fixes #1746 Create a new socket:// transport for socketpair() based connections

This transport only listens, and creates connections when
the application calls setopt on the lister with NNG_OPT_SOCKET_FD,
to pass a file descriptor.  The FD is turned into an nng_stream,
and utilized for SP.  The protocol over the descriptor is identical
to the TCP protocol (not the IPC protocol).

The options for peer information are borrowed from the IPC transport,
as they may be useful for these purposes.

This includes a test suite and full documentation.

2 files changed, 58 insertions, 0 deletions

diff --git a/src/platform/windows/CMakeLists.txt b/src/platform/windows/CMakeLists.txt
index d1d158e0..adf67ebd 100644
--- a/src/platform/windows/CMakeLists.txt
+++ b/src/platform/windows/CMakeLists.txt
@@ -39,6 +39,7 @@ if (NNG_PLATFORM_WINDOWS)
             win_rand.c
             win_resolv.c
             win_sockaddr.c
+            win_socketpair.c
             win_tcp.c
             win_tcpconn.c
             win_tcpdial.c
diff --git a/src/platform/windows/win_socketpair.c b/src/platform/windows/win_socketpair.c
new file mode 100644
index 00000000..0ed0443a
--- /dev/null
+++ b/src/platform/windows/win_socketpair.c
@@ -0,0 +1,57 @@
+//
+// Copyright 2023 Staysail Systems, Inc. <info@staysail.tech>
+//
+// This software is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+#include "core/nng_impl.h"
+
+
+#ifdef NNG_HAVE_SOCKETPAIR_TODO
+// TODO: Windows lacks socketpair.  We can emulate it with an explcit
+// implementation based on AF_UNIX.
+
+#include <errno.h>
+#include <sys/socket.h>
+
+int
+nni_socket_pair(int *fds)
+{
+	int rv;
+	rv = socketpair(PF_UNIX, SOCK_STREAM, 0, fds);
+	if (rv != 0) {
+		return (nni_plat_errno(errno));
+	}
+
+	return (0);
+}
+#else
+int
+nni_socket_pair(int fds[2])
+{
+	NNI_ARG_UNUSED(fds);
+	return (NNG_ENOTSUP);
+}
+
+// This is also the fdc transport.
+
+typedef struct nni_sfd_conn nni_sfd_conn;
+
+void
+nni_sfd_close_fd(int fd)
+{
+	NNI_ARG_UNUSED(fd);
+}
+
+int
+nni_sfd_conn_alloc(nni_sfd_conn **cp, int fd)
+{
+	NNI_ARG_UNUSED(cp);
+	NNI_ARG_UNUSED(fd);
+	return (NNG_ENOTSUP);
+}
+
+#endif