feat: add token-bucket rate limiting for action endpoints

Add per-context and per-action rate limiting using golang.org/x/time/rate.
Configure globally via Options.ActionRateLimit or per-action with
WithRateLimit(). Defaults to 10 req/s with burst of 20.

configuration.go

@@ -61,4 +61,9 @@ type Options struct {
 	// connection before the background reaper disposes it.
 	// Default: 30s. Negative value disables the reaper.
 	ContextTTL time.Duration
+
+	// ActionRateLimit configures the default token-bucket rate limiter for
+	// action endpoints. Zero values use built-in defaults (10 req/s, burst 20).
+	// Set Rate to -1 to disable rate limiting entirely.
+	ActionRateLimit RateLimitConfig
 }

context.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/ryanhamamura/via/h"
+	"golang.org/x/time/rate"
 )
 
 // Context is the living bridge between Go and the browser.
@@ -20,13 +21,15 @@ import (
 type Context struct {
 	id                string
 	route             string
+	csrfToken         string
 	app               *V
 	view              func() h.H
 	routeParams       map[string]string
 	componentRegistry map[string]*Context
 	parentPageCtx     *Context
 	patchChan         chan patch
-	actionRegistry    map[string]func()
+	actionLimiter     *rate.Limiter
+	actionRegistry    map[string]actionEntry
 	signals           *sync.Map
 	mu                sync.RWMutex
 	ctxDisposedChan   chan struct{}
@@ -103,26 +106,31 @@ func (c *Context) isComponent() bool {
 //		 	 	h.Button(h.Text("Increment n"), increment.OnClick()),
 //		 )
 //	})
-func (c *Context) Action(f func()) *actionTrigger {
+func (c *Context) Action(f func(), opts ...ActionOption) *actionTrigger {
 	id := genRandID()
 	if f == nil {
 		c.app.logErr(c, "failed to bind action '%s' to context: nil func", id)
 		return nil
 	}
 
+	entry := actionEntry{fn: f}
+	for _, opt := range opts {
+		opt(&entry)
+	}
+
 	if c.isComponent() {
-		c.parentPageCtx.actionRegistry[id] = f
+		c.parentPageCtx.actionRegistry[id] = entry
 	} else {
-		c.actionRegistry[id] = f
+		c.actionRegistry[id] = entry
 	}
 	return &actionTrigger{id}
 }
 
-func (c *Context) getActionFn(id string) (func(), error) {
-	if f, ok := c.actionRegistry[id]; ok {
-		return f, nil
+func (c *Context) getAction(id string) (actionEntry, error) {
+	if e, ok := c.actionRegistry[id]; ok {
+		return e, nil
 	}
-	return nil, fmt.Errorf("action '%s' not found", id)
+	return actionEntry{}, fmt.Errorf("action '%s' not found", id)
 }
 
 // OnInterval starts a go routine that sets a time.Ticker with the given duration and executes
@@ -477,10 +485,12 @@ func newContext(id string, route string, v *V) *Context {
 	return &Context{
 		id:                id,
 		route:             route,
+		csrfToken:         genCSRFToken(),
 		routeParams:       make(map[string]string),
 		app:               v,
 		componentRegistry: make(map[string]*Context),
-		actionRegistry:    make(map[string]func()),
+		actionLimiter:     newLimiter(v.actionRateLimit, defaultActionRate, defaultActionBurst),
+		actionRegistry:    make(map[string]actionEntry),
 		signals:           new(sync.Map),
 		patchChan:         make(chan patch, 1),
 		ctxDisposedChan:   make(chan struct{}, 1),

go.mod

@@ -14,6 +14,7 @@ require (
 	github.com/rs/zerolog v1.34.0
 	github.com/starfederation/datastar-go v1.0.3
 	github.com/stretchr/testify v1.11.1
+	golang.org/x/time v0.14.0
 )
 
 require (
@@ -37,6 +38,6 @@ require (
 	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	golang.org/x/crypto v0.45.0 // indirect
 	golang.org/x/sys v0.38.0 // indirect
-	golang.org/x/time v0.14.0 // indirect
+	golang.org/x/time v0.14.0
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

