alknet/tasks/call/protocol/pending-request-map.md

id, name, status, depends_on, scope, risk, impact, level

id	name	status	depends_on	scope	risk	impact	level
call/protocol/pending-request-map	Implement PendingRequestMap for correlating call.requested and call.responded events	completed	call/protocol/wire-types	moderate	medium	component	implementation

Description

Implement PendingRequestMap in src/protocol/pending.rs. This manages in-flight calls and subscriptions, correlating call.responded events back to the original call.requested by request ID.

PendingRequestMap

pub struct PendingRequestMap {
    pending: HashMap<String, PendingEntry>,
}

enum PendingEntry {
    Call {
        tx: oneshot::Sender<Result<Value, CallError>>,
        timeout: Instant,
    },
    Subscribe {
        tx: mpsc::Sender<Result<Value, CallError>>,
        timeout: Option<Instant>,
    },
}

Behavior

When a call.responded event arrives:

• If PendingEntry::Call → resolve the oneshot, delete entry
• If PendingEntry::Subscribe → push to the mpsc channel, keep entry alive

When call.completed arrives on a subscription → close the mpsc channel, delete entry.

When call.aborted arrives → cancel/drop whichever side initiated it. A call.aborted for an unknown requestId is silently discarded.

When call.error arrives → resolve the oneshot (Call) or push to channel (Subscribe) with the error, delete entry.

Timeouts

Timeouts prevent dangling entries. A background task sweeps expired entries periodically (every 10 seconds per call-protocol.md).

• Call entries have a timeout (default 30s from CallAdapter.default_timeout)
• Subscribe entries may have timeout: None (unbounded — long-running subscriptions)

When the sweeper finds an expired entry:

• Call: resolve oneshot with CallError { code: "TIMEOUT", retryable: true }, delete
• Subscribe: close mpsc channel with a timeout error, delete

Methods

impl PendingRequestMap {
    pub fn new() -> Self;

    /// Register a pending call. Returns a oneshot receiver for the result.
    pub fn register_call(&mut self, request_id: String, timeout: Instant) -> oneshot::Receiver<Result<Value, CallError>>;

    /// Register a pending subscription. Returns an mpsc receiver for the stream.
    pub fn register_subscribe(&mut self, request_id: String, timeout: Option<Instant>) -> mpsc::Receiver<Result<Value, CallError>>;

    /// Handle an incoming call.responded event.
    /// Returns true if the entry was found and handled.
    pub fn handle_responded(&mut self, request_id: &str, output: Value) -> bool;

    /// Handle an incoming call.completed event (subscriptions only).
    /// Closes the mpsc channel, deletes entry.
    pub fn handle_completed(&mut self, request_id: &str) -> bool;

    /// Handle an incoming call.aborted event.
    /// Cancels the pending request, deletes entry.
    pub fn handle_aborted(&mut self, request_id: &str) -> bool;

    /// Handle an incoming call.error event.
    /// Resolves with the error, deletes entry.
    pub fn handle_error(&mut self, request_id: &str, error: CallError) -> bool;

    /// Sweep expired entries. Called periodically by a background task.
    pub fn evict_expired(&mut self) -> Vec<String>;  // returns evicted request IDs

    /// Fail all pending requests (connection closed). Returns the request IDs that were failed.
    pub fn fail_all(&mut self, error: CallError) -> Vec<String>;

    /// Check if a request ID is pending.
    pub fn contains(&self, request_id: &str) -> bool;

    /// Number of pending entries.
    pub fn len(&self) -> usize;
}

Connection drop handling

When the QUIC connection closes, all pending requests are failed with call.error code INTERNAL and message "connection closed". All subscription channels are closed. This is fail_all().

Stream reset handling

When a QUIC stream is reset mid-operation, the FrameFramedReader returns an error. If the stream was carrying a subscription, the PendingRequestMap entry is removed and the mpsc channel is closed. If the stream was carrying a call, the oneshot is resolved with an error. No call.aborted is sent — the stream is gone.

Correlation is by ID, not by stream

A response arriving on stream N can fulfill a request sent on stream M. The PendingRequestMap is keyed by ID, not by stream. This is the stream-agnostic correlation property from ADR-012.

Acceptance Criteria

• PendingRequestMap struct with pending HashMap
• PendingEntry::Call with oneshot::Sender and timeout
• PendingEntry::Subscribe with mpsc::Sender and optional timeout
• register_call returns oneshot::Receiver
• register_subscribe returns mpsc::Receiver
• handle_responded resolves Call oneshot, pushes to Subscribe channel
• handle_completed closes Subscribe mpsc, deletes entry
• handle_aborted cancels pending, deletes entry
• handle_error resolves with error, deletes entry
• Unknown request_id in handle_* is silently discarded (returns false)
• evict_expired removes timed-out entries, resolves with TIMEOUT error
• fail_all fails all pending with given error (connection close)
• Correlation is by request ID, not by stream
• Unit test: register call, handle_responded → oneshot resolves
• Unit test: register subscribe, handle multiple responded, handle_completed → stream ends
• Unit test: expired call → evict_expired resolves with TIMEOUT
• Unit test: fail_all resolves all pending with INTERNAL error
• Unit test: unknown request_id handle_responded → false (silently discarded)
• cargo test -p alknet-call succeeds
• cargo clippy -p alknet-call succeeds with no warnings

References

• docs/architecture/crates/call/call-protocol.md — PendingRequestMap section
• docs/architecture/decisions/012-call-protocol-stream-model.md — ADR-012 (ID-based correlation)

Notes

Correlation is by request ID, not by stream — a response on stream N can fulfill a request sent on stream M. This is the stream-agnostic property from ADR-012. The sweeper runs every 10 seconds to evict expired entries. Unknown request IDs in handle_* are silently discarded (not an error — the entry may have already been resolved/cleaned up).

Summary

Implemented PendingRequestMap in protocol/pending.rs with Call (oneshot) and Subscribe (mpsc) entries, ID-based correlation (ADR-012), timeout-based eviction, fail_all for connection close, and silent discard of unknown request IDs. 17 unit tests pass; clippy clean. Merged to develop.