>>,
    max_message_bytes: usize,
) -> Result<WsSession, crate::error::ClientError> {
    if max_message_bytes == 0 {
        return Err(crate::error::ClientError::InvalidArgument(
            "connect_ws_with_limit: max_message_bytes must be > 0".to_owned(),
        ));
    }
    // Validate scheme to prevent SSRF via a compromised or MITM'd session.
    // Case-insensitive check per RFC 3986 §3.1: only the SCHEME component is
    // case-insensitive, not the path/query — so split off the scheme and
    // compare with eq_ignore_ascii_case rather than lowercasing the whole
    // URL. Lowercasing the whole URL allocated a fresh String the size of
    // the URL on every connect (bd:JMAP-6lsm.9). The original (unmodified)
    // URL is passed to tungstenite and kept in error messages for diagnostics.
    let scheme_ok = ws_url
        .split_once("://")
        .is_some_and(|(s, _)| s.eq_ignore_ascii_case("ws") || s.eq_ignore_ascii_case("wss"));
    if !scheme_ok {
        return Err(crate::error::ClientError::InvalidArgument(format!(
            "WebSocket URL must start with ws:// or wss://, got: {ws_url:?}"
        )));
    }

    let mut request = ws_url
        .into_client_request()
        .map_err(crate::error::ClientError::from_ws)?;

    if let Some(header) = auth_header {
        // Both arms construct ClientError::InvalidArgument with a fixed
        // string and deliberately discard the http-crate's Display output
        // for the inner error. The original `name` / `value` bytes are
        // credential-adjacent (the name component is less sensitive than
        // the value, but a future http-crate version could begin echoing
        // bytes in its Display impl). Defense-in-depth: keep neither in
        // the error chain.
        let hdr_name = http::HeaderName::from_str(header.name()).map_err(|_| {
            crate::error::ClientError::InvalidArgument("invalid auth header name".to_owned())
        })?;
        let hdr_value = http::HeaderValue::from_str(header.expose_value()).map_err(|_| {
            crate::error::ClientError::InvalidArgument("invalid auth header value".to_owned())
        })?;
        request.headers_mut().insert(hdr_name, hdr_value);
    }

    // WebSocketConfig is #[non_exhaustive] in tungstenite; use Default + field assignment.
    let mut config = WebSocketConfig::default();
    config.max_message_size = Some(max_message_bytes);
    config.max_frame_size = Some(max_message_bytes);

    // Apply a 10-second connect timeout, consistent with the HTTP transport's
    // connect_timeout in DefaultTransport/CustomCaTransport.  tungstenite does
    // not expose a connect timeout parameter, so we wrap at the Future level.
    // A stalled TCP or TLS handshake would otherwise block indefinitely.
    let connect_result = tokio::time::timeout(
        std::time::Duration::from_secs(10),
        tokio_tungstenite::connect_async_with_config(request, Some(config), false),
    )
    .await
    .map_err(|_elapsed| {
        // Synthesize an Io-kind transport error to surface the timeout
        // through the public WebSocketError accessors (is_io() will be
        // true). The third-party error type is constructed locally and
        // immediately wrapped, so it does not leak to callers.
        crate::error::ClientError::from_ws(tokio_tungstenite::tungstenite::Error::Io(
            std::io::Error::new(
                std::io::ErrorKind::TimedOut,
                "WebSocket connect timed out after 10 seconds",
            ),
        ))
    })?;
    let (ws_stream, _response) = connect_result.map_err(crate::error::ClientError::from_ws)?;

    let (sink, stream) = ws_stream.split();
    Ok(WsSession {
        sender: WsSender {
            sink: Arc::new(futures::lock::Mutex::new(sink)),
        },
        receiver: WsReceiver {
            stream,
            keepalive: None,
        },
    })
}

impl std::fmt::Debug for WsSession {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("WsSession").finish_non_exhaustive()
    }
}

impl std::fmt::Debug for WsSender {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("WsSender").finish_non_exhaustive()
    }
}

impl std::fmt::Debug for WsReceiver {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("WsReceiver").finish_non_exhaustive()
    }
}

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

    /// Verify WsFrame does not contain ChatTyping or ChatPresence variants.
    /// This exhaustive match will fail to compile if either variant is reintroduced.
    #[test]
    fn ws_frame_has_no_chat_variants() {
        let frame = WsFrame::Unknown {
            type_name: "test".to_owned(),
            raw: serde_json::Value::Null,
        };
        match frame {
            WsFrame::StateChange(_) => {}
            WsFrame::Response(_) => {}
            WsFrame::RequestError(_) => {}
            WsFrame::Unknown { .. } => {}
        }
    }

