Implement SP wire protocolsp

Implements the SP wire protocol, and infrastructure for legacy wire
protocol support.

Also added an XS_SERVICE_ID socket option to set the service id and renamed
the XS_PROTOCOL option to XS_PATTERN_VERSION.

The following pattern versions are supported:

PAIR:     v3
PUBSUB:   v1 (legacy), v4
REQREP:   v2
PIPELINE: v3
SURVEY:   v2

Note that all existing pattern versions have been bumped by 1 to allow for
use of legacy protocols (otherwise there would be no way to distinguish
between e.g. PUBSUB v3 and PUBSUB v3 using SP).

Signed-off-by: Martin Lucina <martin@lucina.net>

35 files changed, 597 insertions, 83 deletions

diff --git a/include/xs.h b/include/xs.h
index 56efa52..9b09812 100644
--- a/include/xs.h
+++ b/include/xs.h
@@ -206,8 +206,9 @@ XS_EXPORT int xs_setctxopt (void *context, int option, const void *optval,
 #define XS_SNDTIMEO 28
 #define XS_IPV4ONLY 31
 #define XS_KEEPALIVE 32
-#define XS_PROTOCOL 33
+#define XS_PATTERN_VERSION 33
 #define XS_SURVEY_TIMEOUT 35
+#define XS_SERVICE_ID 36
 
 /*  Message options                                                           */
 #define XS_MORE 1
diff --git a/src/options.cpp b/src/options.cpp
index f7bbdc4..bda0c01 100644
--- a/src/options.cpp
+++ b/src/options.cpp
@@ -48,7 +48,12 @@ xs::options_t::options_t () :
     sndtimeo (-1),
     ipv4only (1),
     keepalive (0),
-    protocol (0),
+    legacy_protocol (false),
+    sp_service (0),
+    sp_pattern (-1),
+    sp_version (-1),
+    sp_role (-1),
+    sp_complement (-1),
     filter (XS_FILTER_PREFIX),
     survey_timeout (-1),
     delay_on_close (true),
@@ -236,29 +241,29 @@ int xs::options_t::setsockopt (int option_, const void *optval_,
             return 0;
         }
 
-    case XS_PROTOCOL:
+    case XS_FILTER:
+        if (optvallen_ != sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        filter = *((int*) optval_);
+        return 0;
+
+    case XS_SERVICE_ID:
         {
             if (optvallen_ != sizeof (int)) {
                 errno = EINVAL;
                 return -1;
             }
             int val = *((int*) optval_);
-            if (val < 0) {
+            if (val < 0 || val > 0xffff) {
                 errno = EINVAL;
                 return -1;
             }
-            protocol = val;
+            sp_service = val;
             return 0;
         }
 
-    case XS_FILTER:
-        if (optvallen_ != sizeof (int)) {
-            errno = EINVAL;
-            return -1;
-        }
-        filter = *((int*) optval_);
-        return 0;
-
     case XS_SURVEY_TIMEOUT:
         if (type != XS_SURVEYOR) {
             errno = ENOTSUP;
@@ -452,12 +457,21 @@ int xs::options_t::getsockopt (int option_, void *optval_, size_t *optvallen_)
         *optvallen_ = sizeof (int);
         return 0;
 
-    case XS_PROTOCOL:
+    case XS_PATTERN_VERSION:
+        if (*optvallen_ < sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        *((int*) optval_) = sp_version;
+        *optvallen_ = sizeof (int);
+        return 0;
+
+    case XS_SERVICE_ID:
         if (*optvallen_ < sizeof (int)) {
             errno = EINVAL;
             return -1;
         }
-        *((int*) optval_) = protocol;
+        *((int*) optval_) = sp_service;
         *optvallen_ = sizeof (int);
         return 0;
 
diff --git a/src/options.hpp b/src/options.hpp
index 805f793..9070c0f 100644
--- a/src/options.hpp
+++ b/src/options.hpp
@@ -92,8 +92,16 @@ namespace xs
         //  If 1, keepalives are to be sent periodically.
         int keepalive;
 
-        //  Version of wire protocol to use.
-        int protocol;
+        //  If true, the legacy non-SP wire protocol is in use.
+        bool legacy_protocol;
+
+        //  SP protocol service id, pattern, version, role and complementary
+        //  role.
+        int sp_service;
+        int sp_pattern;
+        int sp_version;
+        int sp_role;
+        int sp_complement;
 
