svelte-adapter-deno

Adapter for SvelteKit apps that generates a standalone Deno server.

Usage

Install with npm i -D svelte-adapter-deno, then add the adapter to your svelte.config.js:

// svelte.config.js
import adapter from 'svelte-adapter-deno';

export default {
  kit: {
    adapter: adapter()
  }
};

After building the server (npm run build), use the following command to start:

# with the default build directory
deno run --allow-env --allow-read --allow-net build/index.js

# with a custom build directory
deno run --allow-env --allow-read --allow-net path/to/build/index.js

You can use the deployctl GitHub Action to automatically deploy your app in Deno Deploy:

.github/workflows/ci.yml

name: ci

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  deploy:
    name: deploy
    runs-on: ubuntu-latest
    permissions:
      id-token: write
      contents: read

    steps:
      - name: Clone repository
        uses: actions/checkout@v2

      - name: Install Node
        uses: actions/setup-node@v2
        with:
          node-version: 16

      - name: Cache pnpm modules
        uses: actions/cache@v2
        with:
          path: ~/.pnpm-store
          key: ${{ runner.os }}-${{ hashFiles('**/pnpm-lock.yaml') }}
          restore-keys: |
            ${{ runner.os }}-

      - name: Install pnpm and node_modules
        uses: pnpm/action-setup@v2
        with:
          version: latest
          run_install: true

      - name: Build site
        run: pnpm build
        working-directory: '<root>' # if necessary, should contain {out}

      - name: Deploy to Deno Deploy
        uses: denoland/deployctl@v1
        with:
          project: <YOUR PROJECT NAME>
          entrypoint: '{out}/index.js' # same as `out` option in config
          root: '<root>' # if necessary

The server needs at least the following permissions to run:

• allow-env - allow environment access, to support runtime configuration via runtime variables (can be further restricted to include just the necessary variables)
• allow-read - allow file system read access (can be further restricted to include just the necessary directories)
• allow-net - allow network access (can be further restricted to include just the necessary domains)

In the documentation deno run -A is used for simplicity rather than as a recommendation, use only the necessary permissions in general use.

Environment variables

PORT and HOST

By default, the server will accept connections on 0.0.0.0 using port 3000. These can be customised with the PORT and HOST environment variables:

HOST=127.0.0.1 PORT=4000 deno run --allow-env --allow-read --allow-net build/server.js

ADDRESS_HEADER and XFF_DEPTH

The RequestEvent object passed to hooks and endpoints includes an event.getClientAddress() function that returns the client's IP address. By default this is the connecting remoteAddress. If your server is behind one or more proxies (such as a load balancer), this value will contain the innermost proxy's IP address rather than the client's, so we need to specify an ADDRESS_HEADER to read the address from:

ADDRESS_HEADER=True-Client-IP node build

Headers can easily be spoofed. As with PROTOCOL_HEADER and HOST_HEADER, you should know what you're doing before setting these.

If the ADDRESS_HEADER is X-Forwarded-For, the header value will contain a comma-separated list of IP addresses. The XFF_DEPTH environment variable should specify how many trusted proxies sit in front of your server. E.g. if there are three trusted proxies, proxy 3 will forward the addresses of the original connection and the first two proxies:

<client address>, <proxy 1 address>, <proxy 2 address>

Some guides will tell you to read the left-most address, but this leaves you vulnerable to spoofing:

<spoofed address>, <client address>, <proxy 1 address>, <proxy 2 address>

We instead read from the right, accounting for the number of trusted proxies. In this case, we would use XFF_DEPTH=3.

If you need to read the left-most address instead (and don't care about spoofing) — for example, to offer a geolocation service, where it's more important for the IP address to be real than trusted, you can do so by inspecting the x-forwarded-for header within your app.

Options

The adapter can be configured with various options:

/// file: svelte.config.js
import adapter from '@sveltejs/adapter-node';

export default {
  kit: {
    adapter: adapter({
      // default options are shown
      out: 'build',
      precompress: false,
      envPrefix: '',
      deps: './deps.ts' // (relative to adapter-deno package)
    })
  }
};

out

The directory to build the server to. It defaults to build — i.e. deno run -A build/index.js would start the server locally after it has been created.

precompress

Enables precompressing using gzip and brotli for assets and prerendered pages. It defaults to false.

envPrefix

If you need to change the name of the environment variables used to configure the deployment (for example, to deconflict with environment variables you don't control), you can specify a prefix:

envPrefix: 'MY_CUSTOM_';

MY_CUSTOM_HOST=127.0.0.1 \
MY_CUSTOM_PORT=4000 \
MY_CUSTOM_ORIGIN=https://my.site \
deno run -A build/index.js

deps

The file re-exporting external runtime dependencies (deps.ts by convention in Deno). It defaults to the deps.ts file included in the package.

Custom server

The adapter creates two files in your build directory — index.js and handler.js. Running index.js — e.g. deno run -A build/index.js, if you use the default build directory — will start a server on the configured port.

Alternatively, you can import the handler.js file, which exports a handler suitable for use with Oak and set up your own server:

/// file: my-server.js
import { Application, Router } from 'https://deno.land/x/oak@v11.1.0/mod.ts';
import { handler } from './build/handler.js';

const app = new Application();

// add a route that lives separately from the SvelteKit app
const router = new Router();
router.get('/healthcheck', (ctx) => {
  ctx.response.body = 'ok';
});
app.use(router.routes());
app.use(router.allowedMethods());

// let SvelteKit handle everything else, including serving prerendered pages and static assets
app.use(handler);

app.addEventListener('listen', () => {
  console.log('listening on port 3000');
});
await app.listen({ port: 3000 });

License

MIT