# Node types

Every type the canvas can place. Each is configured by filling in a form the
editor generates from its parameter schema, so they all behave the same way.

Anything here can also be written as a **Function** node. These types cover the
shapes that come up most often, as a form to fill in rather than repeated code.

`GET /flows/node-types` returns this list with each type's full parameter
schema, including any [connectors](#connectors) installed on your instance.

## Function

**`python`** — your own code, run on every incoming message.

The one type with a source file. Its arguments are its input ports and its own
settings; its return value is a dict keyed by output ports. See
[Writing node code](../code/nodes.md).

Settings on a Function node are free-form: you add them by name, and they
arrive as keyword arguments.

## Integrations

### MQTT

**`mqtt`** — subscribe to topics, or publish what arrives on its inputs.

A node with *outputs only* subscribes; a node with *inputs* publishes.

| Setting | Default | Notes |
|---|---|---|
| `topic` | `*` | one topic for every port, or `{"message": "some/topic"}` per port |
| `broker_host` | `localhost` | |
| `broker_port` | `1883` | |
| `username` / `password` | — | `password` takes a secret reference |
| `client_id` | — | |
| `qos` | `0` | 0, 1 or 2 |
| `retain` | `false` | on published messages |
| `keepalive` | `60` | seconds |
| `timeout` | `10.0` | seconds before a broker operation is given up on |
| `publish_queue_size` | `256` | payloads that may wait for the broker; past this the oldest is dropped and the node reports degraded |
| `json_key` | — | key to lift out of an object payload; one for every port, or `{"port": "key"}` |

A topic may be a filter: `+` matches one level, `#` the rest. Everything a
filter matches lands on the same port, so use one port per topic where the
difference matters.

`json_key` is for a device that wraps its reading: Victron publishes
`{"value": 47}` on every path. Without it, a payload object is unwrapped only
when it happens to carry the port's own name as a key.

### HTTP

**`http`** — receive data on a webhook, or send it to a URL.

Outputs only makes it a **webhook**: the engine mounts a route at
`/hooks/{flow}/{url}/{secret}` while the flow runs. Inputs make it a **sender**.

| Setting | Default | Notes |
|---|---|---|
| `url` | — | the route path in webhook mode, the full URL in sender mode |
| `method` | `POST` | `GET` or `POST` |
| `timeout` | `30` | seconds, sender mode |
| `headers` | `{}` | |
| `query` | `{}` | fixed query parameters; a value may be a secret reference |
| `send_inputs` | `true` | off when the inputs only trigger the request |
| `secret` | — | shared secret appended to the webhook URL; takes a secret reference |

!!! warning "A webhook with no secret is open to anyone who can reach the host."

    The canvas flags this as an advisory issue rather than stopping the flow,
    because a webhook on a private network is a legitimate thing to want.

### InfluxDB

**`influxdb`** — write measurements to a bucket, or read them back.

| Setting | Notes |
|---|---|
| `url`, `token`, `org`, `bucket` | connection; `token` takes a secret reference |
| `write_precision` | `ns`, `us`, `ms` (default) or `s` |
| `query_range` | default window for queries, e.g. `-1h` |
| `writes` | per-input: `measurement`, `field`, `tags` |
| `queries` | per-output: `measurement`, `field`, `tags`, `range`, `aggregation` |

```json
{
  "writes": {
    "living_temperature": {
      "measurement": "environment",
      "field": "temp_c",
      "tags": {"room": "living"}
    }
  }
}
```

**Query passthrough.** An incoming message holding a `flux` key is run as
written, and the rows come back on the first output port as
`{"rows": [{ts, value, field, measurement, tags}], ...}`.

A database node holds the credentials and the connection, nothing else.
Building a query and shaping its rows are Function nodes on either side.

### Notification

**`ntfy`** — push an incoming value to a phone through [ntfy](https://ntfy.sh).

| Setting | Default | Notes |
|---|---|---|
| `server` | `https://ntfy.sh` | |
| `topic` | — | required |
| `title` | — | |
| `priority` | `default` | `min`, `low`, `default`, `high`, `urgent` |
| `tags` | — | comma-separated ntfy tags |
| `token` | — | for a protected topic; takes a secret reference |

This is a *flow* deciding something is worth saying. The engine reporting that
it broke is [Alerts](../interface/operations.md#alerts), which is a different
thing configured elsewhere.

## Timing

### Inject

**`inject`** — emit a value on request, on a timer, or when the flow starts.

| Setting | Default | Notes |
|---|---|---|
| `payload` | current time | what to emit |
| `payloads` | `{}` | per-output-port payloads, keyed by port |
| `interval` | `0` | emit every n seconds; 0 means never on its own |
| `cron` | — | a five-field cron expression |
| `at_start` | `false` | emit once when the flow starts |
| `start_delay` | `1.0` | how long to wait before that first emission |

The scheduler: a `cron` expression here is what makes a flow run by the clock.
It is also the most-placed node in a real instance, mostly as a button someone
presses.

### Delay & schedule

**`delay`** — hold messages back, limit their rate, or emit on a schedule.

| Setting | Default | Notes |
|---|---|---|
| `delay` | `0` | seconds to hold each message, fractional |
| `interval` | `0` | minimum seconds between forwards |
| `mapping` | `{}` | input port → output port; paired in order when empty |
| `cron` | — | five-field expression |

Order of operations: rate check → delay → forward. With a `cron` and no inputs
it emits the current time on each tick; with inputs it emits the last value it
received.

