[Rprotobuf-yada] rpc over http

[Romain François]

I've now reworked the java code a bit so that it can support any 
service/method. To support a service, one must subclass the 
ProtobufMethodInvoker abstract class and define these two methods:

	public abstract Message invoke( Message input ) ;
	
	public abstract Builder getInputMessageBuilder() ;

and register it by calling the register method of the ProtobufMethodPool 
class.

I'll have a look at other rpc implementations to see the kind of 
examples they use.

Romain


On 12/09/2009 11:57 AM, Romain François wrote:
>
> Hello,
>
> I'm moving on with protobuf over http.
>
> ===== java server =====
>
> I have commited a __very__ basic java server (I think it needs java 6)
> to the java directory of the project which receives protobuf http
> requests, invokes the method, and return the result as an http response.
> (At the moment, only the tutorial.EchoService.Echo rpc method is
> implemented, which basically receives a tutorial.Person message and send
> it back as is).
>
> To compile the server, just go to the java directpry and type "ant", you
> should see something like this:
>
> [romain at santorini java]$ ant
> Buildfile: build.xml
>
> clean:
>      [delete] Deleting directory /home/romain/svn/rprotobuf/java/build
>      [delete] Deleting directory /home/romain/svn/rprotobuf/java/javadoc
>      [delete] Deleting directory /home/romain/svn/rprotobuf/java/jar
>
> init:
>       [mkdir] Created dir: /home/romain/svn/rprotobuf/java/build
>       [mkdir] Created dir: /home/romain/svn/rprotobuf/java/javadoc
>       [mkdir] Created dir: /home/romain/svn/rprotobuf/java/jar
>
> build:
>       [javac] Compiling 4 source files to
> /home/romain/svn/rprotobuf/java/build
>         [jar] Building jar:
> /home/romain/svn/rprotobuf/java/jar/RProtoBuf-java-http.jar
>
> all:
>
> BUILD SUCCESSFUL
> Total time: 1 second
>
> To run the server :
>
> $ java -cp jar/RProtoBuf-java-http.jar
> org.rproject.rprotobuf.ProtobufHttpServer
>
>
> ===== R client =====
>
> now it gets interesting with the R client. I have also commited some
> code to invoke a rpc method over http.
>
> To call a rpc method over http, you need 3 things:
> - a method descriptor.
> - an input message which must be of the message type that the method expects
> - a "RpcHTTP" object which represents the protocol used (contains host
> name and port number)
>
> It goes like this :
>
> require( RProtoBuf )
> p<- new( tutorial.Person, name = "foo", id = 2, email = "bla at bla.com" )
> http<- new( "RpcHTTP", host = "127.0.0.1", port = 4444L)
> result<- invoke( tutorial.EchoService.Echo, p, http )
> writeLines( result$toString() )
>
> On the client side (the R console), you should see this (the debugging
> information will eventually go) :
>
>   >  source("send.R" )
> sending http request
> headers : sent 83 bytes
> input message : sent 20 bytes
> reading 59 bytes
> complete line: {HTTP/1.1 200 OK}
> complete line: {Content-length: 20}
> header 'content-length' =>  '20'
> end of request - moving to body
> name: "foo"
> id: 2
> email: "bla at bla.com"
>
> and this on the server side :
>
> ProtobufHandler>>  handle
> http method : POST
> Content-length=[20]
> Connection=[close]
> rpc method : {tutorial.EchoService.Echo}
>    read 20 bytes
> finished reading body
> sending result : 20 bytes
>
>
>
> ===== the protocol =====
>
> This is just (ab)using the http protocol.
>
> The client sends a request that looks like this :
>
> -----------------------------------------------------
> POST /{service full name}/{method name} HTTP/1.0
> Connection: close
> Content-Length: {length of the serialized message}
>
> {raw bytes of the serialized message}
> -----------------------------------------------------
>
> The server replies with something that looks like this :
>
> -----------------------------------------------------
> HTTP/1.1 200 OK
> Content-length: {length of the serialized response}
>
> {raw bytes of the serialized response}
> -----------------------------------------------------
>
> or like this if the method is unknown :
>
> -----------------------------------------------------
> HTTP/1.1 501
> -----------------------------------------------------
>
>
>
>
> ===== what's next =====
>
> I need to make the java server a bit nicer and maybe release it
> separately. I chose http as a first attempt because it will be "easy" to
> implement with other languages, and because that is what kenton
> recommended.
>
> When R is ready to serve, I'll make a server so that two instances of R
> can exchange protobuf messages
>
> I really need to think about another protocol. http "works" but I think
> it is too verbose. In the example, it needs to send 103 bytes (83+20) to
> send a message that takes only 20 bytes. The response also takes too
> much space. No big deal but we can do better than that.
>
> I need some nicer examples of methods. Echo is a bit too dummy.
>
> The code for the R client is all in rpc_over_http.cpp. This is very
> inspired from the Rhttp.c from the R sources, it probably should get c++'ed.
>
> I need to document it.
>
>
> Romain
>
>


-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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