         //  Filter ID to be used with subscriptions and unsubscriptions.
         int filter;
diff --git a/src/pair.cpp b/src/pair.cpp
index 531bfc5..bfb48d3 100644
--- a/src/pair.cpp
+++ b/src/pair.cpp
@@ -23,12 +23,17 @@
 #include "err.hpp"
 #include "pipe.hpp"
 #include "msg.hpp"
+#include "wire.hpp"
 
 xs::pair_t::pair_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     socket_base_t (parent_, tid_, sid_),
     pipe (NULL)
 {
     options.type = XS_PAIR;
+    options.sp_pattern = SP_PAIR;
+    options.sp_role = SP_PAIR_PAIR;
+    options.sp_version = 3;
+    options.sp_complement = SP_PAIR_PAIR;
 }
 
 xs::pair_t::~pair_t ()
@@ -36,6 +41,34 @@ xs::pair_t::~pair_t ()
     xs_assert (!pipe);
 }
 
+int xs::pair_t::xsetsockopt (int option_, const void *optval_,
+    size_t optvallen_)
+{
+    if (option_ != XS_PATTERN_VERSION) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (optvallen_ != sizeof (int)) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (!optval_) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    int version = *(int *) optval_;
+    if (version != 2) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    options.sp_version = version;
+    return 0;
+}
+
 void xs::pair_t::xattach_pipe (pipe_t *pipe_, bool icanhasall_)
 {
     xs_assert (pipe_ != NULL);
diff --git a/src/pair.hpp b/src/pair.hpp
index 07ed6c5..6a5f167 100644
--- a/src/pair.hpp
+++ b/src/pair.hpp
@@ -42,6 +42,7 @@ namespace xs
         ~pair_t ();
 
         //  Overloads of functions from socket_base_t.
+        int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
         void xattach_pipe (xs::pipe_t *pipe_, bool icanhasall_);
         int xsend (xs::msg_t *msg_, int flags_);
         int xrecv (xs::msg_t *msg_, int flags_);
diff --git a/src/pgm_receiver.cpp b/src/pgm_receiver.cpp
index 371c657..9aa1233 100644
--- a/src/pgm_receiver.cpp
+++ b/src/pgm_receiver.cpp
@@ -47,6 +47,11 @@ xs::pgm_receiver_t::pgm_receiver_t (class io_thread_t *parent_,
     pending_bytes (0),
     rx_timer (NULL)
 {
+    //  If not using a legacy protocol, fill in desired protocol header.
+    if (!options.legacy_protocol) {
+        sp_get_header (desired_header, options.sp_service, options.sp_pattern,
+            options.sp_version, options.sp_complement);
+    }
 }
 
 xs::pgm_receiver_t::~pgm_receiver_t ()
@@ -173,7 +178,7 @@ void xs::pgm_receiver_t::in_event (fd_t fd_)
         data = (unsigned char*) tmp;
 
         //  No data to process. This may happen if the packet received is
-        //  neither ODATA nor ODATA.
+        //  neither RDATA nor ODATA.
         if (received == 0) {
             if (errno == ENOMEM || errno == EBUSY) {
                 const long timeout = pgm_socket.get_rx_timeout ();
@@ -200,18 +205,32 @@ void xs::pgm_receiver_t::in_event (fd_t fd_)
             break;
         }
 
-        //  New peer. Add it to the list of know but unjoint peers.
-        if (it == peers.end ()) {
-            peer_info_t peer_info = {false, NULL};
-            it = peers.insert (peers_t::value_type (*tsi, peer_info)).first;
+        //  Check protocol header.
+        if (unlikely (!options.legacy_protocol)) {
+            if (received < (ssize_t) sizeof desired_header)
+                //  Ignore malformed datagram.
+                continue;
+            if (memcmp (data, desired_header, sizeof desired_header) != 0)
+                //  Ignore datagram with incorrect protocol header.
+                continue;
+            data += sizeof desired_header;
+            received -= sizeof desired_header;
         }
 
         //  Read the offset of the fist message in the current packet.
-        xs_assert ((size_t) received >= sizeof (uint16_t));
+        if (received < (ssize_t) sizeof (uint16_t))
+            //  Ignore malformed datagram.
+            continue;
         uint16_t offset = get_uint16 (data);
         data += sizeof (uint16_t);
         received -= sizeof (uint16_t);
 
