fixes #1419 pairv0 performance work

This takes the performance work we did for pairv1, and provides an
implementation for pairv0.  The upshot should be a nice performance
boost for pair v0.

3 files changed, 832 insertions, 90 deletions

diff --git a/src/sp/protocol/pair0/CMakeLists.txt b/src/sp/protocol/pair0/CMakeLists.txt
index b12583ab..2f74e139 100644
--- a/src/sp/protocol/pair0/CMakeLists.txt
+++ b/src/sp/protocol/pair0/CMakeLists.txt
@@ -1,5 +1,5 @@
 #
-# Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
+# Copyright 2021 Staysail Systems, Inc. <info@staysail.tech>
 # Copyright 2018 Capitar IT Group BV <info@capitar.com>
 #
 # This software is supplied under the terms of the MIT License, a
@@ -13,4 +13,5 @@ nng_directory(pair0)
 
 nng_sources_if(NNG_PROTO_PAIR0 pair.c)
 nng_headers_if(NNG_PROTO_PAIR0 nng/protocol/pair0/pair.h)
-nng_defines_if(NNG_PROTO_PAIR0 NNG_HAVE_PAIR0)
\ No newline at end of file
+nng_defines_if(NNG_PROTO_PAIR0 NNG_HAVE_PAIR0)
+nng_test(pair0_test)
diff --git a/src/sp/protocol/pair0/pair.c b/src/sp/protocol/pair0/pair.c
index 41f88c7c..c2407d81 100644
--- a/src/sp/protocol/pair0/pair.c
+++ b/src/sp/protocol/pair0/pair.c
@@ -1,5 +1,5 @@
 //
-// Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2021 Staysail Systems, Inc. <info@staysail.tech>
 // Copyright 2018 Capitar IT Group BV <info@capitar.com>
 //
 // This software is supplied under the terms of the MIT License, a
@@ -24,18 +24,24 @@
 typedef struct pair0_pipe pair0_pipe;
 typedef struct pair0_sock pair0_sock;
 
-static void pair0_send_cb(void *);
-static void pair0_recv_cb(void *);
-static void pair0_getq_cb(void *);
-static void pair0_putq_cb(void *);
+static void pair0_pipe_send_cb(void *);
+static void pair0_pipe_recv_cb(void *);
 static void pair0_pipe_fini(void *);
+static void pair0_send_sched(pair0_sock *);
+static void pair0_pipe_send(pair0_pipe *, nni_msg *);
 
 // pair0_sock is our per-socket protocol private structure.
 struct pair0_sock {
-	pair0_pipe *ppipe;
-	nni_msgq *  uwq;
-	nni_msgq *  urq;
-	nni_mtx     mtx;
+	pair0_pipe * p;
+	nni_mtx      mtx;
+	nni_lmq      wmq;
+	nni_list     waq;
+	nni_lmq      rmq;
+	nni_list     raq;
+	nni_pollable readable;
+	nni_pollable writable;
+	bool         rd_ready; // pipe ready for read
+	bool         wr_ready; // pipe ready for write
 };
 
 // An pair0_pipe is our per-pipe protocol private structure.  We keep
@@ -43,23 +49,28 @@ struct pair0_sock {
 // pipe.  The separate data structure is more like other protocols that do
 // manage multiple pipes.
 struct pair0_pipe {
-	nni_pipe *  npipe;
-	pair0_sock *psock;
+	nni_pipe *  pipe;
+	pair0_sock *pair;
 	nni_aio     aio_send;
 	nni_aio     aio_recv;
-	nni_aio     aio_getq;
-	nni_aio     aio_putq;
 };
 
 static int
-pair0_sock_init(void *arg, nni_sock *nsock)
+pair0_sock_init(void *arg, nni_sock *sock)
 {
 	pair0_sock *s = arg;
+	NNI_ARG_UNUSED(sock);
 
 	nni_mtx_init(&s->mtx);
-	s->ppipe = NULL;
-	s->uwq   = nni_sock_sendq(nsock);
-	s->urq   = nni_sock_recvq(nsock);
+
+	nni_lmq_init(&s->rmq, 0);
+	nni_lmq_init(&s->wmq, 0);
+	nni_aio_list_init(&s->raq);
+	nni_aio_list_init(&s->waq);
+	nni_pollable_init(&s->writable);
+	nni_pollable_init(&s->readable);
+
+	s->p = NULL;
 	return (0);
 }
 
@@ -68,6 +79,8 @@ pair0_sock_fini(void *arg)
 {
 	pair0_sock *s = arg;
 
+	nni_lmq_fini(&s->rmq);
+	nni_lmq_fini(&s->wmq);
 	nni_mtx_fini(&s->mtx);
 }
 
@@ -75,11 +88,28 @@ static void
 pair0_pipe_stop(void *arg)
 {
 	pair0_pipe *p = arg;
+	pair0_sock *s = p->pair;
+
+	nni_mtx_lock(&s->mtx);
+	if (s->p == p) {
+		s->p = NULL;
+		if (s->rd_ready) {
+			nni_msg *m = nni_aio_get_msg(&p->aio_recv);
+			nni_msg_free(m);
+			s->rd_ready = false;
+		}
+		if (s->wr_ready) {
+			s->wr_ready = false;
+			nni_pollable_clear(&s->writable);
+		}
+		if (nni_lmq_empty(&s->rmq)) {
+			nni_pollable_clear(&s->readable);
+		}
+	}
+	nni_mtx_unlock(&s->mtx);
 
