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Static file server for Spin applications

A simple static file server as a Spin HTTP component, written in Rust.

This component is now fully componentized and can be used with any runtime that supports wasi:http@0.2.0-rc-2023-10-18, such as Spin 2.0, wasmtime and NGINX Unit.

Building from source


Compiling the component:

$ cargo component build --release

See the examples directory for examples of using and composing spin-fileserver with applications.



  • Rust at 1.72+ with the wasm32-wasi target configured

Running test cases:

$ make test

Using the component as part of a Spin application

The easiest way to use this the Spin fileserver component in your application is to add it via its Spin template.

To create a new Spin app based on this component, run:

$ spin new -t static-fileserver

To add this component to your existing Spin app, run:

$ spin add -t static-fileserver

If you're looking to upgrade the version of this component in your application from one of the releases, select the release and corresponding checksum and update the component's source in the application's spin.toml, e.g.:

source = { url = "", digest = "sha256:96c76d9af86420b39eb6cd7be5550e3cb5d4cc4de572ce0fd1f6a29471536cb4" }

Next, we'll look at running the file server directly as well as using component composition to integrate this component in with your application logic.

Running the file server

Let's have a look at the component definition (from spin.toml):

route = "/..."
component = "fs"

# For more on configuring a component, see:
source = "target/wasm32-wasi/release/spin_static_fs.wasm"
files = [{ source = "", destination = "/" }]
command = "make"

This component will recursively mount all files from the current directory and will serve them at the configured route. If an index.html file is in the source root, it will be served if no file is specified.

Running the static server:

$ spin up --listen --file spin.toml

At this point, the component is going to serve all files in the current directory, and this can be tested using curl:

$ curl localhost:3000/LICENSE
                              Apache License
                        Version 2.0, January 2004


See also the rust-standalone example showing use of the file server alongside a simple Rust-based application.

Component composition with the file server

The file server can also be composed with application logic to form one binary that can be run as a Spin application. See the following examples using the language and toolchains of your choice:

Configuration options

The Spin fileserver supports various configuration options.

Setting the cache header

Currently, this file server has a single cache header that it can set through the CACHE_CONTROL environment variable. If no value is set, the default max-age=60 is used instead for all media types.

Setting the fallback path

You can configure a FALLBACK_PATH environment variable that points to a file that will be returned instead of the default 404 Not Found response. If no environment value is set, the default behavior is to return a 404 Not Found response. This behavior is useful for Single Page Applications that use view routers on the front-end like React and Vue.

# For more on configuring a component, see:
source = "target/wasm32-wasi/release/spin_static_fs.wasm"
files = [{ source = "test", destination = "/" }]
environment = { FALLBACK_PATH = "index.html" }

Using a custom 404 document

You can configure a CUSTOM_404_PATH environment variable and point to a file that will be served instead of returning a plain 404 Not Found response. Consider the following sample where the spin-fileserver component is configured to serve all files from the test folder. The desired page must exist in the test folder to send a custom 404 HTML page (here, 404.html) instead of a plain 404 Not Found response.

# For more on configuring a component, see:
source = "target/wasm32-wasi/release/spin_static_fs.wasm"
files = [{ source = "test", destination = "/" }]
environment = { CUSTOM_404_PATH = "404.html" }

Fallback favicon

If you haven't specified a favicon in your HTML document, spin-fileserver will serve the Spin logo as the fallback favicon. The spin-fileserver also serves the fallback favicon if the file (called favicon.ico or favicon.png) specified in your <link rel="shortcut icon" ...> element does not exist.

Remember that there are situations where spin-fileserver cannot serve the fallback favicon if no <link rel="shortcut icon" ...> element is specified. Browsers try to find the favicon in the root directory of the origin ( If the application doesn't listen for requests targeting that route, it can't intercept requests to non-existing favicons.