Support DNS seedlist / `mongodb+srv://` about mgo HOT 10 OPEN

imports github.com/globalsign/mgo/internal/scram: use of internal package not allowed

$ git diff session.go
diff --git a/session.go b/session.go
index cd2a53e..488712f 100644
--- a/session.go
+++ b/session.go
@@ -788,7 +788,13 @@ type urlInfoOption struct {
 }

 func extractURL(s string) (*urlInfo, error) {
-       s = strings.TrimPrefix(s, "mongodb://")
+       isSRV := false
+       if strings.Index(s, "mongodb+srv://") == 0 {
+               isSRV = true
+               s = strings.TrimPrefix(s, "mongodb+srv://")
+       } else {
+               s = strings.TrimPrefix(s, "mongodb://")
+       }
        info := &urlInfo{options: []urlInfoOption{}}

        if c := strings.Index(s, "?"); c != -1 {
@@ -824,6 +830,32 @@ func extractURL(s string) (*urlInfo, error) {
                s = s[:c]
        }
        info.addrs = strings.Split(s, ",")
+       if isSRV == true {
+               // auto turn off ssl
+               info.options = append(info.options, urlInfoOption{key: "ssl", value: "true"})
+               srvAddr := info.addrs[0]
+               params, pe := net.LookupTXT(srvAddr)
+               if pe != nil {
+                       return nil, fmt.Errorf(pe.Error())
+               }
+               for _, pair := range strings.FieldsFunc(params[0], isOptSep) {
+                       l := strings.SplitN(pair, "=", 2)
+                       if len(l) != 2 || l[0] == "" || l[1] == "" {
+                               return nil, errors.New("connection option must be key=value: " + pair)
+                       }
+                       info.options = append(info.options, urlInfoOption{key: l[0], value: l[1]})
+               }
+               _, addrs, le := net.LookupSRV("mongodb", "tcp", srvAddr)
+               if le != nil {
+                       return nil, fmt.Errorf(le.Error())
+               }
+               addresses := make([]string, len(addrs))
+               for i, addr := range addrs {
+                       address := strings.TrimSuffix(addr.Target, ".")
+                       addresses[i] = fmt.Sprintf("%s:%d", address, addr.Port)
+               }
+               info.addrs = addresses
+       }
        return info, nil
 }

@@ -2912,7 +2944,6 @@ func (p *Pipe) SetMaxTime(d time.Duration) *Pipe {
        return p
 }