 	nni_aio_stop(&p->aio_send);
 	nni_aio_stop(&p->aio_recv);
-	nni_aio_stop(&p->aio_putq);
-	nni_aio_stop(&p->aio_getq);
 }
 
 static void
@@ -89,48 +119,59 @@ pair0_pipe_fini(void *arg)
 
 	nni_aio_fini(&p->aio_send);
 	nni_aio_fini(&p->aio_recv);
-	nni_aio_fini(&p->aio_putq);
-	nni_aio_fini(&p->aio_getq);
 }
 
 static int
-pair0_pipe_init(void *arg, nni_pipe *npipe, void *psock)
+pair0_pipe_init(void *arg, nni_pipe *pipe, void *pair)
 {
 	pair0_pipe *p = arg;
 
-	nni_aio_init(&p->aio_send, pair0_send_cb, p);
-	nni_aio_init(&p->aio_recv, pair0_recv_cb, p);
-	nni_aio_init(&p->aio_getq, pair0_getq_cb, p);
-	nni_aio_init(&p->aio_putq, pair0_putq_cb, p);
+	nni_aio_init(&p->aio_send, pair0_pipe_send_cb, p);
+	nni_aio_init(&p->aio_recv, pair0_pipe_recv_cb, p);
+
+	p->pipe = pipe;
+	p->pair = pair;
 
-	p->npipe = npipe;
-	p->psock = psock;
 	return (0);
 }
 
+static void
+pair0_cancel(nni_aio *aio, void *arg, int rv)
+{
+	pair0_sock *s = arg;
+
+	nni_mtx_lock(&s->mtx);
+	if (nni_aio_list_active(aio)) {
+		nni_aio_list_remove(aio);
+		nni_aio_finish_error(aio, rv);
+	}
+	nni_mtx_unlock(&s->mtx);
+}
+
 static int
 pair0_pipe_start(void *arg)
 {
 	pair0_pipe *p = arg;
-	pair0_sock *s = p->psock;
+	pair0_sock *s = p->pair;
 
-	if (nni_pipe_peer(p->npipe) != NNI_PROTO_PAIR_V0) {
+	if (nni_pipe_peer(p->pipe) != NNI_PROTO_PAIR_V0) {
 		// Peer protocol mismatch.
 		return (NNG_EPROTO);
 	}
 
 	nni_mtx_lock(&s->mtx);
-	if (s->ppipe != NULL) {
+	if (s->p != NULL) {
 		nni_mtx_unlock(&s->mtx);
 		return (NNG_EBUSY); // Already have a peer, denied.
 	}
-	s->ppipe = p;
+	s->p        = p;
+	s->rd_ready = false;
 	nni_mtx_unlock(&s->mtx);
 
-	// Schedule a getq on the upper, and a read from the pipe.
-	// Each of these also sets up another hold on the pipe itself.
-	nni_msgq_aio_get(s->uwq, &p->aio_getq);
-	nni_pipe_recv(p->npipe, &p->aio_recv);
+	pair0_send_sched(s);
+
+	// And the pipe read of course.
+	nni_pipe_recv(p->pipe, &p->aio_recv);
 
 	return (0);
 }
@@ -139,83 +180,117 @@ static void
 pair0_pipe_close(void *arg)
 {
 	pair0_pipe *p = arg;
-	pair0_sock *s = p->psock;
 
 	nni_aio_close(&p->aio_send);
 	nni_aio_close(&p->aio_recv);
-	nni_aio_close(&p->aio_putq);
-	nni_aio_close(&p->aio_getq);
-
-	nni_mtx_lock(&s->mtx);
-	if (s->ppipe == p) {
-		s->ppipe = NULL;
-	}
-	nni_mtx_unlock(&s->mtx);
 }
 
 static void
-pair0_recv_cb(void *arg)
+pair0_pipe_recv_cb(void *arg)
 {
 	pair0_pipe *p = arg;
-	pair0_sock *s = p->psock;
+	pair0_sock *s = p->pair;
 	nni_msg *   msg;
+	nni_aio *   a;
 
 	if (nni_aio_result(&p->aio_recv) != 0) {
-		nni_pipe_close(p->npipe);
+		nni_pipe_close(p->pipe);
 		return;
 	}
 
 	msg = nni_aio_get_msg(&p->aio_recv);
-	nni_aio_set_msg(&p->aio_putq, msg);
-	nni_aio_set_msg(&p->aio_recv, NULL);
+	// Store the pipe ID.
+	nni_msg_set_pipe(msg, nni_pipe_id(p->pipe));
 
-	nni_msg_set_pipe(msg, nni_pipe_id(p->npipe));
-	nni_msgq_aio_put(s->urq, &p->aio_putq);
-}
-
-static void
-pair0_putq_cb(void *arg)
-{
-	pair0_pipe *p = arg;
+	nni_mtx_lock(&s->mtx);
 
