feat: add Bun adapter

.changeset/new-bun-adapter.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-bun': minor
+---
+
+feat: add a Bun-native adapter with static file serving and single-executable support

.github/workflows/platform-tests-all.yml

@@ -29,9 +29,14 @@ jobs:
     with:
       sha: ${{ inputs.sha }}
 
+  bun:
+    uses: ./.github/workflows/platform-tests-bun.yml
+    with:
+      sha: ${{ inputs.sha }}
+
   report-status:
     if: always()
-    needs: [vercel, netlify, node]
+    needs: [vercel, netlify, node, bun]
     permissions:
       contents: write # to create the repository_dispatch event
     runs-on: ubuntu-latest

.github/workflows/platform-tests-bun.yml

@@ -0,0 +1,59 @@
+name: Platform Tests (Bun)
+
+on:
+  workflow_dispatch:
+    inputs:
+      sha:
+        description: 'Commit SHA to test'
+        required: false
+        default: ''
+  workflow_call:
+    inputs:
+      sha:
+        description: 'Commit SHA to test'
+        required: false
+        type: string
+        default: ''
+
+permissions:
+  contents: read
+
+env:
+  PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: '1'
+
+jobs:
+  test-basic:
+    if: github.repository == 'sveltejs/kit'
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          ref: ${{ inputs.sha || github.sha }}
+          persist-credentials: false
+
+      - uses: ./.github/actions/node-setup
+
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
+        with:
+          bun-version: 1.3.14
+
+      - uses: ./.github/actions/platform-test
+        with:
+          test-app-dir: packages/adapter-bun/test/apps/basic
+          os: ubuntu-latest
+
+      - name: Test compiled executable
+        working-directory: packages/adapter-bun/test/apps/basic
+        env:
+          COMPILE: 'true'
+        run: pnpm test:platform
+
+      - name: Compile optimized cross-target executable
+        working-directory: packages/adapter-bun/test/apps/basic
+        env:
+          ADVANCED_COMPILE: 'true'
+          COMPILE_TARGET: 'bun-linux-x64'
+        run: |
+          bun run --bun build
+          test -x build/advanced-app

documentation/docs/25-build-and-deploy/20-adapters.md

@@ -9,6 +9,7 @@ Official adapters exist for a variety of platforms — these are documented on t
 - [`@sveltejs/adapter-cloudflare`](adapter-cloudflare) for Cloudflare Workers and Cloudflare Pages
 - [`@sveltejs/adapter-netlify`](adapter-netlify) for Netlify
 - [`@sveltejs/adapter-node`](adapter-node) for Node servers
+- [`@sveltejs/adapter-bun`](adapter-bun) for Bun servers
 - [`@sveltejs/adapter-static`](adapter-static) for static site generation (SSG)
 - [`@sveltejs/adapter-vercel`](adapter-vercel) for Vercel
 

