use prng, add --rand-seed argument

coder · johnstcn · Oct 2, 2023 · Sep 28, 2023 · Sep 28, 2023 · Sep 28, 2023
commit cf101511c8a67fac3281bc9d7355c515da944f87
diff --git a/cli/exp_scaletest.go b/cli/exp_scaletest.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"math/rand"
 	"net/http"
 	"os"
 	"strconv"
@@ -1049,6 +1050,7 @@ func (r *RootCmd) scaletestDashboard() *clibase.Cmd {
 		minWait  time.Duration
 		maxWait  time.Duration
 		headless bool
+		randSeed int64
 
 		client          = &codersdk.Client{}
 		tracingFlags    = &scaletestTracingFlags{}
@@ -1106,6 +1108,8 @@ func (r *RootCmd) scaletestDashboard() *clibase.Cmd {
 			}
 
 			for _, usr := range users {
+				//nolint:gosec // not used for cryptographic purposes
+				rndGen := rand.New(rand.NewSource(randSeed))
 				name := fmt.Sprintf("dashboard-%s", usr.Username)
 				userTokResp, err := client.CreateToken(ctx, usr.ID.String(), codersdk.CreateTokenRequest{
 					Lifetime:  30 * 24 * time.Hour,
@@ -1126,6 +1130,7 @@ func (r *RootCmd) scaletestDashboard() *clibase.Cmd {
 					Logger:     logger.Named(name),
 					Headless:   headless,
 					ActionFunc: dashboard.ClickRandomElement,
+					RandIntn:   rndGen.Intn,
 				}
 				//nolint:gocritic
 				logger.Info(ctx, "runner config", slog.F("min_wait", minWait), slog.F("max_wait", maxWait), slog.F("headless", headless), slog.F("trace", tracingEnabled))
@@ -1189,6 +1194,13 @@ func (r *RootCmd) scaletestDashboard() *clibase.Cmd {
 			Description: "Controls headless mode. Setting to false is useful for debugging.",
 			Value:       clibase.BoolOf(&headless),
 		},
+		{
+			Flag:        "rand-seed",
+			Env:         "CODER_SCALETEST_DASHBOARD_RAND_SEED",
+			Default:     "0",
+			Description: "Seed for the random number generator.",
+			Value:       clibase.Int64Of(&randSeed),
+		},
 	}
 
 	tracingFlags.attach(&cmd.Options)

diff --git a/cli/exp_scaletest_test.go b/cli/exp_scaletest_test.go
@@ -156,6 +156,7 @@ func TestScaleTestDashboard(t *testing.T) {
 			"--timeout", "5s",
 			"--scaletest-prometheus-address", "127.0.0.1:0",
 			"--scaletest-prometheus-wait", "0s",
+			"--rand-seed", "1234567890",
 		)
 		clitest.SetupConfig(t, client, root)
 		pty := ptytest.New(t)

diff --git a/scaletest/dashboard/chromedp.go b/scaletest/dashboard/chromedp.go
@@ -2,7 +2,6 @@ package dashboard
 
 import (
 	"context"
-	"math/rand"
 	"net/url"
 	"os"
 	"time"
@@ -91,43 +90,45 @@ var defaultTargets = []Target{
 // If no elements are found, an error is returned.
 // If more than one element is found, one is chosen at random.
 // The label of the clicked element is returned.
-func ClickRandomElement(ctx context.Context) (Label, Action, error) {
+func ClickRandomElement(ctx context.Context, randIntn func(int) int) (Label, Action, error) {
 	var xpath Selector
 	var found bool
 	var err error
-	matches := make(map[Label]Selector)
-	waitFor := make(map[Label]Selector)
+	matches := make([]Target, 0)
 	for _, tgt := range defaultTargets {
-		xpath, found, err = randMatch(ctx, tgt.ClickOn)
+		xpath, found, err = randMatch(ctx, tgt.ClickOn, randIntn)
 		if err != nil {
 			return "", nil, xerrors.Errorf("find matches for %q: %w", tgt.ClickOn, err)
 		}
 		if !found {
 			continue
 		}
-		matches[tgt.Label] = xpath
-		waitFor[tgt.Label] = tgt.WaitFor
+		matches = append(matches, Target{
+			Label:   tgt.Label,
+			ClickOn: xpath,
+			WaitFor: tgt.WaitFor,
+		})
 	}
 
