Support arbitrary network dialers

conn.go

@@ -69,6 +69,18 @@ func (s transactionStatus) String() string {
 	panic("not reached")
 }
 
+type Dialer interface {
+	Dial(network, address string) (net.Conn, error)
+	DialTimeout(network, address string, timeout time.Duration) (net.Conn, error)
+}
+
+type defaultDialer struct{}
+
+func (d defaultDialer) Dial(ntw, addr string) (net.Conn, error) { return net.Dial(ntw, addr) }
+func (d defaultDialer) DialTimeout(ntw, addr string, timeout time.Duration) (net.Conn, error) {
+	return net.DialTimeout(ntw, addr, timeout)
+}
+
 type conn struct {
 	c         net.Conn
 	buf       *bufio.Reader
@@ -89,6 +101,10 @@ func (c *conn) writeBuf(b byte) *writeBuf {
 }
 
 func Open(name string) (_ driver.Conn, err error) {
+	return DialOpen(defaultDialer{}, name)
+}
+
+func DialOpen(d Dialer, name string) (_ driver.Conn, err error) {
 	defer func() {
 		// Handle any panics during connection initialization.  Note that we
 		// specifically do *not* want to use errRecover(), as that would turn
@@ -174,7 +190,7 @@ func Open(name string) (_ driver.Conn, err error) {
 		}
 	}
 
-	c, err := dial(o)
+	c, err := dial(d, o)
 	if err != nil {
 		return nil, err
 	}
@@ -188,7 +204,7 @@ func Open(name string) (_ driver.Conn, err error) {
 	return cn, err
 }
 
-func dial(o values) (net.Conn, error) {
+func dial(d Dialer, o values) (net.Conn, error) {
 	ntw, addr := network(o)
 
 	timeout := o.Get("connect_timeout")
@@ -207,14 +223,14 @@ func dial(o values) (net.Conn, error) {
 		// establishment and set a deadline for doing the initial handshake.
 		// The deadline is then reset after startup() is done.
 		deadline := time.Now().Add(duration)
-		conn, err := net.DialTimeout(ntw, addr, duration)
+		conn, err := d.DialTimeout(ntw, addr, duration)
 		if err != nil {
 			return nil, err
 		}
 		err = conn.SetDeadline(deadline)
 		return conn, err
 	}
-	return net.Dial(ntw, addr)
+	return d.Dial(ntw, addr)
 }
 
 func network(o values) (string, string) {