Add LocalAddresser interface

GODRIVER-1209

Change-Id: I4d16f802f401ed4e0609888ac73cb66f393d3431

Author: eppingere

x/mongo/driver/driver.go

@@ -30,6 +30,11 @@ type Connection interface {
 	Address() address.Address
 }
 
+// LocalAddresser is a type that is able to supply its local address
+type LocalAddresser interface {
+	LocalAddress() address.Address
+}
+
 // Expirable represents an expirable object.
 type Expirable interface {
 	Expire() error

x/mongo/driver/topology/connection.go

@@ -272,6 +272,12 @@ func (c initConnection) Description() description.Server { return description.Se
 func (c initConnection) Close() error                    { return nil }
 func (c initConnection) ID() string                      { return c.id }
 func (c initConnection) Address() address.Address        { return c.addr }
+func (c initConnection) LocalAddress() address.Address {
+	if c.connection == nil || c.nc == nil {
+		return address.Address("0.0.0.0")
+	}
+	return address.Address(c.nc.LocalAddr().String())
+}
 func (c initConnection) WriteWireMessage(ctx context.Context, wm []byte) error {
 	return c.writeWireMessage(ctx, wm)
 }
@@ -430,6 +436,16 @@ func (c *Connection) Address() address.Address {
 	return c.addr
 }
 
+// LocalAddress returns the local address of the connection
+func (c *Connection) LocalAddress() address.Address {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	if c.connection == nil || c.nc == nil {
+		return address.Address("0.0.0.0")
+	}
+	return address.Address(c.nc.LocalAddr().String())
+}
+
 var notMasterCodes = []int32{10107, 13435}
 var recoveringCodes = []int32{11600, 11602, 13436, 189, 91}
 

x/mongo/driver/topology/connection_test.go

@@ -332,6 +332,12 @@ func TestConnection(t *testing.T) {
 			if !cmp.Equal(got, want) {
 				t.Errorf("Addresses do not match. got %v; want %v", got, want)
 			}
+
+			want = address.Address("0.0.0.0")
+			got = conn.LocalAddress()
+			if !cmp.Equal(got, want) {
+				t.Errorf("LocalAddresses do not match. got %v; want %v", got, want)
+			}
 		})
 	})
 }