Reload

Reload is a Go package, which enables "soft reloading" of web server assets and templates, reloading the browser instantly via Websockets. The strength of Reload lies in it's simple API and easy integration to any Go projects.

Installation

go get github.com/aarol/reload

Usage

Create a new Reloader and insert the middleware to your handler chain:

// handler can be anything that implements http.Handler,
// like chi.Router, echo.Echo or gin.Engine
var handler http.Handler = http.DefaultServeMux

if isDevelopment {
   // Call `New()` with a list of directories to recursively watch
   reloader := reload.New("ui/")

   // Optionally, define a callback to
   // invalidate any caches
   reloader.OnReload = func() {
      app.parseTemplates()
   }

   // Use the Handle() method as a middleware
   handler = reloader.Handle(handler)
}

http.ListenAndServe(addr, handler)

Run your application, make changes to files in the specified directories, and see the updated page instantly!

See the full example at https://github.com/aarol/reload/blob/main/example/main.go

Note

The browser often caches resources served by http.FileServer (because of Last-Modified headers generated from filesystem timestamps), which leads to unexpected caching issues when using this middleware. To prevent this, the middleware sends a "Cache-Control: no-cache" header. This is enabled by default, but can be disabled by setting the DisableCaching field to false.

Logging

By default, reload logs errors on stderr, with (*Reloader).ErrorLog. Error logging can be disabled by setting ErrorLog to nil.

There is also a logger which reports debug information, exposed as (*Reloader).DebugLog (nil by default)

How it works

When added to the top of the middleware chain, (*Reloader).Handle() will inject a small <script/> at the end of any HTML file sent by your application. This script will instruct the browser to open a WebSocket connection back to your server, which will be also handled by the middleware.

The injected script is in reload.go.

You can also do the injection yourself, as the package also exposes the methods (*Reloader).ServeWS and (*Reloader).WatchDirectories, which are used by the (*Reloader).Handle middleware.

Currently, injecting the script is done by appending to the end of the document, even after the </html> tag. This makes the library code much simpler, but may break older/less forgiving browsers.

All modern browser accept this and will accept for the forseeable future to avoid breaking the web.

Caveats

Reload works with everything that the server sends to the client (HTML,CSS,JS etc.), but it cannot restart the server itself, since it's just a middleware running on the server.

To reload the entire server, you can use another file watcher on top, like gow:

gow run .

When the websocket connection to the server is lost, the browser will try to reconnect every second. This means that when the server comes back, the browser will still reload, although not as fast :)
Reload will not work for embedded assets, since all go:embed files are baked into the executable at build time.

License

aarol/reload

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