fix: preserve context across SSE reconnects on tab visibility change

Datastar aborts SSE on visibilitychange (tab hidden) and reconnects
when visible. The previous cleanup-on-disconnect destroyed the context
before the client could reconnect. Now SSE disconnect does a soft
teardown (mark disconnected, keep context alive) and reconnect drains
stale patches before resuming. The reaper uses disconnect time instead
of creation time so recently-disconnected contexts aren't prematurely
reaped.

context.go

@@ -5,8 +5,8 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"net/url"
 	"reflect"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -31,6 +31,7 @@ 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
@@ -40,6 +41,7 @@ type Context struct {
 	disposeOnce       sync.Once
 	createdAt           time.Time
 	sseConnected        atomic.Bool
+	sseDisconnectedAt   atomic.Pointer[time.Time]
 }
 
 // View defines the UI rendered by this context.
@@ -272,15 +274,22 @@ 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)})
@@ -396,6 +405,9 @@ func (c *Context) resetPageState() {
 // 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)
@@ -405,29 +417,12 @@ func (c *Context) Navigate(path string, popstate bool) {
 	c.route = route
 	c.injectRouteParams(params)
 	initFn(c)
-	c.syncWithViewTransition()
-	escaped := url.PathEscape(path)
+	c.syncView(true)
+	safe := strings.NewReplacer(`\`, `\\`, `'`, `\'`).Replace(path)
 	if popstate {
-		c.ExecScript(fmt.Sprintf("history.replaceState({},'',decodeURIComponent('%s'))", escaped))
+		c.ExecScript(fmt.Sprintf("history.replaceState({},'','%s')", safe))
 	} else {
-		c.ExecScript(fmt.Sprintf("history.pushState({},'',decodeURIComponent('%s'))", escaped))
-	}
-}
-
-// syncWithViewTransition renders the view and sends it as a PatchElements
-// with the view transition flag, plus any changed signals.
-func (c *Context) syncWithViewTransition() {
-	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{patchTypeElementsWithVT, elemsPatch.String()})
-
-	updatedSigs := c.prepareSignalsForPatch()
-	if len(updatedSigs) != 0 {
-		outgoingSigs, _ := json.Marshal(updatedSigs)
-		c.sendPatch(patch{patchTypeSignals, string(outgoingSigs)})
+		c.ExecScript(fmt.Sprintf("history.pushState({},'','%s')", safe))
 	}
 }
 

h/datastar.go

@@ -14,7 +14,8 @@ func DataIgnoreMorph() H {
 
 // 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.
+// 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)
 }

navigate.js

@@ -38,15 +38,14 @@
       var url = new URL(href, window.location.origin);
       if (url.origin !== window.location.origin) return;
       e.preventDefault();
-      navigate(url.pathname + url.search);
+      navigate(url.pathname + url.search + url.hash);
     } catch(_) {}
   });
 
   var ready = false;
   window.addEventListener('popstate', function() {
-    if (!ready) { ready = true; return; }
-    navigate(window.location.pathname + window.location.search, true);
+    if (!ready) return;
+    navigate(window.location.pathname + window.location.search + window.location.hash, true);
   });
-  // Mark as ready after initial load completes
   setTimeout(function() { ready = true; }, 0);
 })();

via.go

@@ -318,9 +318,20 @@ func (v *V) reapOrphanedContexts(ttl time.Duration) {
 	v.contextRegistryMutex.RLock()
 	var orphans []*Context
 	for _, c := range v.contextRegistry {
-		if !c.sseConnected.Load() && now.Sub(c.createdAt) > ttl {
+		if c.sseConnected.Load() {
+			continue
+		}
+		if dc := c.sseDisconnectedAt.Load(); dc != nil {
+			// SSE was connected then dropped — reap if gone too long
+			if now.Sub(*dc) > ttl {
 				orphans = append(orphans, c)
 			}
+		} else {
+			// SSE never connected — reap based on creation time
+			if now.Sub(c.createdAt) > ttl {
+				orphans = append(orphans, c)
+			}
+		}
 	}
 	v.contextRegistryMutex.RUnlock()
 
@@ -419,6 +430,11 @@ 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:
@@ -619,7 +635,19 @@ func New() *V {
 		// use last-event-id to tell if request is a sse reconnect
 		sse.Send(datastar.EventTypePatchElements, []string{}, datastar.WithSSEEventId("via"))
 
+		// Drain stale patches on reconnect so the client gets fresh state
+		if c.sseDisconnectedAt.Load() != nil {
+			for {
+				select {
+				case <-c.patchChan:
+				default:
+					goto drained
+				}
+			}
+		drained:
+		}
 		c.sseConnected.Store(true)
+		c.sseDisconnectedAt.Store(nil)
 		v.logDebug(c, "SSE connection established")
 
 		go c.Sync()
@@ -628,7 +656,9 @@ func New() *V {
 			select {
 			case <-sse.Context().Done():
 				v.logDebug(c, "SSE connection ended")
-				v.cleanupCtx(c)
+				c.sseConnected.Store(false)
+				now := time.Now()
+				c.sseDisconnectedAt.Store(&now)
 				return
 			case <-c.ctxDisposedChan:
 				v.logDebug(c, "context disposed, closing SSE")