fixes #143 Protocols and transports should be "configurable"

This makes all the protocols and transports optional.  All
of them except ZeroTier are enabled by default, but you can
now disable them (remove from the build) with cmake options.

The test suite is modified so that tests still run as much
as they can, but skip over things caused by missing functionality
from the library (due to configuration).

Further, the constant definitions and prototypes for functions
that are specific to transports or protocols are moved into
appropriate headers, which should be included directly by
applications wishing to use these.

We have also added and improved documentation -- all of the
transports are documented, and several more man pages for
protocols have been added.  (Req/Rep and Surveyor are still
missing.)

5 files changed, 830 insertions, 0 deletions

diff --git a/src/protocol/pubsub0/CMakeLists.txt b/src/protocol/pubsub0/CMakeLists.txt
new file mode 100644
index 00000000..4edcbfae
--- /dev/null
+++ b/src/protocol/pubsub0/CMakeLists.txt
@@ -0,0 +1,23 @@
+#
+# Copyright 2017 Garrett D'Amore <garrett@damore.org>
+# 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.
+#
+
+#  Pub/Sub protocol
+
+if (NNG_PROTO_PUB0)
+    set(PUB0_SOURCES protocol/pubsub0/pub.c protocol/pubsub0/pub.h)
+    install(FILES pub.h DESTINATION include/nng/protocol/pubsub0)
+endif()
+
+if (NNG_PROTO_SUB0)
+    set(SUB0_SOURCES protocol/pubsub0/sub.c protocol/pubsub0/sub.h)
+    install(FILES sub.h DESTINATION include/nng/protocol/pubsub0)
+endif()
+
+set(NNG_SOURCES ${NNG_SOURCES} ${PUB0_SOURCES} ${SUB0_SOURCES} PARENT_SCOPE)
\ No newline at end of file
diff --git a/src/protocol/pubsub0/pub.c b/src/protocol/pubsub0/pub.c
new file mode 100644
index 00000000..f4a33b77
--- /dev/null
+++ b/src/protocol/pubsub0/pub.c
@@ -0,0 +1,344 @@
+//
+// Copyright 2017 Garrett D'Amore <garrett@damore.org>
+// 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 <stdlib.h>
+#include <string.h>
+
+#include "core/nng_impl.h"
+#include "protocol/pubsub0/pub.h"
+
+// Publish protocol.  The PUB protocol simply sends messages out, as
+// a broadcast.  It has nothing more sophisticated because it does not
+// perform sender-side filtering.  Its best effort delivery, so anything
+// that can't receive the message won't get one.
+
+#ifndef NNI_PROTO_SUB_V0
+#define NNI_PROTO_SUB_V0 NNI_PROTO(2, 1)
+#endif
+
+#ifndef NNI_PROTO_PUB_V0
+#define NNI_PROTO_PUB_V0 NNI_PROTO(2, 0)
+#endif
+
+typedef struct pub0_pipe pub0_pipe;
+typedef struct pub0_sock pub0_sock;
+
+static void pub0_pipe_recv_cb(void *);
+static void pub0_pipe_send_cb(void *);
+static void pub0_pipe_getq_cb(void *);
+static void pub0_sock_getq_cb(void *);
+static void pub0_sock_fini(void *);
+static void pub0_pipe_fini(void *);
+
+// pub0_sock is our per-socket protocol private structure.
+struct pub0_sock {
+	nni_msgq *uwq;
+	int       raw;
+	nni_aio * aio_getq;
+	nni_list  pipes;
+	nni_mtx   mtx;
+};
+
+// pub0_pipe is our per-pipe protocol private structure.
