1. Adv. Network Programming RPC (Remote Procedure Call)
Kubilay Akgül

2. RPC (Remote Procedure Call)
Two Paradigms for Distributed Programs.
Smilarities and Differences Conventional Procedure Calls and RPC
SUN RPC
Remote Program Identification
RPC Mapping, Inet.d
Call Semantics
RPCGEN
ADVANCED NETWORK PROGRAMING -- RPC

3. ADVANCED NETWORK PROGRAMING -- RPC
Two Paradigms
A programmer can use one of two approaches:
Communication Oriented Design
- Focus on communication program. (Message format and syntax)
- Design client server components. (Reactions to messages)
May miss important subtitles.
Fundemental errors under stress.
Few programmers have experience with protocol design
Concentration on communication.
Resulting programs will be difficult to understand.
ADVANCED NETWORK PROGRAMING -- RPC

4. ADVANCED NETWORK PROGRAMING -- RPC
Two Paradigms
Application Oriented Design
- Focus on application.
- Design a conventional program that works correctly.
- Build, compile and test it.
- Devide the program into pieces. (Procedure level)
- Communication level and data representation is transparent.
 RPC
ADVANCED NETWORK PROGRAMING -- RPC

5. Conventional Programs and RPC
Smilarities
CALL
Caller transfers control to called procedure.
Caller suspends.
Only one thread of execution continues at any given time.
Values in all variables are frozen.
RESPONSE
Control flows back to the caller
A called procedure may call another procedure. (Server becomes a client)
ADVANCED NETWORK PROGRAMING -- RPC

6. Conventional Programs and RPC
Differences
Server Procedures
- RPC procedures must exist and be waiting to compute a response.
Data Flow
- RPC may accept or return arbitrary amount of data.
Network Delays
- Protocol, lost packets, data representation.
Adress Space
- Conventional programs can pass pointers as argument.
Environment
- RPC does not have direct access to callers I/O descriptors, OS functions...
ADVANCED NETWORK PROGRAMING -- RPC

7. SUN Microsystems’ RPC Definition
SUN defined specific form of RPC  SUNRPC
Wide acceptance, many applications. (NFS)
Defines format of messages and arguments.
Protocol  TCP , UDP.
Data Representation  XDR.
Uses structure instead of multiple arguments.
At most one remote procedure in a remote program can be invoked at a given time  Automatic Mutual Exclusion
A complier tool helps programmers to build distributed programs automatically  RPCGEN
ADVANCED NETWORK PROGRAMING -- RPC

8. Remote Program and Procedure Identification
Program no Description
0x x1fffffff defined by SUN
0x x3fffffff defined by system mng.
0x x5fffffff customer written appl.
0x xffffffff reserved
Program Number
- Each program must be assigned a unique 32 - bit integer
Procedure Number
- Each procedure in a remote program must have an integer. (1,2,3...)
Version number
- Multiple versions may run at the same time.
You can change details with same version number.
Easy to migrate.
(prog, ver, proc)
ADVANCED NETWORK PROGRAMING -- RPC

9. RPC Mapping Machine address + Program no  ?  correct server port
UDP and TCP  16 bit protocol port numbers.
RCP  32 bit program numbers.
Servers uses well known ports.
RPC servers use ephemeral ports. They takes different ports after each time they restart.
Machine address + Program no  ?  correct server port
ADVANCED NETWORK PROGRAMING -- RPC

10. ADVANCED NETWORK PROGRAMING -- RPC
PORT MAPPER, RPCBIND
Uses a database of dynamic port mapping. (TCP/UDP port = 111)
Starts in multiuser mode.
Server’s main function calls svc_create
- Determines protocols supported by clients
- Creates end-points, Binds port to TCP and UDP.
- Contacts RPCBIND and registers itself (port, prog, ver).
- Goes to sleep.
Client calls clnt_create (server_IP, prog_no, ver, protocol)
- Usually makes a UDP connection to RPCBIND on servers machine.
ADVANCED NETWORK PROGRAMING -- RPC

11. ADVANCED NETWORK PROGRAMING -- RPC
PORT MAPPER, RPCBIND
V2  historical (just TCP UDP)
v3,4  newer protocols
Uses /etc/rpc
Solaris % rpcinfo -p
program vers proto port service
tcp 111 rpcbind
tcp 111 rpcbind
tcp 111 rpcbind
udp 111 rpcbind
udp 111 rpcbind
udp 111 rpcbind
....
udp server
tcp server
Solaris % rpcinfo -d sprayd 1
... unregisters sprayd demon.
Solaris % pkill -HUP inetd
... inetd reads the /etc/inetd.conf file and registers sprayd again.
ADVANCED NETWORK PROGRAMING -- RPC

