implement ctx.Render (#107)

* implement render

* add test

context.go

@@ -7,6 +7,7 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"html/template"
 	"io"
 	"net"
 	"net/http"
@@ -266,6 +267,40 @@ func (ctx *Context) Component(name string, data any) error {
 	return ctx.CopyFrom(buf)
 }
 
+// Render renders html template
+func (ctx *Context) Render(tmpl string, data any) error {
+	// TODO: cache template
+	// TODO: use pre-defined template func
+	t, err := template.New("").Parse(tmpl)
+	if err != nil {
+		return err
+	}
+
+	return ctx.executeTemplate(t, data)
+}
+
+func (ctx *Context) executeTemplate(t *template.Template, data any) error {
+	if !ctx.etag {
+		ctx.setContentType("text/html; charset=utf-8")
+		return filterRenderError(t.Execute(ctx.w, data))
+	}
+
+	buf := getBytes()
+	defer putBytes(buf)
+
+	err := t.Execute(buf, data)
+	if err != nil {
+		return err
+	}
+
+	if ctx.setETag(buf.Bytes()) {
+		return nil
+	}
+
+	ctx.setContentType("text/html; charset=utf-8")
+	return ctx.CopyFrom(buf)
+}
+
 func (ctx *Context) setContentType(value string) {
 	if len(ctx.w.Header().Get("Content-Type")) == 0 {
 		ctx.w.Header().Set("Content-Type", value)

context_test.go

@@ -776,6 +776,19 @@ func TestContext(t *testing.T) {
 		assert.Equal(t, w.Body.String(), "hello, world")
 	})
 
+	t.Run("Render", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		r := httptest.NewRequest(http.MethodPost, "/", nil)
+
+		app := hime.New()
+		ctx := hime.NewAppContext(app, w, r)
+
+		assert.NoError(t, ctx.Render(`hello, {{.}}`, "world"))
+		assert.Equal(t, w.Code, http.StatusOK)
+		assert.Equal(t, w.Header().Get("Content-Type"), "text/html; charset=utf-8")
+		assert.Equal(t, w.Body.String(), "hello, world")
+	})
+
 	t.Run("BindJSON", func(t *testing.T) {
 		w := httptest.NewRecorder()
 		r := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader([]byte(`{"a":1}`)))