How StaticDeploy routes requests

Matching requests to entrypoints

A StaticDeploy installation can host thousands of websites, each deployed on a different entrypoint. The first thing StaticDeploy does upon receiving a request is to figure out which entrypoint is targeted by the request.

Every entrypoint specifies a urlMatcher, a domain + path combination which is used to match incoming requests. A request matches a url matcher (and its entrypoint) if its domain + path starts with the url matcher. For instance, a request for domain.com/foo/bar/baz would match all of the following url matchers:

  • domain.com/
  • domain.com/foo/
  • domain.com/foo/bar/
  • domain.com/foo/bar/baz/

It would not however match:

  • www.domain.com/
  • domain.com/foo/baz/

When more than one entrypoint matches the incoming request, StaticDeploy chooses the one with the longest url matcher, using the principle of choosing the "most specific" one.

When no entrypoint matches the incoming request, StaticDeploy responds with a 404 page.

Once an entrypoint for the incoming request has been found, StaticDeploy constructs the response according to the entrypoint's configuration:

  • if the entrypoint specifies a redirectTo, StaticDeploy responds with a 302 to the specified location
  • if the entrypoint specifies a bundleId, StaticDeploy matches the requested path to one of the assets of the entrypoint's bundle (read below how), and serves the asset

In the second case, before performing the requested path / asset match, StaticDeploy removes the path portion of the entrypoint's urlMatcher from the requested path, since it's just the base path at which the entryppoint's bundle is hosted, and the bundle's assets "know nothing" about it.

A note on the domain

An HTTP request contains the requested path in its start-line. The domain of the request can be usually found in the Host header, but that's not always the case, as proxies (eg CDNs) sitting between the user and the StaticDeploy server might modify it. When such modifications occur, proxies usually add the X-Forwarded-Host header to the proxied request, passing the original value of the Host header. If the header is present, StaticDeploy automatically uses its value. However, not all proxies adopt this behavior, and might instead pass the original value in another custom header. To account for this use case, you can configure StaticDeploy to use the custom header by passing it the HOSTNAME_HEADER configuration variable. Proxies that don't allow to pass the original Host header value in any way cannot unfortunately be used with StaticDeploy.

Serving assets

One of the main use cases for StaticDeploy is serving Single Page Applications (SPA). StaticDeploy's routing algorithm was designed to solve the problems that arise when SPAs do client-side routing using the HTML5 history API, i.e. when they change their path in the browser URL.

When StaticDeploy receives a request for a certain path, it tries to match the path to one of the assets of the bundle it's tasked to serve, even if the requested path is not strictly equal to the asset path. If it can't match the path to any asset, it serves the asset designated to be the fallback asset (typically /index.html).

Example

Let's assume StaticDeploy is serving a bundle with the assets: 

/
├── index.html
└── js/
    └── index.js

Falling back to a "catch all" asset

When a request is made for / or for /index.html, naturally StaticDeploy responds with the /index.html file. When a request is made instead for /some/path/, StaticDeploy tries to match it to one of the files in the directory. /some/path/ doesn't look anything like /index.html or /js/index.js, so StaticDeploy determines that no file matches the requested path, and serves the fallback asset, which happens to be /index.html.

This behaviour solves the problem of a user reloading a Single Page Application when the browser URL has been modified by client-side routing: instead of getting a 404 because the reloaded URL is not /, the browser receives the index.html and the app can restart without issues.

Serving files with a "similar" path

When a request is made for /js/index.js, naturally StaticDeploy responds with the /js/index.js file. But when a request is made for /some/path/js/index.js, instead of responding with a 404 or with the fallback asset, StaticDeploy sees that the requested path looks a lot like /js/index.js, assumes that the requester wanted that file, and responds with a 301, redirecting to the file's canonical path, i.e. /js/index.js.

This behavior saves the developer of the app from having to statically specify (in the code or at build time) the exact paths of the app's assets. In the example above, in the index.html file the developer can just point to the index.js file with a relative URL: ./js/index.js. Now even when /index.html is loaded - as a fallback - from /some/path/, ./js/index.js will be resolved by the browser to /some/path/js/index.js, which leads to the correct file.

This is especially useful when the app is deployed to an entrypoint "with a base path", e.g. example.com/base-path/. In this case, if the developer had to statically specify the exact paths, they'd have to know beforehand (or at most at build time) what the base path of the deployed app would be, an information they might not have or that might change over time, requiring the app to be rebuilt.

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