fix: harden SPA navigation with race protection and correctness fixes

- Add navMu to serialize concurrent navigations on the same context
- Replace url.PathEscape with targeted JS string escaper (PathEscape
  mangles full paths and doesn't escape single quotes)
- Collapse syncWithViewTransition into syncView(bool) to remove duplication
- Simplify popstate ready guard in navigate.js
- Preserve URL hash during SPA navigation

README.md

@@ -69,7 +69,7 @@ func main() {
 - **CSRF protection** — automatic token generation and validation on every action
 - **Rate limiting** — token-bucket algorithm, configurable globally and per-action
 - **Event handling** — `OnClick`, `OnChange`, `OnSubmit`, `OnInput`, `OnFocus`, `OnBlur`, `OnMouseEnter`, `OnMouseLeave`, `OnScroll`, `OnDblClick`, `OnKeyDown`, and `OnKeyDownMap` for multi-key bindings
-- **Timed routines** — `OnInterval` with start/stop/update controls, tied to context lifecycle
+- **Timed routines** — `OnInterval` auto-starts a ticker goroutine, returns a stop function, tied to context lifecycle
 - **Redirects** — `Redirect`, `ReplaceURL`, and format-string variants
 - **Plugin system** — `func(v *V)` hooks for integrating CSS/JS libraries
 - **Structured logging** — zerolog with configurable levels; console output in dev, JSON in production

context.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -30,8 +31,11 @@ type Context struct {
 	actionRegistry    map[string]actionEntry
 	signals           *sync.Map
 	mu                sync.RWMutex
+	navMu             sync.Mutex
 	ctxDisposedChan   chan struct{}
+	pageStopChan      chan struct{}
 	reqCtx            context.Context
+	fields            []*Field
 	subscriptions     []Subscription
 	subsMu            sync.Mutex
 	disposeOnce       sync.Once
@@ -47,7 +51,11 @@ func (c *Context) View(f func() h.H) {
 	if f == nil {
 		panic("nil viewfn")
 	}
-	c.view = func() h.H { return h.Div(h.ID(c.id), f()) }
+	if c.app.layout != nil {
+		c.view = func() h.H { return h.Div(h.ID(c.id), c.app.layout(f)) }
+	} else {
+		c.view = func() h.H { return h.Div(h.ID(c.id), f()) }
+	}
 }
 
 // Component registers a subcontext that has self contained data, actions and signals.
@@ -130,17 +138,19 @@ func (c *Context) getAction(id string) (actionEntry, error) {
 	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
-// the given handler func() on every tick. Use *Routine.UpdateInterval to update the interval.
-func (c *Context) OnInterval(duration time.Duration, handler func()) *OnIntervalRoutine {
-	var cn chan struct{}
-	if c.isComponent() { // components use the chan on the parent page ctx
-		cn = c.parentPageCtx.ctxDisposedChan
+// OnInterval starts a goroutine that executes handler on every tick of the given duration.
+// The goroutine is tied to the context lifecycle and will stop when the context is disposed.
+// Returns a func() that stops the interval when called.
+func (c *Context) OnInterval(duration time.Duration, handler func()) func() {
+	var disposeCh, pageCh chan struct{}
+	if c.isComponent() {
+		disposeCh = c.parentPageCtx.ctxDisposedChan
+		pageCh = c.parentPageCtx.pageStopChan
 	} else {
-		cn = c.ctxDisposedChan
+		disposeCh = c.ctxDisposedChan
+		pageCh = c.pageStopChan
 	}
-	r := newOnIntervalRoutine(cn, duration, handler)
-	return r
+	return newOnInterval(disposeCh, pageCh, duration, handler)
 }
 
 // Signal creates a reactive signal and initializes it with the given value.
@@ -263,15 +273,22 @@ func (c *Context) sendPatch(p patch) {
 // Sync pushes the current view state and signal changes to the browser immediately
 // over the live SSE event stream.
 func (c *Context) Sync() {
+	c.syncView(false)
+}
+
+func (c *Context) syncView(viewTransition bool) {
 	elemsPatch := new(bytes.Buffer)
 	if err := c.view().Render(elemsPatch); err != nil {
 		c.app.logErr(c, "sync view failed: %v", err)
 		return
 	}
-	c.sendPatch(patch{patchTypeElements, elemsPatch.String()})
+	typ := patchType(patchTypeElements)
+	if viewTransition {
+		typ = patchTypeElementsWithVT
+	}
+	c.sendPatch(patch{typ, elemsPatch.String()})
 
 	updatedSigs := c.prepareSignalsForPatch()
-
 	if len(updatedSigs) != 0 {
 		outgoingSigs, _ := json.Marshal(updatedSigs)
 		c.sendPatch(patch{patchTypeSignals, string(outgoingSigs)})
@@ -368,6 +385,46 @@ func (c *Context) ReplaceURLf(format string, a ...any) {
 	c.ReplaceURL(fmt.Sprintf(format, a...))
 }
 
+// resetPageState tears down page-specific state (intervals, subscriptions,
+// actions, signals, fields) without disposing the context itself. The SSE
+// connection and context lifetime are unaffected.
+func (c *Context) resetPageState() {
+	close(c.pageStopChan)
+	c.unsubscribeAll()
+	c.mu.Lock()
+	c.actionRegistry = make(map[string]actionEntry)
+	c.signals = new(sync.Map)
+	c.fields = nil
+	c.pageStopChan = make(chan struct{})
+	c.mu.Unlock()
+}
+
+// Navigate performs an SPA navigation to the given path. It resets page state,
+// runs the target page's init function (with middleware), and pushes the new
+// view over the existing SSE connection with a view transition animation.
+// If popstate is true, replaceState is used instead of pushState.
+func (c *Context) Navigate(path string, popstate bool) {
+	c.navMu.Lock()
+	defer c.navMu.Unlock()
+
+	route, initFn, params := c.app.matchRoute(path)
+	if initFn == nil {
+		c.Redirect(path)
+		return
+	}
+	c.resetPageState()
+	c.route = route
+	c.injectRouteParams(params)
+	initFn(c)
+	c.syncView(true)
+	safe := strings.NewReplacer(`\`, `\\`, `'`, `\'`).Replace(path)
+	if popstate {
+		c.ExecScript(fmt.Sprintf("history.replaceState({},'','%s')", safe))
+	} else {
+		c.ExecScript(fmt.Sprintf("history.pushState({},'','%s')", safe))
+	}
+}
+
 // dispose idempotently tears down this context: unsubscribes all pubsub
 // subscriptions and closes ctxDisposedChan to stop routines and exit the SSE loop.
 func (c *Context) dispose() {
@@ -378,7 +435,7 @@ func (c *Context) dispose() {
 }
 
 // stopAllRoutines closes ctxDisposedChan, broadcasting to all listening
-// goroutines (OnIntervalRoutine, SSE loop) that this context is done.
+// goroutines (OnInterval, SSE loop) that this context is done.
 func (c *Context) stopAllRoutines() {
 	select {
 	case <-c.ctxDisposedChan:
@@ -480,6 +537,50 @@ func (c *Context) unsubscribeAll() {
 	}
 }
 
