davy-jones-locker (engine)

Early release. This is 0.2: the API may change between minor versions until 1.0, so pin an exact version if you depend on it.

DAVY JONES' LOCKER's Python engine, which executes flowgraphs on the server (FastAPI, port 3000); the runner, the sandbox it runs Python in; and the node worker, which runs the app's own node kinds. An app built on the framework runs everything it can in the browser; the engine is the second engine, for:

• PythonScript nodes, which can't run in a browser.
• SQL over the backend database: a SQL node whose query reads a table its wired inputs don't supply runs here, over Postgres (attached read-only as db) and the inputs the browser sends.
• The app's own node kinds, written in Python (below): the browser learns them from the engine, and the node worker runs them.
• Whole graphs on the server, for schedulers (n8n, say) to trigger.

There's no sign-in yet (identity is the next part), so the engine starts only for local development: IS_LOCAL=true (compose's .env, or the environment). Then it signs no one in, and the app's node kinds can reach the network; it logs a warning saying so, /health reports local: true, and the app shows LOCAL. Anyone who can reach it can use it, its AI assistant included (and so its LiteLLM key's budget): keep it on your own machine. Without IS_LOCAL=true it counts as deployed, which requires sign-in, so it refuses to start until sign-in exists.

An app's engine

An app builds its engine on this one. Its entry point makes the FastAPI app:

from davy_jones_locker import create_app

app = create_app(title="engine-myapp")

and its image starts from the framework's (Dockerfile), adding that entry point:

FROM ghcr.io/lukewilliams/davy-jones-locker-engine:0.3.1
COPY main.py ./
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "3000"]

The images. The engine's, the runner's and the node worker's are published to GitHub's container registry for each release, from 0.2.0, for linux/amd64 and linux/arm64:

Image	Built from
ghcr.io/lukewilliams/davy-jones-locker-engine	Dockerfile
ghcr.io/lukewilliams/davy-jones-locker-runner	runner/Dockerfile
ghcr.io/lukewilliams/davy-jones-locker-node-worker	nodeworker/Dockerfile

Each is tagged with the version (0.3.1) and its minor (0.3); there's no latest, so an app says which version it builds on. Or build them yourself from this folder (docker build -t davy-jones-locker-engine ., and -f runner/Dockerfile or -f nodeworker/Dockerfile for the others), as ../compose.yaml does.

The runner is used as it is (runner/Dockerfile), until an app adds libraries of its own; so is the node worker (nodeworker/Dockerfile), until the app has node kinds of its own (below). ../compose.yaml runs them, with their safeguards; copy it into the app and name the services for it (engine-myapp, engine-myapp-runner): browsers reach the engine through the app's own origin at /engines/<service>/.

The package is davy-jones-locker (Python 3.12+); pip install -e . here for development. The images don't install it: they copy the package and install the pinned, hashed versions in requirements.txt and runner/requirements.txt.

Settings

.env.example (the engine), runner.env.example (the runner's limits: never credentials, since scripts run beside it) and node-worker.env.example (the node worker's: never credentials either). The app's compose file usually sets RUNNER_URL (the runner's address, default http://runner:3000), NODE_WORKER_URL (the node worker's, when the app has node kinds) and PUBLIC_HOST (what /health reports, default engine). SANDBOX_HOSTS names more hosts whose requests the engine refuses (see Safeguards). RUNNER_PACKAGES_FILE names an app's own runner requirements.in inside the engine's image, when its runner adds libraries (see Python and geometry); the assistant reads it.

API

GET /health	{ status: 'ok', host, port, assistant, nodes }: the app's connection check (assistant: { model, sampleRows }, or null when it isn't set up; nodes: the app's node kinds' names)
GET /nodes	{ categories, kinds }: the app's node kinds and categories, as the browser defines them (below)
POST /query	form data: sql, and an input file per input (Parquet, its filename the reference name: sqlnode1_data, or dataingest1_data.sheet1 for one table of several). Answers with the result as Parquet
POST /run/python	form data: code, and input files as above. Answers with form data: result (JSON) and table (Parquet) when the last expression was a table
POST /run/node	form data: kind, node (JSON, its data), inputs (JSON: [{ ref, id, slot, pin, part }] or with tables: [{ name, part }]), an input file per table (Parquet, its filename the part), and a file per file field's file (its filename the stored key). Checked here, run by the node worker. Answers with form data: result (JSON: { output, value?, error?, outputs: [{ slot, part } or { slot, tables: [{ name, part }] }] }) and a table file per table
POST /execute	JSON { document, targets? }: runs a graph given in full
POST /graphs/{id}/execute	JSON { targets? } (optional): runs a saved graph
GET /graphs, GET /graphs/{id}, PUT /graphs/{id}	saved graphs; PUT takes { name, document } and answers { id, version }
PUT /files/{key}	stores data a DataIngest node read (Parquet), for server runs
POST /assist	JSON { kind, request, code, inputs }: the AI assistant writes a node's code. Answers { code, note, model } (see below)

