optionchain_simulator 0.2.8

OptionChain-Simulator API and Architecture

System Architecture

Two REST surfaces over one set of layers. v1 serves a single expiration per request and stamps it with the wall clock; v2 serves a rolling inventory of absolute expirations on a simulated clock. They share the seeded walk and the error boundary, and nothing else — separate session types, separate stored schemas, separate stores.

flowchart TD
  Client[Client]

  subgraph api["api — REST, f64 at the boundary"]
    V1["/api/v1/chain"]
    V2["/api/v2/simulations"]
    Export["/api/v2/simulations/{id}/export"]
  end

  subgraph session["session — lifecycle, effective parameters"]
    SM[SessionManager]
    SIM[SimulationManager]
  end

  subgraph domain["domain — private, seeded, pure"]
    Simulator[Simulator + Walker]
    Tape[FactorTape]
    Planner[RollingPlanner]
    Series[SeriesBuilder]
  end

  subgraph infra["infrastructure — adapters"]
    Redis[(Redis)]
    Mongo[(MongoDB)]
    CH[(ClickHouse)]
  end

  Client --> V1 & V2 & Export
  V1 --> SM --> Simulator
  V2 --> SIM
  Export --> SIM
  SIM --> Tape
  Tape --> Series
  Planner --> Series
  SM -.sessions.-> Redis
  SIM -.simulations.-> Redis
  SM -.events.-> Mongo
  Simulator -.historical prices.-> CH
  SIM -.snapshots, opt-in.-> CH
  Export -.persisted rows first.-> CH

domain is a private module: the walk, the tape, the planner and the snapshots are implementation, and the REST contract is what is public. The dependency arrows only ever point down — an infrastructure adapter that imported api would invert the layering, which is why the persistence layer carries its own row types instead of naming the domain snapshot.

Session State Transitions

stateDiagram-v2
[*] --> Initialized: POST /api/v1/chain
Initialized --> InProgress: POST /api/v1/chain/step
InProgress --> InProgress: POST /api/v1/chain/step
InProgress --> Modified: PATCH
Modified --> InProgress: POST /api/v1/chain/step
InProgress --> Reinitialized: PUT
Modified --> Reinitialized: PUT
Reinitialized --> InProgress: POST /api/v1/chain/step
Initialized --> [*]: DELETE
InProgress --> [*]: DELETE
Modified --> [*]: DELETE
Reinitialized --> [*]: DELETE

GET /api/v1/chain is a safe, repeatable peek and does not appear here because it never changes the session state — only POST /api/v1/chain/step advances the cursor.

A v2 simulation walks a smaller machine, because it is immutable after creation: there is no PATCH or PUT to reach Modified or Reinitialized, and a stored document in either state is rejected on load rather than served.

stateDiagram-v2
[*] --> Initialized: POST /api/v2/simulations
Initialized --> InProgress: POST /{id}/step
InProgress --> InProgress: POST /{id}/step
InProgress --> Completed: POST /{id}/step (last)
Initialized --> [*]: DELETE or idle TTL
InProgress --> [*]: DELETE or idle TTL
Completed --> [*]: DELETE or idle TTL

The state and the cursor are validated together: Initialized only at step zero, Completed only at the horizon, InProgress strictly between them. GET /{id}/snapshot and the export appear nowhere here — neither moves the cursor, and the idle TTL is measured from the last write, so peeking does not keep a simulation alive.

API Request Flow

sequenceDiagram
participant Client
participant API as REST API
participant SM as Session Manager
participant SS as Simulator Service

Client->>API: POST /api/v1/chain
API->>SM: Create new session
SM->>SS: Initialize simulation
SS-->>SM: Initial state
SM-->>API: Session created (id: abc123)
API-->>Client: 201 Created (session details)

Client->>API: POST /api/v1/chain/step
API->>SM: Advance one step
SM->>SS: Advance simulation
SS-->>SM: Step data
SM-->>API: Chain data
API-->>Client: 200 OK (Chain data)

Client->>API: GET /api/v1/chain
API->>SM: Peek current step
SM->>SS: Read current snapshot
SS-->>SM: Step data (no advance)
SM-->>API: Chain data
API-->>Client: 200 OK (same snapshot, repeatable)

A v2 advance does more work behind the same shape. The tape is built on first use rather than at creation, chains are priced per snapshot from a factor row and the planner's live expirations, and — when persistence is on — the served step is queued for the warehouse after the cursor commits, so the write is never on the response's clock.

sequenceDiagram
participant Client
participant API as REST API
participant SIM as SimulationManager
participant Tape as FactorTape
participant Series as SeriesBuilder
participant CH as ClickHouse

Client->>API: POST /api/v2/simulations
API->>SIM: Resolve seed, start, interval, schedules
SIM-->>API: Simulation created (every replay input echoed)
API-->>Client: 201 Created

Client->>API: POST /api/v2/simulations/{id}/step
API->>SIM: Advance (expected_step precondition)
SIM->>Tape: Build once, then cache (single flight)
Tape-->>SIM: Factor row for the cursor
SIM->>Series: Price the live expirations at that row
Series-->>SIM: Snapshot
SIM->>SIM: Commit the cursor (compare-and-swap)
SIM-->>API: Snapshot + new cursor
API-->>Client: 200 OK
SIM--)CH: Queue the served step (detached, best effort)

Client->>API: GET /api/v2/simulations/{id}/export
API->>CH: Read the persisted range
CH-->>API: Rows for the steps it has
API->>Series: Replay whatever is missing
API-->>Client: 200 OK (streamed JSON or CSV)

REST API Endpoints

The OptionChain-Simulator exposes the following REST API endpoints:

Probes

The two answer different questions, and conflating them is how one outage becomes two. /health says the process is alive: it touches nothing, so a Redis hiccup can never get a healthy instance restarted. /ready says this instance can take work, and it asks: Redis and MongoDB always, ClickHouse when snapshot persistence is enabled, each under a 2-second bound and all of them at once. A 503 body names every dependency and, for the failing ones, a fixed category: unreachable or timed_out. Never a driver's own words — the endpoint is unauthenticated, and a server message can carry internal hosts, paths and tokens no redaction reliably recognises, so the full explanation stays in the service's log. Nothing is cached, so an instance whose Redis came back reports itself ready again without a restart.

