urus/examples/load_profile.rs

//! Causal load-profiling target (RFC 007): the real urus hot path under
//! EXTERNAL load — no planted bottleneck, no in-process load generation.
//!
//! Where `causal_bench` validates the machinery against a planted,
//! known-answer store, this is the discovery tool: boot a bare server,
//! let an external generator (wrk, pinned to different cores) drive it,
//! sweep virtual speedups over the five lib sites (parse, router,
//! pipeline, serialize, socket-write), and report which one causally
//! limits throughput. External load is deliberate: the generator lives
//! outside the smarm runtime, so it cannot absorb injected virtual
//! delay — the same property `causal_bench` gets from plain OS threads.
//!
//! No pass/fail verdict — there is no known answer here. Trust gates
//! only: traffic actually flowed through the sweep, and the ledger
//! audit (printed) balances.
//!
//! Env:
//!   URUS_PORT   listen port (default 8080; binds 0.0.0.0)
//!   COZ_OUT     coz profile output path (default profile.coz)
//!   WARMUP_MS   settle time after first traffic, ms (default 2000)
//!
//! Orchestration contract (the jobrunner run.sh): start this, wait for
//! it to accept, point wrk at `GET /json/:id` with a duration that
//! outlives the sweep, and stop wrk when this process exits.
//!
//!   cargo run --release --example load_profile --features smarm-causal

use std::net::SocketAddr;
use std::time::{Duration, Instant};

use urus::{serve_with_shutdown, shutdown_handle, Config, Conn, Next, Pipeline, Router};

fn env_u64(name: &str, default: u64) -> u64 {
    std::env::var(name).ok().and_then(|v| v.parse().ok()).unwrap_or(default)
}

/// The whole handler: param parse + JSON render. Deliberately thin — the
/// subject is the lib path around it, not application work.
fn json_id(conn: Conn, _next: Next) -> Conn {
    let id: u64 = conn.params.get("id").and_then(|s| s.parse().ok()).unwrap_or(0);
    conn.put_status(200)
        .put_header("content-type", "application/json")
        .put_body(format!("{{\"id\":{id}}}"))
}

fn main() {
    let port = env_u64("URUS_PORT", 8080) as u16;
    let warmup = Duration::from_millis(env_u64("WARMUP_MS", 2000));
    let coz_out = std::env::var("COZ_OUT").unwrap_or_else(|_| "profile.coz".into());

    let addr: SocketAddr = format!("0.0.0.0:{port}").parse().expect("addr");
    let (handle, signal) = shutdown_handle();
    let server = std::thread::spawn(move || {
        let pipe = Pipeline::new().plug(Router::new().get("/json/:id", json_id));
        serve_with_shutdown(Config::new(addr), smarm::Config::default(), pipe, Vec::new(), signal).expect("serve");
    });

    // Readiness is the orchestrator's job (TCP probe); ours is to not
    // sweep before real traffic has registered every site and the
    // progress point — `run_experiments` enumerates *registered* sites.
    // 100 completed responses guarantees full end-to-end coverage.
    let responses = |snap: &[(String, u64)]| {
        snap.iter().find(|(n, _)| n == "responses").map(|(_, c)| *c).unwrap_or(0)
    };
    let t0 = Instant::now();
    let seen = loop {
        let n = responses(&smarm::causal::progress_snapshot());
        if n >= 100 {
            break n;
        }
        assert!(
            t0.elapsed() < Duration::from_secs(120),
            "no load after 120s ({n} responses) — is the generator running?"
        );
        std::thread::sleep(Duration::from_millis(100));
    };
    println!("traffic up: {seen} responses; settling {warmup:?}");
    std::thread::sleep(warmup);

    // Same plan as causal_bench, for comparability across workloads.
    let results = smarm::causal::run_experiments(&smarm::causal::ExperimentPlan {
        speedups_pct: vec![0, 25, 50],
        experiment: Duration::from_millis(700),
        cooldown: Duration::from_millis(150),
    });

    handle.shutdown();
    server.join().expect("server panicked");

    print!("{}", smarm::causal::render_summary(&results));
    print!("{}", smarm::causal::render_ledger_audit(&results));
    match std::fs::write(&coz_out, smarm::causal::render_coz(&results)) {
        Ok(()) => println!("\nwrote {coz_out}"),
        Err(e) => eprintln!("\nfailed to write {coz_out}: {e}"),
    }

    // Trust gate: the sweep is meaningless if load didn't flow through it.
    let total: u64 = results
        .iter()
        .flat_map(|r| r.deltas.iter())
        .filter(|(n, _)| n == "responses")
        .map(|(_, c)| c)
        .sum();
    println!("total responses across windows: {total}");
    assert!(total > 0, "sweep saw zero progress");
}