+struct pub0_pipe {
+	nni_pipe *    pipe;
+	pub0_sock *   pub;
+	nni_msgq *    sendq;
+	nni_aio *     aio_getq;
+	nni_aio *     aio_send;
+	nni_aio *     aio_recv;
+	nni_list_node node;
+};
+
+static void
+pub0_sock_fini(void *arg)
+{
+	pub0_sock *s = arg;
+
+	nni_aio_stop(s->aio_getq);
+	nni_aio_fini(s->aio_getq);
+	nni_mtx_fini(&s->mtx);
+	NNI_FREE_STRUCT(s);
+}
+
+static int
+pub0_sock_init(void **sp, nni_sock *sock)
+{
+	pub0_sock *s;
+	int        rv;
+
+	if ((s = NNI_ALLOC_STRUCT(s)) == NULL) {
+		return (NNG_ENOMEM);
+	}
+	nni_mtx_init(&s->mtx);
+	if ((rv = nni_aio_init(&s->aio_getq, pub0_sock_getq_cb, s)) != 0) {
+		pub0_sock_fini(s);
+		return (rv);
+	}
+
+	s->raw = 0;
+	NNI_LIST_INIT(&s->pipes, pub0_pipe, node);
+
+	s->uwq = nni_sock_sendq(sock);
+
+	*sp = s;
+	return (0);
+}
+
+static void
+pub0_sock_open(void *arg)
+{
+	pub0_sock *s = arg;
+
+	nni_msgq_aio_get(s->uwq, s->aio_getq);
+}
+
+static void
+pub0_sock_close(void *arg)
+{
+	pub0_sock *s = arg;
+
+	nni_aio_cancel(s->aio_getq, NNG_ECLOSED);
+}
+
+static void
+pub0_pipe_fini(void *arg)
+{
+	pub0_pipe *p = arg;
+	nni_aio_fini(p->aio_getq);
+	nni_aio_fini(p->aio_send);
+	nni_aio_fini(p->aio_recv);
+	nni_msgq_fini(p->sendq);
+	NNI_FREE_STRUCT(p);
+}
+
+static int
+pub0_pipe_init(void **pp, nni_pipe *pipe, void *s)
+{
+	pub0_pipe *p;
+	int        rv;
+
+	if ((p = NNI_ALLOC_STRUCT(p)) == NULL) {
+		return (NNG_ENOMEM);
+	}
+
+	// XXX: consider making this depth tunable
+	if (((rv = nni_msgq_init(&p->sendq, 16)) != 0) ||
+	    ((rv = nni_aio_init(&p->aio_getq, pub0_pipe_getq_cb, p)) != 0) ||
+	    ((rv = nni_aio_init(&p->aio_send, pub0_pipe_send_cb, p)) != 0) ||
+	    ((rv = nni_aio_init(&p->aio_recv, pub0_pipe_recv_cb, p)) != 0)) {
+
+		pub0_pipe_fini(p);
+		return (rv);
+	}
+
+	p->pipe = pipe;
+	p->pub  = s;
+	*pp     = p;
+	return (0);
+}
+
+static int
+pub0_pipe_start(void *arg)
+{
+	pub0_pipe *p = arg;
+	pub0_sock *s = p->pub;
+
+	if (nni_pipe_peer(p->pipe) != NNI_PROTO_SUB_V0) {
+		return (NNG_EPROTO);
+	}
+	nni_mtx_lock(&s->mtx);
+	nni_list_append(&s->pipes, p);
+	nni_mtx_unlock(&s->mtx);
+
+	// Start the receiver and the queue reader.
