primitive template cache in Go with os.Stat

templates.go

package core

import (
	"bytes"
	"fmt"
	"html/template"
	"io/ioutil"
	"net/http"
	"os"
	"path/filepath"
)

var TemplateRoot string

var templateCache map[string]cachedTemplate

type cachedTemplate struct {
	*template.Template
	os.FileInfo
}

func readTemplateFile(abspath string) (*template.Template, error) {
	relpath, err := filepath.Rel(TemplateRoot, abspath)
	if err != nil {
		return nil, fmt.Errorf(`core: unable to resolve template file path %v`, abspath)
	}

	t, err := template.ParseFiles(abspath)
	if err != nil {
		return nil, fmt.Errorf(`core: unable to read template file at path %v: %v`, abspath, err)
	}
	fi, err := os.Stat(abspath)
	if err != nil {
		return nil, fmt.Errorf(`core: unable to stat (2) template at path %v: %v`, abspath, err)
	}

	templateCache[relpath] = cachedTemplate{t, fi}
	return t, nil
}

func Template(relpath string) (*template.Template, error) {
	abspath := filepath.Join(TemplateRoot, relpath)
	if cached, ok := templateCache[relpath]; ok {
		fi, err := os.Stat(abspath)
		if err != nil {
			return nil, fmt.Errorf(`core: unable to stat template at path %v: %v`, abspath, err)
		}
		if fi.ModTime().After(cached.ModTime()) {
			return readTemplateFile(abspath)
		}
		return cached.Template, nil
	}
	return readTemplateFile(abspath)
}

func init() {
	templateCache = make(map[string]cachedTemplate, 5)
}