+// Field creates a signal with validation rules attached.
+// The initial value seeds both the signal and the reset target.
+// The field is tracked on the context so ValidateAll/ResetFields
+// can operate on all fields by default.
+func (c *Context) Field(initial any, rules ...Rule) *Field {
+	f := &Field{
+		signal:     c.Signal(initial),
+		rules:      rules,
+		initialVal: initial,
+	}
+	target := c
+	if c.isComponent() {
+		target = c.parentPageCtx
+	}
+	target.fields = append(target.fields, f)
+	return f
+}
+
+// ValidateAll runs Validate on each field, returning true only if all pass.
+// With no arguments it validates every field tracked on this context.
+func (c *Context) ValidateAll(fields ...*Field) bool {
+	if len(fields) == 0 {
+		fields = c.fields
+	}
+	ok := true
+	for _, f := range fields {
+		if !f.Validate() {
+			ok = false
+		}
+	}
+	return ok
+}
+
+// ResetFields resets each field to its initial value and clears errors.
+// With no arguments it resets every field tracked on this context.
+func (c *Context) ResetFields(fields ...*Field) {
+	if len(fields) == 0 {
+		fields = c.fields
+	}
+	for _, f := range fields {
+		f.Reset()
+	}
+}
+
 func newContext(id string, route string, v *V) *Context {
 	if v == nil {
 		panic("create context failed: app pointer is nil")
@@ -494,8 +595,9 @@ func newContext(id string, route string, v *V) *Context {
 		actionLimiter: newLimiter(v.actionRateLimit, defaultActionRate, defaultActionBurst),
 		actionRegistry:    make(map[string]actionEntry),
 		signals:           new(sync.Map),
-		patchChan:         make(chan patch, 1),
+		patchChan:         make(chan patch, 8),
 		ctxDisposedChan:   make(chan struct{}, 1),
+		pageStopChan:      make(chan struct{}),
 		createdAt:         time.Now(),
 	}
 }

field.go

@@ -0,0 +1,58 @@
+package via
+
+// Field is a signal with built-in validation rules and error state.
+// It embeds *signal, so all signal methods (Bind, String, Int, Bool, SetValue, Text, ID)
+// work transparently.
+type Field struct {
+	*signal
+	rules      []Rule
+	errors     []string
+	initialVal any
+}
+
+// Validate runs all rules against the current value.
+// Clears previous errors, populates new ones, returns true if all rules pass.
+func (f *Field) Validate() bool {
+	f.errors = nil
+	val := f.String()
+	for _, r := range f.rules {
+		if err := r.validate(val); err != nil {
+			f.errors = append(f.errors, err.Error())
+		}
+	}
+	return len(f.errors) == 0
+}
+
+// HasError returns true if this field has any validation errors.
+func (f *Field) HasError() bool {
+	return len(f.errors) > 0
+}
+
+// FirstError returns the first validation error message, or "" if valid.
+func (f *Field) FirstError() string {
+	if len(f.errors) > 0 {
+		return f.errors[0]
+	}
+	return ""
+}
+
+// Errors returns all current validation error messages.
+func (f *Field) Errors() []string {
+	return f.errors
+}
+
+// AddError manually adds an error message (useful for server-side or cross-field validation).
+func (f *Field) AddError(msg string) {
+	f.errors = append(f.errors, msg)
+}
+
+// ClearErrors removes all validation errors from this field.
+func (f *Field) ClearErrors() {
+	f.errors = nil
+}
+
+// Reset restores the field value to its initial value and clears all errors.
+func (f *Field) Reset() {
+	f.SetValue(f.initialVal)
+	f.errors = nil
+}

field_test.go

@@ -0,0 +1,206 @@
+package via
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/ryanhamamura/via/h"
+	"github.com/stretchr/testify/assert"
+)
+
+func newTestField(initial any, rules ...Rule) *Field {
+	v := New()
+	var f *Field
+	v.Page("/", func(c *Context) {
+		f = c.Field(initial, rules...)
+		c.View(func() h.H { return h.Div() })
+	})
+	return f
+}
+
+func TestFieldCreation(t *testing.T) {
+	f := newTestField("hello", Required())
+	assert.Equal(t, "hello", f.String())
+	assert.NotEmpty(t, f.ID())
+}
+
+func TestFieldSignalDelegation(t *testing.T) {
+	f := newTestField(42)
+	assert.Equal(t, "42", f.String())
+	assert.Equal(t, 42, f.Int())
+
+	f.SetValue("new")
+	assert.Equal(t, "new", f.String())
+
+	// Bind returns an h.H element
+	assert.NotNil(t, f.Bind())
+}
+
+func TestFieldValidateSingleRule(t *testing.T) {
+	f := newTestField("", Required())
+	assert.False(t, f.Validate())
+	assert.True(t, f.HasError())
+	assert.Equal(t, "This field is required", f.FirstError())
+
+	f.SetValue("ok")
+	assert.True(t, f.Validate())
+	assert.False(t, f.HasError())
+	assert.Equal(t, "", f.FirstError())
+}
+
+func TestFieldValidateMultipleRules(t *testing.T) {
+	f := newTestField("ab", Required(), MinLen(3))
+	assert.False(t, f.Validate())
+	errs := f.Errors()
+	assert.Len(t, errs, 1)
+	assert.Equal(t, "Must be at least 3 characters", errs[0])
+
+	f.SetValue("")
+	assert.False(t, f.Validate())
+	errs = f.Errors()
+	assert.Len(t, errs, 2)
+}
+
+func TestFieldErrors(t *testing.T) {
+	f := newTestField("")
+	assert.Nil(t, f.Errors())
+	assert.False(t, f.HasError())
+	assert.Equal(t, "", f.FirstError())
+}
+
+func TestFieldAddError(t *testing.T) {
+	f := newTestField("ok")
+	f.AddError("username taken")
+	assert.True(t, f.HasError())
+	assert.Equal(t, "username taken", f.FirstError())
+	assert.Len(t, f.Errors(), 1)
+}
+
+func TestFieldClearErrors(t *testing.T) {
+	f := newTestField("", Required())
+	f.Validate()
+	assert.True(t, f.HasError())
+	f.ClearErrors()
+	assert.False(t, f.HasError())
+}
+
+func TestFieldReset(t *testing.T) {
+	f := newTestField("initial", Required(), MinLen(3))
+	f.SetValue("changed")
+	f.AddError("some error")
+
+	f.Reset()
+	assert.Equal(t, "initial", f.String())
+	assert.False(t, f.HasError())
+}
+
+func TestValidateAll(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		c.Field("", Required(), MinLen(3))
+		c.Field("", Required(), Email())
+		c.View(func() h.H { return h.Div() })
+
+		// both empty → both fail
+		assert.False(t, c.ValidateAll())
+	})
+
+	v2 := New()
+	v2.Page("/", func(c *Context) {
+		c.Field("joe", Required(), MinLen(3))
+		c.Field("joe@x.com", Required(), Email())
+		c.View(func() h.H { return h.Div() })
+
+		assert.True(t, c.ValidateAll())
+	})
+}
+
+func TestValidateAllPartialFailure(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		good := c.Field("valid", Required())
+		bad := c.Field("", Required())
+		c.View(func() h.H { return h.Div() })
+
+		ok := c.ValidateAll()
+		assert.False(t, ok)
+		assert.False(t, good.HasError())
+		assert.True(t, bad.HasError())
+	})
+}
+
+func TestValidateAllSelectiveArgs(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("", Required())
+		b := c.Field("ok", Required())
+		cField := c.Field("", Required())
+		c.View(func() h.H { return h.Div() })
+
+		// only validate a and b — cField should be untouched
+		ok := c.ValidateAll(a, b)
+		assert.False(t, ok)
+		assert.True(t, a.HasError())
+		assert.False(t, b.HasError())
+		assert.False(t, cField.HasError(), "unselected field should not be validated")
+	})
+}
+
+func TestResetFields(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("a", Required())
+		b := c.Field("b", Required())
+		c.View(func() h.H { return h.Div() })
+
+		a.SetValue("changed-a")
+		b.SetValue("changed-b")
+		a.AddError("err")
+
+		c.ResetFields()
+		assert.Equal(t, "a", a.String())
+		assert.Equal(t, "b", b.String())
+		assert.False(t, a.HasError())
+	})
+}
+
+func TestResetFieldsSelectiveArgs(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("a")
+		b := c.Field("b")
+		c.View(func() h.H { return h.Div() })
+
+		a.SetValue("changed-a")
+		b.SetValue("changed-b")
+
+		// only reset a
+		c.ResetFields(a)
+		assert.Equal(t, "a", a.String())
+		assert.Equal(t, "changed-b", b.String(), "unselected field should not be reset")
+	})
+}
+
+func TestFieldValidateClearsPreviousErrors(t *testing.T) {
+	f := newTestField("", Required())
+	f.Validate()
+	assert.True(t, f.HasError())
+
+	f.SetValue("ok")
+	f.Validate()
+	assert.False(t, f.HasError())
+}
+
+func TestFieldCustomValidator(t *testing.T) {
+	f := newTestField("bad", Custom(func(val string) error {
+		if val == "bad" {
+			return fmt.Errorf("no bad words")
+		}
+		return nil
+	}))
+	assert.False(t, f.Validate())
+	assert.Equal(t, "no bad words", f.FirstError())
+
+	f.SetValue("good")
+	assert.True(t, f.Validate())
+}

