Begin work on full device<->device unit-test

To simulate a full interaction between two WireGuard
instances without networking, using dummy instances of the interfaces

bind_test.go

@@ -0,0 +1,50 @@
+package main
+
+import "errors"
+
+type DummyDatagram struct {
+	msg      []byte
+	endpoint Endpoint
+	world    bool // better type
+}
+
+type DummyBind struct {
+	in6    chan DummyDatagram
+	ou6    chan DummyDatagram
+	in4    chan DummyDatagram
+	ou4    chan DummyDatagram
+	closed bool
+}
+
+func (b *DummyBind) SetMark(v uint32) error {
+	return nil
+}
+
+func (b *DummyBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
+	datagram, ok := <-b.in6
+	if !ok {
+		return 0, nil, errors.New("closed")
+	}
+	copy(buff, datagram.msg)
+	return len(datagram.msg), datagram.endpoint, nil
+}
+
+func (b *DummyBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
+	datagram, ok := <-b.in4
+	if !ok {
+		return 0, nil, errors.New("closed")
+	}
+	copy(buff, datagram.msg)
+	return len(datagram.msg), datagram.endpoint, nil
+}
+
+func (b *DummyBind) Close() error {
+	close(b.in6)
+	close(b.in4)
+	b.closed = true
+	return nil
+}
+
+func (b *DummyBind) Send(buff []byte, end Endpoint) error {
+	return nil
+}