    /// Oracle: parse_ws_frame dispatches on @type field and produces a typed StateChange.
    /// Wire format from RFC 8620 §7.1.1 example.
    #[test]
    fn parse_state_change() {
        let json = r#"{"@type":"StateChange","changed":{"account1":{"Mail":"s2"}}}"#;
        let frame = parse_ws_frame(json).expect("must parse");
        match frame {
            WsFrame::StateChange(sc) => {
                let account = sc
                    .changed
                    .get("account1")
                    .expect("account1 must be present");
                assert_eq!(account.get("Mail").map(|s| s.as_ref()), Some("s2"));
            }
            other => panic!("expected StateChange, got {other:?}"),
        }
    }

    /// Oracle: a StateChange with missing `changed` field degrades to Unknown.
    #[test]
    fn parse_malformed_state_change_degrades_to_unknown() {
        let json = r#"{"@type":"StateChange","unexpected_field":42}"#;
        let frame = parse_ws_frame(json).expect("must not error");
        match frame {
            WsFrame::Unknown { type_name, .. } => assert_eq!(type_name, "StateChange"),
            other => panic!("expected Unknown, got {other:?}"),
        }
    }

    /// Oracle: parse_ws_frame returns Unknown for unrecognized @type.
    /// Derived from parse_unknown_type test in source ws/mod.rs.
    #[test]
    fn parse_unknown_type() {
        let json = r#"{"@type":"FutureEvent","foo":"bar"}"#;
        let frame = parse_ws_frame(json).expect("must parse");
        match frame {
            WsFrame::Unknown { type_name, .. } => assert_eq!(type_name, "FutureEvent"),
            other => panic!("expected Unknown, got {other:?}"),
        }
    }

    /// Oracle: parse_ws_frame returns Unknown for missing @type.
    /// Derived from parse_missing_type_field test in source ws/mod.rs.
    #[test]
    fn parse_missing_type_field() {
        let json = r#"{"foo":"bar"}"#;
        let frame = parse_ws_frame(json).expect("must parse");
        assert!(matches!(frame, WsFrame::Unknown { .. }));
    }

    /// Oracle: parse_ws_frame returns Err(Parse) for invalid JSON.
    /// Derived from parse_invalid_json_returns_parse_error test in source ws/mod.rs.
    #[test]
    fn parse_invalid_json_returns_parse_error() {
        let err = parse_ws_frame("not json").expect_err("must fail");
        assert!(matches!(err, crate::error::ClientError::Parse(_)));
    }

    /// Oracle: RFC 8887 §4.3.2 — every JMAP request sent over WebSocket MUST
    /// include "@type": "Request".  Tests WsRequestFrame serde directly to
    /// verify the #[serde(rename = "@type")] attribute and flatten are correct.
    #[test]
    fn send_request_includes_at_type_request() {
        let req = jmap_types::JmapRequest::new(
            vec!["urn:ietf:params:jmap:core".to_owned()],
            vec![],
            None,
        );
        let frame = WsRequestFrame {
            ws_type: "Request",
            id: None,
            inner: &req,
        };
        let serialized = serde_json::to_string(&frame).expect("WsRequestFrame must serialize");
        assert!(
            serialized.contains("\"@type\":\"Request\""),
            "RFC 8887 §4.3.2 requires @type:Request in outgoing WS frames; got: {serialized}"
        );
    }

    /// Oracle: RFC 8887 §4.3.2 — optional `id` field is echoed in the response.
    /// When an id is supplied, WsRequestFrame must include it in the serialized frame.
    #[test]
    fn send_request_includes_id_when_provided() {
        let req = jmap_types::JmapRequest::new(
            vec!["urn:ietf:params:jmap:core".to_owned()],
            vec![],
            None,
        );
        let frame = WsRequestFrame {
            ws_type: "Request",
            id: Some("req-42"),
            inner: &req,
        };
        let serialized = serde_json::to_string(&frame).expect("WsRequestFrame must serialize");
        assert!(
            serialized.contains("\"id\":\"req-42\""),
            "RFC 8887 §4.3.2 optional id must be present when provided; got: {serialized}"
        );
    }

    /// Oracle: RFC 8887 §4.3.2 — when id is None, no `id` field appears in the frame.
    /// WsRequestFrame uses skip_serializing_if to omit the field entirely.
    #[test]
    fn send_request_omits_id_when_none() {
        let req = jmap_types::JmapRequest::new(
            vec!["urn:ietf:params:jmap:core".to_owned()],
            vec![],
            None,
        );
        let frame = WsRequestFrame {
            ws_type: "Request",
            id: None,
            inner: &req,
        };
        let serialized = serde_json::to_string(&frame).expect("WsRequestFrame must serialize");
        assert!(
            !serialized.contains("\"id\":"),
            "RFC 8887 §4.3.2: no id field must appear when id is None; got: {serialized}"
        );
    }

