在浏览器中不使用https时，Golang ListenAndServeTLS返回数据

Question

The following is my tls backend:

package main

import (
    "fmt"
    "net/http"
)

const (
    PORT       = ":8443"
    PRIV_KEY   = "./private_key"
    PUBLIC_KEY = "./public_key"
)

func rootHander(w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Nobody should read this.")
}

func main() {
    http.HandleFunc("/", rootHander)
    err := http.ListenAndServeTLS(PORT, PUBLIC_KEY, PRIV_KEY, nil)
    if err != nil {
        fmt.Printf("main(): %s
", err)
    }
}

The keys are generated using these two lines:

openssl genrsa -out private_key 2048
openssl req -new -x509 -key private_key -out public_key -days 365

When I start the tls server, and visit the site with a browser (https://example.com:8443) I get the expected result, after ignoring the browser warning:

Nobody should read this.

So far everything is cool.

Now, when I point my browser to http://example.com:8443 (notice that http is used, not https) I get the following result for Firfox (Chrome does the same, but downloading the site):

Question: Why is there a question mark?

Answer 1

If you pipe the output into od, curl -k -3 http://localhost:8443 | od -A n -t x1, you get the following sequence of bytes 15 03 01 00 02 02 0a which is rendered/handled by the browser.

Which, according to https://code.google.com/p/go/issues/detail?id=2253, is TLS for "I didn't understand what you said."