+        //  New peer. Add it to the list of known but disjoint peers.
+        if (it == peers.end ()) {
+            peer_info_t peer_info = {false, NULL};
+            it = peers.insert (peers_t::value_type (*tsi, peer_info)).first;
+        }
+
         //  Join the stream if needed.
         if (!it->second.joined) {
 
diff --git a/src/pgm_receiver.hpp b/src/pgm_receiver.hpp
index 38c7a7b..c44594a 100644
--- a/src/pgm_receiver.hpp
+++ b/src/pgm_receiver.hpp
@@ -39,6 +39,7 @@
 #include "options.hpp"
 #include "decoder.hpp"
 #include "pgm_socket.hpp"
+#include "wire.hpp"
 
 namespace xs
 {
@@ -125,6 +126,9 @@ namespace xs
         //  Receive timer, if active, otherwise NULL.
         handle_t rx_timer;
 
+        //  Desired protocol header.
+        sp_header_t desired_header;
+
         pgm_receiver_t (const pgm_receiver_t&);
         const pgm_receiver_t &operator = (const pgm_receiver_t&);
     };
diff --git a/src/pgm_sender.cpp b/src/pgm_sender.cpp
index d476cbb..528ac7a 100644
--- a/src/pgm_sender.cpp
+++ b/src/pgm_sender.cpp
@@ -60,6 +60,25 @@ int xs::pgm_sender_t::init (bool udp_encapsulation_, const char *network_)
     out_buffer_size = pgm_socket.get_max_tsdu_size ();
     out_buffer = (unsigned char*) malloc (out_buffer_size);
     alloc_assert (out_buffer);
+    encode_buffer = out_buffer;
+    encode_buffer_size = out_buffer_size;
+    header_size = 0;
+
+    //  If not using a legacy protocol, fill in our datagram header and reserve
+    //  space for it in the datagram.
+    if (!options.legacy_protocol) {
+        sp_get_header (out_buffer, options.sp_service, options.sp_pattern,
+            options.sp_version, options.sp_role);
+        encode_buffer += SP_HEADER_LENGTH;
+        encode_buffer_size -= SP_HEADER_LENGTH;
+        header_size += SP_HEADER_LENGTH;
+    }
+
+    //  Reserve space in the datagram for the offset of the first message.
+    offset_p = encode_buffer;
+    encode_buffer += sizeof (uint16_t);
+    encode_buffer_size -= sizeof (uint16_t);
+    header_size += sizeof (uint16_t);
 
     return rc;
 }
@@ -156,27 +175,25 @@ void xs::pgm_sender_t::in_event (fd_t fd_)
 
 void xs::pgm_sender_t::out_event (fd_t fd_)
 {
-    //  POLLOUT event from send socket. If write buffer is empty, 
-    //  try to read new data from the encoder.
+    //  POLLOUT event from send socket. If write buffer is empty (which means
+    //  that the last write succeeded), try to read new data from the encoder.
     if (write_size == 0) {
 
-        //  First two bytes (sizeof uint16_t) are used to store message 
-        //  offset in following steps. Note that by passing our buffer to
-        //  the get data function we prevent it from returning its own buffer.
-        unsigned char *bf = out_buffer + sizeof (uint16_t);
-        size_t bfsz = out_buffer_size - sizeof (uint16_t);
+        //  Pass our own buffer to the get_data () function to prevent it from
+        //  returning its own buffer.
         int offset = -1;
-        encoder.get_data (&bf, &bfsz, &offset);
+        size_t data_size = encode_buffer_size;
+        encoder.get_data (&encode_buffer, &data_size, &offset);
 
         //  If there are no data to write stop polling for output.
-        if (!bfsz) {
+        if (!data_size) {
             reset_pollout (handle);
             return;
         }
 
         //  Put offset information in the buffer.
-        write_size = bfsz + sizeof (uint16_t);
-        put_uint16 (out_buffer, offset == -1 ? 0xffff : (uint16_t) offset);
+        write_size = header_size + data_size;
+        put_uint16 (offset_p, offset == -1 ? 0xffff : (uint16_t) offset);
     }
 
     if (tx_timer) {
diff --git a/src/pgm_sender.hpp b/src/pgm_sender.hpp
index 89f81bf..5a808b6 100644
--- a/src/pgm_sender.hpp
+++ b/src/pgm_sender.hpp
@@ -84,12 +84,21 @@ namespace xs
         handle_t rdata_notify_handle;
         handle_t pending_notify_handle;
 
