testutils: revert to call url.Parse and update doc

internal/testutils/parse_url.go

@@ -20,32 +20,24 @@ package testutils
 
 import (
 	"fmt"
-	"net"
 	"net/url"
 	"strings"
 )
 
-// Assume url.Parse may fail when rawTarget represents IPV4 or IPV6.
-func parseTargetAsIP(rawTarget string, urlParseError error) *url.URL {
-	ip := net.ParseIP(rawTarget) // TODO (easwars): should this be added to grpc.parseTarget?
-	if ip == nil {
-		panic(fmt.Sprintf("Error parsing target(%s): %v", rawTarget, urlParseError))
-	}
-	return &url.URL{
-		Path: ip.String(),
-	}
-}
-
-// MustParseURL helps create URL struct for resolver.Target by parsing target.
-// Target can be represented as either URL, IPV4, or IPV6.
+// MustParseURL uses RFC 3986 semantics to parse given target into a
+// `URL` struct for `resolver.Target.URL`. The leading "/" are stripped
+// to avoid breaking existing resolver implementations.
+// See resolver.Target.ToEndpoint() for more information.
+//
+// rawTarget represents either URL, IPv4, or IPv6 string.
 func MustParseURL(rawTarget string) *url.URL {
 	u, err := url.Parse(rawTarget)
 	if err != nil {
-		return parseTargetAsIP(rawTarget, err)
+		panic(fmt.Sprintf("Error parsing target(%s): %v", rawTarget, err))
 	}
 	return &url.URL{
 		Scheme: u.Scheme,
 		Path:   strings.TrimPrefix(u.Path, "/"),
-		Opaque: u.Opaque,
+		Opaque: strings.TrimPrefix(u.Opaque, "/"),
 	}
 }