Both are unversioned, unauthenticated, and excluded from the request metrics: an orchestrator polling forever would otherwise add a constant to every series and a flood of 503s to the error series while a dependency is down. Docker/docker-compose.yml points its backend healthcheck at /ready, so docker compose up -d reports the service healthy only once it can actually serve.

Step cursor semantics (serve-then-advance): current_step is the 0-based index of the NEXT snapshot to serve. POST /api/v1/chain/step serves the snapshot at the cursor and then advances it, so a session with steps = N serves EXACTLY indices 0..N-1 over N advances. The advance that serves the last snapshot persists the Completed state, and any further advance returns 410 Gone. GET /api/v1/chain peeks the snapshot the next advance would serve without moving the cursor.

Migration (breaking, issue #21): GET /api/v1/chain used to advance the session and consume a step. It is now a read-only, repeatable peek that returns the current snapshot without mutating state. To advance the cursor, clients must now call POST /api/v1/chain/step (same response shape, same 200/404/410/500 status codes as the old GET). Downstream consumers such as IronCondor must switch their step-advancing call from GET /api/v1/chain to POST /api/v1/chain/step.

v2 rolling simulations

/api/v2/simulations is a second, parallel REST surface for deterministic rolling multi-expiration simulations: a simulated clock instead of a wall-clock timestamp, a rolling inventory of absolute expirations driven by versioned schedule rules (0DTE / weekly / monthly / yearly), and one snapshot per cursor position.

The bid-ask spread is per contract

A v2 chain used to be quoted with one spread applied to every contract, which is not what an option market looks like: a dear in-the-money call and a five-cent far wing do not carry the same absolute bid-ask, and the wing's spread is a far larger fraction of its price. A consumer valuing a position at the touch takes its whole cost of trading from that number.

The spread is now a small parametric model, evaluated per contract:

spread(contract) = max(
    spread_tick,
    spread
      + spread_proportional       * mid
      + spread_moneyness_widening * |ln(strike / underlying)|
      + spread_tenor_widening     * sqrt(days_to_expiration / 365)
)

Every coefficient is an optional create-request field, echoed back in the simulation response so a run can be replayed, and every widening term defaults to zero. A request that carries only the legacy spread therefore quotes exactly as it did: the scalar IS the floor term, and the arithmetic for every quote is unchanged.

A quote is never withdrawn. Upstream's apply_spread sets bid, ask AND mid to None when mid <= spread, so the cheap wings vanished from the chain exactly as they decayed — the moment a consumer most wants to know what closing them costs. A contract that has a mid now always has a two-sided quote, with the bid floored at spread_tick or at the mid, whichever is lower: a contract worth less than a tick is quoted 0.00/0.01 rather than being marked up to a penny it is not worth.

Two things a legacy request sees change, both consequences of that fix:

• The chain is longer. Upstream stopped extending the strike ladder at the first pair of strikes with no price, and that condition WAS the erasure. With nothing erased the ladder runs to the full 2 * chain_size + 1: at spot 5000, 30 days and chain_size = 30, 45 strikes become 61. Response payloads, export rows and warehouse rows grow with it, inside the same configured caps.
• A spread below the tick is raised to it. spread: 0.005 now widens by half a cent each way rather than a quarter. At or above the tick — every request that took the documented default — the quotes are unchanged.

Persisted snapshots are therefore a new tape: CURRENT_SNAPSHOT_GENERATION is 4, so rows written by an older binary stay addressable under the generation they were filed under and are never mixed with these. It moved again with optionstratlib 0.21.1, which quotes an option worth nothing at zero instead of pricing it as absent (OptionStratLib#487): upstream had stopped extending a ladder at a strike whose worthless side carried no price, so a chain near expiry held fewer strikes than chain_size asked for — 23 instead of 41 at a spot of 5100 with a 25-point interval at 0.3125 days. That changes the strike set of those steps for rolling ladders as much as for pinned ones.

The strike ladder can be pinned

The ladder is rebuilt around the current underlying at every step, so the quoted strikes follow the spot and a contract quoted at step 0 can be gone by step 2: a move of 0.27 percent over two steps was enough to drop a strike. chain_size fixes how MANY strikes are quoted, never WHICH.

For a client browsing a chain that is right. For one holding a position it is not: a leg opened at 4850 cannot be marked, closed or settled at a step where 4850 does not exist, and a defined-risk structure loses its furthest wings first, which are the legs that cap its risk.

strike_ladder on the v2 create request chooses:

A pinned simulation must supply strike_interval: without one the interval is derived per expiration and there is no fixed grid to pin, so the request is a 400 naming the field. The effective value is echoed in the simulation response and survives a store round trip, and a document written before the field reads as rolling.

