Appendix: RALF Protocol Reference¶

Status: Normative. This appendix is the single source of truth for the RALF wire contract as implemented by pm-ralf-gwy (ralf_gateway/). For an operational, tutorial-style guide see Post-Trade Dissemination; for the gateway's configuration block see Engine Config Specification §6.4.

1. What RALF is¶

RALF (Reconciliation ALF) is EduMatcher's text post-trade dissemination protocol. It streams executed-trade and end-of-day events over TCP to external back-office consumers (clearing, drop-copy, audit). It is served by pm-ralf-gwy, which subscribes to the engine event bus and re-publishes derived events as RALF lines. RALF is read-only: clients subscribe and receive; they never submit orders.

2. Scope & conformance¶

This document defines the client-visible wire behaviour of RALF version token RALF1: framing, message set, fields, roles, sequencing, timeouts, and errors. The key words MUST, MUST NOT, SHOULD, and MAY are used per RFC 2119. A conforming client or gateway MUST implement the message set in §6 with the field constraints in §6 and §10. Behaviour not stated here is unspecified. Where the current implementation deviates from what a robust protocol would require, the deviation is called out with a ⚠ Known deviation note and tracked in the project's suspected-bugs report.

3. Transport & session model¶

Property	Value
Transport	TCP
Default port	`5580` (`post_trade_gateway.port`)
Encoding	UTF-8 text lines
Delimiter	`\n`
Version token	`RALF1`
Connection model	long-lived, one authenticated session per connection
Direction	gateway → client for all data; client → gateway for control only

A session proceeds: connect → HELLO → WELCOME → one or more SUB/UNSUB → event stream + heartbeats → EXIT/disconnect. A client MUST send HELLO before any other message; a non-HELLO first message is rejected with ERR|CODE=AUTH_REQUIRED.

4. Wire format¶

Every message is one line:

MSGTYPE|KEY=VALUE|KEY=VALUE|...\n

MSGTYPE MUST be uppercase ASCII from A-Z, 0-9, _.
Fields are |-delimited; each field is split into key/value on the first =.
A parser MUST ignore unknown fields (forward compatibility) except where a field is required for validation.
Values do not contain | or \n.

Reserved cross-message keys (present on most messages):

Key	Meaning
`CH`	Channel: `CLEARING`, `DROP_COPY`, or `AUDIT`
`SYM`	Symbol filter (control) or event symbol (data); `*` = all
`SEQ`	Channel-local monotonic message sequence (see §8)
`TS`	UTC ISO-8601 timestamp with milliseconds and `Z` suffix

5. Message catalog¶

Message	Direction	Purpose
`HELLO`	client → gw	open session; authenticate role; optional replay checkpoint
`WELCOME`	gw → client	session accepted; negotiated parameters
`SUB`	client → gw	subscribe channel(s) × symbol scope
`UNSUB`	client → gw	remove subscriptions
`SNAP`	gw → client	subscription/recovery baseline (carries current `SEQ`)
`EXEC`	gw → client	one executed trade (post-trade view)
`EOD`	gw → client	end-of-day per-symbol summary marker
`HB`	gw → client	heartbeat when the stream is quiet
`PING` / `PONG`	client → gw / gw → client	liveness probe and reply
`EXIT`	gw → client	session terminated (e.g. idle timeout)
`ERR`	gw → client	protocol, entitlement, or replay error

6. Message definitions¶

`HELLO` (client → gateway)¶

Field	Type	Req	Constraints
`CLIENT`	string	✔	external client identifier (logging)
`PROTO`	string	✔	MUST equal `RALF1`
`ROLE`	enum	✔	one of `CLEARING`, `DROP_COPY`, `AUDIT`; MUST be in the gateway's `allowed_roles`
`LASTSEQ`	int	–	replay checkpoint; requests events with `SEQ > LASTSEQ` (see §8)

Missing CLIENT/PROTO/ROLE → ERR|CODE=AUTH_REQUIRED. A ROLE outside allowed_roles → ERR|CODE=ENTITLEMENT_DENIED. A non-integer LASTSEQ → ERR|CODE=BAD_MESSAGE.