The engine sleeps until a delay is due rather than polling for it, so a `delay`
fires within a few milliseconds of its deadline on an idle engine, and a due
timer is taken off the queue before work that is merely waiting. It is not a
real-time guarantee: the wait ends on a normal thread, and a node that then
needs a busy cascade slot waits for one.

!!! note "Not in a batch flow"

    A rate limit holds a value back for a timer to release, and a run has no
    timer, since the value would be dropped rather than delayed. Submitting a batch
    flow with a rate-limited port is refused instead.

### Trigger

**`trigger`** — send one value now and another once things go quiet. Despite
the name, a debounce and hold rather than a scheduler: everything it sends
starts from a value arriving. For a cron tick, see [`inject`](#inject).

| Setting | Default | Notes |
|---|---|---|
| `first` | `true` | sent as soon as a value arrives |
| `then` | `false` | sent when the wait expires; empty sends nothing |
| `wait` | `60` | seconds of quiet before the second value |
| `extend` | `true` | a value arriving during the wait starts it over |
| `passthrough` | `false` | send the incoming value instead of `first` |
| `wait_port` | — | an input carrying the wait, when it differs per message |

The shape this exists for: *the door opened, so turn the light on, and off
again in two minutes unless it opens again.*

`wait_port` covers the case where how long to wait is itself a value: a
rollershutter takes 26 seconds up and 28 down, so the node that decides the
direction says how long to run for as well. A wait of zero or less sends
nothing afterwards, and still cancels whatever the last message scheduled,
which is how a *stop* is commanded exactly once.

## Logic

### Switch

**`switch`** — send a value down one branch or another, by rule.

Each rule names an output port; a matching value leaves through that port.
Comparisons: `eq`, `ne`, `gt`, `gte`, `lt`, `lte`, `contains`, `between`.

| Setting | Default | Notes |
|---|---|---|
| `rules` | `[]` | checked in order; each names the output it routes to |
| `stop_at_first` | `true` | leave through the first matching rule only |
| `otherwise` | — | output for a value that matched nothing |

Comparing a string to a number is a mistake in the rule, not a reason to take
the flow down: the rule simply does not match.

### Change

**`change`** — scale, offset, round or map a value on its way past.

| Setting | Default | Notes |
|---|---|---|
| `scale` | `1.0` | multiply numbers by this |
| `offset` | `0.0` | then add this |
| `round_to` | — | decimal places |
| `mapping` | `{}` | replace a value with another, looked up as text |
| `default` | — | value when the lookup misses; empty passes it through |

### Filter unchanged

**`rbe`** — pass a value on only when it has actually changed.

| Setting | Default | Notes |
|---|---|---|
| `deadband` | `0.0` | ignore numeric changes smaller than this |
| `deadband_percent` | `false` | read the deadband as a percentage |

The cheapest fix for a sensor that reports every second and changes every hour.

### Join

**`join`** — gather several inputs into one object or list.

| Setting | Default | Notes |
|---|---|---|
| `mode` | `object` | `object` or `array` |

## System

### Command

**`exec`** — run a command in the engine's container and read its output.

| Setting | Default | Notes |
|---|---|---|
| `command` | — | the command to run |
| `append_payload` | `false` | add the incoming value as one argument |
| `timeout` | `30` | seconds |
| `fail_on_error` | `false` | treat a non-zero exit as a node failure rather than output |

Outputs the command's stdout, stderr and exit code.

!!! warning "Inside the container, not on the host"

    A flow ported from something that read the host's journal, or poked a host
    script, needs either a mount or a small listener on the host side. This
    node cannot see the host.

### File

**`file`** — read a file into the flow, or write one out of it.

| Setting | Default | Notes |
|---|---|---|
| `path` | — | relative to the engine's files directory |
| `mode` | `read` | `read`, `write` or `append` |
| `format` | `text` | `text` or `json` |
| `newline` | `true` | end each written record with a newline |

Confined to a directory the engine owns. A flow that could name any path would
be a way to read the secrets store or overwrite a node's source.

## Numeric

### Perceptron

**`mlp`** — a small neural layer over its numeric inputs.

`output = weights @ inputs + biases`, with weights drawn from `seed` so a node
reloads identically.

| Setting | Default | Notes |
|---|---|---|
| `seed` | `0` | |

A worked example of numeric logic, not a modelling tool. To train something,
use a [batch flow](../concepts/runs.md) and a Function node.

## Connectors

Anything else in the palette came from an installed **connector** package: a
node type written against a published contract and discovered through the
`fluksio.node_types` entry point group. The editor shows which package supplied
it.

A connector declares its contract version, and one written for a version this
engine does not speak is ignored rather than half-loaded. Installing or
upgrading one takes effect on the next engine restart, because Python does not
re-import a changed module and a rescan would promise more than it delivers.

The contract itself is in [The connector contract](connector-contract.md), and
[Writing a connector](../code/connectors.md) walks through building one.

## See also

- [Payload types](payload-types.md) — what a port may carry
- [Writing node code](../code/nodes.md) — the Function node
- [The flow editor](../interface/flow-editor.md) — placing and configuring them