    /// Oracle: connect_ws must reject http:// and https:// URLs with InvalidArgument.
    ///
    /// This is the documented SSRF prevention guard: a compromised or MITM'd session
    /// could send an http:// URL; we must not follow it as a WebSocket URL.
    /// The scheme check runs before any network I/O.
    /// Derived from connect_ws_rejects_non_ws_schemes test in source ws/mod.rs.
    #[tokio::test]
    async fn connect_ws_rejects_non_ws_schemes() {
        for bad_url in &["http://host/", "https://host/", "ftp://host/"] {
            let result = connect_ws(bad_url, None).await.map(|_| ());
            match result {
                Err(crate::error::ClientError::InvalidArgument(_)) => {}
                other => panic!("expected InvalidArgument for {bad_url:?}, got {other:?}"),
            }
        }
    }

    // -----------------------------------------------------------------------
    // classify_message — bd:JMAP-6lsm.6
    // -----------------------------------------------------------------------

    /// Oracle: Text frames classify as Text. The independent oracle is
    /// the next_frame contract in the docstring above.
    #[test]
    fn classify_text_message() {
        let m = Message::Text("hi".into());
        assert_eq!(classify_message(&m), MessageDisposition::Text);
    }

    /// Oracle: Close frames classify as Close, ending the stream.
    #[test]
    fn classify_close_message() {
        let m = Message::Close(None);
        assert_eq!(classify_message(&m), MessageDisposition::Close);
    }

    /// Oracle: Binary frames violate RFC 8887 §4.1 and must classify as
    /// Binary so the next_frame loop surfaces UnexpectedResponse rather
    /// than silently skipping (the bug JMAP-6lsm.6 fixes). The independent
    /// oracle is RFC 8887 §4.1.
    #[test]
    fn classify_binary_message_is_not_skipped() {
        let m = Message::Binary(vec![1, 2, 3].into());
        assert_eq!(classify_message(&m), MessageDisposition::Binary);
        assert_ne!(
            classify_message(&m),
            MessageDisposition::Skip,
            "Binary must NOT be silently skipped (RFC 8887 §4.1)"
        );
    }

    /// Oracle: Ping/Pong frames classify as Skip. Tungstenite handles
    /// them at the protocol layer, so seeing them at the Message layer
    /// is unusual but legal — skip and continue.
    #[test]
    fn classify_ping_pong_messages_are_skipped() {
        let ping = Message::Ping(vec![].into());
        let pong = Message::Pong(vec![].into());
        assert_eq!(classify_message(&ping), MessageDisposition::Skip);
        assert_eq!(classify_message(&pong), MessageDisposition::Skip);
    }

    /// Tripwire: the consecutive-skip cap is the documented value.
    /// A future retune will fail this test loudly so the change is
    /// visible in CI. Documented value is 64 (see the const docstring).
    #[test]
    fn consecutive_skip_cap_matches_documented_value() {
        assert_eq!(MAX_CONSECUTIVE_NON_TEXT_FRAMES, 64);
    }

    /// Oracle: bd:JMAP-6r7c.5 / workspace AGENTS.md "Security testing"
    /// pattern 1 — per-type Debug redaction canary.
    ///
    /// A future contributor restoring `#[derive(Debug)]` on `WsFrame` would
    /// re-expose the credential-grade material that can land in
    /// `Unknown.raw` (push verification codes, federation handshake tokens,
    /// session-rotation challenges). This test constructs a canary literal
    /// inside the `raw` field and asserts the literal does not appear in
    /// the `{:?}`-formatted output of the frame.
    #[test]
    fn ws_frame_unknown_raw_is_redacted_in_debug_output() {
        let canary = "redaction-canary-cred-WFTMr8FoYpfP-do-not-leak";
        let frame = WsFrame::Unknown {
            type_name: "PushVerification".to_owned(),
            raw: serde_json::json!({
                "verificationCode": canary,
            }),
        };
        let rendered = format!("{frame:?}");
        assert!(
            !rendered.contains(canary),
            "WsFrame::Unknown Debug must redact `raw`; the canary literal \
             appeared in the rendered output, indicating either \
             #[derive(Debug)] was restored or the manual Debug impl \
             forgot to redact the raw field. Rendered output: {rendered}"
        );
        assert!(
            rendered.contains("[REDACTED]"),
            "WsFrame::Unknown Debug must render the redaction placeholder; \
             rendered output: {rendered}"
        );
        assert!(
            rendered.contains("PushVerification"),
            "WsFrame::Unknown Debug must still surface type_name for \
             diagnostics; rendered output: {rendered}"
        );
    }

