Why Do My HTML Comments Disappear After Go Template Execution?

Go - HTML Comments Not Escaped after Template Execution

In Go, rendering HTML comments via template execution is often expected, but updates to the Go version may lead to unexpected exclusions of HTML comments in the output. This article explores the issue and provides a solution using the template.HTML type.

Understanding the Problem

When rendering HTML using Go's text/template package, HTML comments are typically escaped to prevent cross-site scripting (XSS) attacks. However, in certain situations, it's desired to retain these comments for proper functionality.

The Solution

The solution is to employ the template.HTML type to mark HTML comments as exempted from escaping. Here's how it's implemented:

1. Register a Custom Function:

   Define a custom function for your template that accepts a string and returns it as template.HTML. This function will prevent escaping of the passed-in string.

2. Transform HTML Comments:

   Replace any HTML comments with template actions that invoke the custom function, passing the original comment as an argument.

For example:

<code class="go">const src = `
{{safe "<!-- This is a comment -->"}}
<div>Some <b>HTML</b> content</div>
`</code>

This template transformation will prevent the HTML comment from being omitted or escaped during rendering.

Caveats

• Escape any quotes ('"') within the HTML comment.
• Avoid using conditional HTML comments as they may disrupt the context-sensitive escaping of html/template. Refer to the documentation for further details on this aspect.

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