Have you looked at the topic_tools/relay node?  It should do exactly
what you're talking about already, and you can also use it as an
example of how to implement nodes that handle arbitrary message types.
--Eric

On Fri, Mar 26, 2010 at 8:08 PM, Ken Tossell <ktossell@umd.edu> wrote:
> Hey ROS,
>
> I'm working on a node to send messages between other nodes (the proxy
> subscribes to a topic, the publisher sends one copy of a message to it,
> then it forwards the message to several nodes). I need to find the MD5 sum
> of all of the topics so that the proxy can advertise its version of /topic
> as /proxy/topic using the correct signature.
>
> I had planned to get the MD5 sum using master::getTopics(), but where
> TopicInfo is supposed to have [name, type, md5], getTopics()'s output is
> [name, type, type]. (The underlying RPC doesn't convey the MD5 sum,
> either.)
>
> Is there any way to determine the MD5 sum of a topic without first
> subscribing to it?
>
> Thanks,
> Ken
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