go.mod

@@ -38,6 +38,5 @@ 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
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

h/datastar.go

@@ -11,3 +11,11 @@ func DataEffect(expression string) H {
 func DataIgnoreMorph() H {
 	return Attr("data-ignore-morph")
 }
+
+// DataViewTransition sets the view-transition-name CSS property on an element
+// via an inline style. Elements with matching names animate between pages
+// during SPA navigation. If the element also needs other inline styles,
+// include view-transition-name directly in the Style() call instead.
+func DataViewTransition(name string) H {
+	return Attr("style", "view-transition-name: "+name)
+}

internal/examples/nats-chatroom/main.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"context"
 	"log"
 	"math/rand"
 	"sync"
@@ -9,7 +8,6 @@ import (
 
 	"github.com/ryanhamamura/via"
 	"github.com/ryanhamamura/via/h"
-	"github.com/ryanhamamura/via/vianats"
 )
 
 var (
@@ -36,15 +34,15 @@ func (u *UserInfo) Avatar() h.H {
 var roomNames = []string{"Go", "Rust", "Python", "JavaScript", "Clojure"}
 
 func main() {
-	ctx := context.Background()
+	v := via.New()
+	v.Config(via.Options{
+		DevMode:       true,
+		DocumentTitle: "NATS Chat",
+		LogLevel:      via.LogLevelInfo,
+		ServerAddress: ":7331",
+	})
 
-	ps, err := vianats.New(ctx, "./data/nats")
-	if err != nil {
-		log.Fatalf("Failed to start embedded NATS: %v", err)
-	}
-	defer ps.Close()
-
-	err = vianats.EnsureStream(ps, vianats.StreamConfig{
+	err := via.EnsureStream(v, via.StreamConfig{
 		Name:     "CHAT",
 		Subjects: []string{"chat.>"},
 		MaxMsgs:  1000,
@@ -54,15 +52,6 @@ func main() {
 		log.Fatalf("Failed to ensure stream: %v", err)
 	}
 
-	v := via.New()
-	v.Config(via.Options{
-		DevMode:       true,
-		DocumentTitle: "NATS Chat",
-		LogLevel:      via.LogLevelInfo,
-		ServerAddress: ":7331",
-		PubSub:        ps,
-	})
-
 	v.AppendToHead(
 		h.Link(h.Rel("stylesheet"), h.Href("https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css")),
 		h.StyleEl(h.Raw(`
@@ -148,7 +137,7 @@ func main() {
 			subject := "chat.room." + room
 
 			// Replay history from JetStream
-			if hist, err := vianats.ReplayHistory[ChatMessage](ps, subject, 50); err == nil {
+			if hist, err := via.ReplayHistory[ChatMessage](v, subject, 50); err == nil {
 				messages = hist
 			}
 

internal/examples/pubsub-crud/main.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"context"
 	"crypto/rand"
 	"fmt"
 	"html"
@@ -11,7 +10,6 @@ import (
 
 	"github.com/ryanhamamura/via"
 	"github.com/ryanhamamura/via/h"
-	"github.com/ryanhamamura/via/vianats"
 )
 
 var WithSignal = via.WithSignal
@@ -49,15 +47,15 @@ func findBookmark(id string) (Bookmark, int) {
 }
 
 func main() {
-	ctx := context.Background()
+	v := via.New()
+	v.Config(via.Options{
+		DevMode:       true,
+		DocumentTitle: "Bookmarks",
+		LogLevel:      via.LogLevelInfo,
+		ServerAddress: ":7331",
+	})
 
-	ps, err := vianats.New(ctx, "./data/nats")
-	if err != nil {
-		log.Fatalf("Failed to start embedded NATS: %v", err)
-	}
-	defer ps.Close()
-
-	err = vianats.EnsureStream(ps, vianats.StreamConfig{
+	err := via.EnsureStream(v, via.StreamConfig{
 		Name:     "BOOKMARKS",
 		Subjects: []string{"bookmarks.>"},
 		MaxMsgs:  1000,
@@ -67,15 +65,6 @@ func main() {
 		log.Fatalf("Failed to ensure stream: %v", err)
 	}
 
-	v := via.New()
-	v.Config(via.Options{
-		DevMode:       true,
-		DocumentTitle: "Bookmarks",
-		LogLevel:      via.LogLevelInfo,
-		ServerAddress: ":7331",
-		PubSub:        ps,
-	})
-
 	v.AppendToHead(
 		h.Link(h.Rel("stylesheet"), h.Href("https://cdn.jsdelivr.net/npm/daisyui@4/dist/full.min.css")),
 		h.Script(h.Src("https://cdn.tailwindcss.com")),

internal/examples/realtimechart/main.go

@@ -37,29 +37,33 @@ func main() {
 			return 1000 / time.Duration(refreshRate.Int()) * time.Millisecond
 		}
 
-		updateData := c.OnInterval(computedTickDuration(), func() {
-			ts := time.Now().UnixMilli()
-			val := rand.ExpFloat64() * 10
+		var stopUpdate func()
+		startInterval := func() {
+			stopUpdate = c.OnInterval(computedTickDuration(), func() {
+				ts := time.Now().UnixMilli()
+				val := rand.ExpFloat64() * 10
 
-			c.ExecScript(fmt.Sprintf(`
-			if (myChart) {
-				myChart.appendData({seriesIndex: 0, data: [[%d, %f]]});
-				myChart.setOption({},{notMerge:false,lazyUpdate:true});
-			};
-		`, ts, val))
-		})
-		updateData.Start()
+				c.ExecScript(fmt.Sprintf(`
+				if (myChart) {
+					myChart.appendData({seriesIndex: 0, data: [[%d, %f]]});
+					myChart.setOption({},{notMerge:false,lazyUpdate:true});
+				};
+			`, ts, val))
+			})
+		}
+		startInterval()
 
 		updateRefreshRate := c.Action(func() {
-			updateData.UpdateInterval(computedTickDuration())
+			stopUpdate()
+			startInterval()
 		})
 
 		toggleIsLive := c.Action(func() {
 			isLive = isLiveSig.Bool()
 			if isLive {
-				updateData.Start()
+				startInterval()
 			} else {
-				updateData.Stop()
+				stopUpdate()
 			}
 		})
 		c.View(func() h.H {

