Sanitization

Sanitization refers to the process of removing or replacing submitted data. When dealing with data, after the proper validation checks have been made, an additional step that is usually taken to strengthen data safety is sanitization.

The most common uses of sanitization are as follows:

Convert single less-than characters < to entity

In the native package html there are two functions used for sanitization: one for escaping HTML text and another for unescaping HTML. The function EscapeString(), accepts a string and returns the same string with the special characters escaped. i.e. < becomes <. Note that this function only escapes the following five characters: <, >, &, ' and ". Conversely there is also the UnescapeString() function to convert from entities to characters.

Strip all tags

Although the html/template package has a stripTags() function, it's unexported. Since no other native package has a function to strip all tags, the alternatives are to use a third-party library, or to copy the whole function along with it's private classes and functions.

Some of the third-party libraries availilable to achieve this are:

• https://github.com/kennygrant/sanitize
• https://github.com/maxwells/sanitize
• https://github.com/microcosm-cc/bluemonday

Remove line breaks, tabs and extra white space

The text/template and the html/template include a way to remove whitespaces from the template, by using a minus sign - inside the action's delimiter.

Executing the template with source

{{- 23}} < {{45 -}}

will lead to the following output

23<45

NOTE: If the minus - sign is not placed immediately after the opening action delimiter {{ or before the closing action delimiter }}, the minus sign - will be applied to the value

Template source

{{ -3 }}

leads to

-3

URL request path

In the net/http package there is an HTTP request multiplexer type called ServeMux. It is used to match the incoming request to the registered patterns, and calls the handler that most closely matches the requested URL. In addition to it's main purpose, it also takes care of sanitizing the URL request path, redirecting any request containing . or .. elements or repeated slashes to an equivalent, cleaner URL.

A simple Mux example to illustrate:

func main() {
  mux := http.NewServeMux()

  rh := http.RedirectHandler("http://yourDomain.org", 307)
  mux.Handle("/login", rh)

  log.Println("Listening...")
  http.ListenAndServe(":3000", mux)
}

NOTE: Keep in mind that ServeMux doesn't change the URL request path for CONNECT requests, thus possibly making an application vulnerable for path traversal attacks if allowed request methods are not limited.

Third-party packages:

• Gorilla Toolkit - MUX