+	nni_pipe_recv(p->pipe, p->aio_recv);
+	nni_msgq_aio_get(p->sendq, p->aio_getq);
+
+	return (0);
+}
+
+static void
+pub0_pipe_stop(void *arg)
+{
+	pub0_pipe *p = arg;
+	pub0_sock *s = p->pub;
+
+	nni_aio_stop(p->aio_getq);
+	nni_aio_stop(p->aio_send);
+	nni_aio_stop(p->aio_recv);
+
+	nni_msgq_close(p->sendq);
+
+	nni_mtx_lock(&s->mtx);
+	if (nni_list_active(&s->pipes, p)) {
+		nni_list_remove(&s->pipes, p);
+	}
+	nni_mtx_unlock(&s->mtx);
+}
+
+static void
+pub0_sock_getq_cb(void *arg)
+{
+	pub0_sock *s   = arg;
+	nni_msgq * uwq = s->uwq;
+	nni_msg *  msg, *dup;
+
+	pub0_pipe *p;
+	pub0_pipe *last;
+	int        rv;
+
+	if (nni_aio_result(s->aio_getq) != 0) {
+		return;
+	}
+
+	msg = nni_aio_get_msg(s->aio_getq);
+	nni_aio_set_msg(s->aio_getq, NULL);
+
+	nni_mtx_lock(&s->mtx);
+	last = nni_list_last(&s->pipes);
+	NNI_LIST_FOREACH (&s->pipes, p) {
+		if (p != last) {
+			rv = nni_msg_dup(&dup, msg);
+			if (rv != 0) {
+				continue;
+			}
+		} else {
+			dup = msg;
+		}
+		if ((rv = nni_msgq_tryput(p->sendq, dup)) != 0) {
+			nni_msg_free(dup);
+		}
+	}
+	nni_mtx_unlock(&s->mtx);
+
+	if (last == NULL) {
+		nni_msg_free(msg);
+	}
+
+	nni_msgq_aio_get(uwq, s->aio_getq);
+}
+
+static void
+pub0_pipe_recv_cb(void *arg)
+{
+	pub0_pipe *p = arg;
+
+	if (nni_aio_result(p->aio_recv) != 0) {
+		nni_pipe_stop(p->pipe);
+		return;
+	}
+
+	nni_msg_free(nni_aio_get_msg(p->aio_recv));
+	nni_aio_set_msg(p->aio_recv, NULL);
+	nni_pipe_recv(p->pipe, p->aio_recv);
+}
+
+static void
+pub0_pipe_getq_cb(void *arg)
+{
+	pub0_pipe *p = arg;
+
+	if (nni_aio_result(p->aio_getq) != 0) {
+		nni_pipe_stop(p->pipe);
+		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->pipe, p->aio_send);
+}
+
+static void
+pub0_pipe_send_cb(void *arg)
+{
+	pub0_pipe *p = arg;
+
+	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_stop(p->pipe);
+		return;
+	}
+
+	nni_aio_set_msg(p->aio_send, NULL);
+	nni_msgq_aio_get(p->sendq, p->aio_getq);
+}
+
+static int
+pub0_sock_setopt_raw(void *arg, const void *buf, size_t sz)
+{
+	pub0_sock *s = arg;
+	return (nni_setopt_int(&s->raw, buf, sz, 0, 1));
+}
+
+static int
+pub0_sock_getopt_raw(void *arg, void *buf, size_t *szp)
+{
+	pub0_sock *s = arg;
+	return (nni_getopt_int(s->raw, buf, szp));
+}
+
+static void
+pub0_sock_recv(void *arg, nni_aio *aio)
+{
+	nni_aio_finish_error(aio, NNG_ENOTSUP);
+}
+
+static void
+pub0_sock_send(void *arg, nni_aio *aio)
+{
+	pub0_sock *s = arg;
+
+	nni_msgq_aio_put(s->uwq, aio);
+}
+
+static nni_proto_pipe_ops pub0_pipe_ops = {
+	.pipe_init  = pub0_pipe_init,
+	.pipe_fini  = pub0_pipe_fini,
+	.pipe_start = pub0_pipe_start,
+	.pipe_stop  = pub0_pipe_stop,
+};
+
+static nni_proto_sock_option pub0_sock_options[] = {
+	{
+	    .pso_name   = NNG_OPT_RAW,
