GODRIVER-383: set server selection timeout in topology from connstring

Change-Id: I61ca1567ee8869756681940f432912306ac1eacd

Author: Sam Kleinman

core/topology/topology_options.go

@@ -50,6 +50,11 @@ func WithConnString(fn func(connstring.ConnString) connstring.ConnString) Option
 	return func(c *config) error {
 		cs := fn(c.cs)
 		c.cs = cs
+
+		if cs.ServerSelectionTimeoutSet {
+			c.serverSelectionTimeout = cs.ServerSelectionTimeout
+		}
+
 		var connOpts []connection.Option
 
 		if cs.AppName != "" {

core/topology/topology_options_test.go

@@ -0,0 +1,27 @@
+package topology
+
+import (
+	"testing"
+	"time"
+
+	"github.com/mongodb/mongo-go-driver/core/connstring"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOptionsSetting(t *testing.T) {
+	conf := &config{}
+	ssts := time.Minute
+	assert.Zero(t, conf.cs)
+
+	opt := WithConnString(func(connstring.ConnString) connstring.ConnString {
+		return connstring.ConnString{
+			ServerSelectionTimeout:    ssts,
+			ServerSelectionTimeoutSet: true,
+		}
+
+	})
+
+	assert.NoError(t, opt(conf))
+
+	assert.Equal(t, ssts, conf.serverSelectionTimeout)
+}