use strings for empty message part check.

lib/sockets/rep.js

@@ -43,7 +43,7 @@ RepSocket.prototype.onmessage = function(sock){
     var envelopes = [];
 
     for (var i = 0; i < msg.length; ++i) {
-      if (0x00 === msg[i][0]) {
+      if ('\u0000' === String(msg[i])) {
         envelopes = msg.splice(0, ++i);
       }
     }

lib/sockets/req.js

@@ -44,7 +44,7 @@ ReqSocket.prototype.onmessage = function(){
   var self = this;
   return function(msg, multipart){
     if (!multipart) return debug('expected multipart');
-    if (0x00 !== msg[0][0]) return debug('malformed message');
+    if ('\u0000' != String(msg[0])) return debug('malformed message');
     self.emit.apply(self, ['message'].concat(msg.slice(1)));
   };
 };

test/test.reqrep.json.js

@@ -0,0 +1,31 @@
+
+var ss = require('../')
+  , should = require('should');
+
+var server = ss.socket('rep')
+  , client = ss.socket('req');
+
+server.format('json');
+client.format('json');
+
+server.bind(3000);
+client.connect(3000);
+
+server.on('message', function(msg, reply){
+  msg.should.have.property('cmd', 'hello');
+  reply({
+    error: null,
+    result: 'thanks'
+  });
+});
+
+client.on('message', function(msg){
+  msg.should.have.property('error', null);
+  msg.should.have.property('result', 'thanks');
+  client.close();
+  server.close();
+});
+
+client.send({
+  cmd: 'hello'
+});