Errors are JSON { error }, their message meant for the user. /run/python's result is { output, value, variables } or { output, error }:

• output: what the script printed.
• value: its last expression's value: { kind: 'table', rows } (the table is the table part), { kind: 'json', type, value }, { kind: 'text', type, text } (anything JSON can't hold), or { kind: 'none' }.
• variables: its top-level variables, [{ name, type, summary }] (for promoting them to outputs of their own, later).

A graph run (/execute, /graphs/{id}/execute, e.g. from n8n) runs targets (default: every node with Auto Run on) and everything upstream, as the browser does, and answers { runId, status, failed, results }: per node { status, error? | rowCount, output?, value?, export? }, an export's file as { filename, contentType, size, base64 }. Nodes inside subnets are in results too, by path (screening/classify), and a target can be one. Runs are recorded in runs when there's a database. On the server:

Kind
SQLQuery	on the server's DuckDB: its inputs and the query database
PythonScript	in the runner
DataIngest	from its tables stored with PUT /files/{key} (the keys in the node's ingest.tables)
DataExport	to CSV, TSV, JSON (geometry as WKT, as in the browser) or Parquet (GeoParquet), returned in the result. The geo formats are written in the browser only, for now. Its CSV quotes every field (pyarrow's writer), which the browser's doesn't
The app's own	by the node worker; a file field's file comes from the stored files (PUT /files/{key})
Subnet	its graph (inline, or shared from the document's subnets), run as it is: what's wired into its pins is put out by its Input nodes, and its Output nodes are its outputs, the topmost first. Errors name where they started (Screening › Classify: …); 8 levels deep at most. As in the browser (SEAMONSTER's README, "Subnets")
JavaScript	refused: browser only until the engine has safeguards for it
anything else	can't run on the server yet

Wires carry what they did in the browser: one from a node's main output pin (source-0) brings all its slots, one from a slot's own pin (source:<slot>) just that slot.

The app's node kinds

An app defines node kinds in Python, beside its engine, and the browser learns them from GET /nodes: they need no JavaScript. nodes/ has the whole of it; in short:

# nodes.py: definitions only (the engine and the node worker both import it)
from davy_jones_locker.nodes import Field, NodeCategory, NodeKind, Rule

CATEGORIES = [NodeCategory("geo", "Geo", colors={"from": "#7dd3a8", "to": "#2f855a"})]
KINDS = [
    NodeKind(
        "geo.buffer", "Buffer", "geo", handler="geo_handlers:buffer",
        fields=[Field("distance", "Distance (m)", "number", default=100,
                      validate=[Rule(min=0, message="A distance can't be negative.")])],
        slots=[{"name": "summary"}],
        timeout_s=120,
    ),
]

# main.py
from davy_jones_locker import create_app
import nodes
app = create_app(title="engine-geo", nodes=nodes.KINDS, categories=nodes.CATEGORIES)

# geo_handlers.py: run only by the node worker
from davy_jones_locker.nodes import NodeError

def buffer(ctx):
    if not ctx.inputs:
        raise NodeError("Wire in the points to buffer.")  # shown as it is, no traceback
    table = ctx.inputs[0].table                     # a pyarrow Table
    ctx.log(f"buffering {table.num_rows} rows by {ctx.node['distance']} m")
    return {"table": ..., "slots": {"summary": ...}}  # pyarrow Tables, DataFrames or rows

• A kind has a namespaced name (app.kind), a label, a category (built in, or one of categories), and a handler, "module:function". The engine never imports the handler, so its libraries needn't be in the engine's image. description says what it does (Manage and the Library show it). fields, slots and input_pins are as SEAMONSTER has them, an input pin's hint and required included, but plain data: hints are text, rules declarative (Rule(required=, min=, max=, pattern=), severity='warn' for a warning), options a fixed list, and there's no custom field type. timeout_s bounds a run (60 by default).

• A handler gets ctx: node (the node's data, with defaults), inputs (what's wired in, one per slot each wire carries: ref, id, slot, pin, and table or tables), input(ref), file_field(key) (the file chosen in that file field: its name as the user chose it, and its bytes), file(stored_key) (the bytes alone, by the key the field holds) and log(text) (print goes to the Terminal too). It returns table or tables (by name), slots (by slot), value (JSON, shown when there's no table): a pyarrow Table, a pandas DataFrame or a list of rows each. A slot left out is an empty table.

