Payload types¶

Every port declares a dtype, and every value that passes through it is checked against that declaration.

This is not decoration. It is what lets the dashboard editor offer you only the messages a gauge can actually draw, what lets the canvas refuse a binding before anything runs, and what lets a downstream node know the shape of what it is getting before the flow starts.

Everything on the wire is JSON. That is what lets the same value pass through the state backend, the work queue and the worker protocol unchanged.

The scalars¶

bool is an int subclass in Python and deliberately not a number here: a flag is not a measurement, and a switch bound to a temperature is a mistake worth catching.

The structured ones¶

These are declared shapes rather than "some JSON", which is what makes a widget binding checkable.

record¶

Flat named scalars.

{"title": "Boiler", "body": "Pressure low", "severity": "warning"}

Nesting is deliberately out: a record that can contain a record is a schema language, and the shape stops being readable from the declaration alone.

Read by the Notification widget. It is also what an alert channel of kind dashboard writes.

list¶

Ordered items of one declared shape. The port also declares item:

A list of lists, or a list of series, is refused. One declared level is the point.

series¶

Labelled lines of (timestamp, value) pairs — what a chart draws.

{
  "lines": [
    {"label": "living", "points": [[1717000000, 21.4], [1717000060, 21.5]]}
  ],
  "range": "-24h"
}

Keys beside lines are carried through untouched, which is how a querying chart puts the window and resolution it asked for on the request and reads them back off the answer. That is what stops an answer to a different question from overwriting the picture.

GET /runs/series/compare answers in this shape, which is why comparing three training curves is a widget binding rather than a screen of its own.

artifact¶

A reference to stored bytes.

{"digest": "sha256:…", "size": 4194304, "media_type": "application/octet-stream", "name": "weights.pt"}

Binary payloads — tensors, checkpoints, images — never travel as a message. The bytes go to a content-addressed store and the message carries this. A thirty-megabyte checkpoint never sits in the state backend, and the reference stays valid wherever the store is reachable from, including on another machine.

Node code produces one with fluksio.save_artifact and opens one with fluksio.load_artifact. See Writing node code.

json¶

Anything JSON-serializable. The escape hatch, and the right answer when a payload genuinely has no fixed shape.

Reach for it last. A json port tells the canvas, the widget picker and the next author nothing.

What a widget will bind to¶

Enforced on the server as well as in the editor.

Type failures¶

A value that does not match its port's declaration raises on the node that published it, naming the port and what arrived. It does not get published, and it does not reach anything downstream — a wrong value stopping at its source is much easier to diagnose than one propagating.

See also¶

• Flows, nodes and messages
• Node types
• Dashboards and panels