Pipe listener

Entry point of a flow that is called from other flows. It opens a local TCP pipe, registers it under its Name, emits every incoming request on Request and, for two-way listeners, sends whatever reaches Response back to the calling Pipe client. The component keeps the flow running.

Pins

Pin	Kind	Types	Description
Request	output	any (type of the connection)	Incoming request data with new metadata that carries the request id.
Response	input	any (type of the connection)	Response for the caller. Only for two-way listeners.
Start	start	any	Opens the pipe. When unconnected, the system calls it when the flow starts.

The metadata of Request contains Viaducta.Plugins.PortListener.PortListenerMetaData (suggested name PortRequest) with PortRequestId, the id used to route the response.

Configuration

Field	Type	Default	Description
Name	string	Port	Required. Port name, unique among Pipe listeners of the flow, at most 128 characters. Pipe clients find the listener by flow id + this name.
IsTwoWay	boolean	false	false: one-way, the caller gets only an acknowledgement. true: request/response, the caller waits for the data that reaches Response.

Behaviour

• On start the listener takes a free TCP port on 127.0.0.1, starts the pipe and registers it with the environment as <flow id>/<Name>. It is unregistered when the flow stops.
• The request type is the type on the Request connection (NoInputData when Request is unconnected); the response type is the type on the Response connection. A Pipe client imports exactly these types when it selects this listener.
• Incoming requests whose type does not match the request type are rejected; the caller receives an exception.
• Each request is emitted on Request with new metadata; correlation id and session id are taken over from the caller.
• One-way listener, or a caller in asynchronous mode: the acknowledgement is sent before the request is processed.
• Two-way listener: when a record reaches Response, its metadata's PortRequestId identifies the waiting request and the record is sent back as the response. Keep the metadata of the request through the flow up to Response; if the id is unknown (already answered or timed out) a warning is shown.
• An exception while processing a two-way request is sent back to the caller as an exception.
• Start-up checks (the flow fails to start): empty or too long Name, two listeners with the same Name in the flow, IsTwoWay = true without a Response connection, IsTwoWay = false with a Response connection.

Notes

• IsTwoWay cannot be changed while the flow runs.
• Answer each two-way request exactly once. A request that never reaches Response keeps the caller waiting until its timeout; only the first response for a request is delivered.
• Renaming the listener breaks existing Pipe clients until they select it again.
• The pipe listens on the loopback address, so callers must run on the same machine.
• For one-way listeners an exception in the flow is only logged; the caller is not informed.

Example

{ "Name": "GetCustomer", "IsTwoWay": true }

Pipe listener Request → Table reader → Data mapper → Pipe listener Response