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internal/render/engine.go

@@ -1,13 +1,22 @@
 package render
 
 import (
+	"context"
 	"net/http"
 
+	"github.com/a-h/templ"
+	templruntime "github.com/a-h/templ/runtime"
+
 	"git.ma-al.com/goc_marek/ps_shop/internal/assets"
 	"git.ma-al.com/goc_marek/ps_shop/internal/viewmodel"
 	"git.ma-al.com/goc_marek/ps_shop/templates"
 )
 
+func init() {
+	// Minimize templ's internal buffering so HTML reaches the client as it is rendered.
+	templruntime.DefaultBufferSize = 1
+}
+
 type Engine struct {
 	assets assets.Manifest
 }
@@ -19,13 +28,13 @@ func New(manifest assets.Manifest) *Engine {
 func (e *Engine) Product(w http.ResponseWriter, r *http.Request, data viewmodel.ProductPageData) error {
 	startHTMLStream(w)
 	component := templates.ProductPage(data, e.assets.CSSPath("app.css"), e.assets.JSPath("app.js"))
-	return component.Render(r.Context(), w)
+	return streamComponent(r.Context(), w, component)
 }
 
 func (e *Engine) Category(w http.ResponseWriter, r *http.Request, data viewmodel.CategoryPageData) error {
 	startHTMLStream(w)
 	component := templates.CategoryPage(data, e.assets.CSSPath("app.css"), e.assets.JSPath("app.js"))
-	return component.Render(r.Context(), w)
+	return streamComponent(r.Context(), w, component)
 }
 
 func startHTMLStream(w http.ResponseWriter) {
@@ -41,3 +50,15 @@ func startHTMLStream(w http.ResponseWriter) {
 		flusher.Flush()
 	}
 }
+
+func streamComponent(ctx context.Context, w http.ResponseWriter, component templ.Component) error {
+	if component == nil {
+		return nil
+	}
+	var buffer templruntime.Buffer
+	buffer.Reset(w)
+	if err := component.Render(ctx, &buffer); err != nil {
+		return err
+	}
+	return buffer.Flush()
+}

internal/render/engine_test.go

@@ -0,0 +1,56 @@
+package render
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"testing"
+
+	"github.com/a-h/templ"
+)
+
+type writeCountingResponseWriter struct {
+	header http.Header
+	writes int
+	body   []byte
+}
+
+func (w *writeCountingResponseWriter) Header() http.Header {
+	if w.header == nil {
+		w.header = make(http.Header)
+	}
+	return w.header
+}
+
+func (w *writeCountingResponseWriter) Write(p []byte) (int, error) {
+	w.writes++
+	w.body = append(w.body, p...)
+	return len(p), nil
+}
+
+func (w *writeCountingResponseWriter) WriteHeader(statusCode int) {}
+
+func (w *writeCountingResponseWriter) Flush() {}
+
+func TestStreamComponentWritesIncrementally(t *testing.T) {
+	w := &writeCountingResponseWriter{}
+	component := templ.ComponentFunc(func(ctx context.Context, writer io.Writer) error {
+		if _, err := writer.Write([]byte("a")); err != nil {
+			return err
+		}
+		if _, err := writer.Write([]byte("b")); err != nil {
+			return err
+		}
+		return nil
+	})
+
+	if err := streamComponent(context.Background(), w, component); err != nil {
+		t.Fatalf("streamComponent() error = %v", err)
+	}
+	if got := string(w.body); got != "ab" {
+		t.Fatalf("body = %q, want %q", got, "ab")
+	}
+	if w.writes < 2 {
+		t.Fatalf("writes = %d, want at least 2 incremental writes", w.writes)
+	}
+}