Check-Driving HTML Templates

Let’s examine learn how to do it in levels: we begin with the next check that
tries to compile the template. In Go we use the usual html/template bundle.

Go

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    _ = templ
  }

In Java, we use jmustache
as a result of it is quite simple to make use of; Freemarker or
Velocity are different widespread selections.

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
  }

If we run this check, it can fail, as a result of the index.tmpl file does
not exist. So we create it, with the above damaged HTML. Now the check ought to go.

Then we create a mannequin for the template to make use of. The appliance manages a todo-list, and
we are able to create a minimal mannequin for demonstration functions.

Go

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    _ = templ
    _ = mannequin
  }

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
      var mannequin = new TodoList();
  }

Now we render the template, saving the leads to a bytes buffer (Go) or as a String (Java).

Go

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    var buf bytes.Buffer
    err := templ.Execute(&buf, mannequin)
    if err != nil {
      panic(err)
    }
  }

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
      var mannequin = new TodoList();
  
      var html = template.execute(mannequin);
  }

At this level, we wish to parse the HTML and we count on to see an
error, as a result of in our damaged HTML there’s a div aspect that
is closed by a p aspect. There may be an HTML parser within the Go
commonplace library, however it’s too lenient: if we run it on our damaged HTML, we do not get an
error. Fortunately, the Go commonplace library additionally has an XML parser that may be
configured to parse HTML (due to this Stack Overflow reply)

Go

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    
    // render the template right into a buffer
    var buf bytes.Buffer
    err := templ.Execute(&buf, mannequin)
    if err != nil {
      panic(err)
    }
  
    // test that the template could be parsed as (lenient) XML
    decoder := xml.NewDecoder(bytes.NewReader(buf.Bytes()))
    decoder.Strict = false
    decoder.AutoClose = xml.HTMLAutoClose
    decoder.Entity = xml.HTMLEntity
    for {
      _, err := decoder.Token()
      swap err {
      case io.EOF:
        return // We're carried out, it is legitimate!
      case nil:
        // do nothing
      default:
        t.Fatalf("Error parsing html: %s", err)
      }
    }
  }

supply

This code configures the HTML parser to have the fitting degree of leniency
for HTML, after which parses the HTML token by token. Certainly, we see the error
message we wished:

--- FAIL: Test_wellFormedHtml (0.00s)
    index_template_test.go:61: Error parsing html: XML syntax error on line 4: sudden finish aspect 

In Java, a flexible library to make use of is jsoup:

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
      var mannequin = new TodoList();
  
      var html = template.execute(mannequin);
  
      var parser = Parser.htmlParser().setTrackErrors(10);
      Jsoup.parse(html, "", parser);
      assertThat(parser.getErrors()).isEmpty();
  }

supply

And we see it fail:

java.lang.AssertionError: 
Anticipating empty however was:<[<1:13>: Unexpected EndTag token [] when in state [InBody],

Success! Now if we copy over the contents of the TodoMVC
template to our index.tmpl file, the check passes.

The check, nonetheless, is simply too verbose: we extract two helper capabilities, in
order to make the intention of the check clearer, and we get

Go

  func Test_wellFormedHtml(t *testing.T) {
    mannequin := todo.NewList()
  
    buf := renderTemplate("index.tmpl", mannequin)
  
    assertWellFormedHtml(t, buf)
  }

supply

Java

  @Check
  void indexIsSoundHtml() {
      var mannequin = new TodoList();
  
      var html = renderTemplate("/index.tmpl", mannequin);
  
      assertSoundHtml(html);
  }

supply