Golang authors have an excellent article on how to build a wiki web application entirely out of go. Towards the middle of the article, they mention the html/template package. For those of you familiar with templating systems like jade, handlebars, or flask/jinja… you should feel right at home. In golang, templating needs no third party frameworks, no extensions… it comes right out the box.
But, I did have a big “D’Oh” moment when using this engine for the first time. While looking up how to include conditional (if…else) and iterative (for loop) structures in the template I ran into a brick wall and simply couldn’t find the syntax. I automatically assumed all the documentation for the package was under the URL:
http://golang.org/pkg/html/template/
No mention of the syntax for the structures I needed. I quite by accident then ran across the text/template package and documentation here:
http://golang.org/pkg/text/template/
The first paragraph mentions:
To generate HTML output, see package html/template, which has the same interface as this package but automatically secures HTML output against certain attacks.
So I tried out the control structures there and it worked perfectly… As an example (using bootstrap for CSS), say we would like to display a bunch of alerts whose content is retrieved from a golang array:
| /* | |
| Start Webserver Section | |
| */ | |
| type Page struct { | |
| Title string | |
| Body string | |
| Alerts []string | |
| } | |
| func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) { | |
| err := templates.ExecuteTemplate(w, tmpl+".html", p) | |
| if err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| } | |
| } |
in the above, we note the “Alerts” string array contained within a “Page” struct, and just as explained in the golang article, we have a function to render templates that accept a variable p which is a pointer to the struct.
Within the html file that is rendered by the html/template package, we have the following:
| <html> | |
| <head> | |
| <link rel="stylesheet" type="text/css" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css"> | |
| <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script> | |
| </head> | |
| <body> | |
| <div class="container well"> | |
| <h2>Alerts</h2> | |
| <hr> | |
| {{range $element := .Alerts}} | |
| <div class="alert alert-danger">{{$element}}</div> | |
| {{end}} | |
| </div> | |
| </body> | |
| </html> |
Note lines 10-12. Golang uses the familiar double curly brackets to enclose it’s syntax within a template. In this example, we used the “range” syntax to assign each element of the array Alerts to the variable $element, which is in turn used within the div.
Make sure to checkout http://golang.org/pkg/text/template/ for more examples of the logic that you can place within templates