A pinned ladder does not follow a large move. If the spot leaves the pinned range every quoted strike ends up on one side of the money — each contract still carries both a call and a put, but they are all deep in or deep out. That is correct and informative: a simulation that silently invented new strikes would not be the closed world the setting exists to provide. Widen the ladder at creation, with chain_size, rather than at step time. A spot that drifts further than the service will widen for is a 400 naming strike_ladder rather than a silently shorter chain.

/api/v1/chain is untouched, model and all: it is frozen, and its chains come from a different upstream path.

Serve-then-advance, as in v1: a simulation with steps = N serves indices 0..N-1 over N calls to /step, and any call after that returns 410 Gone. expected_step on the advance is a precondition — a mismatch is 412 with the actual cursor and consumes nothing, which is what makes a retry after a lost response safe. It is deliberately distinct from 409, which means another writer committed first.

A v2 simulation is immutable after creation. There is no PATCH or PUT: changing the seed, the start, the schedules or the chain shape changes the tape, so it creates a new simulation instead of mutating one.

A historical v2 walk prices itself. A Historical method carries no volatility of its own, so each step is priced by the realized volatility of everything observed up to that step and nothing later — the same expanding window v1 uses, so from step 1 on the two agree on the volatility path as well as the price path. (Step 0 differs by construction: v1 prices its first chain at the request's constant.) The volatility you send prices none of its steps; the values that did are the per-step ones every snapshot and the volatility export report. A series too turbulent to price a chain at, or one whose first three prices are equal, is refused when the simulation is first served.

Advanced steps can be filed in ClickHouse. With OCS_SNAPSHOT_PERSISTENCE_ENABLED on, every step an advance serves is written as one metadata row plus one flattened row per expiration and strike, so a client can query one contract across time instead of unwinding whole documents. A peek and an export replay and persist nothing — only the advance, which is the call that moves the cursor, files anything.

Filing happens after the cursor commits and off the request's clock, so a degraded warehouse can neither fail a response nor delay one. Row identity is derived from (simulation, tape generation, step), which makes a retry replace a row rather than duplicate it, and a reader never sees a snapshot whose quote rows are missing — the metadata row carries the expected count and a mismatch reads as absent. Turning the knob on makes ClickHouse a hard startup dependency: the tables are created at boot, so a schema or connectivity problem fails the boot rather than surfacing later. MongoDB stays event and audit only.

Replay. The creation response echoes the effective seed, effective start, step interval, time frame, timezone, calendar version, IANA tzdb release and normalised schedules — everything needed to reproduce the run without having kept the request. The full contract is in ADR 0001.

/api/v1/chain is frozen. Its routes, DTO fields and types, wall-clock timestamp behaviour, rendered values, status codes and OpenAPI operations are byte- and behaviour-compatible; v2 ships as a separate surface with its own session type and its own stored-session schema, so existing clients need no changes.

Configuration

LOGLEVEL sets the verbosity, case-insensitively, defaulting to INFO. An unrecognised value warns once and falls back rather than aborting startup, and the effective level is logged at that same level, so setting WARN or ERROR still confirms itself. DEBUG includes hyper connection traces on every request, which a batch consumer will want to avoid.

A blank value is an unset value. KNOB= and KNOB=" " are read exactly as if the line were absent, and the documented default applies, so a knob is switched off by commenting it out rather than by emptying it.

One variable is exempt: CLICKHOUSE_PASSWORD, where an empty value is a real configuration — a stock default user has no password — so a present variable is taken as written and only an absent one falls back. Values are never trimmed either: whitespace decides only whether a value is blank, and a credential written with a leading space keeps it. Numbers and host names are trimmed where they are parsed.

Every environment variable the service reads is documented in .env.example with its default and accepted range. Two families, with deliberately different failure behaviour:

• Request caps — OCS_MAX_STEPS, OCS_MAX_CHAIN_SIZE, OCS_MAX_HISTORICAL_PRICES, OCS_MAX_CONCURRENT_PRICING_JOBS, OCS_MAX_CACHED_WALKS, OCS_EXPORT_BLOCK_ROWS — warn and fall back to their defaults when set to something invalid. A bad value there degrades one request.
• v2 operational knobs — OCS_V2_RETENTION_SECS, OCS_V2_CLEANUP_INTERVAL_SECS, OCS_MAX_CACHED_TAPES, OCS_MAX_CACHED_SNAPSHOTS, OCS_MAX_SNAPSHOT_CONTRACTS, OCS_MAX_CACHED_SNAPSHOT_CONTRACTS, OCS_MAX_EXPORT_ROWS, OCS_SNAPSHOT_* — are validated at startup and fail the process with a message naming the variable. Silently reverting a retention window would expire simulations a client is still walking, and silently reverting a cache bound would change the service's memory profile with nothing to show for it.

Where the server listens — OCS_BIND_ADDRESS (an IP address, or the words all and localhost) and OCS_PORT (1..=65535) — is configurable and validated at startup like the second family: two instances quietly fighting over one port is worse than a refusal. The address now defaults to loopback, where it used to be a hardcoded 0.0.0.0; this service has no authentication and no rate limiting, so reachability off the host is a decision. A deployment that relied on the old default must set OCS_BIND_ADDRESS=0.0.0.0 — Docker/docker-compose.yml sets it and the dev override inherits it. Configuring the port is what makes it possible to shard tape materialisation across several instances on one host, which is embarrassingly parallel work: each simulation is independent and shares no state.

v2 retention is real time, not simulated time. A simulation whose simulated clock spans three years is still walked one request at a time, so its idle window is an operational choice independent of the horizon. It defaults to an hour — longer than v1's thirty minutes — and is measured from the last write: peeking a snapshot persists nothing, so a client that only peeks does not refresh it. The in-memory and Redis backends apply the same window from the same constant.