• Errors: raise NodeError (from davy_jones_locker.nodes, or a subclass of it) for anything the node's user can fix, a setting, a file or a wire: its message alone is the node's error. Any other exception is the node's error with its traceback, as a bug. An input or file the node wasn't given raises a NodeError that's also a KeyError.

• Testing a handler: davy_jones_locker.nodes.testing runs one in the test's own process as the worker would: the same ctx, tables through Parquet both ways, print to the log, and settings that break an error rule refused.

  from davy_jones_locker.nodes.testing import Context, run
  
  ctx = Context({"distance": 50}, inputs={"points_data": table}, kind=BUFFER,
                files={"source": ("sites.csv", data)})   # fills in the file field too
  result = run("geo_handlers:buffer", ctx)    # .table, .tables, .slots, .value, .output
  

  An exception from the handler is raised as it is, for pytest.raises. Its docstring has the rest.

• A named input pin can bring several tables. It takes one wire, and a wire from a node's main pin carries every slot of that node, so inputs can hold several items with the same pin. A handler wanting one table there picks it (by slot, or by what's in it).

• Geometry: write it as WKB with GeoParquet geo metadata on the Arrow schema (each geometry column's encoding and CRS, as PROJJSON, or null for unknown). Both engines load it as a GEOMETRY column with that CRS, so SQL downstream can use it as it is, and every table with geometry that reaches a handler comes the same way, a SQL query's output included. No crs key means OGC:CRS84, which both engines load as EPSG:4326 (the same coordinates; see "Spatial SQL").

• How long: the worker kills a run at the kind's timeout_s, and the engine waits for the worker timeout_s plus 30 seconds (for the data both ways).

• The node worker runs them: an image built FROM the framework's (nodeworker/Dockerfile), adding the app's nodes.py, handlers and their libraries, started with NODE_KINDS=nodes:KINDS. It runs only the kinds that list names, each run a process of its own, killed at the kind's timeout_s, its memory capped (NODE_MEMORY_MB), a few at once (NODE_CONCURRENCY).

• Checked twice: the engine refuses a kind it wasn't given, settings that break an error rule, and a required input pin with nothing wired in before asking the worker, and the worker checks again (kind.errors(node, pins=...); nodes.testing.Context does the same).

• Network access: in local development (IS_LOCAL=true) every kind can reach the network, and a kind may say it needs to (network=True). Otherwise network=True is refused: a deployed worker has no way out until sign-in and roadmap step 10e, which gives one through a proxy to hosts the engine's settings allow.

AI assistant

The Assistant field in SEAMONSTER's Manage panel (SQLQuery, PythonScript and JavaScript nodes) asks POST /assist (assist.py), which asks a LiteLLM proxy's /chat/completions, OpenAI-style. Set it up in .env:

LITELLM_BASE_URL	the proxy's address (with or without /v1)
LITELLM_API_KEY	its key: stays on the engine. The browser never sees it, and the runner can't read it
ASSIST_MODEL	a model name the proxy offers. No default: the assistant is off until it's set
ASSIST_SAMPLE_ROWS	rows of each input sent as examples of its values (default 3; 0 sends column names and types only)
ASSIST_TIMEOUT_SECONDS	how long to wait for an answer (default 90)

Off (and hidden in the app) unless all three of the first settings are set. What the model is sent: the request; the node's kind and current code; each input's reference name, columns (name and type), row count and first ASSIST_SAMPLE_ROWS rows (values cut to 200 characters), which the browser works out by running what's upstream; and for SQL, the query database's tables and columns, not their rows. For Python, it's told the packages in runner/requirements.in (or RUNNER_PACKAGES_FILE), so enabling one there tells it too; when geopandas is one, it's also told inputs with geometry are GeoDataFrames. It answers by calling a write_code tool (code and a note), or with a fenced code block. The code only fills the node's editor: nothing runs until the user runs it. Prompts and answers aren't logged, only their size and time.

A LiteLLM proxy on the Docker host rather than on the network: from inside the container, that's host.docker.internal, which needs extra_hosts: ["host.docker.internal:host-gateway"] on the engine's service.

Database

The engine owns its tables, in schema FLOW_SCHEMA (flow), created the first time the database answers (database.py): graphs, files (stored data by key), runs. Without DATABASE_URL, or while the database can't be reached, those endpoints answer 503 and graph runs aren't recorded; everything else still works, and the engine starts either way.