ratelimit.go

@@ -0,0 +1,48 @@
+package via
+
+import "golang.org/x/time/rate"
+
+const (
+	defaultActionRate  float64 = 10.0
+	defaultActionBurst int     = 20
+)
+
+// RateLimitConfig configures token-bucket rate limiting for actions.
+// Zero values fall back to defaults. Rate of -1 disables limiting entirely.
+type RateLimitConfig struct {
+	Rate  float64
+	Burst int
+}
+
+// ActionOption configures per-action behaviour when passed to Context.Action.
+type ActionOption func(*actionEntry)
+
+type actionEntry struct {
+	fn      func()
+	limiter *rate.Limiter // nil = use context default
+}
+
+// WithRateLimit returns an ActionOption that gives this action its own
+// token-bucket limiter, overriding the context-level default.
+func WithRateLimit(r float64, burst int) ActionOption {
+	return func(e *actionEntry) {
+		e.limiter = newLimiter(RateLimitConfig{Rate: r, Burst: burst}, defaultActionRate, defaultActionBurst)
+	}
+}
+
+// newLimiter creates a *rate.Limiter from cfg, substituting defaults for zero
+// values. A Rate of -1 disables limiting (returns nil).
+func newLimiter(cfg RateLimitConfig, defaultRate float64, defaultBurst int) *rate.Limiter {
+	r := cfg.Rate
+	b := cfg.Burst
+	if r == -1 {
+		return nil
+	}
+	if r == 0 {
+		r = defaultRate
+	}
+	if b == 0 {
+		b = defaultBurst
+	}
+	return rate.NewLimiter(rate.Limit(r), b)
+}

ratelimit_test.go

@@ -0,0 +1,101 @@
+package via
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewLimiter_Defaults(t *testing.T) {
+	l := newLimiter(RateLimitConfig{}, defaultActionRate, defaultActionBurst)
+	require.NotNil(t, l)
+	assert.InDelta(t, defaultActionRate, float64(l.Limit()), 0.001)
+	assert.Equal(t, defaultActionBurst, l.Burst())
+}
+
+func TestNewLimiter_CustomValues(t *testing.T) {
+	l := newLimiter(RateLimitConfig{Rate: 5, Burst: 10}, defaultActionRate, defaultActionBurst)
+	require.NotNil(t, l)
+	assert.InDelta(t, 5.0, float64(l.Limit()), 0.001)
+	assert.Equal(t, 10, l.Burst())
+}
+
+func TestNewLimiter_DisabledWithNegativeRate(t *testing.T) {
+	l := newLimiter(RateLimitConfig{Rate: -1}, defaultActionRate, defaultActionBurst)
+	assert.Nil(t, l)
+}
+
+func TestTokenBucket_AllowsBurstThenRejects(t *testing.T) {
+	l := newLimiter(RateLimitConfig{Rate: 1, Burst: 3}, 1, 3)
+	require.NotNil(t, l)
+
+	for i := 0; i < 3; i++ {
+		assert.True(t, l.Allow(), "request %d should be allowed within burst", i)
+	}
+	assert.False(t, l.Allow(), "request beyond burst should be rejected")
+}
+
+func TestWithRateLimit_CreatesLimiter(t *testing.T) {
+	entry := actionEntry{fn: func() {}}
+	opt := WithRateLimit(2, 4)
+	opt(&entry)
+
+	require.NotNil(t, entry.limiter)
+	assert.InDelta(t, 2.0, float64(entry.limiter.Limit()), 0.001)
+	assert.Equal(t, 4, entry.limiter.Burst())
+}
+
+func TestContextAction_WithRateLimit(t *testing.T) {
+	v := New()
+	c := newContext("test-rl", "/", v)
+
+	called := false
+	c.Action(func() { called = true }, WithRateLimit(1, 2))
+
+	// Verify the entry has its own limiter
+	for _, entry := range c.actionRegistry {
+		require.NotNil(t, entry.limiter)
+		assert.InDelta(t, 1.0, float64(entry.limiter.Limit()), 0.001)
+		assert.Equal(t, 2, entry.limiter.Burst())
+	}
+	assert.False(t, called)
+}
+
+func TestContextAction_DefaultNoPerActionLimiter(t *testing.T) {
+	v := New()
+	c := newContext("test-no-rl", "/", v)
+
+	c.Action(func() {})
+
+	for _, entry := range c.actionRegistry {
+		assert.Nil(t, entry.limiter, "entry without WithRateLimit should have nil limiter")
+	}
+}
+
+func TestContextLimiter_DefaultsApplied(t *testing.T) {
+	v := New()
+	c := newContext("test-ctx-limiter", "/", v)
+
+	require.NotNil(t, c.actionLimiter)
+	assert.InDelta(t, defaultActionRate, float64(c.actionLimiter.Limit()), 0.001)
+	assert.Equal(t, defaultActionBurst, c.actionLimiter.Burst())
+}
+
+func TestContextLimiter_DisabledViaConfig(t *testing.T) {
+	v := New()
+	v.actionRateLimit = RateLimitConfig{Rate: -1}
+	c := newContext("test-disabled", "/", v)
+
+	assert.Nil(t, c.actionLimiter)
+}
+
+func TestContextLimiter_CustomConfig(t *testing.T) {
+	v := New()
+	v.Config(Options{ActionRateLimit: RateLimitConfig{Rate: 50, Burst: 100}})
+	c := newContext("test-custom", "/", v)
+
+	require.NotNil(t, c.actionLimiter)
+	assert.InDelta(t, 50.0, float64(c.actionLimiter.Limit()), 0.001)
+	assert.Equal(t, 100, c.actionLimiter.Burst())
+}

