Rocket/examples/handlebars_templates/src/main.rs

#[macro_use] extern crate rocket;

#[cfg(test)] mod tests;

use rocket::Request;
use rocket::response::Redirect;
use rocket_contrib::templates::{Template, handlebars};

#[derive(serde::Serialize)]
struct TemplateContext {
    title: &'static str,
    name: Option<String>,
    items: Vec<&'static str>,
    // This key tells handlebars which template is the parent.
    parent: &'static str,
}

#[get("/")]
fn index() -> Redirect {
    Redirect::to("/hello/Unknown")
}

#[get("/hello/<name>")]
fn hello(name: String) -> Template {
    Template::render("index", &TemplateContext {
        title: "Hello",
        name: Some(name),
        items: vec!["One", "Two", "Three"],
        parent: "layout",
    })
}

#[get("/about")]
fn about() -> Template {
    Template::render("about", &TemplateContext {
        title: "About",
        name: None,
        items: vec!["Four", "Five", "Six"],
        parent: "layout",
    })
}

#[catch(404)]
fn not_found(req: &Request<'_>) -> Template {
    let mut map = std::collections::HashMap::new();
    map.insert("path", req.uri().path());
    Template::render("error/404", &map)
}

use self::handlebars::{Helper, Handlebars, Context, RenderContext, Output, HelperResult, JsonRender};

fn wow_helper(
    h: &Helper<'_, '_>,
    _: &Handlebars,
    _: &Context,
    _: &mut RenderContext<'_, '_>,
    out: &mut dyn Output
) -> HelperResult {
    if let Some(param) = h.param(0) {
        out.write("<b><i>")?;
        out.write(&param.value().render())?;
        out.write("</b></i>")?;
    }

    Ok(())
}

#[launch]
fn rocket() -> rocket::Rocket {
    rocket::ignite()
        .mount("/", routes![index, hello, about])
        .register(catchers![not_found])
        .attach(Template::custom(|engines| {
            engines.handlebars.register_helper("wow", Box::new(wow_helper));
        }))
}