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, 25 insertions, 0 deletions

diff --git a/src/platform/posix/posix_peerid.h b/src/platform/posix/posix_peerid.h
new file mode 100644
index 00000000..57e9abff
--- /dev/null
+++ b/src/platform/posix/posix_peerid.h
@@ -0,0 +1,25 @@
+//
+// 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 PLATFORM_POSIX_PEERID_H
+#define PLATFORM_POSIX_PEERID_H
+
+// This file defines structures we will use for emulating asynchronous I/O
+// on POSIX.  POSIX lacks the support for callback based asynchronous I/O
+// that we have on Windows, although it has a non-widely support aio layer
+// that is not very performant on many systems.   So we emulate this using
+// one of several possible different backends.
+
+#include "core/nng_impl.h"
+#include <sys/types.h>
+
+int nni_posix_peerid(
+    int fd, uint64_t *euid, uint64_t *egid, uint64_t *prid, uint64_t *znid);
+
+#endif // PLATFORM_POSIX_PEERID_H
\ No newline at end of file