via.go

@@ -10,6 +10,7 @@ import (
 	"context"
 	"crypto/rand"
 	_ "embed"
+	"crypto/subtle"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
@@ -47,6 +48,7 @@ type V struct {
 	devModePageInitFnMap map[string]func(*Context)
 	sessionManager       *scs.SessionManager
 	pubsub               PubSub
+	actionRateLimit      RateLimitConfig
 	datastarPath         string
 	datastarContent      []byte
 	datastarOnce         sync.Once
@@ -131,6 +133,9 @@ func (v *V) Config(cfg Options) {
 	if cfg.ContextTTL != 0 {
 		v.cfg.ContextTTL = cfg.ContextTTL
 	}
+	if cfg.ActionRateLimit.Rate != 0 || cfg.ActionRateLimit.Burst != 0 {
+		v.actionRateLimit = cfg.ActionRateLimit
+	}
 }
 
 // AppendToHead appends the given h.H nodes to the head of the base HTML document.
@@ -203,7 +208,7 @@ func (v *V) Page(route string, initContextFn func(c *Context)) {
 		headElements := []h.H{h.Script(h.Type("module"), h.Src(v.datastarPath))}
 		headElements = append(headElements, v.documentHeadIncludes...)
 		headElements = append(headElements,
-			h.Meta(h.Data("signals", fmt.Sprintf("{'via-ctx':'%s'}", id))),
+			h.Meta(h.Data("signals", fmt.Sprintf("{'via-ctx':'%s','via-csrf':'%s'}", id, c.csrfToken))),
 			h.Meta(h.Data("init", "@get('/_sse')")),
 			h.Meta(h.Data("init", fmt.Sprintf(`window.addEventListener('beforeunload', (evt) => {
 			navigator.sendBeacon('/_session/close', '%s');});`, c.id))),
@@ -632,13 +637,29 @@ func New() *V {
 			v.logErr(nil, "action '%s' failed: %v", actionID, err)
 			return
 		}
+		csrfToken, _ := sigs["via-csrf"].(string)
+		if subtle.ConstantTimeCompare([]byte(csrfToken), []byte(c.csrfToken)) != 1 {
+			v.logWarn(c, "action '%s' rejected: invalid CSRF token", actionID)
+			http.Error(w, "invalid CSRF token", http.StatusForbidden)
+			return
+		}
+		if c.actionLimiter != nil && !c.actionLimiter.Allow() {
+			v.logWarn(c, "action '%s' rate limited", actionID)
+			http.Error(w, "rate limited", http.StatusTooManyRequests)
+			return
+		}
 		c.reqCtx = r.Context()
-		actionFn, err := c.getActionFn(actionID)
+		entry, err := c.getAction(actionID)
 		if err != nil {
 			v.logDebug(c, "action '%s' failed: %v", actionID, err)
 			return
 		}
-		// log err if actionFn panics
+		if entry.limiter != nil && !entry.limiter.Allow() {
+			v.logWarn(c, "action '%s' rate limited (per-action)", actionID)
+			http.Error(w, "rate limited", http.StatusTooManyRequests)
+			return
+		}
+		// log err if action panics
 		defer func() {
 			if r := recover(); r != nil {
 				v.logErr(c, "action '%s' failed: %v", actionID, r)
@@ -646,7 +667,7 @@ func New() *V {
 		}()
 
 		c.injectSignals(sigs)
-		actionFn()
+		entry.fn()
 	})
 
 	v.mux.HandleFunc("POST /_session/close", func(w http.ResponseWriter, r *http.Request) {
@@ -675,6 +696,12 @@ func genRandID() string {
 	return hex.EncodeToString(b)[:8]
 }
 
+func genCSRFToken() string {
+	b := make([]byte, 16)
+	rand.Read(b)
+	return hex.EncodeToString(b)
+}
+
 func extractParams(pattern, path string) map[string]string {
 	p := strings.Split(strings.Trim(pattern, "/"), "/")
 	u := strings.Split(strings.Trim(path, "/"), "/")