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Ports and Links

Ports and links are how you connect nodes together to create data flow in your graph. Ports are connection points on nodes, and links are the visual connections you draw between ports. Together, they create the pathways that data follows through your pipeline.

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What are Ports?

Ports are connection points on nodes where data enters or exits:
  • Input ports - Receive data (located on the left side of nodes)
  • Output ports - Send data (located on the right side of nodes)
Think of ports as electrical outlets and plugs. Input ports are like outlets (they receive), and output ports are like plugs (they send). You connect them with cables (links) to complete the circuit.
Ports are strongly typed—each port has a specific schema type. You can only connect ports with compatible types.
Links are visual connections you draw between ports:
  • Connect output to input - Drag from an output port to an input port
  • Create topics automatically - Links automatically create topics
  • Show data flow - Links visually represent how data moves through your graph
Think of links as pipes connecting nodes. When you draw a link, you’re creating a data pathway that the framework will use to route messages.

Visual Design

See data flow at a glance. Links make it immediately clear how data moves through your system.

Type Safety

The editor prevents incompatible connections. You can only link ports with matching types.

Automatic Topics

Links automatically create topics. No manual topic configuration needed.

Easy Refactoring

Redraw links to change data flow. No code changes required.

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Port Types and Appearance

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Input Ports

Input ports appear on the left side of nodes:
  • Blue circle - Normal input port
  • Red circle - Trigger input port (executes node when data arrives)
  • Port label - Shows the port name (e.g., i0, temperature_in)
  • Topic name - Shows the connected topic name

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Output Ports

Output ports appear on the right side of nodes:
  • Green circle - Output port
  • Port label - Shows the port name (e.g., o0, temperature_out)
  • Topic name - Shows the connected topic name
Visual Note: A diagram showing input ports (blue/red circles on left) and output ports (green circles on right) would be helpful here.
Creating links is simple:
1

Enter connection mode

Click the Connect tool in the toolbar (or press C key).
The cursor should change to indicate connection mode is active.
2

Click output port

Click and hold on a green output port (on the right side of a node).
You should see a line starting from the output port, following your cursor.
3

Drag to input port

Drag the line to a blue input port (on the left side of another node).
The input port should highlight when you’re over it, indicating a valid connection.
4

Release to connect

Release the mouse button to create the link.
You should see a line connecting the two ports. A topic is automatically created.
You can also create links by right-clicking an output port and selecting “Connect to…” from the context menu.
The editor validates links before creating them:

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Valid Connections

  • Type match - Output type matches input type
  • Same schema - Both ports use the same schema
  • Compatible types - Types are structurally compatible

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Invalid Connections

  • Type mismatch - Output and input types don’t match
  • Self-connection - Trying to connect a node to itself (usually invalid)
  • Duplicate connection - Ports already connected
The editor will prevent invalid connections. If you can’t connect two ports, check that their types are compatible.
Each link has properties you can configure:
  • Topic name - The name of the topic created by this link
  • Type - The schema type (read-only, determined by port types)
  • Transport - Local or network (auto-selected by framework)
  • QoS settings - Quality of service configuration (optional)

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Renaming Topics

To rename a topic created by a link:
  1. Click the link to select it
  2. Open the properties panel
  3. Edit the topic name
  4. Press Enter to save
Topic names must be unique within a graph. If you try to use a duplicate name, the editor will suggest an alternative.

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One Output, Many Inputs (Fan-Out)

You can connect one output port to multiple input ports: 
Node A (output) → Link 1 → Node B (input)
               → Link 2 → Node C (input)
               → Link 3 → Node D (input)
This creates a fan-out pattern where one publisher sends data to multiple subscribers.
Each link creates a separate topic. All subscribers receive the same data, but through different topics.

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Many Outputs, One Input (Fan-In)

You can connect multiple output ports to one input port: 
Node A (output) → Link 1 ↘
Node B (output) → Link 2 → Node C (input)
Node D (output) → Link 3 ↗
This creates a fan-in pattern where multiple publishers send to one subscriber.
Fan-in can cause race conditions if multiple publishers send simultaneously. Consider using a join node to merge data properly.
Links automatically adjust when you move nodes. The connection remains valid as long as both nodes exist. To delete a link:
  1. Click the link to select it
  2. Press Delete key (or right-click → Delete)
Deleting a link also deletes the associated topic. Make sure no other nodes depend on that topic.
To change which ports a link connects:
  1. Delete the existing link
  2. Create a new link between the desired ports

Clear Layout

Arrange nodes so links don’t cross unnecessarily. A clean layout is easier to understand.

Meaningful Names

Rename topics created by links to have descriptive names. “temperature_readings” is better than “topic1”.

Avoid Loops

Be careful with circular connections. They can cause infinite loops if not handled properly.

Type Safety First

Always ensure port types match before connecting. The editor helps, but understanding types prevents errors.

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Common Patterns

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Linear Pipeline

Simple one-to-one connections: 
Node A → Node B → Node C → Node D
Use when: Data flows sequentially through processing stages.

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Broadcast Pattern

One publisher, many subscribers: 
        → Node B
Node A → → Node C
        → Node D
Use when: Broadcasting data to multiple consumers.

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Merge Pattern

Many publishers, one subscriber: 
Node A →
Node B → → Node C
Node D →
Use when: Collecting data from multiple sources (use with caution).
Problem: The editor won’t let you create a link.Solutions:
  • Check that port types match (output type must match input type)
  • Verify both nodes are in the same graph
  • Ensure ports aren’t already connected (delete existing link first)
  • Check for schema errors that might prevent type validation
Problem: Editor shows type mismatch when trying to connect.Solutions:
  • Verify both ports use the same schema
  • Check that schemas are correctly defined
  • Ensure schema files are saved and loaded
  • Look for schema validation errors

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Next Steps

Now that you understand ports and links, learn more:

Connect Nodes

Step-by-step guide to connecting nodes together.

Topics

Learn how links automatically create topics.

Nodes

Understand how nodes use ports for input and output.

Examples

See examples of different connection patterns.