net.peer.ip not filled for IPv6

[garthk]

Description

Spec check: should net.client.ip be filled consistently for both IPv4 and IPv6?

Environment

• OS: Any
• Architecture: Any
• Go Version: 1.15
• opentelemetry-go version: 1.0.1

Steps To Reproduce

1. Fire up any “hello, world” implementation on port 8090
2. Make requests via HTTP and HTTPS, eg. curl -4 :8090 and curl -6 :8090
3. Observe net.peer.ip is populated for IPv4 ("127.0.0.1") but not for IPv6
4. Observe net.peer.name is populated for IPv6 ("[::1]") but not for IPv4

Expected behavior

I expect net.peer.ip to contain the network peer IP address for both IPv4 and IPv6.

In the IPv6 case, r.RemoteAddr is "[::1]:54321" matching RFC 5952's Notes on Combining IPv6 Addresses with Port Numbers. net.SplitHostPort splits that to {"::1", "54321"} but we're not using it. Rather, we're using strings.LastIndexOf and trusting net.ParseIP will handle [::1]. It doesn't, so we end up with net.peer.name set to [::1] and net.peer.ip absent:

opentelemetry-go/semconv/v1.4.0/http.go

Lines 54 to 78 in cdf67dd

	peerName, peerIP, peerPort := "", "", 0
	{
	hostPart := request.RemoteAddr
	portPart := ""
	if idx := strings.LastIndex(hostPart, ":"); idx >= 0 {
	hostPart = request.RemoteAddr[:idx]
	portPart = request.RemoteAddr[idx+1:]
	}
	if hostPart != "" {
	if ip := net.ParseIP(hostPart); ip != nil {
	peerIP = ip.String()
	} else {
	peerName = hostPart
	}
	if portPart != "" {
	numPort, err := strconv.ParseUint(portPart, 10, 16)
	if err == nil {
	peerPort = (int)(numPort)
	} else {
	peerName, peerIP = "", ""
	}
	}
	}
	}