Dec 27, 2013

Html/Templates Parsing Multiple Files

Working with Django templating engine or Jinja2 you have the ability to inherit/extend templates. which I find very helpful in keeping things DRY. Now working on a golang app I wanted something similar and this is how I ended up doing it using the base packages.

I’m sticking with the base packages for my first few apps, so I can actually learn them. When starting out with Python, I used Django mainly and I feel that was not the correct thing to do, as Django black boxed a lot of functionality and it took a while to get a deeper understanding.

Anyway back to golang and templating. Here I’m making use of the html/template package.

Create the base file;

#!html
<html>
  <body>
    <h1>{{ template "title" }}</h1>


    {{ template "content" }}
  </body>
</html>

So here we are expecting a couple of overrides, title and content which the templates that extend this base file need to provide. A sample file extending this base;

#!html
{{ define "title" }}About{{ end }}


{{ define "content" }}
  <p>About us page now</p>
{{ end }}

In this file you can see that we define the title and content information, which is used/needed by the base file.

Now we can parse these files with the html/template package and the final result will be the combination of these 2 files.

t, err := template.ParseFiles("base.html", "index.html")

The order of the files provided in this call is important. You will always want the base.html file to be the first file in the list, otherwise you will end up with a blank result.

A complete sample go file that does this;

#!golang
package main


import (
    "flag"
    "fmt"
    "html/template"
    "os"
)


var (
    file string
)


func init() {
    flag.StringVar(&file, "file", "index.html", "template file")
    flag.Parse()
}


func main() {
    t, err := template.ParseFiles("base.html", file)
    if err != nil {
    	fmt.Println("template parse error: ", err)
    	return
    }
    err = t.Execute(os.Stdout, "")
    if err != nil {
    	fmt.Println("template executing error: ", err)
    	return
    }
}

Make use the html files are in the same dir as the above file, you can then run it and see the results;

$ go run main.go


<html>
  <body>
    <h1>Home</h1>




  <p>We are at the home page</p>


  </body>
</html>

Or pass in the file option to use a the about.html file

$ go run main.go -file=about.html


<html>
  <body>
    <h1>About</h1>




  <p>About us page now</p>


  </body>
</html>

Take the above with a grain of salt. I’m just starting out with golang and this is just the solution I came up with that works well for me at the moment. Also note that html/template is an extension of text/template, so this should be applicable there as well, so not just limited to html.

Source files can be found at https://github.com/reinbach/html-template-example