topcoat 0.3.1

A modular, batteries-included Rust web framework for server-rendered apps.

Topcoat is a modular, batteries-included Rust framework for building fullstack apps. It prioritizes simplicity and productivity. See Learn Topcoat to get started, or the Roadmap for what's coming next.

Early-stage and experimental. Expect breaking changes.

use topcoat::{
    Result,
    router::{Router, RouterBuilderDiscoverExt, page},
    view::{component, view},
};

#[tokio::main]
async fn main() {
    topcoat::start(Router::builder().discover().build()).await.unwrap();
}

#[page("/")]
async fn home() -> Result {
    view! {
        <!DOCTYPE html>
        <html>
            <body>
                hello(name: "World")
            </body>
        </html>
    }
}

#[component]
async fn hello(name: &str) -> Result {
    view! { <h1>"Hello, " (name) "!"</h1> }
}

What makes Topcoat different

Client reactivity without the boilerplate

Topcoat renders all markup on the server: components can be async and query the database directly, eliminating all the traditional boilerplate needed for a separate API layer. Interactivity does not have to cost a round-trip, though. A $(...) expression is ordinary type-checked Rust that Topcoat evaluates on the server for the initial render and also translates to JavaScript, so it re-runs instantly in the browser. No wasm bundle, no client build step:

view! {
    signal open = false;

    // Runs entirely in the browser; no server round-trip.
    <button @click=$(|_e| open.set(!open.get()))>"What is Topcoat?"</button>
    <p :hidden=$(!open.get())>"A fullstack Rust framework."</p>
}

When an update does need the server, like fresh search results, mark the component as a #[shard]. Topcoat re-renders it on the server whenever one of its $(...) arguments changes and swaps the new HTML in place:

#[component]
async fn search() -> Result {
    view! {
        signal query = String::new();

        <input @input=$(|e: Event| query.set(e.target.value))>

        // Updates as the user types.
        search_results(query: $(query.get()))
    }
}

#[shard]
async fn search_results(cx: &Cx, query: String) -> Result {
    view! {
        <ul>
            // Your own server-side code, like a database query:
            for product in search_products(cx, &query).await? {
                <li>(product.name)</li>
            }
        </ul>
    }
}

Powerful, unsurprising HTML templates

The view! macro stays true to HTML and Rust. Use familiar Rust control flow as part of your templates:

view! {
    <nav>
        for item in nav_items {
            <a
                href=(item.url)
                if item.url == current_path {
                    aria-current="page"
                    class="active"
                }
            >
                (item.label)
            </a>
        }
    </nav>
}

Use the topcoat fmt CLI command to automatically format view! snippets (and other macros) across your codebase.

Module-based routing

Topcoat can optionally infer your route tree from your app's module structure (without a build step):

src/
|-- app.rs              -> /            (and the root <html> layout)
`-- app/
    |-- about.rs        -> /about
    |-- _marketing.rs                  (layout, no URL segment)
    |-- _marketing/
    |   `-- pricing.rs  -> /pricing
    |-- posts.rs        -> /posts
    |-- posts/
    |   `-- id.rs       -> /posts/{post_id}
    `-- api/
        `-- health.rs   -> GET /api/health

Premade components you can edit

Topcoat UI is a component library based on Tailwind inspired by shadcn/ui. Components are copied into your project via the topcoat ui CLI command, meaning you can freely change their design and functionality to fit your use case:

#[component]
async fn delete_card() -> Result {
    view! {
        card(
            card_header(
                card_title("Delete workspace")
                card_description(
                    "This permanently removes the workspace and all of its data."
                )
            )
            card_footer(
                attrs: attributes! { class="justify-end" },
                button(variant: ButtonVariant::Ghost, "Cancel")
                button(variant: ButtonVariant::Destructive, "Delete workspace")
            )
        )
    }
}

Asset bundling

The bundler scans your compiled binary for asset! calls, copies (or even downloads) every file into a local asset directory, and allows Topcoat to serve them efficiently with aggressive browser caching.

const FERRIS: Asset = asset!("./ferris.png");

view! { <img src=(FERRIS)> }

Topcoat also ships with utilities for web fonts and icons, as well as easy integrations for Fontsource (Google Fonts) and Iconify.

Built-in Tailwind support

Enabled the tailwind feature to integrate Tailwind into your project effortlessly:

view! { <link rel="stylesheet" href=(topcoat::tailwind::stylesheet!())> }

Learn Topcoat

Start here

Getting started: create a new project, install the CLI, run the dev server.
Source code formatting: topcoat fmt for macro bodies.

Rendering

The view! macro: templating syntax, control flow, conditional attributes.
The #[component] macro: async functions as components, with child content.
The attributes! macro: reusable runtime attribute fragments.
The class! macro: space-separated class lists from static and conditional entries.

Routing

Router: pages, layouts, and API routes; manual and auto-discovered.
Module-based routing: derive the route table from your module tree.

Working with requests

Request context (Cx): the value pages, layouts, and components read from.
App context: share long-lived values across requests, keyed by type.
Memoization: #[memoize] for per-request caching and fan-out dedup.
Functions, not middlewares: the recommended way to model auth and other request-scoped concerns.
Cookies: read and write the request cookie jar, with signed, encrypted, and prefixed cookies.
Sessions: bring-your-own-storage session authentication: login/logout lifecycle, sliding expiration, and token rotation.

Asset system

Assets: declare assets in Rust, serve them with content-hashed URLs.
Fonts: bundle and serve web fonts.
Icons: download Iconify icon sets or declare your own.

Client reactivity

The runtime: signals, $(...) expressions, @ event handlers, and : bind attributes.
Expressions: the dual Rust/JavaScript expression language and its vocabulary.
Procedures: async server functions callable from the browser.
Shards: components that re-render on the server when their arguments change.

UI components

Topcoat UI: premade components vendored into your project for you to edit.

Third-party integrations

Tailwind: Tailwind CSS without Node, wired into the asset pipeline.
htmx: drive partial HTML swaps from the server with request/response header helpers.

Roadmap

Planned features we'd like to bring to Topcoat. Have an idea? Open an issue.

topcoat new CLI command to bootstrap pre-configured projects
Static export
(More) reactivity (topcoat-runtime)
More Topcoat UI components, full "blocks" e.g. sign-in form
Emailing
Better Toasty integration (safely create/update records from forms without listing out all the fields)
Validations
OpenAPI endpoints
Docs for how to deploy Topcoat
Pre-rendering for static pages
Streaming SSR / Suspense
Client-side navigation + prefetching
WebSockets
Server-sent events
Image optimization / resizing
Easier-to-use middlewares like rate-limiting, compression, etc.
Authentication
Background jobs
Islands