-        //  Output buffer from pgm_socket.
+        //  Output buffer and size for pgm_socket.
         unsigned char *out_buffer;
-        
-        //  Output buffer size.
         size_t out_buffer_size;
 
+        //  Size of header in each datagram.
+        size_t header_size;
+
+        //  Encoder buffer and size, adjusted from output buffer by size of
+        //  datagram header(s).
+        unsigned char *encode_buffer;
+        size_t encode_buffer_size;
+
+        //  Position of offset to first message in output buffer.
+        unsigned char *offset_p;
+
         //  Number of bytes in the buffer to be written to the socket.
         //  If zero, there are no data to be sent.
         size_t write_size;
diff --git a/src/pipe.cpp b/src/pipe.cpp
index 0a15cc0..c14642f 100644
--- a/src/pipe.cpp
+++ b/src/pipe.cpp
@@ -27,7 +27,7 @@
 #include "err.hpp"
 
 int xs::pipepair (class object_t *parents_ [2], class pipe_t* pipes_ [2],
-    int hwms_ [2], bool delays_ [2], int protocol_)
+    int hwms_ [2], bool delays_ [2], int sp_version_)
 {
     //   Creates two pipe objects. These objects are connected by two ypipes,
     //   each to pass messages in one direction.
@@ -38,10 +38,10 @@ int xs::pipepair (class object_t *parents_ [2], class pipe_t* pipes_ [2],
     alloc_assert (upipe2);
 
     pipes_ [0] = new (std::nothrow) pipe_t (parents_ [0], upipe1, upipe2,
-        hwms_ [1], hwms_ [0], delays_ [0], protocol_);
+        hwms_ [1], hwms_ [0], delays_ [0], sp_version_);
     alloc_assert (pipes_ [0]);
     pipes_ [1] = new (std::nothrow) pipe_t (parents_ [1], upipe2, upipe1,
-        hwms_ [0], hwms_ [1], delays_ [1], protocol_);
+        hwms_ [0], hwms_ [1], delays_ [1], sp_version_);
     alloc_assert (pipes_ [1]);
 
     pipes_ [0]->set_peer (pipes_ [1]);
@@ -51,7 +51,7 @@ int xs::pipepair (class object_t *parents_ [2], class pipe_t* pipes_ [2],
 }
 
 xs::pipe_t::pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
-      int inhwm_, int outhwm_, bool delay_, int protocol_) :
+      int inhwm_, int outhwm_, bool delay_, int sp_version_) :
     object_t (parent_),
     inpipe (inpipe_),
     outpipe (outpipe_),
@@ -66,7 +66,7 @@ xs::pipe_t::pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
     sink (NULL),
     state (active),
     delay (delay_),
-    protocol (protocol_)
+    sp_version (sp_version_)
 {
 }
 
@@ -386,9 +386,9 @@ void xs::pipe_t::terminate (bool delay_)
     }
 }
 
-int xs::pipe_t::get_protocol ()
+int xs::pipe_t::get_sp_version ()
 {
-    return protocol;
+    return sp_version;
 }
 
 bool xs::pipe_t::is_delimiter (msg_t &msg_)
diff --git a/src/pipe.hpp b/src/pipe.hpp
index c298154..dbc6b7e 100644
--- a/src/pipe.hpp
+++ b/src/pipe.hpp
@@ -44,7 +44,7 @@ namespace xs
     //  pipe receives all the pending messages before terminating, otherwise it
     //  terminates straight away.
     int pipepair (xs::object_t *parents_ [2], xs::pipe_t* pipes_ [2],
-        int hwms_ [2], bool delays_ [2], int protocol_);
+        int hwms_ [2], bool delays_ [2], int sp_version_);
 
     struct i_pipe_events
     {
@@ -69,7 +69,7 @@ namespace xs
         //  This allows pipepair to create pipe objects.
         friend int pipepair (xs::object_t *parents_ [2],
             xs::pipe_t* pipes_ [2], int hwms_ [2], bool delays_ [2],
-            int protocol_);
+            int sp_version_);
 
     public:
 
