Golang提供静态文件，请解释这三行代码会发生什么

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:

1. http.Dir("public") is casting string "public" to type Dir.
2. then we serve a file (including all its content) with http.FileServer()
3. We strip prefix because now we are inside a handleFunc() for fs
4. StripPrefix() created a HandlerFunc()
5. mux.Handle() registers HandlerFunc() in the mux.
6. Deep goes the rabbit hole... and then this goroutine go c.serve(ctx) by func (srv *Server) Serve(l net.Listener) error {}
7. 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.

Answer 1

After looking at the docs I think this is what happens:

http.Dir("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