Svelte Adapter Bun Next

Adapter for SvelteKit apps that generates a standalone Bun.js server.

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svelte-adapter-bun-next

A modern adapter for SvelteKit apps that generates a standalone Bun server.

This is basically ported from svelte-adapter-bun.

:electric_plug: Features

✅ Full TypeScript support
✅ Up-to-date Bun features
✅ Safe env parsing and validation
✅ Route-specific handlers

:zap: Usage

Install with bun add -d svelte-adapter-bun-next, then add the adapter to your svelte.config.js:

// svelte.config.js
import adapter from "svelte-adapter-bun-next";

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

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

# go to build directory
cd build/

# run Bun
bun run start

:gear: Options

The adapter can be configured with various options:

// svelte.config.js
import adapter from "svelte-adapter-bun-next";
export default {
  kit: {
    adapter: adapter({
      out: "build",
      // precompress: true,
      precompress: {
        brotli: true,
        gzip: true,
        files: ["htm", "html"],
      },
    }),
  },
};

out

The directory to build the server to. Default: build — i.e. bun run start would start the server locally after it has been created.

precompress

Enables precompressing using gzip and brotli for assets and prerendered pages. Default: false.

brotli

Enable brotli precompressing. Default: false.

gzip

Enable gzip precompressing. Default: false.

development

This enables bun's error page. Default: false

:desktop_computer: Environment variables

Bun automatically reads configuration from .env.local, .env.development and .env. (Documentation)

Full schema is defined in env.ts, parsed and validated using t3-env and zod.

`PORT` and `HOST`

Specify the port and host to listen on.

Default: 0.0.0.0, 3000

`BODY_SIZE_LIMIT`

The maximum request body size to accept in bytes including while streaming.

Accepted inputs:

Raw number in bytes, e.g. 1048576.
String with a unit suffix (K, M, G), e.g. 1M.
Literal string "Infinity" or number 0 to disable body size limit.

Default: 512K

`ORIGIN`, `PROTOCOL_HEADER` and `HOST_HEADER`

HTTP doesn't give SvelteKit a reliable way to know the URL that is currently being requested. The simplest way to tell SvelteKit where the app is being served is to set the ORIGIN environment variable.

With this, a request for the /stuff pathname will correctly resolve to https://my.site/stuff. Alternatively, you can specify headers that tell SvelteKit about the request protocol and host, from which it can construct the origin URL.

x-forwarded-proto and x-forwarded-host are de facto standard headers that forward the original protocol and host if you're using a reverse proxy (think load balancers and CDNs). You should only set these variables if your server is behind a trusted reverse proxy; otherwise, it'd be possible for clients to spoof these headers.

Default: http://localhost:3000, X-Forwarded-Proto, X-Forwarded-Host

`DEV_MODE`

This enables bun's error page.

Default: false

Acknowledgements

svelte-adapter-bun

License

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