SQL reads the query database (QUERY_DATABASE_URL, else DATABASE_URL), attached read-only as catalog db: db.public.orders, or just orders (plain names look in the inputs, then db.public). Its role should be read-only: engine-shared's reader role is, and its script makes the same roles on any Postgres.

Safeguards

User code runs in two places here, and neither is trusted. The app's own node kinds run in a third, trusted, but handling what users send.

Refusing the sandboxes. Every request from the runner or the node worker is refused (403), whatever it asks: code runs there, and nothing it does may use the engine (its database, saved graphs, AI budget, or the node kinds it runs). The engine looks up their addresses by name (the hosts in RUNNER_URL and NODE_WORKER_URL, and any in SANDBOX_HOSTS) on every request, so replicas and restarts are covered. Loopback addresses are never refused: with the runner on the same machine (development), they're everyone's.

SQL (sql.py). Each query or graph run gets its own in-memory DuckDB. Once the query database is attached, DuckDB is locked down: no file access, no new extensions or attachments, settings frozen. That doesn't stop postgres_scan() connecting to any server by connection string, so a query must also be one SELECT that calls none of the functions that open connections or run SQL given as text (postgres_*, query, query_table), checked with DuckDB's own parser. Queries stop after QUERY_TIMEOUT_SECONDS and are held to QUERY_MEMORY_LIMIT.

Spatial SQL. DuckDB's spatial extension is installed with the image and loaded before the lockdown, so its functions (ST_Transform, ST_Buffer, ST_Area_Spheroid and the rest) work in server SQL. Axis order is always x, y (easting or longitude first), whatever a CRS's official order is (geometry_always_xy), as in the browser. So ST_Transform(geom, 'EPSG:4326', 'EPSG:7855') needs no always_xy.

The extension's readers are refused twice:

• The query check refuses ST_Read, ST_Read_Meta, ST_ReadOSM, ST_ReadSHP and shapefile_meta. Geo files are read in the browser (DataIngest) and wired in.
• The lockdown refuses them on its own: GDAL goes through DuckDB's file system, so local paths, URLs, /vsicurl/ and its network drivers (WFS, OAPIF, Elasticsearch) are all refused.

PROJ fetches no grids (PROJ_NETWORK=OFF, and the lockdown).

Geometry keeps its CRS through a query, as in the browser. A wired-in table's GeoParquet geo metadata puts each geometry column's CRS on its type (GEOMETRY('EPSG:7855')): the Parquet is read with pyarrow, and its geo becomes geoarrow field metadata, which DuckDB loads with the CRS. Only WKB columns are geometry: GeoParquet 1.1's native encodings stay as they are, as in the browser. A query's output goes back as GeoParquet built from the columns' types (Session.parquet): each CRS as PROJJSON, the geometry types found, and "crs": null for a column with none, since no crs would mean OGC:CRS84. OGC:CRS84 itself is loaded as EPSG:4326 (DuckDB-wasm's spatial can't identify CRS84, so the browser does this, and the engine matches it). Mixing CRSs in one function is refused when the query is bound.

The engine runs without the extension, outside Docker for instance. A warning is logged once, and spatial SQL then fails with a message saying the extension isn't installed.

Python (sandbox/). The engine never runs it: the runner does, in a separate container that holds no credentials (its settings file is separate, and nothing secret goes in it) and can reach nothing but the engine. The container is read-only, unprivileged, capability-free and resource-limited (../compose.yaml). Each script runs in its own process with time, CPU, memory and file limits, in a scratch directory deleted afterwards, one at a time per container (concurrent runs share a user, so could read each other's files: scale with replicas). After each run, every process it started is killed, even ones that left its process group, so nothing a script leaves running sees the next run; the container's init reaps them, so they can't use up its process limit either. Python can't be sandboxed from inside itself, so these limits are the safeguard, not anything the script is told. In production, Azure Container Apps' dynamic sessions (Hyper-V isolated) could replace the runner behind the same API.

The app's node kinds (nodeworker/). Handlers are the app's code, but they parse what users send (uploads, other nodes' tables), often with C libraries. So they never run in the engine, which holds the database's and the AI proxy's credentials: the node worker runs them, in a container like the runner's (read-only, unprivileged, no capabilities, no credentials, on a network shared only with the engine). In local development (IS_LOCAL=true) compose also puts it on outside-true, a network with a way out, so handlers can call web services; otherwise it has none (outside-false is internal). It runs only the kinds NODE_KINDS names, never a handler a request names, each run in its own process with a timeout and a memory cap.

Libraries: scripts get exactly what runner/requirements.in lists (pandas, numpy, pyarrow), compiled to a pinned, hashed runner/requirements.txt and installed at image build; nothing installs at run time. To enable a library, add it there, recompile (the command is in the file), and rebuild. An app adds its own the same way, in a runner image built on this one (see Python and geometry).

