expose methods from underlying connection types

This sucks but I can't think of a better way to do this. We really do want to
expose these features and doing so through type assertions is very go-like.

Author: Stebalien

net.go

@@ -28,8 +28,64 @@ type Conn interface {
 	RemoteMultiaddr() ma.Multiaddr
 }
 
-// WrapNetConn wraps a net.Conn object with a Multiaddr
-// friendly Conn.
+type halfOpen interface {
+	net.Conn
+	CloseRead() error
+	CloseWrite() error
+}
+
+func wrap(nconn net.Conn, laddr, raddr ma.Multiaddr) Conn {
+	endpts := maEndpoints{
+		laddr: laddr,
+		raddr: raddr,
+	}
+	// This sucks. However, it's the only way to reliably expose the
+	// underlying methods. This way, users that need access to, e.g.,
+	// CloseRead and CloseWrite, can do so via type assertions.
+	switch nconn := nconn.(type) {
+	case *net.TCPConn:
+		return &struct {
+			*net.TCPConn
+			maEndpoints
+		}{nconn, endpts}
+	case *net.UDPConn:
+		return &struct {
+			*net.UDPConn
+			maEndpoints
+		}{nconn, endpts}
+	case *net.IPConn:
+		return &struct {
+			*net.IPConn
+			maEndpoints
+		}{nconn, endpts}
+	case *net.UnixConn:
+		return &struct {
+			*net.UnixConn
+			maEndpoints
+		}{nconn, endpts}
+	case halfOpen:
+		return &struct {
+			halfOpen
+			maEndpoints
+		}{nconn, endpts}
+	default:
+		return &struct {
+			net.Conn
+			maEndpoints
+		}{nconn, endpts}
+	}
+}
+
+// WrapNetConn wraps a net.Conn object with a Multiaddr friendly Conn.
+//
+// This function does it's best to avoid "hiding" methods exposed by the wrapped
+// type. Guarantees:
+//
+// * If the wrapped connection exposes the "half-open" closer methods
+//   (CloseWrite, CloseRead), these will be available on the wrapped connection
+//   via type assertions.
+// * If the wrapped connection is a UnixConn, IPConn, TCPConn, or UDPConn, all
+//   methods on these wrapped connections will be available via type assertions.
 func WrapNetConn(nconn net.Conn) (Conn, error) {
 	if nconn == nil {
 		return nil, fmt.Errorf("failed to convert nconn.LocalAddr: nil")
@@ -45,30 +101,23 @@ func WrapNetConn(nconn net.Conn) (Conn, error) {
 		return nil, fmt.Errorf("failed to convert nconn.RemoteAddr: %s", err)
 	}
 
-	return &maConn{
-		Conn:  nconn,
-		laddr: laddr,
-		raddr: raddr,
-	}, nil
+	return wrap(nconn, laddr, raddr), nil
 }
 
-// maConn implements the Conn interface. It's a thin wrapper
-// around a net.Conn
-type maConn struct {
-	net.Conn
+type maEndpoints struct {
 	laddr ma.Multiaddr
 	raddr ma.Multiaddr
 }
 
 // LocalMultiaddr returns the local address associated with
 // this connection
-func (c *maConn) LocalMultiaddr() ma.Multiaddr {
+func (c *maEndpoints) LocalMultiaddr() ma.Multiaddr {
 	return c.laddr
 }
 
 // RemoteMultiaddr returns the remote address associated with
 // this connection
-func (c *maConn) RemoteMultiaddr() ma.Multiaddr {
+func (c *maEndpoints) RemoteMultiaddr() ma.Multiaddr {
 	return c.raddr
 }
 
@@ -135,12 +184,7 @@ func (d *Dialer) DialContext(ctx context.Context, remote ma.Multiaddr) (Conn, er
 			return nil, err
 		}
 	}
-
-	return &maConn{
-		Conn:  nconn,
-		laddr: local,
-		raddr: remote,
-	}, nil
+	return wrap(nconn, local, remote), nil
 }
 
 // Dial connects to a remote address. It uses an underlying net.Conn,
@@ -204,11 +248,7 @@ func (l *maListener) Accept() (Conn, error) {
 		return nil, fmt.Errorf("failed to convert connn.RemoteAddr: %s", err)
 	}
 
-	return &maConn{
-		Conn:  nconn,
-		laddr: l.laddr,
-		raddr: raddr,
-	}, nil
+	return wrap(nconn, l.laddr, raddr), nil
 }
 
 // Multiaddr returns the listener's (local) Multiaddr.

net_test.go

@@ -407,12 +407,14 @@ func TestWrapNetConn(t *testing.T) {
 		defer wg.Done()
 		cB, err := listener.Accept()
 		checkErr(err, "failed to accept")
+		_ = cB.(halfOpen)
 		cB.Close()
 	}()
 
 	cA, err := net.Dial("tcp", listener.Addr().String())
 	checkErr(err, "failed to dial")
 	defer cA.Close()
+	_ = cA.(halfOpen)
 
 	lmaddr, err := FromNetAddr(cA.LocalAddr())
 	checkErr(err, "failed to get local addr")
@@ -422,6 +424,8 @@ func TestWrapNetConn(t *testing.T) {
 	mcA, err := WrapNetConn(cA)
 	checkErr(err, "failed to wrap conn")
 
+	_ = mcA.(halfOpen)
+
 	if mcA.LocalAddr().String() != cA.LocalAddr().String() {
 		t.Error("wrapped conn local addr differs")
 	}