    /// Oracle: bd:JMAP-6r7c.5 — the Debug impl must still render the
    /// other two variants usefully. A naive impl that redacted everything
    /// would also be wrong; the security goal is narrowly scoped to the
    /// `Unknown.raw` field.
    #[test]
    fn ws_frame_other_variants_remain_useful_in_debug_output() {
        let response_frame = WsFrame::Response(jmap_types::JmapResponse::new(
            vec![],
            "test-session".into(),
            None,
        ));
        let rendered = format!("{response_frame:?}");
        assert!(
            rendered.starts_with("Response"),
            "Response variant Debug must surface variant tag; got: {rendered}"
        );
        assert!(
            rendered.contains("test-session"),
            "Response variant Debug must surface session_state for \
             diagnostics; got: {rendered}"
        );
    }

    /// Oracle: RFC 8887 §4.4 — the server's reply to a non-JSON request,
    /// copied from the RFC example: `{"@type": "RequestError", "requestId":
    /// null, "type": "urn:ietf:params:jmap:error:notJSON", "status": 400,
    /// "detail": "The request did not parse as I-JSON."}`. §4.3.4 defines
    /// this as a Problem Details object extended with `@type` and
    /// `requestId`.
    #[test]
    fn parse_request_error_rfc8887_example() {
        let json = r#"{
            "@type": "RequestError",
            "requestId": null,
            "type": "urn:ietf:params:jmap:error:notJSON",
            "status": 400,
            "detail": "The request did not parse as I-JSON."
        }"#;
        let frame = parse_ws_frame(json).expect("must parse");
        assert_eq!(frame.request_id(), None);
        match frame {
            WsFrame::RequestError(e) => {
                assert_eq!(e.problem_type, "urn:ietf:params:jmap:error:notJSON");
                assert_eq!(e.status, Some(400));
                assert_eq!(
                    e.detail.as_deref(),
                    Some("The request did not parse as I-JSON.")
                );
                assert_eq!(e.request_id, None);
            }
            other => panic!("expected RequestError, got {other:?}"),
        }
    }

    /// Oracle: RFC 8887 §4.3.4 — "requestId: ... MUST be returned if given
    /// in the request". A RequestError answering request "R7" must expose
    /// that id for correlation; the `limit` property is RFC 8620 §3.6.1's
    /// extension for `urn:ietf:params:jmap:error:limit`.
    #[test]
    fn request_error_exposes_request_id_and_limit() {
        let json = r#"{"@type":"RequestError","requestId":"R7",
            "type":"urn:ietf:params:jmap:error:limit","status":400,
            "limit":"maxSizeRequest"}"#;
        let frame = parse_ws_frame(json).expect("must parse");
        assert_eq!(frame.request_id(), Some("R7"));
        match frame {
            WsFrame::RequestError(e) => {
                assert_eq!(e.limit.as_deref(), Some("maxSizeRequest"));
            }
            other => panic!("expected RequestError, got {other:?}"),
        }
    }

    /// Oracle: RFC 8887 §4.3.3 — the Response is extended with "requestId:
    /// ... The client-specified identifier in the corresponding request."
    /// JSON is the RFC 8887 §4.4 Core/echo response example (`"requestId":
    /// "R1"`), plus the `sessionState` that RFC 8620 §3.4 makes mandatory
    /// and the RFC example elides.
    #[test]
    fn response_request_id_rfc8887_example() {
        let json = r#"{
            "@type": "Response",
            "requestId": "R1",
            "methodResponses": [
                ["Core/echo", {"hello": true, "high": 5}, "b3ff"]
            ],
            "sessionState": "75128aab4b1b"
        }"#;
        let frame = parse_ws_frame(json).expect("must parse");
        assert!(matches!(frame, WsFrame::Response(_)), "got {frame:?}");
        assert_eq!(frame.request_id(), Some("R1"));
    }

    /// bd:JMAP-6r7c.31 — WsSender and WsReceiver must each be `Send` so a
    /// caller can move one half into a separate tokio task while keeping
    /// the other half in the current task. The whole point of the split
    /// is two-task concurrent send-while-receiving; if either half were
    /// `!Send`, the split would not enable it.
    ///
    /// `Sync` is required because `WsSender` behind `Arc` (for concurrent
    /// sends from multiple tasks) needs `Arc<WsSender>: Send`, which
    /// requires `WsSender: Sync`. Compile-time check only — nothing to
    /// assert at runtime.
    #[test]
    fn ws_sender_and_receiver_are_send_and_sync() {
        fn assert_send_sync<T: Send + Sync>() {}
        assert_send_sync::<WsSender>();
        assert_send_sync::<WsReceiver>();
        // The unified session was already Send+Sync before the split
        // landed; assert here as a regression guard so a future refactor
        // that accidentally introduces a `!Send` or `!Sync` field in
        // WsSession is caught.
        assert_send_sync::<WsSession>();
    }
}