internal/examples/signup/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"github.com/ryanhamamura/via"
+	"github.com/ryanhamamura/via/h"
+)
+
+func main() {
+	v := via.New()
+	v.Config(via.Options{
+		DocumentTitle: "Signup",
+		ServerAddress: ":8080",
+	})
+
+	v.AppendToHead(h.StyleEl(h.Raw(`
+		body { font-family: system-ui, sans-serif; max-width: 420px; margin: 2rem auto; padding: 0 1rem; }
+		label { display: block; font-weight: 600; margin-top: 1rem; }
+		input { display: block; width: 100%; padding: 0.4rem; margin-top: 0.25rem; box-sizing: border-box; }
+		.error { color: #c00; font-size: 0.85rem; margin-top: 0.2rem; }
+		.success { color: #080; margin-top: 1rem; }
+		.actions { margin-top: 1.5rem; display: flex; gap: 0.5rem; }
+	`)))
+
+	v.Page("/", func(c *via.Context) {
+		username := c.Field("", via.Required(), via.MinLen(3), via.MaxLen(20))
+		email := c.Field("", via.Required(), via.Email())
+		age := c.Field("", via.Required(), via.Min(13), via.Max(120))
+		// Optional field — only validated when non-empty
+		website := c.Field("", via.Pattern(`^$|^https?://\S+$`, "Must be a valid URL"))
+
+		var success string
+
+		signup := c.Action(func() {
+			success = ""
+			if !c.ValidateAll() {
+				c.Sync()
+				return
+			}
+			// Server-side check
+			if username.String() == "admin" {
+				username.AddError("Username is already taken")
+				c.Sync()
+				return
+			}
+			success = "Account created for " + username.String() + "!"
+			c.ResetFields()
+			c.Sync()
+		})
+
+		reset := c.Action(func() {
+			success = ""
+			c.ResetFields()
+			c.Sync()
+		})
+
+		c.View(func() h.H {
+			return h.Div(
+				h.H1(h.Text("Sign Up")),
+
+				h.Label(h.Text("Username")),
+				h.Input(h.Type("text"), h.Placeholder("pick a username"), username.Bind()),
+				h.If(username.HasError(), h.Div(h.Class("error"), h.Text(username.FirstError()))),
+
+				h.Label(h.Text("Email")),
+				h.Input(h.Type("email"), h.Placeholder("you@example.com"), email.Bind()),
+				h.If(email.HasError(), h.Div(h.Class("error"), h.Text(email.FirstError()))),
+
+				h.Label(h.Text("Age")),
+				h.Input(h.Type("number"), h.Placeholder("your age"), age.Bind()),
+				h.If(age.HasError(), h.Div(h.Class("error"), h.Text(age.FirstError()))),
+
+				h.Label(h.Text("Website (optional)")),
+				h.Input(h.Type("url"), h.Placeholder("https://example.com"), website.Bind()),
+				h.If(website.HasError(), h.Div(h.Class("error"), h.Text(website.FirstError()))),
+
+				h.Div(h.Class("actions"),
+					h.Button(h.Text("Sign Up"), signup.OnClick()),
+					h.Button(h.Text("Reset"), reset.OnClick()),
+				),
+
+				h.If(success != "", h.P(h.Class("success"), h.Text(success))),
+			)
+		})
+	})
+
+	v.Start()
+}

internal/examples/spa/main.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/ryanhamamura/via"
+	. "github.com/ryanhamamura/via/h"
+)
+
+func main() {
+	v := via.New()
+	v.Config(via.Options{
+		DocumentTitle: "SPA Navigation",
+		ServerAddress: ":7331",
+	})
+
+	v.AppendToHead(
+		Raw(`<link rel="preconnect" href="https://fonts.googleapis.com">`),
+		Raw(`<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>`),
+		Raw(`<link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;600;700&display=swap" rel="stylesheet">`),
+		Raw(`<style>body{font-family:'Inter',sans-serif;margin:0;background:#111;color:#eee}</style>`),
+	)
+
+	v.Layout(func(content func() H) H {
+		return Div(
+			Nav(
+				Style("display:flex;gap:1rem;padding:1rem;background:#222;"),
+				A(Href("/"), Text("Home"), Style("color:#fff")),
+				A(Href("/counter"), Text("Counter"), Style("color:#fff")),
+				A(Href("/clock"), Text("Clock"), Style("color:#fff")),
+				A(Href("https://github.com"), Text("GitHub (external)"), Style("color:#888")),
+				A(Href("/"), Text("Full Reload"), Attr("data-via-no-boost"), Style("color:#f88")),
+			),
+			Main(Style("padding:1rem"), content()),
+		)
+	})
+
+	// Home page
+	v.Page("/", func(c *via.Context) {
+		goCounter := c.Action(func() { c.Navigate("/counter", false) })
+
+		c.View(func() H {
+			return Div(
+				H1(Text("Home"), DataViewTransition("page-title")),
+				P(Text("Click the nav links above — no page reload, no white flash.")),
+				P(Text("Or navigate programmatically:")),
+				Button(Text("Go to Counter"), goCounter.OnClick()),
+			)
+		})
+	})
+
+	// Counter page — demonstrates signals and actions survive within a page,
+	// but reset on navigate away and back.
+	v.Page("/counter", func(c *via.Context) {
+		count := 0
+		increment := c.Action(func() { count++; c.Sync() })
+		goHome := c.Action(func() { c.Navigate("/", false) })
+
+		c.View(func() H {
+			return Div(
+				H1(Text("Counter"), DataViewTransition("page-title")),
+				P(Textf("Count: %d", count)),
+				Button(Text("+1"), increment.OnClick()),
+				Button(Text("Go Home"), goHome.OnClick(), Style("margin-left:0.5rem")),
+			)
+		})
+	})
+
+	// Clock page — demonstrates OnInterval cleanup on navigate.
+	v.Page("/clock", func(c *via.Context) {
+		now := time.Now().Format("15:04:05")
+		c.OnInterval(time.Second, func() {
+			now = time.Now().Format("15:04:05")
+			c.Sync()
+		})
+
+		c.View(func() H {
+			return Div(
+				H1(Text("Clock"), DataViewTransition("page-title")),
+				P(Text("This page has an OnInterval that ticks every second.")),
+				P(Textf("Current time: %s", now)),
+				P(Text("Navigate away and back — the old interval stops, a new one starts.")),
+				P(Textf("Proof this is a fresh page init: random = %d", time.Now().UnixNano()%1000)),
+			)
+		})
+	})
+
+	fmt.Println("SPA example running at http://localhost:7331")
+	v.Start()
+}

