fixes #863 socket activation: for TCP and IPC (POSIX only)

This introduces a new option "NNG_OPT_LISTEN_FD", understood by TCP, TLS,
and (on POSIX systems) IPC.  This option is used to pass a file descriptor
or handle (Windows) that is already listening (ready for ACCEPT to be called).

For TCP and TLS, the socket must be of type AF_INET or AF_INET6, and for IPC
it must be of type AF_UNIX.

3 files changed, 130 insertions, 0 deletions

diff --git a/src/platform/posix/posix_debug.c b/src/platform/posix/posix_debug.c
index 912000cc..3c0a6604 100644
--- a/src/platform/posix/posix_debug.c
+++ b/src/platform/posix/posix_debug.c
@@ -90,6 +90,9 @@ static struct {
 	{ ENFILE,	   NNG_ENOFILES	    },
 	{ EMFILE,	   NNG_ENOFILES	    },
 	{ EEXIST,	   NNG_EEXIST	    },
+#ifdef ENOTSOCK
+	{ ENOTSOCK,	   NNG_EINVAL	    },
+#endif
 	// must be last
 	{		0,		  0 },
 	// clang-format on
diff --git a/src/platform/posix/posix_ipclisten.c b/src/platform/posix/posix_ipclisten.c
index aa6ffda8..d13ac063 100644
--- a/src/platform/posix/posix_ipclisten.c
+++ b/src/platform/posix/posix_ipclisten.c
@@ -252,6 +252,60 @@ ipc_listener_set_perms(void *arg, const void *buf, size_t sz, nni_type t)
 	return (0);
 }
 
+static int
+ipc_listener_set_listen_fd(void *arg, const void *buf, size_t sz, nni_type t)
+{
+	ipc_listener           *l = arg;
+	int                     fd;
+	struct sockaddr_storage ss;
+	socklen_t               len = sizeof(ss);
+	int                     rv;
+
+	if ((rv = nni_copyin_int(&fd, buf, sz, 0, NNI_MAXINT, t)) != 0) {
+		return (rv);
+	}
+
+	if (getsockname(fd, (void *) &ss, &len) != 0) {
+		return (nni_plat_errno(errno));
+	}
+
+	if (((nni_posix_sockaddr2nn(&l->sa, &ss, len)) != 0) ||
+	    (ss.ss_family != AF_UNIX)) {
+		return (NNG_EADDRINVAL);
+	}
+
+	nni_mtx_lock(&l->mtx);
+	if (l->started) {
+		nni_mtx_unlock(&l->mtx);
+		return (NNG_EBUSY);
+	}
+	if (l->closed) {
+		nni_mtx_unlock(&l->mtx);
+		return (NNG_ECLOSED);
+	}
+	nni_posix_pfd_init(&l->pfd, fd, ipc_listener_cb, l);
+	l->started = true;
+	nni_mtx_unlock(&l->mtx);
+	return (0);
+}
+
+#ifdef NNG_TEST_LIB
+// this is readable only for test code -- user code should never rely on this
+static int
+ipc_listener_get_listen_fd(void *arg, void *buf, size_t *szp, nni_type t)
+{
+	int           rv;
+	ipc_listener *l = arg;
+
+	nni_mtx_lock(&l->mtx);
+	NNI_ASSERT(l->started);
+	NNI_ASSERT(!l->closed);
+	rv = nni_copyout_int(nni_posix_pfd_fd(&l->pfd), buf, szp, t);
+	nni_mtx_unlock(&l->mtx);
+	return (rv);
+}
+#endif
+
 static const nni_option ipc_listener_options[] = {
 	{
 	    .o_name = NNG_OPT_LOCADDR,
@@ -262,6 +316,13 @@ static const nni_option ipc_listener_options[] = {
 	    .o_set  = ipc_listener_set_perms,
 	},
 	{
+	    .o_name = NNG_OPT_LISTEN_FD,
+	    .o_set  = ipc_listener_set_listen_fd,
+#ifdef NNG_TEST_LIB
+	    .o_get = ipc_listener_get_listen_fd,
+#endif
+	},
+	{
 	    .o_name = NULL,
 	},
 };
diff --git a/src/platform/posix/posix_tcplisten.c b/src/platform/posix/posix_tcplisten.c
index 6e7f4d14..29b5ea65 100644
--- a/src/platform/posix/posix_tcplisten.c
+++ b/src/platform/posix/posix_tcplisten.c
@@ -10,6 +10,7 @@
 //
 
 #include "core/nng_impl.h"
+#include "nng/nng.h"
 
 #include <arpa/inet.h>
 #include <errno.h>
@@ -402,6 +403,64 @@ tcp_listener_get_port(void *arg, void *buf, size_t *szp, nni_type t)
 	return (nni_copyout_int(port, buf, szp, t));
 }
 
+static int
+tcp_listener_set_listen_fd(void *arg, const void *buf, size_t sz, nni_type t)
+{
+	tcp_listener           *l = arg;
+	int                     fd;
+	struct sockaddr_storage ss;
+	socklen_t               len = sizeof(ss);
+	int                     rv;
+
+	if ((rv = nni_copyin_int(&fd, buf, sz, 0, NNI_MAXINT, t)) != 0) {
+		return (rv);
+	}
+
+	if (getsockname(fd, (void *) &ss, &len) != 0) {
+		return (nni_plat_errno(errno));
+	}
+
+	if (((nni_posix_sockaddr2nn(&l->sa, &ss, len)) != 0) ||
+#ifdef NNG_ENABLE_IPV6
+	    ((ss.ss_family != AF_INET) && (ss.ss_family != AF_INET6))
+#else
+	    (ss.ss_family != AF_INET)
+#endif
+	) {
+		return (NNG_EADDRINVAL);
+	}
+
+	nni_mtx_lock(&l->mtx);
+	if (l->started) {
+		nni_mtx_unlock(&l->mtx);
+		return (NNG_EBUSY);
+	}
+	if (l->closed) {
+		nni_mtx_unlock(&l->mtx);
+		return (NNG_ECLOSED);
+	}
+	nni_posix_pfd_init(&l->pfd, fd, tcp_listener_cb, l);
+	l->started = true;
+	nni_mtx_unlock(&l->mtx);
+	return (0);
+}
+
+#ifdef NNG_TEST_LIB
+// this is readable only for test code -- user code should never rely on this
+static int
+tcp_listener_get_listen_fd(void *arg, void *buf, size_t *szp, nni_type t)
+{
+	int           rv;
+	tcp_listener *l = arg;
+	nni_mtx_lock(&l->mtx);
+	NNI_ASSERT(l->started);
+	NNI_ASSERT(!l->closed);
+	rv = nni_copyout_int(nni_posix_pfd_fd(&l->pfd), buf, szp, t);
+	nni_mtx_unlock(&l->mtx);
+	return (rv);
+}
+#endif
+
 static const nni_option tcp_listener_options[] = {
 	{
 	    .o_name = NNG_OPT_LOCADDR,
@@ -422,6 +481,13 @@ static const nni_option tcp_listener_options[] = {
 	    .o_get  = tcp_listener_get_port,
 	},
 	{
+	    .o_name = NNG_OPT_LISTEN_FD,
+	    .o_set  = tcp_listener_set_listen_fd,
+#ifdef NNG_TEST_LIB
+	    .o_get = tcp_listener_get_listen_fd,
+#endif
+	},
+	{
 	    .o_name = NULL,
 	},
 };