@@ -111,8 +111,8 @@ namespace xs
         //  before actual shutdown.
         void terminate (bool delay_);
 
-        //  Returns the ID of the protocol associated with the pipe.
-        int get_protocol ();
+        //  Returns the SP pattern version in use on this pipe.
+        int get_sp_version ();
 
     private:
 
@@ -132,7 +132,7 @@ namespace xs
         //  Constructor is private. Pipe can only be created using
         //  pipepair function.
         pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
-            int inhwm_, int outhwm_, bool delay_, int protocol_);
+            int inhwm_, int outhwm_, bool delay_, int sp_version_);
 
         //  Pipepair uses this function to let us know about
         //  the peer pipe object.
@@ -192,9 +192,9 @@ namespace xs
         //  asks us to.
         bool delay;
 
-        //  ID of the protocol to use. This value is not used by the pipe
-        //  itself, rather it's used by the users of the pipe.
-        int protocol;
+        //  SP pattern version in use on this pipe. This value is used by the
+        //  pattern classes using the pipe, not the pipe itself.
+        int sp_version;
 
         //  Identity of the writer. Used uniquely by the reader side.
         blob_t identity;
diff --git a/src/pull.cpp b/src/pull.cpp
index 8ae8208..0cedc39 100644
--- a/src/pull.cpp
+++ b/src/pull.cpp
@@ -23,17 +23,50 @@
 #include "err.hpp"
 #include "msg.hpp"
 #include "pipe.hpp"
+#include "wire.hpp"
 
 xs::pull_t::pull_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     socket_base_t (parent_, tid_, sid_)
 {
     options.type = XS_PULL;
+    options.sp_pattern = SP_PIPELINE;
+    options.sp_version = 3;
+    options.sp_role = SP_PIPELINE_PULL;
+    options.sp_complement = SP_PIPELINE_PUSH;
 }
 
 xs::pull_t::~pull_t ()
 {
 }
 
+int xs::pull_t::xsetsockopt (int option_, const void *optval_,
+    size_t optvallen_)
+{
+    if (option_ != XS_PATTERN_VERSION) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (optvallen_ != sizeof (int)) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (!optval_) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    int version = *(int *) optval_;
+    if (version != 2) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    options.sp_version = version;
+    return 0;
+}
+
 void xs::pull_t::xattach_pipe (pipe_t *pipe_, bool icanhasall_)
 {
     xs_assert (pipe_);
diff --git a/src/pull.hpp b/src/pull.hpp
index 04da465..5453bbd 100644
--- a/src/pull.hpp
+++ b/src/pull.hpp
@@ -45,6 +45,7 @@ namespace xs
     protected:
 
         //  Overloads of functions from socket_base_t.
+        int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
         void xattach_pipe (xs::pipe_t *pipe_, bool icanhasall_);
         int xrecv (xs::msg_t *msg_, int flags_);
         bool xhas_in ();
diff --git a/src/push.cpp b/src/push.cpp
index 59f508f..729c97a 100644
--- a/src/push.cpp
+++ b/src/push.cpp
@@ -23,17 +23,50 @@
 #include "pipe.hpp"
 #include "err.hpp"
 #include "msg.hpp"
+#include "wire.hpp"
 
 xs::push_t::push_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     socket_base_t (parent_, tid_, sid_)
 {
     options.type = XS_PUSH;
+    options.sp_pattern = SP_PIPELINE;
+    options.sp_version = 3;
+    options.sp_role = SP_PIPELINE_PUSH;
+    options.sp_complement = SP_PIPELINE_PULL;
 }
 
 xs::push_t::~push_t ()
 {
 }
 
+int xs::push_t::xsetsockopt (int option_, const void *optval_,
+    size_t optvallen_)
+{
+    if (option_ != XS_PATTERN_VERSION) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (optvallen_ != sizeof (int)) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (!optval_) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    int version = *(int *) optval_;
+    if (version != 2) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    options.sp_version = version;
+    return 0;
+}
+
 void xs::push_t::xattach_pipe (pipe_t *pipe_, bool icanhasall_)
 {
     xs_assert (pipe_);
diff --git a/src/push.hpp b/src/push.hpp
index a112f31..ffe16cc 100644
--- a/src/push.hpp
+++ b/src/push.hpp
@@ -45,6 +45,7 @@ namespace xs
     protected:
 