nats.go

@@ -0,0 +1,190 @@
+package via
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/delaneyj/toolbelt/embeddednats"
+	"github.com/nats-io/nats.go"
+)
+
+// defaultNATS is the process-scoped embedded NATS server.
+type defaultNATS struct {
+	server  *embeddednats.Server
+	nc      *nats.Conn
+	js      nats.JetStreamContext
+	cancel  context.CancelFunc
+	dataDir string
+}
+
+var (
+	sharedNATS     *defaultNATS
+	sharedNATSOnce sync.Once
+	sharedNATSErr  error
+)
+
+// getSharedNATS returns a process-level singleton embedded NATS server.
+// The server starts once and is reused across all V instances.
+func getSharedNATS() (*defaultNATS, error) {
+	sharedNATSOnce.Do(func() {
+		sharedNATS, sharedNATSErr = startDefaultNATS()
+	})
+	return sharedNATS, sharedNATSErr
+}
+
+func startDefaultNATS() (dn *defaultNATS, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("nats server panic: %v", r)
+		}
+	}()
+
+	dataDir, err := os.MkdirTemp("", "via-nats-*")
+	if err != nil {
+		return nil, fmt.Errorf("create temp dir: %w", err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	ns, err := embeddednats.New(ctx, embeddednats.WithDirectory(dataDir))
+	if err != nil {
+		cancel()
+		os.RemoveAll(dataDir)
+		return nil, fmt.Errorf("start embedded nats: %w", err)
+	}
+	ns.WaitForServer()
+
+	nc, err := ns.Client()
+	if err != nil {
+		ns.Close()
+		cancel()
+		os.RemoveAll(dataDir)
+		return nil, fmt.Errorf("connect nats client: %w", err)
+	}
+
+	js, err := nc.JetStream()
+	if err != nil {
+		nc.Close()
+		ns.Close()
+		cancel()
+		os.RemoveAll(dataDir)
+		return nil, fmt.Errorf("init jetstream: %w", err)
+	}
+
+	return &defaultNATS{
+		server:  ns,
+		nc:      nc,
+		js:      js,
+		cancel:  cancel,
+		dataDir: dataDir,
+	}, nil
+}
+
+func (n *defaultNATS) Publish(subject string, data []byte) error {
+	return n.nc.Publish(subject, data)
+}
+
+func (n *defaultNATS) Subscribe(subject string, handler func(data []byte)) (Subscription, error) {
+	sub, err := n.nc.Subscribe(subject, func(msg *nats.Msg) {
+		handler(msg.Data)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return sub, nil
+}
+
+// natsRef wraps a shared defaultNATS as a PubSub. Close is a no-op because
+// the underlying server is process-scoped and outlives individual V instances.
+type natsRef struct {
+	dn *defaultNATS
+}
+
+func (r *natsRef) Publish(subject string, data []byte) error {
+	return r.dn.Publish(subject, data)
+}
+
+func (r *natsRef) Subscribe(subject string, handler func(data []byte)) (Subscription, error) {
+	return r.dn.Subscribe(subject, handler)
+}
+
+func (r *natsRef) Close() error {
+	return nil
+}
+
+// NATSConn returns the underlying NATS connection from the built-in embedded
+// server, or nil if a custom PubSub backend is in use.
+func (v *V) NATSConn() *nats.Conn {
+	if v.defaultNATS != nil {
+		return v.defaultNATS.nc
+	}
+	return nil
+}
+
+// JetStream returns the JetStream context from the built-in embedded server,
+// or nil if a custom PubSub backend is in use.
+func (v *V) JetStream() nats.JetStreamContext {
+	if v.defaultNATS != nil {
+		return v.defaultNATS.js
+	}
+	return nil
+}
+
+// StreamConfig holds the parameters for creating or updating a JetStream stream.
+type StreamConfig struct {
+	Name     string
+	Subjects []string
+	MaxMsgs  int64
+	MaxAge   time.Duration
+}
+
+// EnsureStream creates or updates a JetStream stream matching cfg.
+func EnsureStream(v *V, cfg StreamConfig) error {
+	js := v.JetStream()
+	if js == nil {
+		return fmt.Errorf("jetstream not available")
+	}
+	_, err := js.AddStream(&nats.StreamConfig{
+		Name:      cfg.Name,
+		Subjects:  cfg.Subjects,
+		Retention: nats.LimitsPolicy,
+		MaxMsgs:   cfg.MaxMsgs,
+		MaxAge:    cfg.MaxAge,
+	})
+	return err
+}
+
+// ReplayHistory fetches the last limit messages from subject,
+// deserializing each as T. Returns an empty slice if nothing is available.
+func ReplayHistory[T any](v *V, subject string, limit int) ([]T, error) {
+	js := v.JetStream()
+	if js == nil {
+		return nil, fmt.Errorf("jetstream not available")
+	}
+	sub, err := js.SubscribeSync(subject, nats.DeliverAll(), nats.OrderedConsumer())
+	if err != nil {
+		return nil, err
+	}
+	defer sub.Unsubscribe()
+
+	var msgs []T
+	for {
+		raw, err := sub.NextMsg(200 * time.Millisecond)
+		if err != nil {
+			break
+		}
+		var msg T
+		if json.Unmarshal(raw.Data, &msg) == nil {
+			msgs = append(msgs, msg)
+		}
+	}
+
+	if limit > 0 && len(msgs) > limit {
+		msgs = msgs[len(msgs)-limit:]
+	}
+	return msgs, nil
+}

nats_test.go

@@ -2,7 +2,6 @@ package via
 
 import (
 	"sync"
-	"sync/atomic"
 	"testing"
 	"time"
 
@@ -11,88 +10,36 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-type mockHandler struct {
-	id     int64
-	fn     func([]byte)
-	active atomic.Bool
-}
-
-// mockPubSub implements PubSub for testing without NATS.
-type mockPubSub struct {
-	mu    sync.Mutex
-	subs  map[string][]*mockHandler
-	nextID atomic.Int64
-}
-
-func newMockPubSub() *mockPubSub {
-	return &mockPubSub{subs: make(map[string][]*mockHandler)}
-}
-
-func (m *mockPubSub) Publish(subject string, data []byte) error {
-	m.mu.Lock()
-	handlers := make([]*mockHandler, len(m.subs[subject]))
-	copy(handlers, m.subs[subject])
-	m.mu.Unlock()
-	for _, h := range handlers {
-		if h.active.Load() {
-			h.fn(data)
-		}
-	}
-	return nil
-}
-
-func (m *mockPubSub) Subscribe(subject string, handler func(data []byte)) (Subscription, error) {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	mh := &mockHandler{
-		id: m.nextID.Add(1),
-		fn: handler,
-	}
-	mh.active.Store(true)
-	m.subs[subject] = append(m.subs[subject], mh)
-	return &mockSub{handler: mh}, nil
-}
-
-func (m *mockPubSub) Close() error { return nil }
-
-type mockSub struct {
-	handler *mockHandler
-}
-
-func (s *mockSub) Unsubscribe() error {
-	s.handler.active.Store(false)
-	return nil
-}
-
 func TestPubSub_RoundTrip(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	var received []byte
-	var wg sync.WaitGroup
-	wg.Add(1)
+	done := make(chan struct{})
 
 	c := newContext("test-ctx", "/", v)
 	c.View(func() h.H { return h.Div() })
 
 	_, err := c.Subscribe("test.topic", func(data []byte) {
 		received = data
-		wg.Done()
+		close(done)
 	})
 	require.NoError(t, err)
 
 	err = c.Publish("test.topic", []byte("hello"))
 	require.NoError(t, err)
 
-	wg.Wait()
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for message")
+	}
 	assert.Equal(t, []byte("hello"), received)
 }
 
 func TestPubSub_MultipleSubscribers(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	var mu sync.Mutex
 	var results []string
@@ -119,7 +66,17 @@ func TestPubSub_MultipleSubscribers(t *testing.T) {
 	})
 
 	c1.Publish("broadcast", []byte("msg"))
-	wg.Wait()
+
+	done := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for messages")
+	}
 
 	assert.Len(t, results, 2)
 	assert.Contains(t, results, "c1:msg")
@@ -127,9 +84,8 @@ func TestPubSub_MultipleSubscribers(t *testing.T) {
 }
 
 func TestPubSub_SubscriptionCleanupOnDispose(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	c := newContext("cleanup-ctx", "/", v)
 	c.View(func() h.H { return h.Div() })
@@ -144,9 +100,8 @@ func TestPubSub_SubscriptionCleanupOnDispose(t *testing.T) {
 }
 
 func TestPubSub_ManualUnsubscribe(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	c := newContext("unsub-ctx", "/", v)
 	c.View(func() h.H { return h.Div() })
@@ -160,28 +115,13 @@ func TestPubSub_ManualUnsubscribe(t *testing.T) {
 	sub.Unsubscribe()
 
 	c.Publish("topic", []byte("ignored"))
-	time.Sleep(10 * time.Millisecond)
+	time.Sleep(50 * time.Millisecond)
 	assert.False(t, called)
 }
 
