feat: polyglot script engine for code-based load testing

README.md

@@ -133,6 +133,118 @@ make run-server
 # Endpoints: /health, /api/users, /api/stats, /api/echo
 ```
 
+## Script Engine (Code-Based Load Testing)
+
+Write load tests in your preferred language — like k6, but polyglot with chaos patterns built-in.
+
+```bash
+kar script test.star                          # Starlark (Python-like)
+kar script test.js                            # JavaScript
+kar script test.py                            # Python
+kar script test.rb                            # Ruby
+kar script test.star --vus 50 --duration 5m   # Override VUs and duration
+kar script test.star --dashboard              # Enable real-time web dashboard
+```
+
+### Starlark (.star)
+
+```python
+scenario(
+    name = "api-load-test",
+    pattern = chaos(preset = "aggressive", spike_factor = 3.0),
+    vus = ramp([
+        stage("30s", 10),   # Ramp to 10 VUs over 30s
+        stage("2m", 50),    # Ramp to 50 VUs over 2m
+        stage("30s", 0),    # Ramp down
+    ]),
+    thresholds = {
+        "http_req_duration{p95}": "< 500ms",
+        "http_req_failed": "< 0.05",
+    },
+)
+
+def setup():
+    resp = http.post("http://api.example.com/auth", json={"user": "test"})
+    return {"token": resp.json()["token"]}
+
+def default(data):
+    headers = {"Authorization": "Bearer " + data["token"]}
+    resp = http.get("http://api.example.com/products", headers=headers)
+    check(resp, {
+        "status 200": lambda r: r.status == 200,
+        "has items":  lambda r: len(r.json()) > 0,
+    })
+    sleep(think_time("1s", "3s"))
+```
+
+### JavaScript (.js)
+
+```javascript
+scenario({
+    name: "api-load-test",
+    pattern: chaos({ preset: "moderate" }),
+    thresholds: {
+        "http_req_duration{p95}": "< 500ms",
+    },
+});
+
+function run(data) {
+    var resp = http.get("http://api.example.com/health");
+    check(resp, {
+        "status 200": function(r) { return r.status === 200; },
+    });
+}
+```
+
+### Python (.py)
+
+```python
+from kar98k import scenario, chaos, http, check, sleep, think_time
+
+scenario(name="api-load-test", pattern=chaos(preset="moderate"))
+
+def default(data):
+    resp = http.get("http://api.example.com/health")
+    check(resp, {
+        "status 200": lambda r: r.status == 200,
+        "has status":  lambda r: "status" in r.json(),
+    })
+    sleep(think_time("1s", "3s"))
+```
+
+### Ruby (.rb)
+
+```ruby
+require_relative "../sdk/ruby/kar98k"
+
+scenario name: "api-load-test", pattern: chaos(preset: "moderate")
+
+def default(data)
+  resp = Http.get("http://api.example.com/health")
+  check resp,
+    "status 200" => ->(r) { r.status == 200 }
+  sleep_dur think_time("1s", "3s")
+end
+```
+
+### Real-Time Dashboard
+
+![kar98k Dashboard](./assets/dashboard.png)
+
+Enable with `--dashboard`:
+
+```bash
+kar script test.star --vus 20 --duration 5m --dashboard
+# Dashboard: http://localhost:8888
+```
+
+Opens a web UI showing:
+- Live RPS and latency graphs
+- P95/P99 latency tracking
+- Error rate and status codes
+- Check pass/fail rates
+- VU count and iteration progress
+
 ## Commands
 
 | Command | Description |

examples/basic_test.js

@@ -0,0 +1,18 @@
+// basic_test.js - Basic load test example (JavaScript)
+
+scenario({
+    name: "basic-health-check",
+    pattern: chaos({ preset: "gentle" }),
+    thresholds: {
+        "http_req_duration{p95}": "< 500ms",
+        "http_req_failed": "< 0.05",
+    },
+});
+
+// Main iteration function — called per VU
+function run(data) {
+    var resp = http.get("http://localhost:8080/health");
+    check(resp, {
+        "status is 200": function(r) { return r.status === 200; },
+    });
+}

examples/basic_test.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+"""k6-style load test written in Python."""
