Escape exclamation mark in http request

I have a URL like

http://app.chat.com/avert!Callbcak.htm

to request.

I created the request with golang

req, _ := http.NewRequest("GET", "http://app.chat.com/avert!Callbcak.htm", nil)
fmt.Printf("%v\n", req.URL.String())

result is

http://app.chat.com/avert%21Callbcak.htm

which is not going to work, the website needs URL that exclamation mark not escaped.

How can I request that URL correctly?

finally I found answer here

I process the request before sending:

func (s *Sender) regulateRequestURL(req *http.Request) {
    if strings.Contains(req.URL.Path, "!") {
        req.URL.Opaque = fmt.Sprintf("//%s%s", req.URL.Host, req.URL.Path)
    }
}

From https://www.rfc-editor.org/rfc/rfc3986

> Section 2, on characters, has been rewritten to explain what
> characters are reserved, when they are reserved, and why they are
> reserved, even when they are not used as delimiters by the generic
> syntax. The mark characters that are typically unsafe to decode,
> including the exclamation mark ("!"), asterisk ("*"), single-quote
> ("'"), and open and close parentheses ("(" and ")"), have been moved
> to the reserved set in order to clarify the distinction between
> reserved and unreserved and, hopefully, to answer the most common
> question of scheme designers. Likewise, the section on
> percent-encoded characters has been rewritten, and URI normalizers
> are now given license to decode any percent-encoded octets

This means that ! is an unfortunate choice of a separator because although the grammar allows its use in segment (as part of the pchar non-terminal) it is also a part of the reserved non-terminal.

As I read it the RFC is slightly ambivalent about ! reservedness, depending upon the context in which it is used.

Escaping the character seems the most safe assumption to make since the recipient is "licenced to decode the percent-encoded octet". You should consider using another separator or decoding the entity on the endpoint.