-	if (nni_aio_result(&p->aio_putq) != 0) {
-		nni_msg_free(nni_aio_get_msg(&p->aio_putq));
-		nni_aio_set_msg(&p->aio_putq, NULL);
-		nni_pipe_close(p->npipe);
+	// if anyone is blocking, then the lmq will be empty, and
+	// we should deliver it there.
+	if ((a = nni_list_first(&s->raq)) != NULL) {
+		nni_aio_list_remove(a);
+		nni_aio_set_msg(a, msg);
+		nni_pipe_recv(p->pipe, &p->aio_recv);
+		nni_mtx_unlock(&s->mtx);
+		nni_aio_finish_sync(a, 0, nni_msg_len(msg));
 		return;
 	}
-	nni_pipe_recv(p->npipe, &p->aio_recv);
+
+	// maybe we have room in the rmq?
+	if (!nni_lmq_full(&s->rmq)) {
+		nni_lmq_putq(&s->rmq, msg);
+		nni_aio_set_msg(&p->aio_recv, NULL);
+		nni_pipe_recv(p->pipe, &p->aio_recv);
+	} else {
+		s->rd_ready = true;
+	}
+	nni_pollable_raise(&s->readable);
+	nni_mtx_unlock(&s->mtx);
 }
 
 static void
-pair0_getq_cb(void *arg)
+pair0_send_sched(pair0_sock *s)
 {
-	pair0_pipe *p = arg;
+	pair0_pipe *p;
+	nni_msg *   m;
+	nni_aio *   a = NULL;
+	size_t      l = 0;
 
-	if (nni_aio_result(&p->aio_getq) != 0) {
-		nni_pipe_close(p->npipe);
+	nni_mtx_lock(&s->mtx);
+
+	if ((p = s->p) == NULL) {
+		nni_mtx_unlock(&s->mtx);
 		return;
 	}
 
-	nni_aio_set_msg(&p->aio_send, nni_aio_get_msg(&p->aio_getq));
-	nni_aio_set_msg(&p->aio_getq, NULL);
-	nni_pipe_send(p->npipe, &p->aio_send);
+	s->wr_ready = true;
+
+	// if message waiting in buffered queue, then we prefer that.
+	if (nni_lmq_getq(&s->wmq, &m) == 0) {
+		pair0_pipe_send(p, m);
+
+		if ((a = nni_list_first(&s->waq)) != NULL) {
+			nni_aio_list_remove(a);
+			m = nni_aio_get_msg(a);
+			l = nni_msg_len(m);
+			nni_lmq_putq(&s->wmq, m);
+		}
+
+	} else if ((a = nni_list_first(&s->waq)) != NULL) {
+		// Looks like we had the unbuffered case, but
+		// someone was waiting.
+		nni_aio_list_remove(a);
+
+		m = nni_aio_get_msg(a);
+		l = nni_msg_len(m);
+		pair0_pipe_send(p, m);
+	}
+
+	// if we were blocked before, but not now, update.
+	if ((!nni_lmq_full(&s->wmq)) || s->wr_ready) {
+		nni_pollable_raise(&s->writable);
+	}
+
+	nni_mtx_unlock(&s->mtx);
+
+	if (a != NULL) {
+		nni_aio_set_msg(a, NULL);
+		nni_aio_finish_sync(a, 0, l);
+	}
 }
 
 static void
-pair0_send_cb(void *arg)
+pair0_pipe_send_cb(void *arg)
 {
 	pair0_pipe *p = arg;
-	pair0_sock *s = p->psock;
 
 	if (nni_aio_result(&p->aio_send) != 0) {
 		nni_msg_free(nni_aio_get_msg(&p->aio_send));
 		nni_aio_set_msg(&p->aio_send, NULL);
-		nni_pipe_close(p->npipe);
+		nni_pipe_close(p->pipe);
 		return;
 	}
 
-	nni_msgq_aio_get(s->uwq, &p->aio_getq);
+	pair0_send_sched(p->pair);
 }
 
 static void
@@ -227,25 +302,259 @@ pair0_sock_open(void *arg)
 static void
 pair0_sock_close(void *arg)
 {
-	NNI_ARG_UNUSED(arg);
+	pair0_sock *s = arg;
+	nni_aio *   a;
+	nni_msg *   m;
+	nni_mtx_lock(&s->mtx);
+	while (((a = nni_list_first(&s->raq)) != NULL) ||
+	    ((a = nni_list_first(&s->waq)) != NULL)) {
+		nni_aio_list_remove(a);
+		nni_aio_finish_error(a, NNG_ECLOSED);
+	}
+	while ((nni_lmq_getq(&s->rmq, &m) == 0) ||
+	    (nni_lmq_getq(&s->wmq, &m) == 0)) {
+		nni_msg_free(m);
+	}
+	nni_mtx_unlock(&s->mtx);
+}
+
+static void
+pair0_pipe_send(pair0_pipe *p, nni_msg *m)
+{
+	pair0_sock *s = p->pair;
+	// assumption: we have unique access to the message at this point.
+	NNI_ASSERT(!nni_msg_shared(m));
+
+	nni_aio_set_msg(&p->aio_send, m);
+	nni_pipe_send(p->pipe, &p->aio_send);
+	s->wr_ready = false;
 }
 
