# Receive real-time order updates

**SUBSCRIBE /orders**

Real-time order updates stream with resume capability.

Query Parameters:
  - since=<uint64>   Last applied seq for resume (optional; must be >0; absent or 0 → start from live tail)
  - market=<id>      Repeatable; filter by market_id
  - account_id=<id>  Repeatable; filter by account_id

Resume Semantics:
  1. Client connects with since=S (last applied seq)
  2. Server replays frames with seq >= S in order
  3. Sends backlog_end (last_seq = current max)
  4. Continues live streaming
  If S > current max → immediate live (no backlog)
  If S too old (retention gap) → error frame (code=resume_too_old) then close (4009)

Idempotency / Ordering:
  - seq strictly monotonic per broker; no gaps (gap ⇒ operational incident)
  - Client drops any frame with seq <= last_applied_seq
  - Expected next seq = last_applied_seq + 1 (else trigger reconnect + resume)

Heartbeats:
  - Sent when no order_update within configured interval
  - Heartbeat does NOT advance seq; only order_update frames advance seq
  - Heartbeat and backlog_end both repeat the last data seq

Flow Control:
  - Server may enforce max_pending_frames/bytes and close with code 4008 (flow_control)

Close Codes:
  1000 normal
  1001 going_away
  1011 internal_error
  4008 flow_control
  4009 resume_too_old / protocol_version
  4401 unauthorized


## Messages

### Order Update Frame

Order state change notification

#### Payload

- **type** (string)

- **seq** (integer(int64))

- **ts_ns** (integer(int64))

- **payload** (object)
  Current state of an order.





### Order Reject Frame

Notification of a rejected order command (Amend/Cancel)

#### Payload

- **type** (string)

- **seq** (integer(int64))

- **ts_ns** (integer(int64))

- **payload** (object)





### Heartbeat Frame

Keep-alive heartbeat (does not advance seq)

#### Payload

- **type** (string)

- **seq** (integer(int64))
  Repeats last delivered data seq; heartbeat does not advance global seq

- **ts_ns** (integer(int64))

- **payload** (object)





### Backlog End Marker

Signals end of historical replay; live streaming begins

#### Payload

- **type** (string)

- **seq** (integer(int64))

- **ts_ns** (integer(int64))

- **payload** (object)





### Error Frame

Error notification before close

#### Payload

- **type** (string)

- **seq** (integer(int64))

- **ts_ns** (integer(int64))

- **payload** (object)






## Bindings
#### Operation WebSockets-specific information

- **headers** (object)

- **query** (object)