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.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/core/sockfd.h b/src/core/sockfd.h
new file mode 100644
index 00000000..ca37f0e1
--- /dev/null
+++ b/src/core/sockfd.h
@@ -0,0 +1,28 @@
+//
+// 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.
+//
+
+#ifndef CORE_FDC_H
+#define CORE_FDC_H
+
+#include "core/nng_impl.h"
+
+// the nni_sfd_conn struct is provided by platform code to wrap
+// an arbitrary byte stream file descriptor (UNIX) or handle (Windows)
+// with a nng_stream.
+typedef struct nni_sfd_conn nni_sfd_conn;
+extern int nni_sfd_conn_alloc(nni_sfd_conn **cp, int fd);
+extern int nni_sfd_dialer_alloc(nng_stream_dialer **, const nng_url *);
+extern int nni_sfd_listener_alloc(nng_stream_listener **, const nng_url *);
+
+// this is used to close a file descriptor, in case we cannot
+// create a connection (or if the listener is closed before the
+// connection is accepted.)
+extern void nni_sfd_close_fd(int fd);
+
+#endif // CORE_FDC_H