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Do We Need Another OO RPC Mechanism?
Paul68 queries: "I am looking for an RPC mechanism for a project. Granted, there are many to choose from, yet there seem none that meet my requirements! When one has toyed with the requirements the solution generaly becomes obvious. So, yeah sure, I can set out and create the next RPC mechanism, but it is a lot of hassle. But does the world need yet another OORPC, or have I simply not looked in the right corners?"
Does anyone have any options that I may have missed?"
"My requirements are:
- object oriented
- extensible
- platform independent
- supports signatures for integrity and sender checking
- supports privacy of the message contents (i.e. encryption)
- time sensitive: I should be able to detect a dead server and do failover while the user is waiting for the response
- bandwidth efficient, as I am looking to deploy it in wireless environments
Does anyone have any options that I may have missed?"
...that bugs me is that there's no way to make a call that will return multiple pieces of data over a long period. Like, I want to connect to a server and say "tell me every time the price of IBM stock changes". I can use SOAP for most of a trader type UI but for streaming the data back to the client, you have to use another protocol (unless I'm missing something).
The dude asking the quesiton here is, I think, a little too worried about overhead - the overhead of XML is fairly tiny, and the overhead of TCP/IP isn't that great either - if both of those really are too much then you're probably on your own as there isn't likely to be a "general purpose" solution that will work for you.
- Steve
It's easily capable of representing objects, platform independent, encryptable (via SSL), compressable (via gzip [and probably SSL as well]), and textual.
The advantages of being textual in your protocols is well laid out in Eric Raymond's book The Art of Unix Programming. He even treats it as a case study.
You might want to take a look at the Neutral Message Language, NML. Developed at the Intelligent Systems Division of the National Instute of Standards and Technology is was intended from the start for use in real-time/time critical situations. I know that it currently has support cor C, C++ and Java.
RPC causes untold security/authentication headaches and is often hard to program with besides.
See ESR
char a[]="lbiitgt l e \n\n\0";main(){for(char*c=a; *(short*)c;c+=2){putchar(*(short*)c);}}
When I experimented with SOAP, it was around 60% metadata, and the bytes sent by the protocol were 600% more than the equivialent done with SunRPC.
(That was for one particular application, others will vary.)
You could probably implement what you want using
some type of message queuing server, like IBM Websphere MQ, or equivelant.
As a mental exercise, and to make sure I'm not talking out my ass, let's run down your list of requirements:
equirements are:
1. object oriented
Well, in the case of Websphere MQ, I'd say "yes" to this one, at least partially. There is a C++ based client library, IIRC, a (IBM specific) Java client library, and a JMS client. And even if the client libraries weren't OO, you could write OO wrappers for procedural calls more easily than writing your own RPC mechanism from scratch, I think.
2. extensible
Check. If you use pub/sub messaging instead of point to point messaging, even more so. And if you use a message type (MapMessage in JMS) that is based on name / value pairs, it's easy to extend your messages without breaking backwards compatibility.
3. platform independent
Not completely, but with both Java and C++ clients available, you should be able to support most everything.
4. supports signatures for integrity and sender checking
Not sure if it has native support for signatures, but a signature can always be added to a message as a property.
5. supports privacy of the message contents (i.e. encryption)
Again, using Websphere MQ as an example, it does support the use of SSL for communications, if that helps meet your requirements.
6. time sensitive: I should be able to detect a dead server and do failover while the user is waiting for the response
You're right, that's the tricky one. I think there are ways to achieve this goal using message passing servers, but it might take some work.
7. bandwidth efficient, as I am looking to deploy it in wireless environments
I think this requirement is met as well. Most messaging products support a message type that is nothing more than a stream of bytes that you interpret as you will... and even if you use a slightly move involved message type (MapMessage or StreamMessage to use JMS types as examples) you're still not carrying a lot of overhead.
Now #1-3 are no problem, #4 and #5 can be found, and #7 rules out anything XML-based. #6 seems to be the killer, as this rules out anything over TCP, and at that point the list gets pretty short.
Depending on just how "time sensitive" #6 really is, I do think you could come up with a solution using a message passing server. If you're able to use Java for the clients, JMS makes doing an RPC style messaging very easy, using the QueueRequestor and TopicRequestor interfaces. And even if you can't use Java, it shouldn't be to hard to cook up your own request / reply mechanism, built on top of the messaging system.
// TODO: Insert Cool Sig