Add custom Dialer to ClientOptions

GODRIVER-195

Change-Id: I4060ae2af015d13b0ba206eb0a597c319a550c49

mongo/client.go

@@ -25,12 +25,13 @@ const defaultLocalThreshold = 15 * time.Millisecond
 
 // Client performs operations on a given topology.
 type Client struct {
-	topology       *topology.Topology
-	connString     connstring.ConnString
-	localThreshold time.Duration
-	readPreference *readpref.ReadPref
-	readConcern    *readconcern.ReadConcern
-	writeConcern   *writeconcern.WriteConcern
+	topologyOptions []topology.Option
+	topology        *topology.Topology
+	connString      connstring.ConnString
+	localThreshold  time.Duration
+	readPreference  *readpref.ReadPref
+	readConcern     *readconcern.ReadConcern
+	writeConcern    *writeconcern.WriteConcern
 }
 
 // NewClient creates a new client to connect to a cluster specified by the uri.
@@ -78,7 +79,11 @@ func newClient(cs connstring.ConnString, opts *ClientOptions) (*Client, error) {
 		}
 	}
 
-	topo, err := topology.New(topology.WithConnString(func(connstring.ConnString) connstring.ConnString { return client.connString }))
+	topts := append(
+		client.topologyOptions,
+		topology.WithConnString(func(connstring.ConnString) connstring.ConnString { return client.connString }),
+	)
+	topo, err := topology.New(topts...)
 	if err != nil {
 		return nil, err
 	}

mongo/client_options.go

@@ -9,7 +9,9 @@ package mongo
 import (
 	"time"
 
+	"github.com/mongodb/mongo-go-driver/core/connection"
 	"github.com/mongodb/mongo-go-driver/core/connstring"
+	"github.com/mongodb/mongo-go-driver/core/topology"
 )
 
 type option func(*Client) error
@@ -83,6 +85,30 @@ func (co *ClientOptions) ConnectTimeout(d time.Duration) *ClientOptions {
 	return &ClientOptions{next: co, opt: fn}
 }
 
+// Dialer specifies a custom dialer used to dial new connections to a server.
+func (co *ClientOptions) Dialer(d Dialer) *ClientOptions {
+	var fn option = func(c *Client) error {
+		c.topologyOptions = append(
+			c.topologyOptions,
+			topology.WithServerOptions(func(opts ...topology.ServerOption) []topology.ServerOption {
+				return append(
+					opts,
+					topology.WithConnectionOptions(func(opts ...connection.Option) []connection.Option {
+						return append(
+							opts,
+							connection.WithDialer(func(connection.Dialer) connection.Dialer {
+								return d
+							}),
+						)
+					}),
+				)
+			}),
+		)
+		return nil
+	}
+	return &ClientOptions{next: co, opt: fn}
+}
+
 // HeartbeatInterval specifies the interval to wait between server monitoring checks.
 func (co *ClientOptions) HeartbeatInterval(d time.Duration) *ClientOptions {
 	var fn option = func(c *Client) error {

mongo/client_options_test.go

@@ -1,6 +1,9 @@
 package mongo
 
 import (
+	"context"
+	"net"
+	"sync/atomic"
 	"testing"
 
 	"time"
@@ -97,3 +100,26 @@ func TestClientOptions_chainAll(t *testing.T) {
 		opts = opts.next
 	}
 }
+
+func TestClientOptions_CustomDialer(t *testing.T) {
+	td := &testDialer{d: &net.Dialer{}}
+	opts := ClientOpt.Dialer(td)
+	client, err := newClient(testutil.ConnString(t), opts)
+	require.NoError(t, err)
+	_, err = client.ListDatabases(context.Background(), nil)
+	require.NoError(t, err)
+	got := atomic.LoadInt32(&td.called)
+	if got < 1 {
+		t.Errorf("Custom dialer was not used when dialing new connections")
+	}
+}
+
+type testDialer struct {
+	called int32
+	d      Dialer
+}
+
+func (td *testDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	atomic.AddInt32(&td.called, 1)
+	return td.d.DialContext(ctx, network, address)
+}

mongo/mongo.go

@@ -7,16 +7,23 @@
 package mongo
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
+	"net"
 	"reflect"
 	"strings"
 
 	"github.com/mongodb/mongo-go-driver/bson"
 	"github.com/mongodb/mongo-go-driver/bson/objectid"
 )
 
+// Dialer is used to make network connections.
+type Dialer interface {
+	DialContext(ctx context.Context, network, address string) (net.Conn, error)
+}
+
 // TransformDocument handles transforming a document of an allowable type into
 // a *bson.Document. This method is called directly after most methods that
 // have one or more parameters that are documents.