 static void
 pair0_sock_send(void *arg, nni_aio *aio)
 {
 	pair0_sock *s = arg;
+	nni_msg *   m;
+	size_t      len;
+	int         rv;
+
+	if (nni_aio_begin(aio) != 0) {
+		return;
+	}
+
+	m   = nni_aio_get_msg(aio);
+	len = nni_msg_len(m);
+
+	nni_mtx_lock(&s->mtx);
+	if (s->wr_ready) {
+		pair0_pipe *p = s->p;
+		if (nni_lmq_full(&s->wmq)) {
+			nni_pollable_clear(&s->writable);
+		}
+		nni_aio_set_msg(aio, NULL);
+		nni_aio_finish(aio, 0, len);
+		pair0_pipe_send(p, m);
+		nni_mtx_unlock(&s->mtx);
+		return;
+	}
+
+	// Can we maybe queue it.
+	if (nni_lmq_putq(&s->wmq, m) == 0) {
+		// Yay, we can.  So we're done.
+		nni_aio_set_msg(aio, NULL);
+		nni_aio_finish(aio, 0, len);
+		if (nni_lmq_full(&s->wmq)) {
+			nni_pollable_clear(&s->writable);
+		}
+		nni_mtx_unlock(&s->mtx);
+		return;
+	}
 
-	nni_msgq_aio_put(s->uwq, aio);
+	if ((rv = nni_aio_schedule(aio, pair0_cancel, s)) != 0) {
+		nni_aio_finish_error(aio, rv);
+		nni_mtx_unlock(&s->mtx);
+		return;
+	}
+	nni_aio_list_append(&s->waq, aio);
+	nni_mtx_unlock(&s->mtx);
 }
 
 static void
 pair0_sock_recv(void *arg, nni_aio *aio)
 {
 	pair0_sock *s = arg;
+	pair0_pipe *p;
+	nni_msg *   m;
+	int         rv;
 
-	nni_msgq_aio_get(s->urq, aio);
+	if (nni_aio_begin(aio) != 0) {
+		return;
+	}
+
+	nni_mtx_lock(&s->mtx);
+	p = s->p;
+
+	// Buffered read.  If there is a message waiting for us, pick
+	// it up.  We might need to post another read request as well.
+	if (nni_lmq_getq(&s->rmq, &m) == 0) {
+		nni_aio_set_msg(aio, m);
+		nni_aio_finish(aio, 0, nni_msg_len(m));
+		if (s->rd_ready) {
+			s->rd_ready = false;
+			m           = nni_aio_get_msg(&p->aio_recv);
+			nni_aio_set_msg(&p->aio_recv, NULL);
+			nni_lmq_putq(&s->rmq, m);
+			nni_pipe_recv(p->pipe, &p->aio_recv);
+		}
+		if (nni_lmq_empty(&s->rmq)) {
+			nni_pollable_clear(&s->readable);
+		}
+		nni_mtx_unlock(&s->mtx);
+		return;
+	}
+
+	// Unbuffered -- but waiting.
+	if (s->rd_ready) {
+		s->rd_ready = false;
+		m           = nni_aio_get_msg(&p->aio_recv);
+		nni_aio_set_msg(&p->aio_recv, NULL);
+		nni_aio_set_msg(aio, m);
+		nni_aio_finish(aio, 0, nni_msg_len(m));
+		nni_pipe_recv(p->pipe, &p->aio_recv);
+		nni_pollable_clear(&s->readable);
+		nni_mtx_unlock(&s->mtx);
+		return;
+	}
+
+	if ((rv = nni_aio_schedule(aio, pair0_cancel, s)) != 0) {
+		nni_aio_finish_error(aio, rv);
+	} else {
+		nni_aio_list_append(&s->raq, aio);
+	}
+	nni_mtx_unlock(&s->mtx);
 }
 
