Delayer

The Delayer is a System Management pattern from Hohpe and Woolf. It holds an exchange in the pipeline for a fixed or dynamic duration. The exchange then moves to the next step.

    let fixed_route = RouteBuilder::from("timer:tick?period=2000&repeatCount=5")
        .route_id("delayer-fixed")
        .delay(Duration::from_millis(500))
        .to("log:delayed?showBody=true")
        .build()?;

- id: delayer-fixed
  from: timer:tick?period=2000&repeatCount=5
  steps:
    - delay:
        delay_ms: 500
    - to: log:delayed?showBody=true

The included route fires a timer every two seconds. The .delay(Duration::from_millis(500)) step suspends the exchange for a fixed half-second. The log:delayed step receives the exchange only after the timer elapses. In the YAML DSL the same fixed pause is the delay_ms field. Use a fixed delay to space messages apart by a known interval. Common cases are rate-limited APIs and scheduled batches.

For a per-message pause, set the dynamic_header option to a header name. Write the delay in milliseconds to that header on each exchange. The service reads the header value and clamps it to max_delay_ms (default 3,600,000 ms, one hour). A missing or non-numeric header falls back to delay_ms. The builder equivalent is delay_with_header. The example registers it on a second route that sets CamelDelayMs to 1000. A dynamic delay suits routes where the producer supplies a retry-after or backoff value.

The Delayer differs from the Throttler. The Delayer pauses every exchange by the configured amount. The Throttler paces the rate of accepted exchanges over a window. A route that needs both can place a Delayer after a Throttler.

Per ADR-0001, the delayer compiles into a Service<Exchange> step. Its call method awaits a tokio::time::sleep and returns the exchange when the timer elapses. The processor contract is documented in camel-processor/CONTEXT.md.

The example source is at examples/delayer.