Akka Streams and Pekko Streams (Scala)

Quick start

• Think twice before using Streams: prefer plain functions, even for I/O.
• Test stream components using TestSource, TestSink, and TestProbe from akka-stream-testkit.
• Always define supervision strategies for error handling; default behavior tears down the entire stream.
• Read references/akka-streams.md for core concepts and patterns.
• Read references/best-practices.md for critical guidance on when NOT to use streams.
• Read references/testing.md for comprehensive testing examples.

When NOT to use Streams

• Don't model plain data transformations as stream operators; use regular functions instead.
• Don't use streams for general I/O; prefer plain functions or other abstractions.

Workflow

1. Verify that Streams are the right tool: do you need dataflow or reactive programming patterns?
2. Design Source, Flow, and Sink components as separate, testable units.
3. Define error handling with recover, recoverWithRetries, or supervision strategies.
4. Test each component with TestSource/TestSink or TestProbe before integration.
5. Compose the final graph and materialize with explicit error handling.

Testing rules

• Write tests using akka-stream-testkit for custom stream components.
• Use TestSource.probe and TestSink.probe for fine-grained control over element flow.
• Test backpressure behavior explicitly using request() and expectNoMessage().
• Test error scenarios with expectError() or supervision strategies.

Pekko Streams

• Pekko Streams is a fork of Akka Streams with identical APIs (package names change from akka.* to org.apache.pekko.*).
• All guidance for Akka Streams applies equally to Pekko Streams.
• When working with Pekko, adjust imports but keep patterns and testing approaches identical.

Output expectations

• Keep stream topologies simple and testable; break complex graphs into named components.
• Make error handling explicit via supervision or recovery operators.
• Prefer immutability; stream graphs are blueprints until materialized.

References

• Load references/akka-streams.md for core concepts, operators, and materialization.
• Load references/best-practices.md for critical guidance on avoiding stream overuse.
• Load references/testing.md for testing patterns and complete examples.