+static int
+pair0_set_send_buf_len(void *arg, const void *buf, size_t sz, nni_type t)
+{
+	pair0_sock *s = arg;
+	int         val;
+	int         rv;
+
+	if ((rv = nni_copyin_int(&val, buf, sz, 0, 8192, t)) != 0) {
+		return (rv);
+	}
+	nni_mtx_lock(&s->mtx);
+	rv = nni_lmq_resize(&s->wmq, (size_t) val);
+	// Changing the size of the queue can affect our readiness.
+	if (!nni_lmq_full(&s->wmq)) {
+		nni_pollable_raise(&s->writable);
+	} else if (!s->wr_ready) {
+		nni_pollable_clear(&s->writable);
+	}
+	nni_mtx_unlock(&s->mtx);
+	return (rv);
+}
+
+static int
+pair0_get_send_buf_len(void *arg, void *buf, size_t *szp, nni_opt_type t)
+{
+	pair0_sock *s = arg;
+	int         val;
+
+	nni_mtx_lock(&s->mtx);
+	val = nni_lmq_cap(&s->wmq);
+	nni_mtx_unlock(&s->mtx);
+
+	return (nni_copyout_int(val, buf, szp, t));
+}
+
+static int
+pair0_set_recv_buf_len(void *arg, const void *buf, size_t sz, nni_type t)
+{
+	pair0_sock *s = arg;
+	int         val;
+	int         rv;
+
+	if ((rv = nni_copyin_int(&val, buf, sz, 0, 8192, t)) != 0) {
+		return (rv);
+	}
+	nni_mtx_lock(&s->mtx);
+	rv = nni_lmq_resize(&s->rmq, (size_t) val);
+	// Changing the size of the queue can affect our readiness.
+	if (!nni_lmq_empty(&s->rmq)) {
+		nni_pollable_raise(&s->readable);
+	} else if (!s->rd_ready) {
+		nni_pollable_clear(&s->readable);
+	}
+	nni_mtx_unlock(&s->mtx);
+	return (rv);
+}
+
+static int
+pair0_get_recv_buf_len(void *arg, void *buf, size_t *szp, nni_opt_type t)
+{
+	pair0_sock *s = arg;
+	int         val;
+
+	nni_mtx_lock(&s->mtx);
+	val = nni_lmq_cap(&s->rmq);
+	nni_mtx_unlock(&s->mtx);
+
+	return (nni_copyout_int(val, buf, szp, t));
+}
+
+static int
+pair0_sock_get_recv_fd(void *arg, void *buf, size_t *szp, nni_opt_type t)
+{
+	pair0_sock *s = arg;
+	int         rv;
+	int         fd;
+
+	if ((rv = nni_pollable_getfd(&s->readable, &fd)) != 0) {
+		return (rv);
+	}
+	return (nni_copyout_int(fd, buf, szp, t));
+}
+
+static int
+pair0_sock_get_send_fd(void *arg, void *buf, size_t *szp, nni_opt_type t)
+{
+	pair0_sock *s = arg;
+	int         rv;
+	int         fd;
+
+	if ((rv = nni_pollable_getfd(&s->writable, &fd)) != 0) {
+		return (rv);
+	}
+	return (nni_copyout_int(fd, buf, szp, t));
+}
+
+static nni_option pair0_sock_options[] = {
+    {
+	.o_name = NNG_OPT_RECVFD,
+	.o_get  = pair0_sock_get_recv_fd,
+    },
+    {
+	.o_name = NNG_OPT_SENDFD,
+	.o_get  = pair0_sock_get_send_fd,
+    },
+    {
+	.o_name = NNG_OPT_SENDBUF,
+	.o_get  = pair0_get_send_buf_len,
+	.o_set  = pair0_set_send_buf_len,
+    },
+    {
+	.o_name = NNG_OPT_RECVBUF,
+	.o_get  = pair0_get_recv_buf_len,
+	.o_set  = pair0_set_recv_buf_len,
+    },
+    // terminate list
+    {
+	.o_name = NULL,
+    },
+};
+
 static nni_proto_pipe_ops pair0_pipe_ops = {
 	.pipe_size  = sizeof(pair0_pipe),
 	.pipe_init  = pair0_pipe_init,
@@ -255,13 +564,6 @@ static nni_proto_pipe_ops pair0_pipe_ops = {
 	.pipe_stop  = pair0_pipe_stop,
 };
 
-static nni_option pair0_sock_options[] = {
-	// terminate list
-	{
-	    .o_name = NULL,
-	}
-};
-
 static nni_proto_sock_ops pair0_sock_ops = {
 	.sock_size    = sizeof(pair0_sock),
 	.sock_init    = pair0_sock_init,
@@ -293,13 +595,13 @@ static nni_proto pair0_proto_raw = {
 };
 
 int
-nng_pair0_open(nng_socket *sidp)
+nng_pair0_open(nng_socket *sock)
 {
-	return (nni_proto_open(sidp, &pair0_proto));
+	return (nni_proto_open(sock, &pair0_proto));
 }
 
