Go Golang to serve a specific html file

Maybe using a custom http.HandlerFunc would be easier:

Except in your case, your func would be the http.ServeFile one, for serving just one file.

See for instance “Go Web Applications: Serving Static Files”:

Add the following below your home handler (see below):

http.HandleFunc("/static/", func(w http.ResponseWriter, r *http.Request) {
   // do NOT do this. (see below)
    http.ServeFile(w, r, r.URL.Path[1:])
})

This is using the net/http package’s ServeFile function to serve our content.
Effectively anything that makes a request starting with the /static/ path will be handled by this function.
One thing I found I had to do in order for the request to be handled correctly was trim the leading ‘/’ using:

r.URL.Path[1:]

Actually, do not do that.
This won’t be possible in Go 1.6, as sztanpet comments, with commit 9b67a5d:

If the provided file or directory name is a relative path, it is
interpreted relative to the current directory and may ascend to parent
directories.
If the provided name is constructed from user input, it should be sanitized before calling ServeFile.
As a precaution, ServeFile will reject requests where r.URL.Path contains a “..” path element.

That will protect against the following “url”:

/../file
/..
/../
/../foo
/..\\foo
/file/a
/file/a..
/file/a/..
/file/a\\..