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+1 to (eventually) allowing header/envelope modification and treating
message content as immutable. I understand for Folsom compatibility, you
will currently need to modify the message contents.

Best,
-jay

On 02/13/2013 03:42 PM, Eric Windisch wrote:
> At present, at least for some message types, the AMQP drivers are
> modifying message contents by adding key/values to the dict passed by
> the developer. With the RPC envelope, it will become possible to begin
> treating these dict as immutable types. For instance, the ZeroMQ driver
> which already wraps the message dict in its own envelope, treats the
> original message as immutable.
> 
> At present, I've been talking with Ray Pekowski about passing additional
> metadata along with messages. For instance, adding a unique nonce or
> identifier for purposes of replay detection. We have been debating if
> this should belong in the envelope, treating the original message dict
> as immutable, or if we should feel comfortable modifying the message
> contents in the long-term.  I believe we both agree that we need to
> modify the message contents in the short-term for Folsom compatibility.
> 
> Ray and I discussed SMTP headers and how they are modified by the
> implementations. However, when messages are multi-part, the non-header
> parts are left unmodified. I feel that with envelopes providing an
> analogue to multi-part messaging, we can look to begin a process of
> treating messages as immutable.
> 
> The other argument is that as long as the message is structured, we just
> treat some fields of the user-supplied message as immutable. However,
> I'm not certain that we can expect that messages are structured in the
> case of, say, notifications. I believe that other than the RPC envelope
> itself, these are often passed simply as strings, yes? We certainly
> can't add new key/vals to that.
> 
> I also feel that we lose some of the value of envelope versioning if we
> simply manipulate the content of the data being passed (besides wrapping
> around it).
> 
> I'd appreciate feedback from the other developers involved with RPC
> messaging as well as those generating and consuming notifications.
> 
> Regards,
> Eric Windisch
> 
> 
> 
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