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Remote Procedure Call and Remote Method Invocation

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1 Remote Procedure Call and Remote Method Invocation
INF 123 – Software architecture

2 Outline RPC theory Sun RPC XML RPC RMI

3 RPC: theory

4 The Problem 1980s: Internet and web servers
How can a client make a server do something? Sockets are used to transmit data, not functions Sending function code as text is a bad idea Client in Python, server in C#? Server runs eval(evil_code)? Eval is evil …

5 Dr. Eval eval(readline()), eval(message), …

6 Reminder: main and subroutines
Main calls subroutines Subroutines return values Subroutines have no side-effects AKA “call and return” “Not a real architecture” <- really? Why?

7 RPC Transparently call a procedure located in another process or machine “make the invocation of a procedure on a remote machine appear as though it were local”

8 Solution: RPC Local Procedure Calls Remote Procedure Calls host host 1
program program caller caller r = foo(a, b) r = foo(a, b) Caller stub host 2 callee program define foo(a, b) end Callee stub define foo(a, b) end callee

9 RPC with words The local procedure calls a caller stub
The caller stub serializes the call (function name + arguments) and sends it to the callee stub on a remote machine The callee stub calls the remote procedure The remote procedure does its job, and gives the return value to the callee stub The callee stub sends the value back to the caller stub The caller stub passes that value back to the local procedure

10 Stubs Caller = client (initiate, active end)
Callee = server (listen, passive end) The stubs are coupled Client stub must know server stub’s IP and port Sometimes, a port is reserved for RPC Stubs are usually generated by tools Rpcgen for Sun RPC, wscompile for JAX-RPC, … Other naming: server stub = skeleton

11 (in Interface Def Language)
RPC Usual code RPC code RPC belongs to the application layer Caller program (in client language) Procedure Interface Definition (in Interface Def Language) Callee Program (in server language) call generate call Client Stub (in client language) Server Stub (in server language) Serialize and send Deserialize and receive Network OS Network OS

12 RPC Request-reply protocol, and RPC serialization format
RPC as middleware Middleware: software between OS and application Application RPC stubs Middleware layers RPC Request-reply protocol, and RPC serialization format OS

13 RPC is not P2P In both cases, nodes are clients and servers to each other But in RPC, the goal is to execute a function remotely A client and a server could use RPC Peers could use RPC with each other Peers could simply exchange data, and not use RPC RPC stubs use a client-server paradigm With a request-response messaging pattern

14 Sun RPC: DATE/Time server example IN C
From Unix Network Programming, by Stevens et al. Sun RPC: DATE/Time server example IN C

15 Sun RPC AKA Open Network Computing Created in the mid 80s by Sun
The developer writes: interface.x, the interface definition, in Interface Definition Language callee.c, the server with the remote procedure caller.c, the client calling the remote procedure The rpcgen compiler generates: interface.h, to be imported by caller.c and callee.c callee_stub.c caller_stub.c

16 XDR eXternal Data Representation Created in the mid 80s by Sun
Binary encoding The data format exchanged between stubs Serialization format used by: Network File System (created by Sun) SpiderMonkey (Firefox JS engine, XDR used to exchange compiled JS) R (stats tool)

17 Sun RPC generated Hand-written Import function signature
caller.c interface.h callee.c Generate Call interface.x Call caller_stub.c callee_stub.c Generate Send XDR Recv XDR network

18 caller.c (I adapted it) server = ‘ ’; client = create_client(server, DATE_PROG, DATE_VERS, "udp"); bin_date = get_binary_date(NULL, client); str_date = bin2str_date(bin_date, client); printf("time on server %s: %s", server, *str_date);

19 caller_stub.c (generated and adapted)
#include "date.h" static struct timeval TIMEOUT = { 25, 0 }; long * get_binary_date(void *argp, CLIENT *clnt) { static long clnt_res; // return value is a long memset((char *)&clnt_res, 0, sizeof (clnt_res)); // allocate memory cli_call = client_call(clnt, GET_BIN_DATE, // RPC function number (xdrproc_t) xdr_void, // argument type (caddr_t) argp, // argument value (xdrproc_t) xdr_long, // return value type (caddr_t) &clnt_res, // store in this memory area TIMEOUT); if (cli_call != RPC_SUCCESS) { return (NULL); } return (&clnt_res);

20 Sun RPC API client_call create_client And more …


22 XML RPC Over HTTP POST 1998, many language bindings

23 XML RPC - request POST /RPC2 HTTP/1.1
User-Agent: Frontier/5.1.2 (WinNT) Host: Content-Type: text/xml Content-length: 181 <?xml version="1.0"?> <methodCall> <methodName>examples.getStateName</methodName> <params> <param> <value><int>41</int></value> </param> </params> </methodCall>

24 XML RPC – success response
HTTP/ OK Connection: close Content-Length: 158 Content-Type: text/xml Date: Fri, 17 Jul :55:08 GMT Server: UserLand Frontier/5.1.2-WinNT <?xml version="1.0"?> <methodResponse> <params> <param> <value><string>South Dakota</string></value> </param> </params> </methodResponse>

25 XML RPC – failure response
HTTP/ OK Connection: close Content-Length: 426 Content-Type: text/xml Date: Fri, 17 Jul :55:02 GMT Server: UserLand Frontier/5.1.2-WinNT <?xml version="1.0"?> <methodResponse> <fault> <value> <struct> <member> <name>faultCode</name> <value><int>4</int></value> </member> <name>faultString</name> <value><string>Too many parameters. </string> </value> </struct> </value> </fault> </methodResponse>

26 XML RPC vs XML: bandwidth 
<struct> <member> <name>ROOM_ID</name> <value> <int>1</int> </value> </member> <name>CODE</name> <value> <string>MR-101</string> </value> <name>NAME</name> <value> <string>Math Room</string> </value> <name>CAPACITY</name> <value> <int>30</int> </value> </struct> <room> <ROOM_ID>1</ROOM_ID> <CODE>MR-101</CODE> <NAME>Math Room</NAME> <CAPACITY>30</CAPACITY> </room> class Room { int id=1; String code="MR-101"; String name="Maths room"; int capacity=30; };

27 Remote method invocation

28 Proxy objects Equivalent of stub, but for client objects
Goal: make RMI transparent to clients Proxy objects behave like a local object to the invoker Instead of executing, proxy objects serialize arguments and forward the call + arguments to the remote object Human writes class interface with method names RMI compiler generates proxy classes, skeleton classes, and server dispatcher

29 Remote Method Invocation
Client Process Proxy Object B Object A Proxy object is a hollow container of Method names. Remote Reference Module translates between local and remote object references. Remote Reference Module Comm. Module Server Process Comm. Module Remote Reference Module Dispatcher sends the request to Skeleton Object Skeleton deserializes parameters, sends it to the object, & marshals the results for return Dispatcher Object B Skeleton for B’s Class MIDDLEWARE

30 More Implementing Remote Procedure Calls, Birrell et al. 1984

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