A retention sweep runs every OCS_V2_CLEANUP_INTERVAL_SECS, reaping expired simulations and evicting the factor tapes and snapshots they left behind. Eviction is never observable in what is served: both rebuild identically from the effective parameters, so it costs latency and nothing else. The sweep publishes v2_simulations_expired_total, and the caches publish v2_tape_cache_size and v2_snapshot_cache_size.

Testing against a deployment

The default suite is hermetic: LOGLEVEL=WARN cargo test --workspace passes with no Redis, no MongoDB and no ClickHouse running, and opens no socket. It covers the code, and not the thing an operator runs: a service on a port, behind a container, with those three behind it.

examples/integration covers that. It talks to the service named by OCS_INTEGRATION_BASE_URL over HTTP, scheme and port included, and every test in it SKIPS when the variable is unset or blank, which is why it can live in the workspace without costing the hermetic suite anything. Run it with make test-integration.

Two things follow from testing a DEPLOYMENT rather than a build. A deployed service can be older than the working tree, so the suite reports the version it found and skips a feature that is not deployed yet rather than failing it. And it is shared, so every test deletes the simulations it creates, including when it fails.

Exporting a tape

GET /api/v2/simulations/{id}/export?dataset=…&format=…&from_step=&to_step= streams a simulation's tape, which is what turns a walked-one-request-at-a-time simulation into something a backtester loads in one go. With persistence on it reads the steps the warehouse already holds, in windows, and replays the rest; with it off, or for a simulation nobody has walked, every step is replayed. Either source renders the same bytes.

Read-only in the strong sense. The export works from an immutable copy of the effective parameters and, where it reads them, from rows already written: it never advances the cursor, changes the state or version, writes a snapshot of its own, or alters what the next peek returns. A simulation that has never been walked exports its whole tape, a completed one still does, and two clients can export the same simulation at once.

The greek columns are opt-in and append-only. greeks takes the same three values, with the same meaning and the same default, as the chain endpoints, so a tape and a live step agree on what a level means. first appends call_theta, put_theta, call_vega, put_vega, call_rho, put_rho, call_rho_d, put_rho_d; all appends fourteen more, gamma through color, per style. delta is not among them — it already has its call_delta / put_delta columns, and a second copy could only drift.

Each level's header is a prefix of the next, so raising the level appends columns and never moves one: a consumer parsing by position keeps working, and the default export is byte-identical to what it was before the parameter existed. The column set is fixed per level, so a strike with no computable greeks writes empty fields rather than fewer of them.

Measured on a 5 996-row export, release build:

first and all cost the same to compute — upstream builds the snapshot whole and the level only decides what is written — so the step from first to all is paid in bytes, not in time.

The binary encodings

json and csv are text, so every consumer pays a parse, and for the two that matter that parse IS the bottleneck: a browser materialising a whole tape spends hundreds of milliseconds in JSON.parse and allocates an object per row, and a Rust consumer writing Parquet re-parses text this service already held in typed form.

• arrow — an Arrow IPC stream, one record batch per block. Content-Type: application/vnd.apache.arrow.stream, extension arrow. Available only when the service is built with the arrow-export feature, which is off by default because the arrow crate is a large tree and a deployment that never exports should not carry it. Asking for format=arrow without it is a typed 400 naming the format, never a 500 and never a silent fallback.
• packed — a dependency-free columnar block format for the browser. Content-Type: application/octet-stream, extension ocsp.

Both carry the same column names in the same order as the CSV header, so a reader moves between encodings without a mapping table, and both are f64 for every numeric column — exactly what json and csv render. Binary is a faster route to the same numbers, NOT a route to the underlying Decimal(38, 28) precision.

Both stream, in blocks. A columnar encoding cannot emit a column until its last row is known, so rows are buffered OCS_EXPORT_BLOCK_ROWS at a time (default 4096) and written a block at a time. An export's memory is therefore a function of the block width and not of the number of steps.

The packed layout, little-endian throughout:

file        := header block* footer
header      := "OCSP" u32:version u32:block_rows
               u32:dictionary_count dictionary_entry*
               u32:column_count column_desc*
               pad to 8
dict_entry  := u32:len utf8:value             (the symbol, then the rule ids)
column_desc := u32:name_len utf8:name u8:type_code u8:nullable pad to 4
block       := u32:row_count pad to 8 column_payload*
payload     := [validity bitmap if nullable, padded to 8] values, padded to 8
footer      := u32:0xFFFFFFFF pad to 8 u64:total_rows

The footer is required, and a decoder must check it. No block can carry 0xFFFFFFFF rows, so that value is what says the blocks have ended, and the u64 after it is the total the writer emitted. A document that ends without it was truncated and must be REJECTED rather than read as a shorter tape: the response is a 200 whose header goes out before the first byte is produced, so a dropped connection is otherwise indistinguishable from a smaller export. A total that disagrees with the blocks is the same error.

Type codes: 0 = f64, 1 = i64, 2 = timestamp in nanoseconds since the epoch, 3 = an index into the header dictionary, 4 = a label bitmask, one bit per dictionary entry. Every payload starts on an 8-byte boundary, which is the whole point: it is what lets a browser do new Float64Array(buffer, offset, count) with no copy, and an unaligned offset would make that constructor throw. Validity bitmaps follow Arrow's convention — LSB-first, 1 = valid — so one decoder serves both formats, and a null is a cleared bit rather than a sentinel or a NaN, which are values a chain can legitimately hold.