 int
-nng_pair0_open_raw(nng_socket *sidp)
+nng_pair0_open_raw(nng_socket *sock)
 {
-	return (nni_proto_open(sidp, &pair0_proto_raw));
+	return (nni_proto_open(sock, &pair0_proto_raw));
 }
diff --git a/src/sp/protocol/pair0/pair0_test.c b/src/sp/protocol/pair0/pair0_test.c
new file mode 100644
index 00000000..20acc200
--- /dev/null
+++ b/src/sp/protocol/pair0/pair0_test.c
@@ -0,0 +1,439 @@
+//
+// Copyright 2021 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2017 Capitar IT Group BV <info@capitar.com>
+//
+// 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 <nuts.h>
+
+#define SECOND 1000
+
+#define APPEND_STR(m, s) NUTS_TRUE(nng_msg_append(m, s, strlen(s)) == 0)
+#define CHECK_STR(m, s)                         \
+	NUTS_TRUE(nng_msg_len(m) == strlen(s)); \
+	NUTS_TRUE(memcmp(nng_msg_body(m), s, strlen(s)) == 0)
+
+static void
+test_identity(void)
+{
+	nng_socket s;
+	int        p;
+	char *     n;
+
+	NUTS_PASS(nng_pair0_open(&s));
+	NUTS_PASS(nng_socket_get_int(s, NNG_OPT_PROTO, &p));
+	NUTS_TRUE(p == NUTS_PROTO(1u, 0u)); // 16
+	NUTS_PASS(nng_socket_get_int(s, NNG_OPT_PEER, &p));
+	NUTS_TRUE(p == NUTS_PROTO(1u, 0u)); // 17
+	NUTS_PASS(nng_socket_get_string(s, NNG_OPT_PROTONAME, &n));
+	NUTS_MATCH(n, "pair");
+	nng_strfree(n);
+	NUTS_PASS(nng_socket_get_string(s, NNG_OPT_PEERNAME, &n));
+	NUTS_MATCH(n, "pair");
+	nng_strfree(n);
+	NUTS_CLOSE(s);
+}
+
+void
+test_cooked(void)
+{
+	nng_socket s1;
+	nng_socket c1;
+	nng_msg *  msg;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair0_open(&c1));
+	NUTS_PASS(nuts_marry(s1, c1));
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	NUTS_PASS(nng_msg_append(msg, "ALPHA", strlen("ALPHA") + 1));
+	NUTS_PASS(nng_sendmsg(c1, msg, 0));
+	NUTS_PASS(nng_recvmsg(s1, &msg, 0));
+	NUTS_TRUE(nng_msg_len(msg) == strlen("ALPHA") + 1);
+	NUTS_MATCH(nng_msg_body(msg), "ALPHA");
+	nng_msg_free(msg);
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	NUTS_PASS(nng_msg_append(msg, "BETA", strlen("BETA") + 1));
+	NUTS_PASS(nng_sendmsg(s1, msg, 0));
+	NUTS_PASS(nng_recvmsg(c1, &msg, 0));
+	NUTS_TRUE(nng_msg_len(msg) == strlen("BETA") + 1);
+	NUTS_MATCH(nng_msg_body(msg), "BETA");
+
+	nng_msg_free(msg);
+	NUTS_CLOSE(c1);
+	NUTS_CLOSE(s1);
+}
+
+void
+test_faithful(void)
+{
+	nng_socket  s1;
+	nng_socket  c1;
+	nng_socket  c2;
+	nng_msg *   msg;
+	const char *addr = "inproc://pair0_mono_faithful";
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair0_open(&c1));
+	NUTS_PASS(nng_pair0_open(&c2));
+	NUTS_PASS(nng_setopt_ms(s1, NNG_OPT_RECVTIMEO, SECOND / 4));
+	NUTS_PASS(nng_setopt_ms(c1, NNG_OPT_SENDTIMEO, SECOND));
+	NUTS_PASS(nng_setopt_ms(c2, NNG_OPT_SENDTIMEO, SECOND));
+	NUTS_PASS(nng_setopt_int(c2, NNG_OPT_SENDBUF, 2));
+
+	NUTS_PASS(nng_listen(s1, addr, NULL, 0));
+	NUTS_MARRY(s1, c1);
+	NUTS_PASS(nng_dial(c2, addr, NULL, 0));
+
+	NUTS_SLEEP(100);
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	APPEND_STR(msg, "ONE");
+	NUTS_PASS(nng_sendmsg(c1, msg, 0));
+	NUTS_PASS(nng_recvmsg(s1, &msg, 0));
+	CHECK_STR(msg, "ONE");
+	nng_msg_free(msg);
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	APPEND_STR(msg, "TWO");
+	NUTS_PASS(nng_sendmsg(c2, msg, 0));
+	NUTS_FAIL(nng_recvmsg(s1, &msg, 0), NNG_ETIMEDOUT);
+
+	NUTS_CLOSE(s1);
+	NUTS_CLOSE(c1);
+	NUTS_CLOSE(c2);
+}
+
+void
+test_back_pressure(void)
+{
+	nng_socket   s1;
+	nng_socket   c1;
+	int          i;
+	int          rv;
+	nng_msg *    msg;
+	nng_duration to = 100;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair0_open(&c1));
+	NUTS_PASS(nng_setopt_int(s1, NNG_OPT_RECVBUF, 1));
+	NUTS_PASS(nng_setopt_int(s1, NNG_OPT_SENDBUF, 1));
+	NUTS_PASS(nng_setopt_int(c1, NNG_OPT_RECVBUF, 1));
+	NUTS_PASS(nng_setopt_ms(s1, NNG_OPT_SENDTIMEO, to));
+
+	NUTS_MARRY(s1, c1);
+
+	// We choose to allow some buffering.  In reality the
+	// buffer size is just 1, and we will fail after 2.
+	for (i = 0, rv = 0; i < 10; i++) {
+		NUTS_PASS(nng_msg_alloc(&msg, 0));
+		if ((rv = nng_sendmsg(s1, msg, 0)) != 0) {
+			nng_msg_free(msg);
+			break;
+		}
+	}
+	NUTS_FAIL(rv, NNG_ETIMEDOUT);
+	NUTS_TRUE(i < 10);