Python and geometry

Tables with geometry reach the runner as GeoParquet, each column's CRS in its geo metadata ("crs": null when it's unknown). Where geopandas is installed in the runner, the worker reads such an input with geopandas.read_parquet: it's a GeoDataFrame, each geometry column a GeoSeries with its CRS (None when unknown). A GeoDataFrame or GeoSeries the script ends with is written back with geopandas' to_parquet, so the engine and the browser load it as GEOMETRY with its CRS; a plain DataFrame holding GeoSeries columns is made a GeoDataFrame first. A variable's summary names its CRS (3 × 4, EPSG:7855).

Without geopandas nothing changes: geometry is WKB bytes in a DataFrame, and a DataFrame returned with them comes back as a blob, not geometry. Shapely objects in a plain column (not a GeoSeries) can't be returned.

The framework's runner has no geopandas: which geo libraries scripts get is an app's choice. To add them, build the app's runner on the framework's: list the framework's libraries and the app's own in the app's runner/requirements.in (geopandas, shapely, pyproj, pyogrio, at versions that work with the framework's pandas and pyarrow), compile it with hashes as the framework's is, and install it in an image built on the runner's:

FROM ghcr.io/lukewilliams/davy-jones-locker-runner:0.3.1
USER root
COPY runner/requirements.txt /tmp/app-requirements.txt
RUN pip install --no-cache-dir --require-hashes -r /tmp/app-requirements.txt && rm /tmp/app-requirements.txt
USER 65534:65534

Then copy the app's runner/requirements.in into the engine's image too, and set RUNNER_PACKAGES_FILE to it, so the assistant knows what scripts can import. Checked with geopandas 1.2.0, shapely 2.1.2 and pyproj 3.8.0.

Layout

davy_jones_locker/
  main.py        the API, create_app, refusing the sandboxes
  settings.py    environment settings (.env.example)
  nodes/         the app's node kinds: NodeKind, Field, Rule, NodeCategory, NodeError
    context.py   what a handler is given (ctx), for the worker and for tests
    testing.py   running a handler in a test
  noderunner.py  the app's kinds as the engine knows them, and calls to the node worker
  database.py    the engine's tables in Postgres
  sql.py         locked-down DuckDB sessions (with spatial), query checks
  runner.py      calls to the runner
  executor.py    whole-graph runs
  assist.py      the AI assistant (through LiteLLM)
  formdata.py    multipart/form-data both ways (the runner uses it too)
  sandbox/
    server.py    the runner's API, limits, one process per run
    worker.py    runs one script
  nodeworker/
    server.py    the node worker's API, one process per run
    child.py     runs one node's handler
runner/          the runner's Dockerfile and libraries
nodeworker/      the node worker's Dockerfile and libraries
tests/           the engine's tests (pytest)
Dockerfile       the engine's image

Developing without Docker

With Python 3.12 and the packages from both lock files installed, from this folder:

IS_LOCAL=true RUNNER_URL=http://127.0.0.1:9002 uvicorn davy_jones_locker.main:app --port 9001
uvicorn davy_jones_locker.sandbox.server:app --port 9002

Install DuckDB's extensions once, as the image does at build: the engine locks DuckDB down and can't install them itself.

python -c "import duckdb; duckdb.sql('INSTALL postgres'); duckdb.sql('INSTALL spatial')"

The tests need no database:

pip install --group test
python -m pytest

test_python.py runs the runner's worker, so it needs the runner's libraries too (and geopandas for most of it); without them it's skipped. test_parity.py checks spatial SQL gives the numbers the browser gave: a query of its own, and fixtures/screening.sql, site screening as an app writes it (a projection centred on the site built per row, buffers, distances, overlaps, geodesic areas) over made-up data. When DuckDB or its spatial extension is upgraded, run them in the browser again and update the numbers (the file says how).

With node kinds, from the app's folder (where its nodes.py and handlers are), with the engine installed from PyPI (pip install davy-jones-locker, the version you pin) or this folder on PYTHONPATH:

IS_LOCAL=true NODE_WORKER_URL=http://127.0.0.1:9003 RUNNER_URL=http://127.0.0.1:9002 uvicorn main:app --port 9001
NODE_KINDS=nodes:KINDS uvicorn davy_jones_locker.nodeworker.server:app --port 9003

(There's no container around the runner or the worker here: development only. On macOS it can't limit a script's memory (the system refuses RLIMIT_AS), and on Windows it sets no process limits at all. In the Linux container every limit applies, and a run fails rather than go without one.)