*With all systems entitled under channel*:

[388553]$ ./reproducer.py
{'selectable': 1, 'id': 1000010003, 'name': 'system-1'}
{'selectable': 1, 'id': 1000010025, 'name': 'system-2'}
{'selectable': 1, 'id': 1000010125, 'name': 'system-3'}
{'selectable': 1, 'id': 1000010105, 'name': 'system-4'}

*After un-entitling system-3*:

[388553]$ ./reproducer.py
Traceback (most recent call last):
 File "./reproducer.py", line 22, in ?
   subsystems = getSubSystems()
 File "./reproducer.py", line 19, in getSubSystems
   subsystems = server.channel.software.list_subscribed_systems(session,channel_label)
 File "/usr/lib/python2.3/xmlrpclib.py", line 1029, in __call__
   return self.__send(self.__name, args)
 File "/usr/lib/python2.3/xmlrpclib.py", line 1316, in __request
   verbose=self.__verbose
 File "/usr/lib/python2.3/xmlrpclib.py", line 1080, in request
   return self._parse_response(h.getfile(), sock)
 File "/usr/lib/python2.3/xmlrpclib.py", line 1219, in _parse_response
   return u.close()
 File "/usr/lib/python2.3/xmlrpclib.py", line 740, in close
   raise ResponseError()
xmlrpclib.ResponseError: <xmlrpclib.ResponseError instance at 0xb7d08e4c>

The query used by the API call is in System_queries - systems_subscribed_to_channel :

SELECT
      S.id as id,
      S.name as name,
         (SELECT 1
         FROM rhnServerFeaturesView SFV
        WHERE SFV.server_id = S.id
          AND SFV.label = 'ftr_system_grouping') AS selectable
 FROM rhnServerChannel SC,
      rhnServer S
WHERE S.org_id = 1
  AND S.id = SC.server_id
  AND SC.channel_id = 101
  AND EXISTS (SELECT 1 FROM rhnUserServerPerms USP WHERE USP.user_id = 1 AND USP.server_id = S.id)
ORDER BY UPPER(NVL(S.NAME, '(none)')), S.ID;

which returns:

       ID
----------
NAME
--------------------------------------------------------------------------------
SELECTABLE
----------
1000010003
system-1
        1

1000010025
system-2
        1

1000010125
system-3


1000010105
system-4
        1

So it appears with un-entitled systems 'selectable' returns as null in the underlying dataquery used by the API call, and that's causing the NullPointerException when writing response.  

Proposed fix: change the dataquery so it returns 0 in case of NULL?


Relevant code -

spacewalk-java-0.5.44/code/src/com/redhat/rhn/frontend/xmlrpc/channel/software/ChannelSoftwareHandler.java
...
   /**
    * Returns list of subscribed systems for the given channel label.
    * @param sessionKey WebSession containing User information.
    * @param label Label of the channel in question.
    * @return Returns an array of maps representing a system. Contains system id and
    * system name for each system subscribed to this channel.
    * @throws FaultException A FaultException is thrown if:
    *   - Logged in user is not a channel admin.
    *   - Channel does not exist.
    *
    * @xmlrpc.doc Returns list of subscribed systems for the given channel label
    * @xmlrpc.param #session_key()
    * @xmlrpc.param #param_desc("string", "channelLabel", "channel to query")
    * @xmlrpc.returntype
    *          #array()
    *              #struct("system")
    *                  #prop("int", "id")
    *                  #prop("string", "name")
    *              #struct_end()
    *           #array_end()
    */
   public Object[] listSubscribedSystems(String sessionKey, String label)
       throws FaultException {

       User user = getLoggedInUser(sessionKey);

       // Make sure user has access to the orgs channels
       if (!user.hasRole(RoleFactory.CHANNEL_ADMIN)) {
           throw new PermissionCheckFailureException();
       }

       // Get the channel.
       Channel channel = lookupChannelByLabel(user.getOrg(), label);

       DataResult dr = SystemManager.systemsSubscribedToChannel(channel, user);
       return dr.toArray();
   }
...

spacewalk-java-0.5.44/code/src/com/redhat/rhn/manager/system/SystemManager.java
...
   /**
    * Returns a DataResult containing the systems subscribed to a particular channel.
    * @param channel The channel in question
    * @param user The user making the call
    * @return Returns a DataResult of maps containing the ids and names of systems
    * subscribed to a channel.
    */
   public static DataResult systemsSubscribedToChannel(Channel channel, User user) {
       Map params = new HashMap();
       params.put("user_id", user.getId());
       params.put("cid", channel.getId());
       params.put("org_id", user.getOrg().getId());

       SelectMode m = ModeFactory.getMode("System_queries",
                          "systems_subscribed_to_channel", Map.class);
       return m.execute(params);
   }
...

...
<mode name="systems_subscribed_to_channel">
 <query params="org_id, cid, user_id">
SELECT
      S.id as id,
      S.name as name,
         (SELECT 1
         FROM rhnServerFeaturesView SFV
        WHERE SFV.server_id = S.id
          AND SFV.label = 'ftr_system_grouping') AS selectable
 FROM rhnServerChannel SC,
      rhnServer S
WHERE S.org_id = :org_id
  AND S.id = SC.server_id
  AND SC.channel_id = :cid
  AND EXISTS (SELECT 1 FROM rhnUserServerPerms USP WHERE USP.user_id = :user_id AND USP.server_id = S.id)
ORDER BY UPPER(NVL(S.NAME, '(none)')), S.ID
 </query>
 <elaborator name="system_overview" />
 <elaborator name="entitlements"/>
</mode>
...
<query name="entitlements" params="" multiple="t">
 SELECT SEV.server_id AS ID,
        SEV.label AS ENTITLEMENT,
        SEV.server_group_type_id,
        SEV.permanent AS entitlement_permanent,
        SEV.is_base AS entitlement_is_base
   FROM rhnServerEntitlementView SEV
  WHERE SEV.server_id IN (%s)
ORDER BY DECODE(SEV.is_base,'Y',1,'N',2), SEV.label
</query>
...

3088b972b25a41ad567f9b84b53cf3acac631ff8

Fixed in master.  Ended up just removing that item from the map.  Not the cleanest solution, but it works ok.

satellite.git: 10137f86712537156300d0fb9ab6782b9c2e5de5

# VERIFIED

The following brewroot build(s) fixing the issue:
RHEL-4-RHNSAT5.3: http://brewweb.devel.redhat.com/brew/buildinfo?buildID=125979
RHEL-5-RHNSAT5.3: http://brewweb.devel.redhat.com/brew/buildinfo?buildID=125978

call of the channel.software.list_subscribed_systems for a channel that contains unentitled systems goes fine without any exceptions now.

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2010-0128.html