[jira] [Created] (PROTON-713) TransportImpl#setChannelMax does not enforce legal value range, may cause unexpected results

["Robbie Gemmell (JIRA)" <ji...@apache.org>]

Robbie Gemmell created PROTON-713:
-------------------------------------

             Summary: TransportImpl#setChannelMax does not enforce legal value range, may cause unexpected results
                 Key: PROTON-713
                 URL: https://issues.apache.org/jira/browse/PROTON-713
             Project: Qpid Proton
          Issue Type: Bug
          Components: proton-j
    Affects Versions: 0.8
            Reporter: Robbie Gemmell
            Priority: Minor


Whilst helping debug an issue yesterday with Tim (which turned out to be with the old Qpid 0.2X/0.3X AMQP 1.0 JMS client), we noticed some unexpected results from using Transport#setChannelMax method.

The chanel-max field of the Open frame is a ushort. The API expsoses this via the signed Java int to allow easily onfiguring the values outwith the signed short range. When using the value in TransportImp, it is cast to a short, which truncates the bit length of the value and may turn it negative (which is expected by the UnsignedShort wrapper). If a value over 2^16-1 is used, you thus do not get quite what you expect, and if you happen to use 2^16 then you will actually see 0.

{noformat}
            if (_channelMax > 0) {
                open.setChannelMax(UnsignedShort.valueOf((short) _channelMax));
            }
{noformat}

The legal range should be enforced so that the outgoing Open frame actually contains what the user asked for, and the legal values are clear.



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