+	    .pso_getopt = pub0_sock_getopt_raw,
+	    .pso_setopt = pub0_sock_setopt_raw,
+	},
+	// terminate list
+	{ NULL, NULL, NULL },
+};
+
+static nni_proto_sock_ops pub0_sock_ops = {
+	.sock_init    = pub0_sock_init,
+	.sock_fini    = pub0_sock_fini,
+	.sock_open    = pub0_sock_open,
+	.sock_close   = pub0_sock_close,
+	.sock_send    = pub0_sock_send,
+	.sock_recv    = pub0_sock_recv,
+	.sock_options = pub0_sock_options,
+};
+
+static nni_proto pub0_proto = {
+	.proto_version  = NNI_PROTOCOL_VERSION,
+	.proto_self     = { NNI_PROTO_PUB_V0, "pub" },
+	.proto_peer     = { NNI_PROTO_SUB_V0, "sub" },
+	.proto_flags    = NNI_PROTO_FLAG_SND,
+	.proto_sock_ops = &pub0_sock_ops,
+	.proto_pipe_ops = &pub0_pipe_ops,
+};
+
+int
+nng_pub0_open(nng_socket *sidp)
+{
+	return (nni_proto_open(sidp, &pub0_proto));
+}
diff --git a/src/protocol/pubsub0/pub.h b/src/protocol/pubsub0/pub.h
new file mode 100644
index 00000000..2388a292
--- /dev/null
+++ b/src/protocol/pubsub0/pub.h
@@ -0,0 +1,28 @@
+//
+// Copyright 2017 Garrett D'Amore <garrett@damore.org>
+// 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.
+//
+
+#ifndef NNG_PROTOCOL_PUBSUB0_PUB_H
+#define NNG_PROTOCOL_PUBSUB0_PUB_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+NNG_DECL int nng_pub0_open(nng_socket *);
+
+#ifndef nng_pub_open
+#define nng_pub_open nng_pub0_open
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NNG_PROTOCOL_PUBSUB0_PUB_H
diff --git a/src/protocol/pubsub0/sub.c b/src/protocol/pubsub0/sub.c
new file mode 100644
index 00000000..6c504d75
--- /dev/null
+++ b/src/protocol/pubsub0/sub.c
@@ -0,0 +1,404 @@
+//
+// Copyright 2017 Garrett D'Amore <garrett@damore.org>
+// 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 <stdlib.h>
+#include <string.h>
+
+#include "core/nng_impl.h"
+#include "protocol/pubsub0/sub.h"
+
+// Subscriber protocol.  The SUB protocol receives messages sent to
+// it from publishers, and filters out those it is not interested in,
+// only passing up ones that match known subscriptions.
+
+#ifndef NNI_PROTO_SUB_V0
+#define NNI_PROTO_SUB_V0 NNI_PROTO(2, 1)
+#endif
+
+#ifndef NNI_PROTO_PUB_V0
+#define NNI_PROTO_PUB_V0 NNI_PROTO(2, 0)
+#endif
+
+typedef struct sub0_pipe  sub0_pipe;
+typedef struct sub0_sock  sub0_sock;
+typedef struct sub0_topic sub0_topic;
+
+static void sub0_recv_cb(void *);
+static void sub0_putq_cb(void *);
+static void sub0_pipe_fini(void *);
+
+struct sub0_topic {
+	nni_list_node node;
+	size_t        len;
+	void *        buf;
+};
+
+// sub0_sock is our per-socket protocol private structure.
+struct sub0_sock {
+	nni_list  topics;
+	nni_msgq *urq;
+	int       raw;
+	nni_mtx   lk;
+};
+
+// sub0_pipe is our per-pipe protocol private structure.
