Operator Logging

SDF operators can output logs using standard output (stdout), which can then be viewed using the sdf log command. This allows developers to debug and monitor the behavior of their operators.

Within Rust operators, you can use the standard println! macro to write to stdout. The output will be captured and displayed when you execute sdf log.

This is particularly useful for debugging and understanding the context in which your operator is running. You can, for example, print the key using key() or the window boundaries using window().

Example

Code example of an update-state operator with some output sent to standard output.

fn add_count(input: String) -> Result<()> {
    if let Some(k) = key() {
        println!("Key: {:?}", k); // Print the key if it exists
    }

    let (window_start, window_end) = window();
    println!("Window start timestamp: {}, Window end timestamp: {}", window_start, window_end);

    let new_value = counter().increment(1);
    println!("New counter value: {}", new_value);

    Ok(())
}