Don't use an intermediate buffer when rendering templates

context.go

@@ -4,7 +4,6 @@
 package echo
 
 import (
-	"bytes"
 	"encoding/xml"
 	"errors"
 	"fmt"
@@ -414,11 +413,9 @@ func (c *Context) Render(code int, name string, data any) (err error) {
 	if c.echo.Renderer == nil {
 		return ErrRendererNotRegistered
 	}
-	buf := new(bytes.Buffer)
-	if err = c.echo.Renderer.Render(c, buf, name, data); err != nil {
-		return
-	}
-	return c.HTMLBlob(code, buf.Bytes())
+	return c.HTMLWrite(code, func(wr io.Writer) error {
+		return c.echo.Renderer.Render(c, wr, name, data)
+	})
 }
 
 // HTML sends an HTTP response with status code.
@@ -431,6 +428,10 @@ func (c *Context) HTMLBlob(code int, b []byte) (err error) {
 	return c.Blob(code, MIMETextHTMLCharsetUTF8, b)
 }
 
+func (c *Context) HTMLWrite(code int, w func(io.Writer) error) (err error) {
+	return c.BlobWrite(code, MIMETextHTMLCharsetUTF8, w)
+}
+
 // String sends a string response with status code.
 func (c *Context) String(code int, s string) (err error) {
 	return c.Blob(code, MIMETextPlainCharsetUTF8, []byte(s))
@@ -535,6 +536,13 @@ func (c *Context) Blob(code int, contentType string, b []byte) (err error) {
 	return
 }
 
+func (c *Context) BlobWrite(code int, contentType string, w func(io.Writer) error) (err error) {
+	c.writeContentType(contentType)
+	c.response.WriteHeader(code)
+	err = w(c.response)
+	return
+}
+
 // Stream sends a streaming response with status code and content type.
 func (c *Context) Stream(code int, contentType string, r io.Reader) (err error) {
 	c.writeContentType(contentType)

context_test.go

@@ -138,6 +138,25 @@ func TestContextRenderTemplate(t *testing.T) {
 	}
 }
 
+func BenchmarkContextRenderTemplate(b *testing.B) {
+	e := New()
+	req := httptest.NewRequest(http.MethodPost, "/", strings.NewReader(userJSON))
+
+	tmpl := &Template{
+		templates: template.Must(template.New("hello").Parse("Hello, {{.}}!")),
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		rec := httptest.NewRecorder()
+		c := e.NewContext(req, rec)
+		c.Echo().Renderer = tmpl
+		_ = c.Render(http.StatusOK, "hello", "Jon Snow")
+	}
+}
+
 func TestContextRenderErrorsOnNoRenderer(t *testing.T) {
 	e := New()
 	req := httptest.NewRequest(http.MethodPost, "/", strings.NewReader(userJSON))
@@ -200,6 +219,23 @@ func TestContextHTMLBlob(t *testing.T) {
 	}
 }
 
+func TestContextHTMLWrite(t *testing.T) {
+	e := New()
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	c := e.NewContext(req, rec)
+
+	err := c.HTMLWrite(http.StatusOK, func(w io.Writer) error {
+		_, err := w.Write([]byte("Hi, Jon Snow"))
+		return err
+	})
+	if assert.NoError(t, err) {
+		assert.Equal(t, http.StatusOK, rec.Code)
+		assert.Equal(t, MIMETextHTMLCharsetUTF8, rec.Header().Get(HeaderContentType))
+		assert.Equal(t, "Hi, Jon Snow", rec.Body.String())
+	}
+}
+
 func TestContextJSON(t *testing.T) {
 	e := New()
 	rec := httptest.NewRecorder()