+struct sub0_pipe {
+	nni_pipe * pipe;
+	sub0_sock *sub;
+	nni_aio *  aio_recv;
+	nni_aio *  aio_putq;
+};
+
+static int
+sub0_sock_init(void **sp, nni_sock *sock)
+{
+	sub0_sock *s;
+
+	if ((s = NNI_ALLOC_STRUCT(s)) == NULL) {
+		return (NNG_ENOMEM);
+	}
+	nni_mtx_init(&s->lk);
+	NNI_LIST_INIT(&s->topics, sub0_topic, node);
+	s->raw = 0;
+
+	s->urq = nni_sock_recvq(sock);
+	*sp    = s;
+	return (0);
+}
+
+static void
+sub0_sock_fini(void *arg)
+{
+	sub0_sock * s = arg;
+	sub0_topic *topic;
+
+	while ((topic = nni_list_first(&s->topics)) != NULL) {
+		nni_list_remove(&s->topics, topic);
+		nni_free(topic->buf, topic->len);
+		NNI_FREE_STRUCT(topic);
+	}
+	nni_mtx_fini(&s->lk);
+	NNI_FREE_STRUCT(s);
+}
+
+static void
+sub0_sock_open(void *arg)
+{
+	NNI_ARG_UNUSED(arg);
+}
+
+static void
+sub0_sock_close(void *arg)
+{
+	NNI_ARG_UNUSED(arg);
+}
+
+static void
+sub0_pipe_fini(void *arg)
+{
+	sub0_pipe *p = arg;
+
+	nni_aio_fini(p->aio_putq);
+	nni_aio_fini(p->aio_recv);
+	NNI_FREE_STRUCT(p);
+}
+
+static int
+sub0_pipe_init(void **pp, nni_pipe *pipe, void *s)
+{
+	sub0_pipe *p;
+	int        rv;
+
+	if ((p = NNI_ALLOC_STRUCT(p)) == NULL) {
+		return (NNG_ENOMEM);
+	}
+	if (((rv = nni_aio_init(&p->aio_putq, sub0_putq_cb, p)) != 0) ||
+	    ((rv = nni_aio_init(&p->aio_recv, sub0_recv_cb, p)) != 0)) {
+		sub0_pipe_fini(p);
+		return (rv);
+	}
+
+	p->pipe = pipe;
+	p->sub  = s;
+	*pp     = p;
+	return (0);
+}
+
+static int
+sub0_pipe_start(void *arg)
+{
+	sub0_pipe *p = arg;
+
+	nni_pipe_recv(p->pipe, p->aio_recv);
+	return (0);
+}
+
+static void
+sub0_pipe_stop(void *arg)
+{
+	sub0_pipe *p = arg;
+
+	nni_aio_stop(p->aio_putq);
+	nni_aio_stop(p->aio_recv);
+}
+
+static void
+sub0_recv_cb(void *arg)
+{
+	sub0_pipe *p   = arg;
+	sub0_sock *s   = p->sub;
+	nni_msgq * urq = s->urq;
+	nni_msg *  msg;
+
+	if (nni_aio_result(p->aio_recv) != 0) {
+		nni_pipe_stop(p->pipe);
+		return;
+	}
+
+	msg = nni_aio_get_msg(p->aio_recv);
+	nni_aio_set_msg(p->aio_recv, NULL);
+	nni_msg_set_pipe(msg, nni_pipe_id(p->pipe));
+	nni_aio_set_msg(p->aio_putq, msg);
+	nni_msgq_aio_put(urq, p->aio_putq);
+}
+
+static void
+sub0_putq_cb(void *arg)
+{
+	sub0_pipe *p = arg;
+
+	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_stop(p->pipe);
+		return;
+	}
+
+	nni_pipe_recv(p->pipe, p->aio_recv);
+}
+
+// For now we maintain subscriptions on a sorted linked list.  As we do not
+// expect to have huge numbers of subscriptions, and as the operation is
+// really O(n), we think this is acceptable.  In the future we might decide
+// to replace this with a patricia trie, like old nanomsg had.