+
+import sys, os
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "sdk", "python"))
+
+from kar98k import scenario, chaos, http, check, sleep, think_time
+
+# Configure scenario
+scenario(
+    name="python-api-test",
+    pattern=chaos(preset="moderate", spike_factor=2.5),
+    thresholds={
+        "http_req_duration{p95}": "< 500ms",
+        "http_req_failed": "< 0.05",
+    },
+)
+
+# Setup — runs once
+def setup():
+    return {"session": "py-session-abc"}
+
+# Main iteration — runs per VU
+def default(data):
+    # GET health
+    resp = http.get("http://localhost:8080/health")
+    check(resp, {
+        "health status 200": lambda r: r.status == 200,
+        "has status field": lambda r: "status" in r.json(),
+    })
+
+    sleep(think_time("100ms", "500ms"))
+
+    # GET users
+    resp = http.get("http://localhost:8080/api/users")
+    check(resp, {
+        "users status 200": lambda r: r.status == 200,
+    })
+
+# Teardown — runs once at end
+def teardown(data):
+    pass

examples/basic_test.rb

@@ -0,0 +1,33 @@
+#!/usr/bin/env ruby
+# k6-style load test written in Ruby.
+
+require_relative "../sdk/ruby/kar98k"
+
+scenario name: "ruby-api-test",
+         pattern: chaos(preset: "moderate", spike_factor: 2.0),
+         thresholds: {
+           "http_req_duration{p95}" => "< 500ms",
+           "http_req_failed" => "< 0.05"
+         }
+
+def setup
+  { "session" => "rb-session-xyz" }
+end
+
+def default(data)
+  # GET health
+  resp = Http.get("http://localhost:8080/health")
+  check resp,
+    "health status 200" => ->(r) { r.status == 200 },
+    "has status field"  => ->(r) { r.json&.key?("status") }
+
+  sleep_dur think_time("100ms", "500ms")
+
+  # GET users
+  resp = Http.get("http://localhost:8080/api/users")
+  check resp,
+    "users status 200" => ->(r) { r.status == 200 }
+end
+
+def teardown(data)
+end

examples/basic_test.star

@@ -0,0 +1,16 @@
+# basic_test.star - Basic load test example (Starlark)
+
+scenario(
+    name = "basic-health-check",
+    pattern = chaos(preset = "gentle"),
+    thresholds = {
+        "http_req_duration{p95}": "< 500ms",
+        "http_req_failed": "< 0.05",
+    },
+)
+
+def default(data):
+    resp = http.get("http://localhost:8080/health")
+    check(resp, {
+        "status is 200": lambda r: r.status == 200,
+    })

examples/checkout_test.star

@@ -0,0 +1,47 @@
+# checkout_test.star - Multi-step user flow with chaos patterns
+
+scenario(
+    name = "checkout-flow",
+    pattern = chaos(
+        preset = "aggressive",
+        spike_factor = 3.0,
+    ),
+    vus = ramp([
+        stage("10s", 5),
+        stage("30s", 20),
+        stage("10s", 0),
+    ]),
+    thresholds = {
+        "http_req_duration{p95}": "< 1000ms",
+        "http_req_failed": "< 0.1",
+        "checks": "> 0.9",
+    },
+)
+
+def setup():
+    resp = http.post("http://localhost:8080/api/echo", json = {
+        "action": "auth",
+        "user": "loadtest",
+    })
+    return {"session": "test-session-id"}
+
+def default(data):
+    headers = {"X-Session": data["session"]}
+
+    # Step 1: List products
+    resp = http.get("http://localhost:8080/api/users", headers = headers)
+    check(resp, {
+        "list ok": lambda r: r.status == 200,
+    })
+
+    # Think time — compresses during chaos spikes