`WELCOME` (gateway → client)¶

Field	Meaning
`PROTO`	negotiated version (`RALF1`)
`GW`	gateway id (`post_trade_gateway.name`)
`ROLE`	accepted role
`REPLAY`	replay retention window, seconds (`replay_retention_sec`)
`HBINT`	heartbeat interval, seconds (`heartbeat_interval_sec`)

`SUB` / `UNSUB` (client → gateway)¶

Field	Type	Req	Default	Constraints
`CH`	csv of channels	✔	—	each ∈ {`CLEARING`,`DROP_COPY`,`AUDIT`}; entitlement checked (§7)
`SYM`	csv of symbols or `*`	–	`*`	scope filter

A subscription is the set of (channel, symbol) pairs. SUB is cumulative; UNSUB removes matching pairs and is idempotent. After a SUB, the gateway emits one SNAP. A missing/empty CH → ERR|CODE=INVALID_CHANNEL; an unknown channel → ERR|CODE=INVALID_CHANNEL; a channel the role may not access → ERR|CODE=ENTITLEMENT_DENIED.

`SNAP` (gateway → client)¶

Baseline emitted after a SUB and on replay-miss recovery. Carries CH (the subscribed channels, comma-joined), SYM, SEQ (the highest current sequence over the CH set in that SNAP), and TS. RALF SNAP carries no book/position state — it is a sequence baseline only.

`EXEC` (gateway → client)¶

One line per executed trade, per subscribed channel.

Field	Description
`CH` `SYM` `SEQ` `TS`	envelope (§4)
`EXEC_ID`	execution id (engine trade id)
`MATCH_ID`	match id — identical to `EXEC_ID` in `RALF1`
`BUY_ORDER_ID` / `SELL_ORDER_ID`	resting/aggressing order ids
`BUY_GW` / `SELL_GW`	buy-side / sell-side gateway ids
`SIDE`	aggressor side (`BUY`/`SELL`)
`QTY`	executed quantity
`PX`	execution price (display units)

A single trade is emitted once per channel (CLEARING, DROP_COPY, AUDIT), each copy consuming its own SEQ (§8).

`EOD` (gateway → client)¶

Per-symbol end-of-day marker, derived from the engine system.eod broadcast.

Field	Description
`CH` `SYM` `SEQ` `TS`	envelope
`TRADE_COUNT`	trades seen for the symbol this session
`EXEC_COUNT`	execution count — identical to `TRADE_COUNT` in `RALF1`

EOD is emitted once per symbol on all three channels: CLEARING, DROP_COPY, and AUDIT.

`HB`, `PING`/`PONG`, `EXIT`¶

HB|TS=… is sent to authenticated clients when the stream is otherwise quiet (cadence HBINT). A client MAY send PING; the gateway replies PONG|TS=…. EXIT|REASON=…|TS=… signals gateway-initiated termination (e.g. idle_timeout).

7. Roles & entitlements¶

Roles and channels share the same three names. Entitlement rules:

Role	May subscribe to
`CLEARING`	`CLEARING` only
`DROP_COPY`	`DROP_COPY` only
`AUDIT`	any channel (`CLEARING`, `DROP_COPY`, `AUDIT`)

A role subscribing outside its entitlement receives ERR|CODE=ENTITLEMENT_DENIED. Only roles listed in post_trade_gateway.allowed_roles may authenticate.

8. Sequencing & recovery¶

SEQ is maintained per channel (CLEARING, DROP_COPY, AUDIT).

Within one channel, SEQ is strictly increasing by 1 per emitted line.
Across different channels, SEQ values are independent and are not globally ordered or globally unique.
Clients MUST do gap detection and ordering within a given CH stream, not across mixed channels.

