Sanitize but log stack traces from errors sent to client

lib/agent.js

@@ -188,9 +188,24 @@ Agent.prototype._sendOps = function(collection, id, ops) {
 
 Agent.prototype._reply = function(request, err, message) {
   if (err) {
-    request.error = (typeof err === 'string') ?
-      {message: err} :
-      {code: err.code, message: err.message, stack: err.stack};
+    if (typeof err === 'string') {
+      request.error = {message: err};
+    } else {
+      if (err.stack) {
+        // Log stack trace on the server
+        var message = 'Error: ' + err.message;
+        if (err.code) message = message + ' (' + err.code + ')';
+        console.warn(message);
+        console.warn(err.stack);
+        console.warn();
+
+        // Then hide stack trace from client
+        request.error = JSON.parse(JSON.stringify(err));
+        delete request.error.stack;
+      } else {
+        request.error = err;
+      }
+    }
     this.send(request);
     return;
   }