         //  Overloads of functions from socket_base_t.
+        int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
         void xattach_pipe (xs::pipe_t *pipe_, bool icanhasall_);
         int xsend (xs::msg_t *msg_, int flags_);
         bool xhas_out ();
diff --git a/src/session_base.cpp b/src/session_base.cpp
index 48d8811..da9ee8e 100644
--- a/src/session_base.cpp
+++ b/src/session_base.cpp
@@ -298,7 +298,7 @@ void xs::session_base_t::process_attach (i_engine *engine_)
         pipe_t *pipes [2] = {NULL, NULL};
         int hwms [2] = {options.rcvhwm, options.sndhwm};
         bool delays [2] = {options.delay_on_close, options.delay_on_disconnect};
-        int rc = pipepair (parents, pipes, hwms, delays, options.protocol);
+        int rc = pipepair (parents, pipes, hwms, delays, options.sp_version);
         errno_assert (rc == 0);
 
         //  Plug the local end of the pipe.
diff --git a/src/socket_base.cpp b/src/socket_base.cpp
index 86c01b0..960bd2c 100644
--- a/src/socket_base.cpp
+++ b/src/socket_base.cpp
@@ -451,7 +451,7 @@ int xs::socket_base_t::connect (const char *addr_)
         pipe_t *ppair [2] = {NULL, NULL};
         int hwms [2] = {sndhwm, rcvhwm};
         bool delays [2] = {options.delay_on_disconnect, options.delay_on_close};
-        rc = pipepair (parents, ppair, hwms, delays, options.protocol);
+        rc = pipepair (parents, ppair, hwms, delays, options.sp_version);
         errno_assert (rc == 0);
 
         //  Attach local end of the pipe to this socket object.
@@ -535,7 +535,7 @@ int xs::socket_base_t::connect (const char *addr_)
     pipe_t *ppair [2] = {NULL, NULL};
     int hwms [2] = {options.sndhwm, options.rcvhwm};
     bool delays [2] = {options.delay_on_disconnect, options.delay_on_close};
-    rc = pipepair (parents, ppair, hwms, delays, options.protocol);
+    rc = pipepair (parents, ppair, hwms, delays, options.sp_version);
     errno_assert (rc == 0);
 
     // PGM does not support subscription forwarding; ask for all data to be
diff --git a/src/stream_engine.cpp b/src/stream_engine.cpp
index e70d1d3..45a6af6 100644
--- a/src/stream_engine.cpp
+++ b/src/stream_engine.cpp
@@ -53,8 +53,21 @@ xs::stream_engine_t::stream_engine_t (fd_t fd_, const options_t &options_) :
     session (NULL),
     leftover_session (NULL),
     options (options_),
-    plugged (false)
+    plugged (false),
+    header_pos (in_header),
+    header_remaining (sizeof in_header),
+    header_received (false),
+    header_sent (false)
 {
+    //  Fill in outgoing SP protocol header and the complementary (desired)
+    //  header.
+    if (!options.legacy_protocol) {
+        sp_get_header (out_header, options.sp_service, options.sp_pattern,
+            options.sp_version, options.sp_role);
+        sp_get_header (desired_header, options.sp_service, options.sp_pattern,
+            options.sp_version, options.sp_complement);
+    }
+
     //  Get the socket into non-blocking mode.
     unblock_socket (s);
 
@@ -155,6 +168,35 @@ void xs::stream_engine_t::in_event (fd_t fd_)
 {
     bool disconnection = false;
 
+    //  If we have not yet received the full protocol header...
+    if (unlikely (!options.legacy_protocol && !header_received)) {
+
+        //  Read remaining header bytes.
+        int hbytes = read (header_pos, header_remaining);
+
+        //  Check whether the peer has closed the connection.
+        if (hbytes == -1) {
+            error ();
+            return;
+        }
+
+        header_remaining -= hbytes;
+        header_pos += hbytes;
+
+        //  If we did not read the whole header, poll for more.
+        if (header_remaining)
+            return;
+
+        //  If the protocol headers do not match, close the connection.
+        if (memcmp (in_header, desired_header, sizeof in_header) != 0) {
+            error ();
+            return;
+        }
+
+        //  Done with protocol header; proceed to read data.
+        header_received = true;
+    }
+
     //  If there's no data to process in the buffer...
     if (!insize) {
 
