Creates the NormalizeAddr Func to Format IPv6 Addresses (#157)

Create NormalizeAddr which accepts addresses and returns a formatted copy of that address conformant with RFC5952

---------

Co-authored-by: Danielle Miu <29378233+DanielleMiu@users.noreply.github.com>

Author: kheina

parseutil/normalize.go

@@ -0,0 +1,121 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package parseutil
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"strings"
+)
+
+// general delimiters as defined in RFC-3986 §2.2
+// See: https://www.rfc-editor.org/rfc/rfc3986#section-2.2
+const genDelims = ":/?#[]@"
+
+func normalizeHostPort(host string, port string) (string, error) {
+	if host == "" {
+		return "", fmt.Errorf("empty hostname")
+	}
+	if ip := net.ParseIP(host); ip != nil {
+		if ip.To4() == nil && ip.To16() != nil && port == "" {
+			// this is a unique case, host is ipv6 and requires brackets due to
+			// being part of a url, but they won't be added by net.JoinHostPort
+			// as there is no port
+			// See: https://www.rfc-editor.org/rfc/rfc3986#section-3.2.2
+			return "[" + ip.String() + "]", nil
+		}
+		host = ip.String()
+	} else if strings.Contains(host, ":") {
+		// host is an invalid ipv6 literal.
+		// hosts cannot contain certain reserved characters, including ":"
+		// See: https://www.rfc-editor.org/rfc/rfc3986#section-2.2,
+		//      https://www.rfc-editor.org/rfc/rfc3986#section-3.2.2
+		return "", fmt.Errorf("host contains an invalid IPv6 literal")
+	}
+	if port == "" {
+		return host, nil
+	}
+	return net.JoinHostPort(host, port), nil
+}
+
+func parseUrl(addr string) (string, error) {
+	if u, err := url.Parse(addr); err == nil {
+		if strings.HasSuffix(u.Host, ":") {
+			return "", fmt.Errorf("url has malformed host: missing port value after colon")
+		}
+		if u.Host, err = normalizeHostPort(u.Hostname(), u.Port()); err != nil {
+			return "", err
+		}
+		return u.String(), nil
+	}
+	return "", fmt.Errorf("failed to parse address")
+}
+
+// NormalizeAddr takes an address as a string and returns a normalized copy.
+// If the address is a URL, IP Address, or host:port address that includes an
+// IPv6 address, the normalized copy will be conformant with RFC-5952 §4. If
+// the address cannot be parsed, an error will be returned.
+//
+// There are two valid formats:
+//
+// - hosts: "host"
+//   - may be any of: IPv6 literal, IPv4 literal, dns name, or [sub]domain name
+//   - IPv6 literals cannot be encapsulated within square brackets in this format
+//
+// - URIs: "[scheme://] [user@] host [:port] [/path] [?query] [#frag]"
+//   - format should conform with RFC-3986 §3 or else the returned address may
+//     be parsed and formatted incorrectly
+//   - hosts containing IPv6 literals MUST be encapsulated within square brackets,
+//     as defined in RFC-3986 §3.2.2 and RFC-5952 §6
+//   - all non-host components are optional
+//
+// See:
+//   - https://www.rfc-editor.org/rfc/rfc5952
+//   - https://www.rfc-editor.org/rfc/rfc3986
+func NormalizeAddr(address string) (string, error) {
+	if address == "" {
+		return "", fmt.Errorf("empty address")
+	}
+
+	if strings.HasPrefix(address, "[") && strings.HasSuffix(address, "]") {
+		return "", fmt.Errorf("address cannot be encapsulated by brackets")
+	}
+
+	if ip := net.ParseIP(address); ip != nil {
+		return ip.String(), nil
+	}
+
+	// if the provided address does not have a scheme provided, attempt to
+	// provide one and re-parse the result. this is done by looking for the
+	// first general delimiter and checking if it exists or if it's not a colon
+	// or by subsequently checking if the first character of the address is a
+	// letter or a colon or if the colon is part of "://"
+	// See: https://www.rfc-editor.org/rfc/rfc3986#section-3
+	//
+	// though the first character being a colon is not mentioned in the scheme
+	// spec, we check for it as url.Parse will read certain invalid ipv6
+	// addresses as valid urls, and we want to avoid that
+	idx := strings.IndexAny(address, genDelims)
+	switch {
+	case idx < 0:
+		fallthrough
+	case address[idx] != ':':
+		fallthrough
+		// by this point we already know that idx > 0 and that address[idx] == ':'
+	case idx > 1 && !strings.HasPrefix(address[idx:], "://"):
+		const scheme = "default://"
+		// attempt to parse it as a url. we only want to try this func when we
+		// know for sure it has a scheme, since it will parse ANYTHING, but
+		// just put it into u.Path when called without the scheme
+		u, err := parseUrl(scheme + address)
+		if err != nil {
+			return "", err
+		}
+		return strings.TrimPrefix(u, scheme), nil
+
+	default:
+		return parseUrl(address)
+	}
+}