GoLang Get String at Line N in Byte Slice

In a personal project I am implementing a function that returns a random line from a long file. For it to work I have to create a function that returns a string at line N, a second function that creates a random number between 0 and lines in file. While I was implementing those I figured it may be more efficient to store the data in byte slices by default, rather than storing them in separate files, which have to be read at run time.

Question: How would I go about implementing a function that returns a string at a random line of the []byte representation of my file.

My function for getting a string from a file:

func atLine(n int) (s string) {
    f, err := os.Open("./path/to/file")
    if err != nil {
        panic("Could not read file.")
    }
    defer f.Close()
    r := bufio.NewReader(f)
    for i := 1; ; i++ {
        line, _, err := r.ReadLine()
        if err != nil {
            break
        }
        if i == n {
            s = string(line[:])
            break
        }
    }
    return s
}

Additional info:

• Lines are not longer than 50 characters at most
• Lines have no special characters (although a solution handling those is welcome)
• Number of lines in the files is known and so the same can be applied for []byte