Keeping the text columns out of the blocks is what the dictionary is for: the symbol is fixed for a simulation and the schedule's rule ids are fixed by its parameters, so both are known before the first row. labels is a bitmask over those rule ids, and joining the bits it sets reproduces the csv column character for character, since both orders are lexicographic. A simulation is capped at 16 schedule rules at creation, well inside the 63 a mask carries, and a compile-time assertion keeps the two from drifting apart.

Measured on the reference fixture at greeks=all, release build:

Deterministic. Repeating an export is byte-identical: every value is a function of the effective parameters and the cursor, timestamps render as whole-second RFC 3339, and numbers use shortest round-trip formatting with no locale. JSON is a single valid array; CSV is RFC 4180 with a header row and CRLF endings, and an absent optional is an empty field rather than null or 0. Chain labels are joined with | so a shared expiration stays one column.

The two encodings carry the same values, though not always the same notation. JSON writes 4950.0 where the CSV writes 4950, so every integral value differs, on every row; and JSON takes exponent form below 1e-5 — a color of 6.4101559520200445e-6 — where the CSV spells the zeros out. Compare the two as numbers, never as text. JSON key order is not part of the contract; parse by name.

The greeks are f64 here, where the chain endpoints carry them as exact decimal strings. A CSV column has no type to make that distinction, and this surface's contract is that two runs compare byte for byte. So a tape and a live step agree on which greeks a level carries and on what they mean — but reconcile their numbers by value, not by string.

gamma appears three times at all: the shared gamma column plus call_gamma / put_gamma. They agree for a European option. The shared one is upstream's convenience mirror and stays defined at expiry and at zero volatility, where the per-style pair goes blank — which is the case where diffing them is informative rather than a bug.

The rows are produced on a blocking thread and handed over a bounded channel, so a long option_chains export never occupies an Actix worker and a slow client applies backpressure instead of accumulating priced chains in memory. OCS_MAX_EXPORT_ROWS bounds how many steps one request may cover.

Request/Response Models

1. Create Session (POST /api/v1/chain)

Request Body:

{
  "symbol": "AAPL",
  "steps": 10,
  "initial_price": 185.5,
  "days_to_expiration": 45.0,
  "volatility": 0.25,
  "risk_free_rate": 0.04,
  "dividend_yield": 0.005,
  "method": {
    "GeometricBrownian": {
      "dt": 0.004,
      "drift": 0.05,
      "volatility": 0.25
    }
  },
  "time_frame": "Day",
  "chain_size": 15,
  "strike_interval": 5.0,
  "smile_curve": 0.0005,
  "spread": 0.02
}

Response (201 Created):

{
    "id": "6af613b6-569c-5c22-9c37-2ed93f31d3af",
    "created_at": "2025-04-21T15:37:30.518022+00:00",
    "updated_at": "2025-04-21T15:37:30.518022+00:00",
    "parameters": {
        "symbol": "AAPL",
        "initial_price": 185.5,
        "volatility": 0.25,
        "risk_free_rate": 0.04,
        "method": "GeometricBrownian { dt: 0.004, drift: 0.05, volatility: 0.25 }",
        "time_frame": "day",
        "dividend_yield": 0.005,
        "smile_curve": 0.0005,
        "spread": 0.02,
        "seed": 13748925402398765431
    },
    "current_step": 0,
    "total_steps": 10,
    "state": "Initialized"
}

The request omitted seed, so one was generated at conversion and echoed here. Recording it is what lets the same session be recreated later: the same parameters and the same seed reproduce the identical sequence of snapshots, which is the guarantee IronCondor's replay depends on.

2. Peek Current Step (GET /api/v1/chain?sessionid=6af613b6-569c-5c22-9c37-2ed93f31d3af)

Safe and repeatable: returns the session's current snapshot without advancing the cursor or persisting anything. To advance the session and consume a step, use POST /api/v1/chain/step?sessionid=... (issue #21) — it takes the same query parameter and returns the same body shown below.

Response (200 OK):