+    sleep(think_time("500ms", "2s"))
+
+    # Step 2: Get stats
+    resp = http.get("http://localhost:8080/api/stats", headers = headers)
+    check(resp, {
+        "stats ok": lambda r: r.status == 200,
+    })
+
+def teardown(data):
+    http.post("http://localhost:8080/api/echo", json = {"action": "logout"})

examples/echoserver/main.go

@@ -112,9 +112,24 @@ func handleHealth(w http.ResponseWriter, r *http.Request) {
 	atomic.AddInt64(&stats.TotalRequests, 1)
 	atomic.AddInt64(&stats.GetRequests, 1)
 
-	// Simulate occasional slow responses
+	// 10% chance of failure: 500 error + 1~3s delay
+	if rand.Float32() < 0.10 {
+		delay := time.Duration(1000+rand.Intn(2000)) * time.Millisecond
+		time.Sleep(delay)
+		atomic.AddInt64(&stats.Errors, 1)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusInternalServerError)
+		json.NewEncoder(w).Encode(map[string]interface{}{
+			"status": "error",
+			"error":  "internal server error",
+			"delay":  delay.String(),
+		})
+		return
+	}
+
+	// 5% chance of slow response (no error)
 	if rand.Float32() < 0.05 {
-		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
+		time.Sleep(time.Duration(200+rand.Intn(500)) * time.Millisecond)
 	}
 
 	w.Header().Set("Content-Type", "application/json")
@@ -171,7 +186,35 @@ func handleUserByID(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func maybeFail(w http.ResponseWriter) bool {
+	roll := rand.Float32()
+	// 10% → 500 with 1~3s delay
+	if roll < 0.10 {
+		delay := time.Duration(1000+rand.Intn(2000)) * time.Millisecond
+		time.Sleep(delay)
+		atomic.AddInt64(&stats.Errors, 1)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusInternalServerError)
+		json.NewEncoder(w).Encode(map[string]string{"error": "internal server error"})
+		return true
+	}
+	// 5% → 400
+	if roll < 0.15 {
+		atomic.AddInt64(&stats.Errors, 1)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		json.NewEncoder(w).Encode(map[string]string{"error": "bad request"})
+		return true
+	}
+	// 3% → slow (no error)
+	if roll < 0.18 {
+		time.Sleep(time.Duration(200+rand.Intn(500)) * time.Millisecond)
+	}
+	return false
+}
+
 func listUsers(w http.ResponseWriter, r *http.Request) {
+	if maybeFail(w) { return }
 	store.mu.RLock()
 	defer store.mu.RUnlock()
 
@@ -285,6 +328,8 @@ func handleEcho(w http.ResponseWriter, r *http.Request) {
 	atomic.AddInt64(&stats.TotalRequests, 1)
 	atomic.AddInt64(&stats.PostRequests, 1)
 
+	if maybeFail(w) { return }
+
 	w.Header().Set("Content-Type", "application/json")
 
 	var body interface{}

go.mod

@@ -27,7 +27,11 @@ require (
 	github.com/clipperhouse/displaywidth v0.9.0 // indirect
 	github.com/clipperhouse/stringish v0.1.1 // indirect
 	github.com/clipperhouse/uax29/v2 v2.5.0 // indirect
+	github.com/dlclark/regexp2 v1.11.4 // indirect
+	github.com/dop251/goja v0.0.0-20260311135729-065cd970411c // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
+	github.com/go-sourcemap/sourcemap v2.1.3+incompatible // indirect
+	github.com/google/pprof v0.0.0-20230207041349-798e818bf904 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
@@ -44,6 +48,7 @@ require (
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
+	go.starlark.net v0.0.0-20260326113308-fadfc96def35 // indirect
 	go.yaml.in/yaml/v2 v2.4.2 // indirect
 	golang.org/x/sys v0.42.0 // indirect
 	golang.org/x/text v0.35.0 // indirect