-func TestPubSub_NoOpWhenNotConfigured(t *testing.T) {
-	v := New()
-
-	c := newContext("noop-ctx", "/", v)
-	c.View(func() h.H { return h.Div() })
-
-	err := c.Publish("topic", []byte("data"))
-	assert.Error(t, err)
-
-	sub, err := c.Subscribe("topic", func(data []byte) {})
-	assert.Error(t, err)
-	assert.Nil(t, sub)
-}
-
 func TestPubSub_NoOpDuringPanicCheck(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	// Panic-check context has id=""
 	c := newContext("", "/", v)

navigate.js

@@ -0,0 +1,51 @@
+(function() {
+  const meta = document.querySelector('meta[data-signals]');
+  if (!meta) return;
+  const raw = meta.getAttribute('data-signals');
+  const parsed = JSON.parse(raw.replace(/'/g, '"'));
+  const ctxID = parsed['via-ctx'];
+  const csrf = parsed['via-csrf'];
+  if (!ctxID || !csrf) return;
+
+  function navigate(url, popstate) {
+    const params = new URLSearchParams({
+      'via-ctx': ctxID,
+      'via-csrf': csrf,
+      'url': url,
+    });
+    if (popstate) params.set('popstate', '1');
+    fetch('/_navigate', {
+      method: 'POST',
+      headers: {'Content-Type': 'application/x-www-form-urlencoded'},
+      body: params.toString()
+    }).then(function(res) {
+      if (!res.ok) window.location.href = url;
+    }).catch(function() {
+      window.location.href = url;
+    });
+  }
+
+  document.addEventListener('click', function(e) {
+    var el = e.target;
+    while (el && el.tagName !== 'A') el = el.parentElement;
+    if (!el) return;
+    if (e.ctrlKey || e.metaKey || e.shiftKey || e.altKey) return;
+    if (el.hasAttribute('target')) return;
+    if (el.hasAttribute('data-via-no-boost')) return;
+    var href = el.getAttribute('href');
+    if (!href || href.startsWith('#')) return;
+    try {
+      var url = new URL(href, window.location.origin);
+      if (url.origin !== window.location.origin) return;
+      e.preventDefault();
+      navigate(url.pathname + url.search + url.hash);
+    } catch(_) {}
+  });
+
+  var ready = false;
+  window.addEventListener('popstate', function() {
+    if (!ready) return;
+    navigate(window.location.pathname + window.location.search + window.location.hash, true);
+  });
+  setTimeout(function() { ready = true; }, 0);
+})();

pubsub.go

@@ -1,7 +1,8 @@
 package via
 
 // PubSub is an interface for publish/subscribe messaging backends.
-// The vianats sub-package provides an embedded NATS implementation.
+// By default, New() starts an embedded NATS server. Supply a custom
+// implementation via Config(Options{PubSub: yourBackend}) to override.
 type PubSub interface {
 	Publish(subject string, data []byte) error
 	Subscribe(subject string, handler func(data []byte)) (Subscription, error)

pubsub_helpers_test.go

@@ -1,8 +1,8 @@
 package via
 
 import (
-	"sync"
 	"testing"
+	"time"
 
 	"github.com/ryanhamamura/via/h"
 	"github.com/stretchr/testify/assert"
@@ -10,9 +10,8 @@ import (
 )
 
 func TestPublishSubscribe_RoundTrip(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	type event struct {
 		Name  string `json:"name"`
@@ -20,30 +19,32 @@ func TestPublishSubscribe_RoundTrip(t *testing.T) {
 	}
 
 	var got event
-	var wg sync.WaitGroup
-	wg.Add(1)
+	done := make(chan struct{})
 
 	c := newContext("typed-ctx", "/", v)
 	c.View(func() h.H { return h.Div() })
 
 	_, err := Subscribe(c, "events", func(e event) {
 		got = e
-		wg.Done()
+		close(done)
 	})
 	require.NoError(t, err)
 
 	err = Publish(c, "events", event{Name: "click", Count: 42})
 	require.NoError(t, err)
 
-	wg.Wait()
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for message")
+	}
 	assert.Equal(t, "click", got.Name)
 	assert.Equal(t, 42, got.Count)
 }
 
 func TestSubscribe_SkipsBadJSON(t *testing.T) {
-	ps := newMockPubSub()
 	v := New()
-	v.Config(Options{PubSub: ps})
+	defer v.Shutdown()
 
 	type msg struct {
 		Text string `json:"text"`
@@ -62,5 +63,6 @@ func TestSubscribe_SkipsBadJSON(t *testing.T) {
 	err = c.Publish("topic", []byte("not json"))
 	require.NoError(t, err)
 
+	time.Sleep(50 * time.Millisecond)
 	assert.False(t, called)
 }

routine.go

@@ -1,76 +1,34 @@
 package via
 
 import (
-	"sync"
 	"sync/atomic"
 	"time"
 )
 
-// OnIntervalRoutine allows for defining concurrent goroutines safely. Goroutines started by *OnIntervalRoutine
-// are tied to the *Context lifecycle.
-type OnIntervalRoutine struct {
-	mu             sync.RWMutex
-	ctxDisposed    chan struct{}
-	localInterrupt chan struct{}
-	isRunning      atomic.Bool
-	routineFn      func()
-	tckDuration    time.Duration
-	updateTkrChan  chan time.Duration
-}
+func newOnInterval(ctxDisposedChan, pageStopChan chan struct{}, duration time.Duration, handler func()) func() {
+	localInterrupt := make(chan struct{})
+	var stopped atomic.Bool
 
-// UpdateInterval sets a new interval duration for the internal *time.Ticker. If the provided
-// duration is equal of less than 0, UpdateInterval does nothing.
-func (r *OnIntervalRoutine) UpdateInterval(d time.Duration) {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-	r.tckDuration = d
-	r.updateTkrChan <- d
-
-}
-
-// Start executes the predifined goroutine. If no predifined goroutine exists, or it already
-// started, Start does nothing.
-func (r *OnIntervalRoutine) Start() {
-	if !r.isRunning.CompareAndSwap(false, true) || r.routineFn == nil {
-		return
-	}
-	go r.routineFn()
-}
-
-// Stop interrupts the predifined goroutine. If no predifined goroutine exists, or it already
-// ustopped, Stop does nothing.
-func (r *OnIntervalRoutine) Stop() {
-	if !r.isRunning.CompareAndSwap(true, false) || r.routineFn == nil {
-		return
-	}
-	r.localInterrupt <- struct{}{}
-}
-
-func newOnIntervalRoutine(ctxDisposedChan chan struct{},
-	duration time.Duration, handler func()) *OnIntervalRoutine {
-	r := &OnIntervalRoutine{
-		ctxDisposed:    ctxDisposedChan,
-		localInterrupt: make(chan struct{}),
-		updateTkrChan:  make(chan time.Duration),
-	}
-	r.tckDuration = duration
-	r.routineFn = func() {
-		r.mu.RLock()
-		tkr := time.NewTicker(r.tckDuration)
-		r.mu.RUnlock()
-		defer tkr.Stop() // clean up the ticker when routine stops
+	go func() {
+		tkr := time.NewTicker(duration)
+		defer tkr.Stop()
 		for {
 			select {
-			case <-r.ctxDisposed: // dispose of the routine when ctx is disposed
+			case <-ctxDisposedChan:
 				return
-			case <-r.localInterrupt: // dispose of the routine on interrupt signal
+			case <-pageStopChan:
+				return
+			case <-localInterrupt:
 				return
-			case d := <-r.updateTkrChan:
-				tkr.Reset(d)
 			case <-tkr.C:
 				handler()
 			}
 		}
+	}()
+
+	return func() {
+		if stopped.CompareAndSwap(false, true) {
+			close(localInterrupt)
+		}
 	}
-	return r
 }

