contrib/globalsign/mgo: check for error after dialing to avoid panic (#…

…937)

This commit fixes a bug causing a panic when mgo fails to dial the database.

Fixes #870

contrib/globalsign/mgo/mgo.go

@@ -22,13 +22,19 @@ import (
 // for tracing.
 func Dial(url string, opts ...DialOption) (*Session, error) {
 	session, err := mgo.Dial(url)
-	info, _ := session.BuildInfo()
+	if err != nil {
+		return nil, err
+	}
+	version := "unknown"
+	if info, err := session.BuildInfo(); err == nil {
+		version = info.Version
+	}
 	s := &Session{
 		Session: session,
 		cfg:     newConfig(),
 		tags: map[string]string{
 			"hosts":       strings.Join(session.LiveServers(), ", "),
-			"mgo_version": info.Version,
+			"mgo_version": version,
 		},
 	}
 	for _, fn := range opts {

contrib/globalsign/mgo/mgo_test.go

@@ -387,6 +387,10 @@ func TestCollection_Bulk(t *testing.T) {
 	assert.Equal("mongodb.query", spans[0].OperationName())
 }
 
+func TestBadDial(t *testing.T) {
+	assert.NotPanics(t, func() { Dial("this_is_not_valid?foo&bar") })
+}
+
 func TestAnalyticsSettings(t *testing.T) {
 	assertRate := func(t *testing.T, mt mocktracer.Tracer, rate interface{}, opts ...DialOption) {
 		assert := assert.New(t)