Implement protocol versioning (except PGM)

Implements SP protocol versioning, legacy protocol support, and the
following pattern protocol versions:

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

Engine support is only for stream_engine_t at this stage.

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

1 files changed, 57 insertions, 1 deletions

diff --git a/src/stream_engine.cpp b/src/stream_engine.cpp
index 15b566b..a39b410 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_pattern, options.sp_version,
+            options.sp_role);
+        sp_get_header (desired_header, 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) {