rule.go

@@ -0,0 +1,130 @@
+package via
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+)
+
+// Rule defines a single validation check for a Field.
+type Rule struct {
+	validate func(val string) error
+}
+
+// Required rejects empty or whitespace-only values.
+func Required(msg ...string) Rule {
+	m := "This field is required"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if strings.TrimSpace(val) == "" {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// MinLen rejects values shorter than n characters.
+func MinLen(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at least %d characters", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if utf8.RuneCountInString(val) < n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// MaxLen rejects values longer than n characters.
+func MaxLen(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at most %d characters", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if utf8.RuneCountInString(val) > n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Min parses the value as an integer and rejects values less than n.
+func Min(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at least %d", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		v, err := strconv.Atoi(val)
+		if err != nil {
+			return errors.New("Must be a valid number")
+		}
+		if v < n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Max parses the value as an integer and rejects values greater than n.
+func Max(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at most %d", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		v, err := strconv.Atoi(val)
+		if err != nil {
+			return errors.New("Must be a valid number")
+		}
+		if v > n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Pattern rejects values that don't match the regular expression re.
+func Pattern(re string, msg ...string) Rule {
+	m := "Invalid format"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	compiled := regexp.MustCompile(re)
+	return Rule{func(val string) error {
+		if !compiled.MatchString(val) {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+var emailRegexp = regexp.MustCompile(`^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$`)
+
+// Email rejects values that don't look like an email address.
+func Email(msg ...string) Rule {
+	m := "Invalid email address"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if !emailRegexp.MatchString(val) {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Custom creates a rule from a user-provided validation function.
+// The function should return nil for valid input and an error for invalid input.
+func Custom(fn func(string) error) Rule {
+	return Rule{validate: fn}
+}

rule_test.go

@@ -0,0 +1,116 @@
+package via
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRequired(t *testing.T) {
+	r := Required()
+	assert.NoError(t, r.validate("hello"))
+	assert.Error(t, r.validate(""))
+	assert.Error(t, r.validate("   "))
+}
+
+func TestRequiredCustomMessage(t *testing.T) {
+	r := Required("name needed")
+	err := r.validate("")
+	assert.EqualError(t, err, "name needed")
+}
+
+func TestMinLen(t *testing.T) {
+	r := MinLen(3)
+	assert.NoError(t, r.validate("abc"))
+	assert.NoError(t, r.validate("abcd"))
+	assert.Error(t, r.validate("ab"))
+	assert.Error(t, r.validate(""))
+}
+
+func TestMinLenCustomMessage(t *testing.T) {
+	r := MinLen(5, "too short")
+	err := r.validate("ab")
+	assert.EqualError(t, err, "too short")
+}
+
+func TestMaxLen(t *testing.T) {
+	r := MaxLen(5)
+	assert.NoError(t, r.validate("abc"))
+	assert.NoError(t, r.validate("abcde"))
+	assert.Error(t, r.validate("abcdef"))
+}
+
+func TestMaxLenCustomMessage(t *testing.T) {
+	r := MaxLen(2, "too long")
+	err := r.validate("abc")
+	assert.EqualError(t, err, "too long")
+}
+
+func TestMin(t *testing.T) {
+	r := Min(5)
+	assert.NoError(t, r.validate("5"))
+	assert.NoError(t, r.validate("10"))
+	assert.Error(t, r.validate("4"))
+	assert.Error(t, r.validate("abc"))
+}
+
+func TestMinCustomMessage(t *testing.T) {
+	r := Min(10, "need 10+")
+	err := r.validate("3")
+	assert.EqualError(t, err, "need 10+")
+}
+
+func TestMax(t *testing.T) {
+	r := Max(10)
+	assert.NoError(t, r.validate("10"))
+	assert.NoError(t, r.validate("5"))
+	assert.Error(t, r.validate("11"))
+	assert.Error(t, r.validate("abc"))
+}
+
+func TestMaxCustomMessage(t *testing.T) {
+	r := Max(5, "too big")
+	err := r.validate("6")
+	assert.EqualError(t, err, "too big")
+}
+
+func TestPattern(t *testing.T) {
+	r := Pattern(`^\d{3}$`)
+	assert.NoError(t, r.validate("123"))
+	assert.Error(t, r.validate("12"))
+	assert.Error(t, r.validate("abcd"))
+}
+
+func TestPatternCustomMessage(t *testing.T) {
+	r := Pattern(`^\d+$`, "digits only")
+	err := r.validate("abc")
+	assert.EqualError(t, err, "digits only")
+}
+
+func TestEmail(t *testing.T) {
+	r := Email()
+	assert.NoError(t, r.validate("user@example.com"))
+	assert.NoError(t, r.validate("a.b+c@foo.co"))
+	assert.Error(t, r.validate("notanemail"))
+	assert.Error(t, r.validate("@example.com"))
+	assert.Error(t, r.validate("user@"))
+	assert.Error(t, r.validate(""))
+}
+
+func TestEmailCustomMessage(t *testing.T) {
+	r := Email("bad email")
+	err := r.validate("nope")
+	assert.EqualError(t, err, "bad email")
+}
+
+func TestCustom(t *testing.T) {
+	r := Custom(func(val string) error {
+		if val != "magic" {
+			return fmt.Errorf("must be magic")
+		}
+		return nil
+	})
+	assert.NoError(t, r.validate("magic"))
+	assert.EqualError(t, r.validate("other"), "must be magic")
+}

via.go

@@ -35,6 +35,9 @@ import (
 //go:embed datastar.js
 var datastarJS []byte
 
+//go:embed navigate.js
+var navigateJS []byte
+
 // V is the root application.
 // It manages page routing, user sessions, and SSE connections for live updates.
 type V struct {
@@ -47,14 +50,17 @@ type V struct {
 	documentHeadIncludes []h.H
 	documentFootIncludes []h.H
 	devModePageInitFnMap map[string]func(*Context)
+	pageRegistry         map[string]func(*Context)
 	sessionManager       *scs.SessionManager
 	pubsub               PubSub
+	defaultNATS          *defaultNATS
 	actionRateLimit      RateLimitConfig
 	datastarPath         string
 	datastarContent      []byte
 	datastarOnce         sync.Once
 	reaperStop           chan struct{}
 	middleware           []Middleware
+	layout               func(func() h.H) h.H
 }
 
 func (v *V) logEvent(evt *zerolog.Event, c *Context) *zerolog.Event {
@@ -130,6 +136,7 @@ func (v *V) Config(cfg Options) {
 		v.datastarPath = cfg.DatastarPath
 	}
 	if cfg.PubSub != nil {
+		v.defaultNATS = nil
 		v.pubsub = cfg.PubSub
 	}
 	if cfg.ContextTTL != 0 {
@@ -194,6 +201,7 @@ func (v *V) page(route string, raw, wrapped func(*Context)) {
 		c.stopAllRoutines()
 	}()
 
+	v.pageRegistry[route] = wrapped
 	if v.cfg.DevMode {
 		v.devModePageInitFnMap[route] = wrapped
 	}
@@ -221,6 +229,8 @@ func (v *V) page(route string, raw, wrapped func(*Context)) {
 			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))),
+			h.Meta(h.Attr("name", "view-transition"), h.Attr("content", "same-origin")),
+			h.Script(h.Raw(string(navigateJS))),
 		)
 
 		bodyElements := []h.H{c.view()}
@@ -379,6 +389,7 @@ func (v *V) Shutdown() {
 			v.logErr(nil, "pubsub close error: %v", err)
 		}
 	}
+	v.defaultNATS = nil
 
 	v.logInfo(nil, "shutdown complete")
 }
@@ -408,6 +419,11 @@ func (v *V) HTTPServeMux() *http.ServeMux {
 	return v.mux
 }
 
+// PubSub returns the configured PubSub backend, or nil if none is set.
+func (v *V) PubSub() PubSub {
+	return v.pubsub
+}
+
 // Static serves files from a filesystem directory at the given URL prefix.
 //
 // Example:
@@ -554,6 +570,7 @@ type patchType int
 
 const (
 	patchTypeElements = iota
+	patchTypeElementsWithVT
 	patchTypeSignals
 	patchTypeScript
 	patchTypeRedirect
@@ -574,6 +591,7 @@ func New() *V {
 		logger:               newConsoleLogger(zerolog.InfoLevel),
 		contextRegistry:      make(map[string]*Context),
 		devModePageInitFnMap: make(map[string]func(*Context)),
+		pageRegistry:         make(map[string]func(*Context)),
 		sessionManager:       scs.New(),
 		datastarPath:         "/_datastar.js",
 		datastarContent:      datastarJS,
@@ -624,11 +642,16 @@ func New() *V {
 				switch patch.typ {
 				case patchTypeElements:
 					if err := sse.PatchElements(patch.content); err != nil {
-						// Only log if connection wasn't closed (avoids noise during shutdown/tests)
 						if sse.Context().Err() == nil {
 							v.logErr(c, "PatchElements failed: %v", err)
 						}
 					}
+				case patchTypeElementsWithVT:
+					if err := sse.PatchElements(patch.content, datastar.WithViewTransitions()); err != nil {
+						if sse.Context().Err() == nil {
+							v.logErr(c, "PatchElements (view transition) failed: %v", err)
+						}
+					}
 				case patchTypeSignals:
 					if err := sse.PatchSignals([]byte(patch.content)); err != nil {
 						if sse.Context().Err() == nil {
@@ -708,6 +731,39 @@ func New() *V {
 		}
 	})
 