+
+static int
+sub0_subscribe(void *arg, const void *buf, size_t sz)
+{
+	sub0_sock * s = arg;
+	sub0_topic *topic;
+	sub0_topic *newtopic;
+
+	nni_mtx_lock(&s->lk);
+	NNI_LIST_FOREACH (&s->topics, topic) {
+		int rv;
+
+		if (topic->len >= sz) {
+			rv = memcmp(topic->buf, buf, sz);
+		} else {
+			rv = memcmp(topic->buf, buf, topic->len);
+		}
+		if (rv == 0) {
+			if (topic->len == sz) {
+				// Already inserted.
+				nni_mtx_unlock(&s->lk);
+				return (0);
+			}
+			if (topic->len > sz) {
+				break;
+			}
+		} else if (rv > 0) {
+			break;
+		}
+	}
+
+	if ((newtopic = NNI_ALLOC_STRUCT(newtopic)) == NULL) {
+		nni_mtx_unlock(&s->lk);
+		return (NNG_ENOMEM);
+	}
+	if ((newtopic->buf = nni_alloc(sz)) == NULL) {
+		nni_mtx_unlock(&s->lk);
+		return (NNG_ENOMEM);
+	}
+	NNI_LIST_NODE_INIT(&newtopic->node);
+	newtopic->len = sz;
+	memcpy(newtopic->buf, buf, sz);
+	if (topic != NULL) {
+		nni_list_insert_before(&s->topics, newtopic, topic);
+	} else {
+		nni_list_append(&s->topics, newtopic);
+	}
+	nni_mtx_unlock(&s->lk);
+	return (0);
+}
+
+static int
+sub0_unsubscribe(void *arg, const void *buf, size_t sz)
+{
+	sub0_sock * s = arg;
+	sub0_topic *topic;
+	int         rv;
+
+	nni_mtx_lock(&s->lk);
+	NNI_LIST_FOREACH (&s->topics, topic) {
+		if (topic->len >= sz) {
+			rv = memcmp(topic->buf, buf, sz);
+		} else {
+			rv = memcmp(topic->buf, buf, topic->len);
+		}
+		if (rv == 0) {
+			if (topic->len == sz) {
+				nni_list_remove(&s->topics, topic);
+				nni_mtx_unlock(&s->lk);
+				nni_free(topic->buf, topic->len);
+				NNI_FREE_STRUCT(topic);
+				return (0);
+			}
+			if (topic->len > sz) {
+				nni_mtx_unlock(&s->lk);
+				return (NNG_ENOENT);
+			}
+		}
+		if (rv > 0) {
+			nni_mtx_unlock(&s->lk);
+			return (NNG_ENOENT);
+		}
+	}
+	nni_mtx_unlock(&s->lk);
+	return (NNG_ENOENT);
+}
+
+static int
+sub0_sock_setopt_raw(void *arg, const void *buf, size_t sz)
+{
+	sub0_sock *s = arg;
+	return (nni_setopt_int(&s->raw, buf, sz, 0, 1));
+}
+
+static int
+sub0_sock_getopt_raw(void *arg, void *buf, size_t *szp)
+{
+	sub0_sock *s = arg;
+	return (nni_getopt_int(s->raw, buf, szp));
+}
+
+static void
+sub0_sock_send(void *arg, nni_aio *aio)
+{
+	nni_aio_finish_error(aio, NNG_ENOTSUP);
+}
+
+static void
+sub0_sock_recv(void *arg, nni_aio *aio)
+{
+	sub0_sock *s = arg;
+
+	nni_msgq_aio_get(s->urq, aio);
+}
+
+static nni_msg *
+sub0_sock_filter(void *arg, nni_msg *msg)
+{
+	sub0_sock * s = arg;
+	sub0_topic *topic;
+	char *      body;
+	size_t      len;
+	int         match;
+
+	nni_mtx_lock(&s->lk);
+	if (s->raw) {
+		nni_mtx_unlock(&s->lk);
+		return (msg);
+	}
+
+	body = nni_msg_body(msg);
+	len  = nni_msg_len(msg);
+
+	match = 0;
+	// Check to see if the message matches one of our subscriptions.