12. ADVANCED NETWORK PROGRAMING -- RPC
RPC - Inetd
RPCgen created servers may be invoked by inetd.
/etc/inetd.conf file needs ti be updated.
...
Rstatd/2-4 tli rpc/datagram_V wait root /usr/.../rpc.rstatd rpc.rstatd
Inetd
- creates endpoint, registers to RPCBIND.
- listens for ports, fork, exec, waits until server terminates.
Server
- std. input is a xti endpoint (no need to re-register).
- waits for ~2 minutes before terminate ( to prevent new fork and exec)
- generates SIGCHLD to inetd.
ADVANCED NETWORK PROGRAMING -- RPC

13. ADVANCED NETWORK PROGRAMING -- RPC
Call Semantics
Procedure calls can be placed into one of these categories:
1. Exactly once
2. At most once
3. At least once
4. Zero or more
ADVANCED NETWORK PROGRAMING -- RPC

14. Call Semantics - Scenarios
TCP
Reply received: Exactly Once
No reply: At most once (server may have crashed)
UDP without server cash
Reply received: at least once
No reply: zero or more
UDP with server cash
No reply: At most once
ADVANCED NETWORK PROGRAMING -- RPC

15. Stub Procedure Consept & RPCGEN
Sun RPC specifications are extensive and complicated without a software tool.
Assistance:
1. XDR library routines: internal data items  XDR standard
2. RPC untime library: correctly make call, receive call, registration...
3. RPCgen: A program generater
ADVANCED NETWORK PROGRAMING -- RPC

16. ADVANCED NETWORK PROGRAMING -- RPC
Stub Procedures
Additional procedures added to program to implement RPC.
Client Side Stub : They replaces the called procedure.
Server Side Stub : They replaces the caller procedure.
Computer 1
Computer 2
PROC A
Server Stub
Client Stub
Proc B
ADVANCED NETWORK PROGRAMING -- RPC

17. ADVANCED NETWORK PROGRAMING -- RPC
RPCGEN
Rpcgen reads an input file that contains a specification of remote program.
IT produces four output (source code) files.
If specification file has name Q.x all output files will begin with Q.
- Q.h Declarations of constants and types used in the code generated for both client and server.
- Q_xdr.c XDR procedure calls used in the client and server to marshal arg.
- Q_clnt.c Client side stub procedure.
- Q_svc.c Server side stub procedure.
ADVANCED NETWORK PROGRAMING -- RPC

18. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
ADVANCED NETWORK PROGRAMING -- RPC

19. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
Specification file
struct square_in { /* input (argument) */
long arg1; };
struct square_out { /* output (result) */
long res1;
program SQUARE_PROG {
version SQUARE_VERS {
square_out SQUAREPROC(square_in) = 1; /* procedure number = 1 */
} = 1; /* version number */
} = 0x ; /* program number */
ADVANCED NETWORK PROGRAMING -- RPC

20. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
Client.c (Client main function)
#include "unpipc.h" /* our header */
#include "square.h" /* generated by rpcgen */
int main(int argc, char **argv) {
CLIENT *cl;
square_in in;
square_out *outp;
if (argc != 3)
err_quit("usage: client <hostname> <integer-value>");
cl = clnt_create(argv[1], SQUARE_PROG, SQUARE_VERS, "tcp");
in.arg1 = atol(argv[2]);
if ( (outp = squareproc_1(&in, cl)) == NULL)
err_quit("%s", clnt_sperror(cl, argv[1]));
printf("result: %ld\n", outp->res1);
exit(0); }
Client handle
ADVANCED NETWORK PROGRAMING -- RPC

21. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
Server Procedure
#include "unpipc.h"
#include "square.h"
square_out *
squareproc_1_svc(square_in *inp, struct svc_req *rqstp) {
static square_out out;
out.res1 = inp->arg1 * inp->arg1;
return(&out); }
ADVANCED NETWORK PROGRAMING -- RPC

22. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
Client executable
Solaris % rpcgen -C square.x
Solaris % cc -c client.c -o client.o
Solaris % cc -c square_clnt.c -o square_clnt.o
Solaris % cc -c square_xdr.c -o square_xdr.o
Solaris % cc -o client client.o square_clnt.o square_xdr.o libunpipc.a -lnsl
Server executable
Solaris % cc -c server.c -o server.o
Solaris % cc -c square_svc.c -o square.svc.o
Solaris % cc -o server server.o square_svc.o square_xdr.o libunpipc.a -lnsl
ADVANCED NETWORK PROGRAMING -- RPC

23. ADVANCED NETWORK PROGRAMING -- RPC
RPC Example
ADVANCED NETWORK PROGRAMING -- RPC