@@ -210,6 +252,20 @@ void xs::stream_engine_t::out_event (fd_t fd_)
 {
     bool more_data = true;
 
+    //  If protocol header was not yet sent...
+    if (unlikely (!options.legacy_protocol && !header_sent)) {
+        int hbytes = write (out_header, sizeof out_header);
+
+        //  It should always be possible to write the full protocol header to a
+        //  freshly connected TCP socket. Therefore, if we get an error or
+        //  partial write here the peer has disconnected.
+        if (hbytes != sizeof out_header) {
+            error ();
+            return;
+        }
+        header_sent = true;
+    }
+
     //  If write buffer is empty, try to read new data from the encoder.
     if (!outsize) {
 
diff --git a/src/stream_engine.hpp b/src/stream_engine.hpp
index 46a6080..70c9ddb 100644
--- a/src/stream_engine.hpp
+++ b/src/stream_engine.hpp
@@ -30,6 +30,7 @@
 #include "encoder.hpp"
 #include "decoder.hpp"
 #include "options.hpp"
+#include "wire.hpp"
 
 namespace xs
 {
@@ -98,6 +99,22 @@ namespace xs
 
         bool plugged;
 
+        //  Outgoing protocol header.
+        sp_header_t out_header;
+
+        //  Desired protocol header.
+        sp_header_t desired_header;
+
+        //  Incoming protocol header.
+        sp_header_t in_header;
+
+        unsigned char *header_pos;
+        size_t header_remaining;
+
+        //  Protocol header has been received/sent.
+        bool header_received;
+        bool header_sent;
+
         stream_engine_t (const stream_engine_t&);
         const stream_engine_t &operator = (const stream_engine_t&);
     };
diff --git a/src/sub.cpp b/src/sub.cpp
index d29ae8d..79cb63c 100644
--- a/src/sub.cpp
+++ b/src/sub.cpp
@@ -48,8 +48,7 @@ int xs::sub_t::xsetsockopt (int option_, const void *optval_,
     size_t optvallen_)
 {
     if (option_ != XS_SUBSCRIBE && option_ != XS_UNSUBSCRIBE) {
-        errno = EINVAL;
-        return -1;
+        return xsub_t::xsetsockopt (option_, optval_, optvallen_);
     }
 
     if (optvallen_ > 0 && !optval_) {
@@ -202,7 +201,7 @@ int xs::sub_t::filter_subscribed (const unsigned char *data_, size_t size_)
     int rc = msg.init_size (size_ + 4);
     errno_assert (rc == 0);
     unsigned char *data = (unsigned char*) msg.data ();
-    put_uint16 (data, XS_CMD_SUBSCRIBE);
+    put_uint16 (data, SP_PUBSUB_CMD_SUBSCRIBE);
     put_uint16 (data + 2, options.filter);
     memcpy (data + 4, data_, size_);
 
@@ -225,7 +224,7 @@ int xs::sub_t::filter_unsubscribed (const unsigned char *data_, size_t size_)
     int rc = msg.init_size (size_ + 4);
     errno_assert (rc == 0);
     unsigned char *data = (unsigned char*) msg.data ();
-    put_uint16 (data, XS_CMD_UNSUBSCRIBE);
+    put_uint16 (data, SP_PUBSUB_CMD_UNSUBSCRIBE);
     put_uint16 (data + 2, options.filter);
     memcpy (data + 4, data_, size_);
 
diff --git a/src/wire.hpp b/src/wire.hpp
index f840fce..014021b 100644
--- a/src/wire.hpp
+++ b/src/wire.hpp
@@ -24,11 +24,52 @@
 #include "stdint.hpp"
 
 //  Protocol-related constants.
-#define XS_CMD_SUBSCRIBE 1
-#define XS_CMD_UNSUBSCRIBE 2
+
+//  Protocol header.
+#define SP_HEADER_LENGTH 8
+
+//  Patterns.
+#define SP_PAIR 1
+#define SP_PUBSUB 2
+#define SP_REQREP 3
+#define SP_PIPELINE 4
+#define SP_SURVEY 5
+
+//  Roles.
+#define SP_PAIR_PAIR 1
+#define SP_PUBSUB_PUB 1
+#define SP_PUBSUB_SUB 2
+#define SP_REQREP_REQ 1