+	NNI_LIST_FOREACH (&s->topics, topic) {
+		if (len >= topic->len) {
+			int rv = memcmp(topic->buf, body, topic->len);
+			if (rv == 0) {
+				// Matched!
+				match = 1;
+				break;
+			}
+			if (rv > 0) {
+				match = 0;
+				break;
+			}
+		} else if (memcmp(topic->buf, body, len) >= 0) {
+			match = 0;
+			break;
+		}
+	}
+	nni_mtx_unlock(&s->lk);
+	if (!match) {
+		nni_msg_free(msg);
+		return (NULL);
+	}
+	return (msg);
+}
+
+// This is the global protocol structure -- our linkage to the core.
+// This should be the only global non-static symbol in this file.
+static nni_proto_pipe_ops sub0_pipe_ops = {
+	.pipe_init  = sub0_pipe_init,
+	.pipe_fini  = sub0_pipe_fini,
+	.pipe_start = sub0_pipe_start,
+	.pipe_stop  = sub0_pipe_stop,
+};
+
+static nni_proto_sock_option sub0_sock_options[] = {
+	{
+	    .pso_name   = NNG_OPT_RAW,
+	    .pso_getopt = sub0_sock_getopt_raw,
+	    .pso_setopt = sub0_sock_setopt_raw,
+	},
+	{
+	    .pso_name   = NNG_OPT_SUB_SUBSCRIBE,
+	    .pso_getopt = NULL,
+	    .pso_setopt = sub0_subscribe,
+	},
+	{
+	    .pso_name   = NNG_OPT_SUB_UNSUBSCRIBE,
+	    .pso_getopt = NULL,
+	    .pso_setopt = sub0_unsubscribe,
+	},
+	// terminate list
+	{ NULL, NULL, NULL },
+};
+
+static nni_proto_sock_ops sub0_sock_ops = {
+	.sock_init    = sub0_sock_init,
+	.sock_fini    = sub0_sock_fini,
+	.sock_open    = sub0_sock_open,
+	.sock_close   = sub0_sock_close,
+	.sock_send    = sub0_sock_send,
+	.sock_recv    = sub0_sock_recv,
+	.sock_filter  = sub0_sock_filter,
+	.sock_options = sub0_sock_options,
+};
+
+static nni_proto sub0_proto = {
+	.proto_version  = NNI_PROTOCOL_VERSION,
+	.proto_self     = { NNI_PROTO_SUB_V0, "sub" },
+	.proto_peer     = { NNI_PROTO_PUB_V0, "pub" },
+	.proto_flags    = NNI_PROTO_FLAG_RCV,
+	.proto_sock_ops = &sub0_sock_ops,
+	.proto_pipe_ops = &sub0_pipe_ops,
+};
+
+int
+nng_sub0_open(nng_socket *sidp)
+{
+	return (nni_proto_open(sidp, &sub0_proto));
+}
diff --git a/src/protocol/pubsub0/sub.h b/src/protocol/pubsub0/sub.h
new file mode 100644
index 00000000..1a09145d
--- /dev/null
+++ b/src/protocol/pubsub0/sub.h
@@ -0,0 +1,31 @@
+//
+// Copyright 2017 Garrett D'Amore <garrett@damore.org>
+// 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.
+//
+
+#ifndef NNG_PROTOCOL_PUBSUB0_SUB_H
+#define NNG_PROTOCOL_PUBSUB0_SUB_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+NNG_DECL int nng_sub0_open(nng_socket *);
+
+#ifndef nng_sub_open
+#define nng_sub_open nng_sub0_open
+#endif
+
+#define NNG_OPT_SUB_SUBSCRIBE "sub:subscribe"
+#define NNG_OPT_SUB_UNSUBSCRIBE "sub:unsubscribe"
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NNG_PROTOCOL_PUBSUB0_SUB_H