documentation/docs/25-build-and-deploy/45-adapter-bun.md

@@ -0,0 +1,254 @@
+---
+title: Bun servers
+---
+
+[`adapter-bun`](https://github.com/sveltejs/kit/tree/main/packages/adapter-bun) builds a SvelteKit application into a standalone [Bun](https://bun.com/) server. The generated server uses `Bun.serve` for requests and `Bun.file` responses for client assets, prerendered output, and files read with [`read`](https://svelte.dev/docs/kit/$app-server#read) from `$app/server`.
+
+## Usage
+
+Install the adapter:
+
+```sh
+bun add -D @sveltejs/adapter-bun
+```
+
+Configure it in `vite.config.js`:
+
+```js
+// @errors: 2307 2554
+/// file: vite.config.js
+import adapter from '@sveltejs/adapter-bun';
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [
+		sveltekit({
+			adapter: adapter()
+		})
+	]
+});
+```
+
+The adapter calls Bun's build API, so the production build itself must run in Bun. The `--bun` flag overrides Vite's Node.js shebang:
+
+```sh
+bun run --bun build
+```
+
+The default build is written to `build`. Start it with:
+
+```sh
+bun ./build
+```
+
+The JavaScript server, client files, and prerendered files in the output directory are all required at runtime. Application imports are processed according to Bun's bundler behavior.
+
+Client assets and prerendered output are registered as native Bun routes. Only `GET` and `HEAD` requests are served by those routes; other methods continue to SvelteKit. Every asset carries an ETag computed during the build, so conditional requests revalidate with an empty `304` response. Bun supplies MIME types, byte ranges for filesystem-backed files, and streaming without buffering every asset in memory. Files below SvelteKit's `immutable` directory receive `Cache-Control: public,max-age=31536000,immutable`.
+
+> [!NOTE] Bun treats `*` in a route pathname as a wildcard. The adapter rejects client and prerendered filenames that contain a literal `*`; rename those files before building.
+
+## Options
+
+```js
+// @errors: 2307 2554
+/// file: vite.config.js
+import adapter from '@sveltejs/adapter-bun';
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [
+		sveltekit({
+			adapter: adapter({
+				out: 'build',
+				envPrefix: '',
+				serverOptions: {
+					idleTimeout: 30
+				},
+				buildOptions: {
+					sourcemap: 'external'
+				}
+			})
+		})
+	]
+});
+```
+
+### out
+
+The output directory. It defaults to `build`.
+
+### precompress
+
+Set `precompress: true` to generate `.br` and `.gz` variants of client and prerendered assets during the build. The generated routes negotiate `Accept-Encoding` per request, preferring brotli over gzip, and each variant carries its own ETag. The option is ignored when `buildOptions.compile` is set, because embedded assets are imported by identity path.
+
+### envPrefix
+
+A prefix for every deployment environment variable documented below. This is useful when the unprefixed names conflict with variables managed by your host:
+
+```js
+adapter({ envPrefix: 'MY_APP_' });
+```
+
+```sh
+MY_APP_HOST=127.0.0.1 MY_APP_PORT=4000 bun ./build
+```
+
+When a prefix is configured, the server fails at startup if it finds an unknown environment variable with that prefix. This catches collisions and misspellings.
+
+### serverOptions
+
+JSON-serializable defaults passed to `Bun.serve`. The supported properties are:
+
+- `hostname`
+- `port`
+- `unix`
+- `reusePort`
+- `ipv6Only`
+- `idleTimeout`
+- `maxRequestBodySize`
+- `development`
+
+Environment variables take precedence over these defaults. A configured Unix socket takes precedence over `hostname`, `port`, `reusePort`, and `ipv6Only`.
+
+The generated server owns `fetch` and `routes`. It does not expose `websocket`, `error`, TLS, HTTP/3, or HTTP/1 configuration through `serverOptions`. Use a custom Bun integration if your application requires those `Bun.serve` options.
+
+### buildOptions
+
+Advanced Bun build settings can be supplied with `buildOptions`. The adapter currently accepts `sourcemap`, `minify`, `bytecode`, `banner`, `footer`, `drop`, `features`, `optimizeImports`, `splitting`, and `compile`. Code splitting is enabled by default; `splitting: false` bundles the server into a single file, which works around [`Bun.build` output path collisions](https://github.com/oven-sh/bun/issues/17674) on applications whose module graph produces identically-hashed chunks.
+
+The generated entrypoint, output directory, top-level `target`, and module `format` are reserved. Generated servers target Bun and use ESM. Source maps default to `external`; set `sourcemap: 'none'` to disable them.
+
+#### Compiled executables
+
+Set `compile: true` to generate a single executable at `<out>/server`:
+
+```js
+adapter({
+	buildOptions: {
+		compile: true
+	}
+});
+```
+
+Build and run it without a separately installed Bun runtime:
+
+```sh
+bun run --bun build
+./build/server
+```
+
+The executable embeds the server code, client assets, prerendered output, and Bun runtime. `compile` can also be a Bun target string, which keeps the default `server` filename, or an options object. To change the executable name or cross-compile, provide an options object:
+
+```js
+adapter({
+	out: 'dist',
+	buildOptions: {
+		compile: {
+			outfile: 'application',
+			target: 'bun-linux-x64'
+		},
+		minify: true,
+		bytecode: true,
+		sourcemap: 'linked'
+	}
+});
+```
+
+The result in this example is `dist/application`. Platform targets, native dependencies, and other limitations follow [Bun's executable compilation rules](https://bun.com/docs/bundler/executables).
+
+## Environment variables
+
+Bun loads `.env` files automatically. If `envPrefix` is set, add that prefix to each name in this section.
+
+### Listener
+