{
    "underlying": "AAPL",
    "timestamp": "2025-04-21T15:33:03.597061+00:00",
    "price": 185.299430466522,
    "contracts": [
        {
            "strike": 160.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 26.08,
                "ask": 26.1,
                "mid": 26.09,
                "delta": 0.9993778215543331
            },
            "put": {
                "bid": null,
                "ask": null,
                "mid": null,
                "delta": -4.2479708093406946e-6
            },
            "implied_volatility": 0.09731095458186256,
            "gamma": 3.121236702609213e-6
        },
        {
            "strike": 165.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 21.14,
                "ask": 21.16,
                "mid": 21.15,
                "delta": 0.9888998386575956
            },
            "put": {
                "bid": 0.03,
                "ask": 0.05,
                "mid": 0.04,
                "delta": -0.010482230867546823
            },
            "implied_volatility": 0.15077922021760087,
            "gamma": 0.0028266289100911603
        },
        {
            "strike": 170.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 16.62,
                "ask": 16.64,
                "mid": 16.63,
                "delta": 0.9153696474659715
            },
            "put": {
                "bid": 0.49,
                "ask": 0.51,
                "mid": 0.5,
                "delta": -0.08401242205917087
            },
            "implied_volatility": 0.1927733286389461,
            "gamma": 0.012279670056243013
        },
        {
            "strike": 175.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 12.87,
                "ask": 12.89,
                "mid": 12.88,
                "delta": 0.7964192920937592
            },
            "put": {
                "bid": 1.71,
                "ask": 1.73,
                "mid": 1.72,
                "delta": -0.2029627774313833
            },
            "implied_volatility": 0.22329327984589836,
            "gamma": 0.019409579420062936
        },
        {
            "strike": 180.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 9.76,
                "ask": 9.78,
                "mid": 9.77,
                "delta": 0.6700429413591044
            },
            "put": {
                "bid": 3.57,
                "ask": 3.59,
                "mid": 3.58,
                "delta": -0.3293391281660381
            },
            "implied_volatility": 0.24233907383845762,
            "gamma": 0.022910122989513254
        },
        {
            "strike": 185.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 7.09,
                "ask": 7.11,
                "mid": 7.1,
                "delta": 0.5468721177394451
            },
            "put": {
                "bid": 5.87,
                "ask": 5.89,
                "mid": 5.88,
                "delta": -0.45250995178569736
            },
            "implied_volatility": 0.24991071061662393,
            "gamma": 0.024315069945191076
        },
        {
            "strike": 190.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 4.68,
                "ask": 4.7,
                "mid": 4.69,
                "delta": 0.4237521134194814
            },
            "put": {
                "bid": 8.45,
                "ask": 8.47,
                "mid": 8.46,
                "delta": -0.5756299561056611
            },
            "implied_volatility": 0.24385078722742481,
            "gamma": 0.024638652336979393
        },
        {
            "strike": 195.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 2.62,
                "ask": 2.64,
                "mid": 2.63,
                "delta": 0.29452137751494756
            },
            "put": {
                "bid": 11.36,
                "ask": 11.38,
                "mid": 11.37,
                "delta": -0.7048606920101947
            },
            "implied_volatility": 0.22617927813392658,
            "gamma": 0.023389127623181388
        },
        {
            "strike": 200.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 1.03,
                "ask": 1.05,
                "mid": 1.04,
                "delta": 0.15952905609846607
            },
            "put": {
                "bid": 14.75,
                "ask": 14.77,
                "mid": 14.76,
                "delta": -0.8398530134266764
            },
            "implied_volatility": 0.19703361182603538,
            "gamma": 0.01891326128023662
        },
        {
            "strike": 205.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": 0.16,
                "ask": 0.18,
                "mid": 0.17,
                "delta": 0.04271051015963935
            },
            "put": {
                "bid": 18.85,
                "ask": 18.87,
                "mid": 18.86,
                "delta": -0.9566715593655031
            },
            "implied_volatility": 0.15641378830375124,
            "gamma": 0.008916660747165772
        },
        {
            "strike": 210.0,
            "expiration": "2025-06-05",
            "call": {
                "bid": null,
                "ask": null,
                "mid": null,
                "delta": 0.0005597778266970925
            },
            "put": {
                "bid": 23.66,
                "ask": 23.68,
                "mid": 23.67,
                "delta": -0.9988222916984453
            },
            "implied_volatility": 0.10431980756707404,
            "gamma": 0.0002902662707065403
        }
    ],
    "session_info": {
        "id": "6af613b6-569c-5c22-9c37-2ed93f31d3af",
        "current_step": 1,
        "total_steps": 10
    }
}

The greeks query parameter

Both chain-serving endpoints on each version — GET /api/v1/chain, POST /api/v1/chain/step, GET /api/v2/simulations/{id}/snapshot and POST /api/v2/simulations/{id}/step — accept an optional greeks level. It is opt-in, and its default is the response shown above: the full set is twelve values per option style, and a chain can be a thousand strikes wide across many expirations, so a play-loop client that does not need them must not be made to download them.

Any other value is a 400 naming greeks, never a silent fall back to the default: a client that asked for all and quietly received nothing would price a position against greeks it never got.

One quoted side at greeks=all: the 105 strike of a chain built on a 100 underlying, 30 days to expiration, a 4% rate and a 1.5% dividend yield, with a base volatility of 20% that the skew and smile shape to 0.1983 at this strike:

"call": {
    "bid": 0.66,
    "ask": 0.68,
    "mid": 0.67164031192058,
    "delta": 0.21342098496717668,
    "greeks": {
        "delta": 0.21342098496717668,
        "gamma": 0.051153162287244945,
        "theta": -0.028939075152022566,
        "vega": 0.0833669467282696,
        "rho": 0.016989417686134593,
        "rho_d": -0.01754145081922,
        "alpha": -1.7676156552525426,
        "vanna": 1.2473442995808184,
        "vomma": 0.28383006074363937,
        "veta": 0.00003481610090995518,
        "charm": -0.0044637844401925674,
        "color": -0.00023019242252391244
    }
}

The put of the same strike carries "rho": -0.06902868754146463 and "charm": -0.004504829695657003: the sign flips on rho and the value differs on charm, so the two sides are genuinely computed rather than one copied twice. gamma, vega, vanna, vomma, veta and color are style-independent and do agree. alpha differs too — it is a ratio, and the two sides have different thetas.

Three things a client has to know about those numbers:

• Every value is per ONE LONG CONTRACT. The client applies position sign and size, exactly once. Upstream builds the snapshot as a long position and applies the side sign inside every greek, so a consumer that applies it again double-counts.
• They are f64, like every other number on this surface. The DTOs are this crate's own twelve- and four-field types, converted from upstream's Decimal exactly once at the boundary, so upstream's serialisation never becomes part of this service's contract by accident.
• null means not meaningful for these inputs, never zero. Only rho, rho_d and alpha can be null. Distinct from that: a strike whose option cannot be built carries no greeks key at all, which on the wire looks like the default level. Its implied_volatility, gamma and delta are still there — they are defined where the full set is not.

delta and gamma keep their existing places on the quote and the contract. They are computed independently of the snapshot and stay defined at expiry and at zero volatility, where the full set is not, so the default response is unchanged at every strike — degenerate ones included.

