Include remote address in request header

[TheHackerDev]

Includes the remote address in the request, following RFC 7239, section 4.

This is not going to be exact for every case, because http.Request.RemoteAddr has no defined format (see https://golang.org/src/net/http/request.go#L260). However, http.Server sets the address to IP:port, so it is safe to go with that.

NOTE: I was unable to check this with an IPv6 source address. Please do so before merging, to confirm that IPv6 source addresses get transformed to look like the following header:

Forwarded: For="[2001:db8:cafe::17]"

I was mostly unsure as to whether the http.Server set the remoteAddr value for IPv6 addresses with square brackets or not. The assumption in the code's logic right now is that it does not.

Cheers,
Aaron (insp3ctre)

[yanc0]

Thanks Aaron !

[TheHackerDev]

No problem, Yann!

Cheers,
Aaron (insp3ctre)

[yanc0]

Hi Aaron,

I've just fetch your PR locally and bound Beeping on an IPv6 address. It almost works, I get the header but with too much surround brackets:

Forwarded: for="[[2002:c000:203::1]]"

There is no need to add brackets when you split IP:PORT, they are apparently already there in the request.RemoteAddr

The fix could be:

-               srcIP := "["
+               var srcIP string
                for index := 0; index < len(srcSlice)-2; index++ {
                        srcIP += fmt.Sprintf("%s:", srcSlice[index])
                }
-               srcIP += fmt.Sprintf("%s]", srcSlice[len(srcSlice)-2])
+               srcIP += fmt.Sprintf("%s", srcSlice[len(srcSlice)-2])
                req.Header.Set("Forwarded", fmt.Sprintf("for=\"%s\"", srcIP))

Here are my tests on Debian:
Create HTTP bin on https://requestb.in

$ sudo ip -6 addr add 2002:c000:203::1/64 dev wlan0
$ ./beeping -listen "[2002:c000:203::1]"
$ curl -6 '[2002:c000:203::1]:8080/check' -d '{"url": "https://requestb.in/15qre161"}'

Thanks Aaron !
Cheers,
Yann