Using Request Context in Go Templates

In Go templates, you may encounter a situation where you need to access information from the triggering request, such as determining if the current user is an administrator. However, templates lack inherent awareness of the request context.

Solution: Pipelines

One common approach is to use pipelines to pass the necessary data from the handler to the template. This involves creating a pipeline variable that contains the relevant context information and then accessing it within the template. For example:

type TemplateData struct {
    IsUserAdmin bool
}

func handler(w http.ResponseWriter, r *http.Request) {
    isUserAdmin := isAdmin(r)
    data := TemplateData{IsUserAdmin: isUserAdmin}
    t.Execute(w, data)
}

Within the template:

{{if .IsUserAdmin}}
    Go to the big red nuclear button
{{end}}

Embedding Context

Another option is to embed the request context into a custom template data structure. This allows you to access both the template data and the context simultaneously:

type TemplateData struct {
    Data interface{}
    Context *http.Request
}

Within the template:

{{if .Context.IsAdmin}}
    Go to the big red nuclear button
{{end}}

Funnel Method

While the Funcs method can be used to define custom functions, it's not recommended for handling complex logic like determining user permissions. It's better to keep such tasks within the handlers or controllers.

Best Practice

Generally, it's considered best practice to limit templates to handling display logic and avoid introducing business logic or request context dependencies. However, in certain situations, it may be necessary to access specific request information, hence the methods described above.