+`HOST` and `PORT` configure the TCP listener. Without either value or a `serverOptions` default, the server listens on port `3000`.
+
+```sh
+HOST=127.0.0.1 PORT=4000 bun ./build
+```
+
+`SOCKET_PATH` selects a Unix domain socket instead. When it is present, TCP-only options are ignored:
+
+```sh
+SOCKET_PATH=/tmp/sveltekit.sock bun ./build
+```
+
+`REUSE_PORT` enables Bun's `reusePort` option and `IPV6_ONLY` enables `ipv6Only`. Boolean variables accept `1`, `true`, `yes`, and `on`, or `0`, `false`, `no`, and `off`, without regard to letter case.
+
+### Request limits and diagnostics
+
+`BODY_SIZE_LIMIT` controls `Bun.serve`'s `maxRequestBodySize`. It defaults to `512K`. The value must resolve to a whole number of bytes and may use a case-insensitive binary `K`, `M`, or `G` suffix, such as `768K` or `1.5M`. `Infinity` disables the limit.
+
+`CONNECTION_IDLE_TIMEOUT` sets Bun's per-request inactivity timeout in seconds. It must be an integer from `0` through `255`; `0` disables the timeout. The generated handler disables the timeout for responses whose content type starts with `text/event-stream` and also adds `X-Accel-Buffering: no`. It is deliberately not called `IDLE_TIMEOUT`, which on adapter-node means something different (shut the server down after N seconds without requests).
+
+`DEVELOPMENT` enables Bun's development-mode error pages. It defaults to `false` for the generated server.
+
+### Public origin behind a proxy
+
+If [`paths.origin`](configuration#paths) is configured, that value is the trusted origin for every request. Otherwise, the adapter derives the host from the `Host` header and assumes the scheme is `https`, since production deployments usually terminate TLS upstream. Configure `paths.origin` or `PROTOCOL_HEADER` if that assumption is wrong, for example when serving plain HTTP directly.
+
+Behind a trusted reverse proxy, `PROTOCOL_HEADER`, `HOST_HEADER`, and `PORT_HEADER` name headers that contain the public scheme, host, and port:
+
+```sh
+PROTOCOL_HEADER=x-forwarded-proto \
+HOST_HEADER=x-forwarded-host \
+PORT_HEADER=x-forwarded-port \
+bun ./build
+```
+
+The protocol header must contain `http` or `https`, without a colon. The port header must contain a number. Invalid values produce a `400 Bad Request` response. A header that is present but empty is ignored in favour of the fallback.
+
+> [!CAUTION] Only trust forwarded headers when requests can reach the server through a proxy you control. A direct client can spoof these headers.
+
+### Client addresses behind a proxy
+
+[`event.getClientAddress()`](https://svelte.dev/docs/kit/@sveltejs-kit#RequestEvent) uses `server.requestIP(request).address` by default. Set `ADDRESS_HEADER` to the name of a trusted proxy header when the direct peer is a proxy:
+
+```sh
+ADDRESS_HEADER=true-client-ip bun ./build
+```
+
+For `x-forwarded-for`, also set `XFF_DEPTH` to the number of trusted proxies. The default depth is `1`, and the adapter selects from the right side of the comma-separated list so client-supplied entries to the left cannot change the trusted result:
+
+```sh
+ADDRESS_HEADER=x-forwarded-for XFF_DEPTH=2 bun ./build
+```
+
+`XFF_DEPTH` must be an integer of at least `1`. `getClientAddress()` throws if the configured header is absent or contains fewer addresses than the configured depth.
+
+## Platform API
+
+The request event's `platform` property exposes the original Web API request received by Bun and the Bun server instance:
+
+```js
+/** @type {import('./$types').RequestHandler} */
+export function GET({ getClientAddress, platform }) {
+	return Response.json({
+		address: getClientAddress(),
+		requestUrl: platform.request.url,
+		serverId: platform.server.id,
+		pendingRequests: platform.server.pendingRequests,
+		pendingWebSockets: platform.server.pendingWebSockets
+	});
+}
+```
+
+`platform.request` remains the original request even when the adapter normalizes the request URL to a configured or proxy-derived public origin before passing it to SvelteKit.
+
+## Graceful shutdown
+
+On `SIGINT` or `SIGTERM`, the generated server calls `server.stop()`. Bun stops accepting new connections and the adapter waits for pending requests before emitting a `sveltekit:shutdown` process event with the signal name:
+
+```js
+process.on('sveltekit:shutdown', async (reason) => {
+	await jobs.stop();
+	await db.close();
+});
+```
+
+Connections that are still open after `SHUTDOWN_TIMEOUT` seconds are closed forcefully, so idle connections such as open event streams cannot delay the shutdown indefinitely. The value must be a non-negative integer and defaults to `30`.
+
+Sending a second shutdown signal forces the process to exit with status `1`.

packages/adapter-bun/.gitignore

@@ -0,0 +1,5 @@
+.DS_Store
+node_modules
+/files
+coverage/
+

packages/adapter-bun/CHANGELOG.md

@@ -0,0 +1,7 @@
+# @sveltejs/adapter-bun
+
+## 1.0.0-next.0
+
+### Patch Changes
+
+- Initial release

packages/adapter-bun/README.md

@@ -0,0 +1,30 @@
+# @sveltejs/adapter-bun
+
+SvelteKit adapter that builds a standalone server for the [Bun](https://bun.com/) runtime.
+
+```sh
+bun add -D @sveltejs/adapter-bun
+```
+
+```js
+import adapter from '@sveltejs/adapter-bun';
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+  plugins: [sveltekit({ adapter: adapter() })]
+});
+```
+
+Build with `bun run --bun build`, then run the default output with `bun ./build`.
+
+See the [adapter-bun documentation](https://svelte.dev/docs/kit/adapter-bun) for configuration,
+environment variables, compiled executables, proxy setup, and the Bun-specific platform API.
+
+## Changelog
+
+[View the package changelog](https://github.com/sveltejs/kit/blob/main/packages/adapter-bun/CHANGELOG.md).
+
+## License
+
+[MIT](LICENSE)