+	if len(matches) == 0 {
+		return "", nil, xerrors.Errorf("no matches found")
+	}
+	match := pick(matches, randIntn)
 	// rely on map iteration order being random
-	for lbl, tgt := range matches {
-		act := func(actx context.Context) error {
-			if err := clickAndWait(actx, tgt, waitFor[lbl]); err != nil {
-				return xerrors.Errorf("click %q: %w", tgt, err)
-			}
-			return nil
+	act := func(actx context.Context) error {
+		if err := clickAndWait(actx, match.ClickOn, match.WaitFor); err != nil {
+			return xerrors.Errorf("click %q: %w", match.ClickOn, err)
 		}
-		return lbl, act, nil
+		return nil
 	}
-
-	return "", nil, xerrors.Errorf("no matches found")
+	return match.Label, act, nil
 }
 
 // randMatch returns a random match for the given selector.
 // The returned selector is the full XPath of the matched node.
 // If no matches are found, an error is returned.
 // If multiple matches are found, one is chosen at random.
-func randMatch(ctx context.Context, s Selector) (Selector, bool, error) {
+func randMatch(ctx context.Context, s Selector, randIntn func(int) int) (Selector, bool, error) {
 	var nodes []*cdp.Node
 	err := chromedp.Run(ctx, chromedp.Nodes(s, &nodes, chromedp.NodeVisible, chromedp.AtLeast(0)))
 	if err != nil {
@@ -136,7 +137,7 @@ func randMatch(ctx context.Context, s Selector) (Selector, bool, error) {
 	if len(nodes) == 0 {
 		return "", false, nil
 	}
-	n := pick(nodes)
+	n := pick(nodes, randIntn)
 	return Selector(n.FullXPath()), true, nil
 }
 
@@ -210,11 +211,11 @@ func visitMainPage(ctx context.Context, u *url.URL) error {
 
 // pick chooses a random element from a slice.
 // If the slice is empty, it returns the zero value of the type.
-func pick[T any](s []T) T {
+func pick[T any](s []T, randIntn func(int) int) T {
 	if len(s) == 0 {
 		var zero T
 		return zero
 	}
 	// nolint:gosec
-	return s[rand.Intn(len(s))]
+	return s[randIntn(len(s))]
 }
diff --git a/scaletest/dashboard/config.go b/scaletest/dashboard/config.go
@@ -21,7 +21,9 @@ type Config struct {
 	// Headless controls headless mode for chromedp.
 	Headless bool `json:"headless"`
 	// ActionFunc is a function that returns an action to run.
-	ActionFunc func(ctx context.Context) (Label, Action, error) `json:"-"`
+	ActionFunc func(ctx context.Context, randIntn func(int) int) (Label, Action, error) `json:"-"`
+	// RandIntn is a function that returns a random number between 0 and n-1.
+	RandIntn func(int) int `json:"-"`
 }
 
 func (c Config) Validate() error {

diff --git a/scaletest/dashboard/run.go b/scaletest/dashboard/run.go
@@ -60,7 +60,7 @@ func (r *Runner) Run(ctx context.Context, _ string, _ io.Writer) error {
 			return nil
 		case <-t.C:
 			t.Reset(r.randWait())
-			l, act, err := r.cfg.ActionFunc(cdpCtx)
+			l, act, err := r.cfg.ActionFunc(cdpCtx, r.cfg.RandIntn)
 			if err != nil {
 				r.cfg.Logger.Error(ctx, "calling ActionFunc", slog.Error(err))
 				continue

diff --git a/scaletest/dashboard/run_test.go b/scaletest/dashboard/run_test.go
@@ -36,6 +36,9 @@ func Test_Run(t *testing.T) {
 		return assert.AnError
 	}
 
+	//nolint: gosec // just for testing
+	rg := rand.New(rand.NewSource(0)) // deterministic for testing
+
 	client := coderdtest.New(t, nil)
 	_ = coderdtest.CreateFirstUser(t, client)
 
@@ -48,12 +51,13 @@ func Test_Run(t *testing.T) {
 		MaxWait:  500 * time.Millisecond,
 		Logger:   log,
 		Headless: true,
-		ActionFunc: func(ctx context.Context) (dashboard.Label, dashboard.Action, error) {
-			if rand.Intn(2) == 0 { //nolint:gosec // just for testing
+		ActionFunc: func(_ context.Context, rnd func(int) int) (dashboard.Label, dashboard.Action, error) {
+			if rnd(2) == 0 {
 				return "fails", failAction, nil
 			}
 			return "succeeds", successAction, nil
 		},
+		RandIntn: rg.Intn,
 	}
 	r := dashboard.NewRunner(client, m, cfg)
 	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)