Problem: artificial restriction on binary identities

Applications that use ZMQ_IDENTITY can be trapped by the artificial
restriction on not using a binary zero as first byte. It's specially
nasty on random generated identities, e.g. UUIDs, as the chance of a
binary zero is low, so it will pass 255 out of 256 times.

Solution: remove the restriction.

doc/zmq_setsockopt.txt

@@ -190,7 +190,7 @@ ZMQ_IDENTITY: Set socket identity
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_IDENTITY' option shall set the identity of the specified 'socket'
 when connecting to a ROUTER socket. The identity should be from 1 to 255
-bytes long and MAY NOT start with binary zero.
+bytes long and may contain any values.
 
 If two clients use the same identity when connecting to a ROUTER, the
 results shall depend on the ZMQ_ROUTER_HANDOVER option setting. If that

src/options.cpp

@@ -89,11 +89,8 @@ int zmq::options_t::setsockopt (int option_, const void *optval_,
             break;
 
         case ZMQ_IDENTITY:
-            //  Empty identity is invalid as well as identity longer than
-            //  255 bytes. Identity starting with binary zero is invalid
-            //  as these are used for auto-generated identities.
-            if (optvallen_ > 0 && optvallen_ < 256
-            && *((const unsigned char *) optval_) != 0) {
+            //  Identity is any binary string from 1 to 255 octets
+            if (optvallen_ > 0 && optvallen_ < 256) {
                 identity_size = optvallen_;
                 memcpy (identity, optval_, identity_size);
                 return 0;