3. Update Session Parameters (PATCH /api/v1/chain?sessionid=6af613b6-569c-5c22-9c37-2ed93f31d3af)

Request Body:

{
  "symbol": "AAPL",
   "initial_price": 385.5,
  "steps": 8,
  "volatility": 0.2,
  "risk_free_rate": 0.03,
  "dividend_yield": 0.005,
  "days_to_expiration": 30.0,
  "time_frame": "Day"
}

Response (200 OK):

{
    "id": "6af613b6-569c-5c22-9c37-2ed93f31d3af",
    "created_at": "2025-04-21T15:32:59.551486+00:00",
    "updated_at": "2025-04-21T15:33:19.515911+00:00",
    "parameters": {
        "symbol": "AAPL",
        "initial_price": 385.5,
        "volatility": 0.2,
        "risk_free_rate": 0.03,
        "method": "GeometricBrownian { dt: 0.004, drift: 0.05, volatility: 0.25 }",
        "time_frame": "day",
        "dividend_yield": 0.005,
        "smile_curve": 0.0005,
        "spread": 0.02
    },
    "current_step": 0,
    "total_steps": 30,
    "state": "Reinitialized"
}

4. Replace Session (PUT /api/v1/chain)

Request Body:

{
  "symbol": "AAPL",
  "steps": 30,
  "initial_price": 385.5,
  "days_to_expiration": 45.0,
  "volatility": 0.25,
  "risk_free_rate": 0.04,
  "dividend_yield": 0.005,
  "method": {
    "GeometricBrownian": {
      "dt": 0.004,
      "drift": 0.05,
      "volatility": 0.25
    }
  },
  "time_frame": "Day",
  "chain_size": 15,
  "strike_interval": 5.0,
  "smile_curve": 0.0005,
  "spread": 0.02
}

Response (200 OK):

{
    "id": "6af613b6-569c-5c22-9c37-2ed93f31d3af",
    "created_at": "2025-04-21T15:37:30.518022+00:00",
    "updated_at": "2025-04-21T15:37:33.951540+00:00",
    "parameters": {
        "symbol": "AAPL",
        "initial_price": 385.5,
        "volatility": 0.25,
        "risk_free_rate": 0.04,
        "method": "GeometricBrownian { dt: 0.004, drift: 0.05, volatility: 0.25 }",
        "time_frame": "day",
        "dividend_yield": 0.005,
        "smile_curve": 0.0005,
        "spread": 0.02
    },
    "current_step": 0,
    "total_steps": 30,
    "state": "Reinitialized"
}

5. Delete Session (DELETE /api/v1/chain?sessionid=6af613b6-569c-5c22-9c37-2ed93f31d3af)

Response (200 OK):

{
    "message": "Session deleted successfully: 6af613b6-569c-5c22-9c37-2ed93f31d3af",
    "session_id": "6af613b6-569c-5c22-9c37-2ed93f31d3af"
}

Domain Models

v1 — one expiration, one chain per step

classDiagram
class SessionManager {
+createSession(params) Session
+getNextStep(id) (Session, OptionChain)
+updateSession(id, params) Session
+reinitializeSession(id, params) Session
+deleteSession(id) bool
}

class Session {
+id Uuid
+createdAt SystemTime
+updatedAt SystemTime
+parameters SimulationParameters
+currentStep usize
+totalSteps usize
+state SessionState
+version u64
}

class SessionState {
<<enumeration>>
Initialized
InProgress
Modified
Reinitialized
Completed
Error
}

class SimulationParameters {
+symbol String
+steps usize
+initialPrice Positive
+daysToExpiration Positive
+volatility Positive
+riskFreeRate Decimal
+dividendYield Positive
+method SimulationMethod
+timeFrame TimeFrame
+chainSize Option~usize~
+strikeInterval Option~Positive~
+seed Option~u64~
}

class Simulator {
+simulateNextStep(session) OptionChain
-walkCache Map~Uuid, RandomWalk~
}

class Walker {
+rng Arc~Mutex~StdRng~~
+overrides every stochastic kernel
}

Session --> SimulationParameters
Session --> SessionState
SessionManager --> Session: manages
SessionManager --> Simulator: uses
Simulator --> Walker: draws from
Simulator --> OptionChain: produces

OptionChain and its OptionData are upstream optionstratlib types — the pricing lives there, and nothing here reimplements it. The seed is optional on the way in and resolved exactly once, so the response always carries the effective one.

v2 — a rolling inventory, priced from a factor row

classDiagram
class SimulationManager {
+create(params) SessionV2
+peek(id) (SessionV2, SeriesSnapshot)
+advance(id) (SessionV2, SeriesSnapshot)
+delete(id) bool
+cleanup() Vec~Uuid~
}

class SessionV2 {
+id Uuid
+schemaVersion u32
+parameters SimulationParametersV2
+currentStep usize
+totalSteps usize
+state SessionState
+version u64
}

class SimulationParametersV2 {
+symbol String
+steps usize
+effectiveStart DateTime~Utc~
+stepIntervalSeconds u64
+schedule ExpirationSchedule
+tzdbVersion String
+initialPrice Positive
+volatility Positive
+method SimulationMethod
+seed u64
}

class ExpirationSchedule {
+calendar CalendarVersion
+timezone Tz
+expirationTime NaiveTime
+rules Vec~ExpiryRule~
}

class ExpiryRule {
+ruleId String
+kind ExpiryRuleKind
+targetCount NonZeroUsize
}

class ExpiryRuleKind {
<<enumeration>>
Daily
Weekly
Monthly
Yearly
}

class RollingPlanner {
+activeAt(instant) Vec~ActiveExpiry~
}

class FactorTape {
+rows Vec~FactorRow~
+build(params, method) FactorTape
}

class FactorRow {
+step usize
+simulatedAt DateTime~Utc~
+spot Positive
+baseVolatility Positive
}

class SeriesBuilder {
+snapshot(step) SeriesSnapshot
}

class SeriesSnapshot {
+step usize
+simulatedAt DateTime~Utc~
+spot Positive
+baseVolatility Positive
+chains Vec~ExpiryChain~
}

class ExpiryChain {
+expiresAt DateTime~Utc~
+daysToExpiration Positive
+labels Vec~String~
+chain OptionChain
}