+	v.mux.HandleFunc("POST /_navigate", func(w http.ResponseWriter, r *http.Request) {
+		_ = r.ParseForm()
+		cID := r.FormValue("via-ctx")
+		csrfToken := r.FormValue("via-csrf")
+		navURL := r.FormValue("url")
+		popstate := r.FormValue("popstate") == "1"
+
+		if cID == "" || navURL == "" || !strings.HasPrefix(navURL, "/") {
+			http.Error(w, "missing or invalid parameters", http.StatusBadRequest)
+			return
+		}
+		c, err := v.getCtx(cID)
+		if err != nil {
+			v.logErr(nil, "navigate failed: %v", err)
+			http.Error(w, "context not found", http.StatusNotFound)
+			return
+		}
+		if subtle.ConstantTimeCompare([]byte(csrfToken), []byte(c.csrfToken)) != 1 {
+			v.logWarn(c, "navigate rejected: invalid CSRF token")
+			http.Error(w, "invalid CSRF token", http.StatusForbidden)
+			return
+		}
+		if c.actionLimiter != nil && !c.actionLimiter.Allow() {
+			v.logWarn(c, "navigate rate limited")
+			http.Error(w, "rate limited", http.StatusTooManyRequests)
+			return
+		}
+		c.reqCtx = r.Context()
+		v.logDebug(c, "SPA navigate to %s", navURL)
+		c.Navigate(navURL, popstate)
+		w.WriteHeader(http.StatusOK)
+	})
+
 	v.mux.HandleFunc("POST /_session/close", func(w http.ResponseWriter, r *http.Request) {
 		body, err := io.ReadAll(r.Body)
 		if err != nil {
@@ -725,6 +781,15 @@ func New() *V {
 		v.logDebug(c, "session close event triggered")
 		v.cleanupCtx(c)
 	})
+
+	dn, err := getSharedNATS()
+	if err != nil {
+		v.logWarn(nil, "embedded NATS unavailable: %v", err)
+	} else {
+		v.defaultNATS = dn
+		v.pubsub = &natsRef{dn: dn}
+	}
+
 	return v
 }
 
@@ -757,3 +822,19 @@ func extractParams(pattern, path string) map[string]string {
 	}
 	return params
 }
+
+// matchRoute finds the registered page init function and extracted params for the given path.
+func (v *V) matchRoute(path string) (route string, initFn func(*Context), params map[string]string) {
+	for pattern, fn := range v.pageRegistry {
+		if p := extractParams(pattern, path); p != nil {
+			return pattern, fn, p
+		}
+	}
+	return "", nil, nil
+}
+
+// Layout sets a layout function that wraps every page's view.
+// The layout receives the page content as a function and returns the full view.
+func (v *V) Layout(f func(func() h.H) h.H) {
+	v.layout = f
+}

vianats/vianats.go

@@ -1,127 +0,0 @@
-// Package vianats provides an embedded NATS server with JetStream as a
-// pub/sub backend for Via applications.
-package vianats
-
-import (
-	"context"
-	"encoding/json"
-	"fmt"
-	"time"
-
-	"github.com/delaneyj/toolbelt/embeddednats"
-	"github.com/nats-io/nats.go"
-	"github.com/ryanhamamura/via"
-)
-
-// NATS implements via.PubSub using an embedded NATS server with JetStream.
-type NATS struct {
-	server *embeddednats.Server
-	nc     *nats.Conn
-	js     nats.JetStreamContext
-}
-
-// New starts an embedded NATS server with JetStream enabled and returns a
-// ready-to-use NATS instance. The server stores data in dataDir and shuts
-// down when ctx is cancelled.
-func New(ctx context.Context, dataDir string) (*NATS, error) {
-	ns, err := embeddednats.New(ctx, embeddednats.WithDirectory(dataDir))
-	if err != nil {
-		return nil, fmt.Errorf("vianats: start server: %w", err)
-	}
-	ns.WaitForServer()
-
-	nc, err := ns.Client()
-	if err != nil {
-		ns.Close()
-		return nil, fmt.Errorf("vianats: connect client: %w", err)
-	}
-
-	js, err := nc.JetStream()
-	if err != nil {
-		nc.Close()
-		ns.Close()
-		return nil, fmt.Errorf("vianats: init jetstream: %w", err)
-	}
-
-	return &NATS{server: ns, nc: nc, js: js}, nil
-}
-
-// Publish sends data to the given subject using core NATS publish.
-// JetStream captures messages automatically if a matching stream exists.
-func (n *NATS) Publish(subject string, data []byte) error {
-	return n.nc.Publish(subject, data)
-}
-
-// Subscribe creates a core NATS subscription for real-time fan-out delivery.
-func (n *NATS) Subscribe(subject string, handler func(data []byte)) (via.Subscription, error) {
-	sub, err := n.nc.Subscribe(subject, func(msg *nats.Msg) {
-		handler(msg.Data)
-	})
-	if err != nil {
-		return nil, err
-	}
-	return sub, nil
-}
-
-// Close shuts down the client connection and embedded server.
-func (n *NATS) Close() error {
-	n.nc.Close()
-	return n.server.Close()
-}
-
-// Conn returns the underlying NATS connection for advanced usage.
-func (n *NATS) Conn() *nats.Conn {
-	return n.nc
-}
-
-// JetStream returns the JetStream context for stream configuration and replay.
-func (n *NATS) JetStream() nats.JetStreamContext {
-	return n.js
-}
-
-// StreamConfig holds the parameters for creating or updating a JetStream stream.
-type StreamConfig struct {
-	Name     string
-	Subjects []string
-	MaxMsgs  int64
-	MaxAge   time.Duration
-}
-
-// EnsureStream creates or updates a JetStream stream matching cfg.
-func EnsureStream(n *NATS, cfg StreamConfig) error {
-	_, err := n.js.AddStream(&nats.StreamConfig{
-		Name:      cfg.Name,
-		Subjects:  cfg.Subjects,
-		Retention: nats.LimitsPolicy,
-		MaxMsgs:   cfg.MaxMsgs,
-		MaxAge:    cfg.MaxAge,
-	})
-	return err
-}
-
-// ReplayHistory fetches the last limit messages from subject,
-// deserializing each as T. Returns an empty slice if nothing is available.
-func ReplayHistory[T any](n *NATS, subject string, limit int) ([]T, error) {
-	sub, err := n.js.SubscribeSync(subject, nats.DeliverAll(), nats.OrderedConsumer())
-	if err != nil {
-		return nil, err
-	}
-	defer sub.Unsubscribe()
-
-	var msgs []T
-	for {
-		raw, err := sub.NextMsg(200 * time.Millisecond)
-		if err != nil {
-			break
-		}
-		var msg T
-		if json.Unmarshal(raw.Data, &msg) == nil {
-			msgs = append(msgs, msg)
-		}
-	}
-
-	if limit > 0 && len(msgs) > limit {
-		msgs = msgs[len(msgs)-limit:]
-	}
-	return msgs, nil
-}