LASTSEQ in HELLO is a single integer checkpoint. The gateway applies that same threshold to each entitled channel independently and replays events where event.SEQ > LASTSEQ for that event's channel.

Replay. If HELLO carries LASTSEQ, the gateway attempts to resend journalled events with SEQ > LASTSEQ (per channel, as above) and only for channels the role is entitled to receive (§7). If LASTSEQ predates the retained journal window for any entitled channel (replay_retention_sec), the gateway emits ERR|CODE=REPLAY_MISS followed by a SNAP baseline; the client MUST reset to that baseline.

⚠ Known deviation — replay is entitlement-filtered but not subscription-filtered

Replay happens during HELLO, before any SUB is processed, so replay cannot apply symbol/channel subscription state from the current connection. The current gateway filters replay by role entitlement (§7), but does not filter by subscriptions.

9. Liveness & timeouts¶

Parameter	Source	Default
Heartbeat interval (`HBINT`)	`heartbeat_interval_sec`	1 s
Idle timeout	`idle_timeout_sec`	5 s
Replay retention (`REPLAY`)	`replay_retention_sec`	86400 s

The gateway sends HB when no other line has been sent within the heartbeat interval. A session with no inbound activity for the idle timeout is dropped (EXIT|REASON=idle_timeout). A client whose outbound queue exceeds max_client_queue receives ERR|CODE=SLOW_CLIENT and is disconnected.

10. Error codes¶

Code	Meaning / trigger
`AUTH_REQUIRED`	first message was not `HELLO`, or `HELLO` missing `CLIENT`/`PROTO`/`ROLE`
`BAD_MESSAGE`	unparseable line, unsupported message type, or malformed field (e.g. non-integer `LASTSEQ`)
`INVALID_CHANNEL`	`SUB` with missing/empty or unknown `CH`
`ENTITLEMENT_DENIED`	role not in `allowed_roles`, or channel outside the role's entitlement
`REPLAY_MISS`	requested `LASTSEQ` is older than the retained journal window
`SLOW_CLIENT`	outbound queue exceeded `max_client_queue`; session disconnected

ERR carries CODE and a human-readable DETAIL, e.g. ERR|CODE=REPLAY_MISS|DETAIL=requested seq outside retention.

11. Configuration reference¶

pm-ralf-gwy reads the post_trade_gateway block of engine_config.yaml (consumed only by this process). Full field law is in Engine Config Specification §6.4.

Key	Default	Purpose
`name`	`ralf-gwy01`	gateway id in `WELCOME\\|GW=`
`bind_address`	`0.0.0.0`	TCP listen address
`port`	`5580`	TCP listen port
`replay_retention_sec`	`86400`	journal window; advertised as `WELCOME\\|REPLAY=`
`heartbeat_interval_sec`	`1`	`HB` cadence; advertised as `WELCOME\\|HBINT=`
`idle_timeout_sec`	`5`	inbound-idle disconnect
`max_client_queue`	`10000`	outbound backlog before `SLOW_CLIENT`
`allowed_roles`	`[CLEARING, DROP_COPY, AUDIT]`	roles permitted to authenticate

12. Conformance notes¶

A conforming RALF1 implementation:

derives events solely from engine broadcasts: trade.executed → EXEC, system.eod → EOD. No other event families exist in RALF1.
MUST send HELLO/WELCOME before any data; MUST reject pre-auth data with AUTH_REQUIRED.
MUST enforce the §7 entitlement matrix on SUB (live path).
MUST apply per-channel SEQ semantics from §8 (no global SEQ stream).
MUST advertise REPLAY/HBINT in WELCOME matching its configuration.
SHOULD treat replay as role-entitled but pre-SUB (therefore not subscription-filtered) on reconnect.

Future revisions may add CORRECT, BUST, ALLOC, and SETTLE event families as the corresponding engine events become available; they are not part of RALF1.