+	NUTS_CLOSE(s1);
+	NUTS_CLOSE(c1);
+}
+
+void
+test_send_no_peer(void)
+{
+	nng_socket   s1;
+	nng_msg *    msg;
+	nng_duration to = 100;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_setopt_ms(s1, NNG_OPT_SENDTIMEO, to));
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	NUTS_FAIL(nng_sendmsg(s1, msg, 0), NNG_ETIMEDOUT);
+	nng_msg_free(msg);
+	NUTS_CLOSE(s1);
+}
+
+void
+test_raw_exchange(void)
+{
+	nng_socket s1;
+	nng_socket c1;
+
+	nng_msg *msg;
+
+	NUTS_PASS(nng_pair0_open_raw(&s1));
+	NUTS_PASS(nng_pair0_open_raw(&c1));
+
+	NUTS_PASS(nng_setopt_ms(s1, NNG_OPT_RECVTIMEO, SECOND));
+	NUTS_PASS(nng_setopt_ms(c1, NNG_OPT_RECVTIMEO, SECOND));
+	NUTS_MARRY(s1, c1);
+
+	nng_pipe p = NNG_PIPE_INITIALIZER;
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	APPEND_STR(msg, "GAMMA");
+	NUTS_PASS(nng_sendmsg(c1, msg, 0));
+	NUTS_PASS(nng_recvmsg(s1, &msg, 0));
+	p = nng_msg_get_pipe(msg);
+	NUTS_TRUE(nng_pipe_id(p) > 0);
+
+	CHECK_STR(msg, "GAMMA");
+	nng_msg_free(msg);
+
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	APPEND_STR(msg, "EPSILON");
+	NUTS_PASS(nng_sendmsg(s1, msg, 0));
+	NUTS_PASS(nng_recvmsg(c1, &msg, 0));
+	CHECK_STR(msg, "EPSILON");
+	p = nng_msg_get_pipe(msg);
+	NUTS_TRUE(nng_pipe_id(p) > 0);
+
+	nng_msg_free(msg);
+
+	NUTS_CLOSE(s1);
+	NUTS_CLOSE(c1);
+}
+
+void
+test_pair0_send_closed_aio(void)
+{
+	nng_socket s1;
+	nng_aio *  aio;
+	nng_msg *  msg;
+
+	NUTS_PASS(nng_aio_alloc(&aio, NULL, NULL));
+	NUTS_PASS(nng_msg_alloc(&msg, 0));
+	NUTS_PASS(nng_pair0_open(&s1));
+	nng_aio_set_msg(aio, msg);
+	nng_aio_stop(aio);
+	nng_send_aio(s1, aio);
+	nng_aio_wait(aio);
+	NUTS_FAIL(nng_aio_result(aio), NNG_ECANCELED);
+	nng_msg_free(msg);
+	nng_aio_free(aio);
+	NUTS_PASS(nng_close(s1));
+}
+
+void
+test_pair0_raw(void)
+{
+	nng_socket s1;
+	bool       raw;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_getopt_bool(s1, NNG_OPT_RAW, &raw));
+	NUTS_TRUE(raw == false);
+	NUTS_FAIL(nng_setopt_bool(s1, NNG_OPT_RAW, true), NNG_EREADONLY);
+	NUTS_PASS(nng_close(s1));
+
+	NUTS_PASS(nng_pair0_open_raw(&s1));
+	NUTS_PASS(nng_getopt_bool(s1, NNG_OPT_RAW, &raw));
+	NUTS_TRUE(raw == true);
+	NUTS_FAIL(nng_setopt_bool(s1, NNG_OPT_RAW, false), NNG_EREADONLY);
+	NUTS_PASS(nng_close(s1));
+}
+
+void
+test_pair0_validate_peer(void)
+{
+	nng_socket s1, s2;
+	nng_stat * stats;
+	nng_stat * reject;
+	char *     addr;
+
+	NUTS_ADDR(addr, "inproc");
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair1_open(&s2));
+
+	NUTS_PASS(nng_listen(s1, addr, NULL, 0));
+	NUTS_PASS(nng_dial(s2, addr, NULL, NNG_FLAG_NONBLOCK));
+
+	NUTS_SLEEP(100);
+	NUTS_PASS(nng_stats_get(&stats));
+
+	NUTS_TRUE(stats != NULL);
+	NUTS_TRUE((reject = nng_stat_find_socket(stats, s1)) != NULL);
+	NUTS_TRUE((reject = nng_stat_find(reject, "reject")) != NULL);
+
+	NUTS_TRUE(nng_stat_type(reject) == NNG_STAT_COUNTER);
+	NUTS_TRUE(nng_stat_value(reject) > 0);
+
+	NUTS_CLOSE(s1);
+	NUTS_CLOSE(s2);
+	nng_stats_free(stats);
+}
+
+static void
+test_pair0_no_context(void)
+{
+	nng_socket s;
+	nng_ctx    ctx;
+
+	NUTS_PASS(nng_pair0_open(&s));
+	NUTS_FAIL(nng_ctx_open(&ctx, s), NNG_ENOTSUP);
+	NUTS_CLOSE(s);
+}
+
+static void
+test_pair0_send_buffer(void)
+{
+	nng_socket s;
+	int        v;
+	bool       b;
+	size_t     sz;
+
+	NUTS_PASS(nng_pair0_open(&s));
+	NUTS_PASS(nng_getopt_int(s, NNG_OPT_SENDBUF, &v));
+	NUTS_TRUE(v == 0);
+	NUTS_FAIL(nng_getopt_bool(s, NNG_OPT_SENDBUF, &b), NNG_EBADTYPE);
+	sz = 1;
+	NUTS_FAIL(nng_getopt(s, NNG_OPT_SENDBUF, &b, &sz), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_int(s, NNG_OPT_SENDBUF, -1), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_int(s, NNG_OPT_SENDBUF, 100000), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_bool(s, NNG_OPT_SENDBUF, false), NNG_EBADTYPE);
+	NUTS_FAIL(nng_setopt(s, NNG_OPT_SENDBUF, &b, 1), NNG_EINVAL);
+	NUTS_PASS(nng_setopt_int(s, NNG_OPT_SENDBUF, 100));
+	NUTS_PASS(nng_getopt_int(s, NNG_OPT_SENDBUF, &v));
+	NUTS_TRUE(v == 100);
+	NUTS_CLOSE(s);
+}
+
+static void
+test_pair0_recv_buffer(void)
+{
+	nng_socket s;
+	int        v;
+	bool       b;
+	size_t     sz;
