template service: add Render() method

service/template/service.go

@@ -1,6 +1,7 @@
 package template
 
 import (
+	"io"
 	"net/http"
 
 	"github.com/pkg/errors"
@@ -13,6 +14,7 @@ const ServiceName service.Name = "template"
 // Service is a templating service
 type Service interface {
 	RenderPage(w http.ResponseWriter, templateName string, data interface{}) error
+	Render(w io.Writer, templateName string, data interface{}) error
 }
 
 // From retrieves the template service in the given container

template/html/service.go

@@ -3,6 +3,7 @@ package html
 import (
 	"fmt"
 	"html/template"
+	"io"
 	"io/ioutil"
 	"net/http"
 	"path/filepath"
@@ -102,6 +103,28 @@ func (t *TemplateService) RenderPage(w http.ResponseWriter, templateName string,
 
 }
 
+// Render renders a template to the given io.Writer
+func (t *TemplateService) Render(w io.Writer, templateName string, data interface{}) error {
+
+	// Ensure the template exists in the map.
+	tmpl, ok := t.templates[templateName]
+	if !ok {
+		return fmt.Errorf("the template '%s' does not exist", templateName)
+	}
+
+	// Create a buffer to temporarily write to and check if any errors were encountered.
+	buf := t.pool.Get()
+	defer t.pool.Put(buf)
+
+	if err := tmpl.ExecuteTemplate(buf, templateName, data); err != nil {
+		return err
+	}
+
+	_, err := buf.WriteTo(w)
+
+	return err
+}
+
 // NewTemplateService returns a new Service
 func NewTemplateService(funcs ...OptionFunc) *TemplateService {
 	options := defaultOptions()