[rabbitmq-discuss] Python AMQPLib causes exception when trying to declare queue with X-Expires

[Stephen Day]

Small correction:

x-expires granularity is in milliseconds, so changing to a 4 byte
integer will limit the expiry range to 24 days, which doesn't provide
as much headroom.

On Sun, Aug 29, 2010 at 1:50 AM, Stephen Day <stevvooe at gmail.com> wrote:
> Here is the traceback showing the exception as thrown by amqplib, with
> the channel exception code:
>
>>>> ch.queue_declare('bdirect', arguments={"x-expires": 600})
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "/usr/lib/pymodules/python2.6/amqplib/client_0_8/channel.py",
> line 1294, in queue_declare
>    (50, 11),    # Channel.queue_declare_ok
>  File "/usr/lib/pymodules/python2.6/amqplib/client_0_8/abstract_channel.py",
> line 105, in wait
>    return amqp_method(self, args)
>  File "/usr/lib/pymodules/python2.6/amqplib/client_0_8/channel.py",
> line 273, in _close
>    (class_id, method_id))
> amqplib.client_0_8.exceptions.AMQPChannelException: (406,
> u"PRECONDITION_FAILED - invalid arg 'x-expires' for queue 'bdirect' in
> vhost '/': expires_not_of_type_long", (50, 10),
> 'Channel.queue_declare')
>
> In the library code, it looks like it properly packs the integer, but
> 0-8 doesn't support the desired integer type:
>
> amqplib/client_0_8/serialization.py
>
> 372             elif isinstance(v, (int, long)):
> 373                 table_data.write('I')
> 374                 table_data.write(pack('>i', v))
>
> The problem might actually lie in the server side parser code:
>
> src/rabbit_binary_parser.erl
>
> 99 parse_field_value(<<"l", Value:64/signed, Rest/binary>>) ->
> 100     {long, Value, Rest};
>
> The 0-8 specification doesn't define a long type outside of the "I"
> type, so this excludes this feature (which is a *great* feature) from
> older clients.
>
> You should probably just have x-expires look for a regular 0-8
> supported, 4-byte "I"-type integer. It will limit queue time expiry
> maximum to 68 years, but one has to make design tradeoffs every once
> and awhile ;).
>
> Good work on the 2.0 release. Its looking fantastic thus far.
>
> Stephen
>