+
+	NUTS_PASS(nng_pair0_open(&s));
+	NUTS_PASS(nng_getopt_int(s, NNG_OPT_RECVBUF, &v));
+	NUTS_TRUE(v == 0);
+	NUTS_FAIL(nng_getopt_bool(s, NNG_OPT_RECVBUF, &b), NNG_EBADTYPE);
+	sz = 1;
+	NUTS_FAIL(nng_getopt(s, NNG_OPT_RECVBUF, &b, &sz), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_int(s, NNG_OPT_RECVBUF, -1), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_int(s, NNG_OPT_RECVBUF, 100000), NNG_EINVAL);
+	NUTS_FAIL(nng_setopt_bool(s, NNG_OPT_RECVBUF, false), NNG_EBADTYPE);
+	NUTS_FAIL(nng_setopt(s, NNG_OPT_RECVBUF, &b, 1), NNG_EINVAL);
+	NUTS_PASS(nng_setopt_int(s, NNG_OPT_RECVBUF, 100));
+	NUTS_PASS(nng_getopt_int(s, NNG_OPT_RECVBUF, &v));
+	NUTS_TRUE(v == 100);
+	NUTS_CLOSE(s);
+}
+
+static void
+test_pair0_poll_readable(void)
+{
+	int        fd;
+	nng_socket s1;
+	nng_socket s2;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair0_open(&s2));
+	NUTS_PASS(nng_socket_set_ms(s1, NNG_OPT_RECVTIMEO, 1000));
+	NUTS_PASS(nng_socket_set_ms(s2, NNG_OPT_SENDTIMEO, 1000));
+	NUTS_PASS(nng_socket_get_int(s1, NNG_OPT_RECVFD, &fd));
+	NUTS_TRUE(fd >= 0);
+
+	// Not readable if not connected!
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	// Even after connect (no message yet)
+	NUTS_MARRY(s1, s2);
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	// But once we send messages, it is.
+	// We have to send a request, in order to send a reply.
+	NUTS_SEND(s2, "abc");
+	NUTS_SLEEP(100);
+	NUTS_TRUE(nuts_poll_fd(fd));
+
+	// and receiving makes it no longer ready
+	NUTS_RECV(s1, "abc");
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	// also let's confirm handling when we shrink the buffer size.
+	NUTS_PASS(nng_socket_set_int(s1, NNG_OPT_RECVBUF, 1));
+	NUTS_SEND(s2, "def");
+	NUTS_SLEEP(100);
+	NUTS_TRUE(nuts_poll_fd(fd));
+	NUTS_PASS(nng_socket_set_int(s1, NNG_OPT_RECVBUF, 0));
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+	// growing doesn't magically make it readable either
+	NUTS_PASS(nng_socket_set_int(s1, NNG_OPT_RECVBUF, 10));
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	NUTS_CLOSE(s1);
+	NUTS_CLOSE(s2);
+}
+
+static void
+test_pair0_poll_writable(void)
+{
+	int        fd;
+	nng_socket s1;
+	nng_socket s2;
+
+	NUTS_PASS(nng_pair0_open(&s1));
+	NUTS_PASS(nng_pair0_open(&s2));
+	NUTS_PASS(nng_socket_set_ms(s1, NNG_OPT_RECVTIMEO, 1000));
+	NUTS_PASS(nng_socket_set_ms(s2, NNG_OPT_SENDTIMEO, 1000));
+	NUTS_PASS(nng_socket_get_int(s1, NNG_OPT_SENDFD, &fd));
+	NUTS_TRUE(fd >= 0);
+
+	// Not writable if not connected!
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	// But after connect, we can.
+	NUTS_MARRY(s1, s2);
+	NUTS_TRUE(nuts_poll_fd(fd));
+
+	// We are unbuffered.
+	NUTS_SEND(s1, "abc"); // first one in the receiver
+	NUTS_SEND(s1, "def"); // second one on the sending pipe
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	// and receiving makes it ready
+	NUTS_RECV(s2, "abc");
+	NUTS_SLEEP(100); // time for the sender to complete
+	NUTS_TRUE(nuts_poll_fd(fd));
+
+	// close the peer for now.
+	NUTS_CLOSE(s2);
+	NUTS_SLEEP(100);
+
+	// resize up, makes us writable.
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+	NUTS_PASS(nng_socket_set_int(s1, NNG_OPT_SENDBUF, 1));
+	NUTS_TRUE(nuts_poll_fd(fd));
+	// resize down and we aren't anymore.
+	NUTS_PASS(nng_socket_set_int(s1, NNG_OPT_SENDBUF, 0));
+	NUTS_TRUE(nuts_poll_fd(fd) == false);
+
+	NUTS_CLOSE(s1);
+}
+
+NUTS_TESTS = {
+	{ "pair0 identity", test_identity },
+	{ "pair0 cooked", test_cooked },
+	{ "pair0 faithful", test_faithful },
+	{ "pair0 back pressure", test_back_pressure },
+	{ "pair0 send no peer", test_send_no_peer },
+	{ "pair0 raw exchange", test_raw_exchange },
+	{ "pair0 send closed aio", test_pair0_send_closed_aio },
+	{ "pair0 raw", test_pair0_raw },
+	{ "pair0 validate peer", test_pair0_validate_peer },
+	{ "pair0 no context", test_pair0_no_context },
+	{ "pair0 send buffer", test_pair0_send_buffer },
+	{ "pair0 recv buffer", test_pair0_recv_buffer },
+	{ "pair0 poll readable", test_pair0_poll_readable },
+	{ "pair0 poll writable", test_pair0_poll_writable },
+
+	{ NULL, NULL },
+};