Golang serving static files, please explain what is happening in these 3 lines of code

Question

I'm learning go web programming and understand everthing but I'm getting lost in this 3 apparently simple lines:
fs := http.FileServer(http.Dir("public"))
handler := http.StripPrefix("/static/", fs)
mux.Handle("/static/", handler)

...I have read the go src for the following lines and this is what I can infer:
http.Dir("public") is casting string "public" to type Dir.
then we serve a file (including all its content) with http.FileServer()
We strip prefix because now we are inside a handleFunc() for fs
StripPrefix() created a HandlerFunc()
mux.Handle() registers HandlerFunc() in the mux.
Deep goes the rabbit hole... and then this goroutine go c.serve(ctx) by func (srv *Server) Serve(l net.Listener) error {}
So each static file inside /public/ dir is served concurrently by our server.

Can someone confirm or explain what exactly is happening in the 3 lines of code.

Aditya Agrawal · Accepted Answer

After looking at the docs I think this is what happens: http.Di("public") you are converting the string "public" to the type Dir which implements the FileSystem interface fs := http.FileServer(http.Dir("public")) which according to the docs does: FileServer returns a handler that serves HTTP requests with the contents of the file system rooted at root. root being the Dir you are passing as a parameter handler := http.StripPrefix("/static/", fs) you wrap the Handler fs in the Handler created by the StripPrefix func which according to the docs does: StripPrefix returns a handler that serves HTTP requests by removing the given prefix from the request URL's Path and invoking the handler h h being the Handler fs you are passing as a parameter mux.Handle("/static/", handler) you let all requests starting with the path /static/ be handled by handler So in short all requests for the the path /static/ will get stripped of the /static/ prefix and will return a file from the public directory on you server with the same name, eg. a request to /static/requestedFile.txt will return the file under public/requestedFile.txt

Aditya Agrawal · Answer

package main import ( "log" "net/http" ) func main() { fs := http.FileServer(http.Dir("static")) http.Handle("/", fs) log.Println("Listening...") http.ListenAndServe(":3000", nil) } The selected route is /static/, then later all requests initiated by /static/will be directed here. Register a route using http.Handle()is different from using routing http.HandleFunc(), more clearly there will be a little explanation in another chapter. Function http.FileServer()returns object of type http.Handler. This function is useful for serving all http requests, with content defined in the parameters. In this context what is meant is http.Dir("assets"). All contents, whether files or folders, that are in the folder assetswill be processed in the handler.

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