SessionV2 --> SimulationParametersV2
SimulationParametersV2 --> ExpirationSchedule
ExpirationSchedule --> ExpiryRule
ExpiryRule --> ExpiryRuleKind
SimulationManager --> SessionV2: manages
SimulationManager --> FactorTape: builds once, caches
FactorTape --> FactorRow: one per step
SeriesBuilder --> FactorRow: prices at
SeriesBuilder --> RollingPlanner: asks what is alive
SeriesBuilder --> SeriesSnapshot: produces
SeriesSnapshot --> ExpiryChain: one per live expiration

The split is what makes a long horizon affordable. The tape is O(steps) four-field rows and carries the whole market path; chains are priced on demand from one row plus the planner's output, so memory does not grow with steps × expirations × strikes. Both halves are pure functions of the effective parameters, which is why evicting either is invisible in what a client is served.

Infrastructure Components

Every external system sits behind a trait, and every driver error converts into ChainError at the boundary that meets it — no redis::, mongodb:: or clickhouse:: type appears in a public signature.

classDiagram
class SessionStore {
<<interface>>
+get(id) Session
+save(session) void
+saveCas(session, expectedVersion) void
+delete(id) bool
+cleanup() int
}

class InMemorySessionStore
class InRedisSessionStore

class SimulationStore {
<<interface>>
+get(id) SessionV2
+create(simulation) void
+saveCas(simulation, expectedVersion) void
+delete(id) bool
+cleanup() Vec~Uuid~
}

class InMemorySimulationStore
class InRedisSimulationStore

class HistoricalDataRepository {
<<interface>>
+getHistoricalPrices(symbol, timeframe, start, end) Vec~Positive~
+listAvailableSymbols() Vec~String~
+getDateRangeForSymbol(symbol) (DateTime, DateTime)
}

class ClickHouseHistoricalRepository

class SimulationSnapshotRepository {
<<interface>>
+persist(record) void
+get(simulation, generation, step) Option~SnapshotRecord~
+readRange(simulation, generation, from, to) Vec~SnapshotRecord~
+contractSeries(query) Vec~ContractQuote~
}

class ClickHouseSnapshotRepository {
+ensureSchema() void
-simulation_snapshots ReplacingMergeTree
-simulation_option_quotes ReplacingMergeTree
}

class MongoDBRepository {
+saveChainStep(step) void
+saveEvent(event) void
}

SessionStore <|.. InMemorySessionStore: implements
SessionStore <|.. InRedisSessionStore: implements
SimulationStore <|.. InMemorySimulationStore: implements
SimulationStore <|.. InRedisSimulationStore: implements
HistoricalDataRepository <|.. ClickHouseHistoricalRepository: implements
SimulationSnapshotRepository <|.. ClickHouseSnapshotRepository: implements

The two ClickHouse repositories point in opposite directions. ClickHouseHistoricalRepository is an input: it feeds real price series into a Historical walk. ClickHouseSnapshotRepository is an output, and an optional one: with OCS_SNAPSHOT_PERSISTENCE_ENABLED on it files every advanced step as one metadata row plus one flattened row per expiration and strike, and the export reads those back before falling back to replay.

Both v2 tables are ReplacingMergeTree sorted on (simulation, generation, step, …) and partitioned on simulated_at — a content key, because the engine only collapses duplicates within a partition and an ingestion-derived key would let a backfilled step survive as a permanent second copy. The generation is the tape's, not the session's compare-and-swap revision, and it moves whenever a release changes what a step is priced at, so two builds that disagree address different rows instead of overwriting each other.

🚀 Deploy the project

To deploy the services defined in Docker/docker-compose.yml, run the following command:

make deploy

This will:

• Build the Docker images (--build)
• Force container recreation (--force-recreate)
• Run everything in detached mode (-d)
• Use optionchain-simulator as the project name to namespace containers and resources

Make sure Docker and Docker Compose are installed and running on your system.

Makefile Commands for Development

The project includes a Makefile with useful commands for development:

Additional commands for CI/CD and deployment:

Contribution and Contact

We welcome contributions to this project! If you would like to contribute, please follow these steps:

1. Fork the repository.
2. Create a new branch for your feature or bug fix.
3. Make your changes and ensure that the project still builds and all tests pass.
4. Commit your changes and push your branch to your forked repository.
5. Submit a pull request to the main repository.

If you have any questions, issues, or would like to provide feedback, please feel free to contact the project maintainer:

Contact Information

• Author: Joaquín Béjar García
• Email: jb@taunais.com
• Telegram: @joaquin_bejar
• Repository: https://github.com/joaquinbejar/OptionChain-Simulator
• Documentation: https://docs.rs/optionchain_simulator

We appreciate your interest and look forward to your contributions!

✍️ License

Licensed under the MIT license. See LICENSE for the full text.