Adv' Network Programming RPC Remote Procedure Call

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Adv. Network ProgrammingRPC (Remote Procedure
Call)

• Kubilay Akgül

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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

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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.

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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
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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)

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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...

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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

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Remote Program and Procedure Identification
Program no Description 0x00000000 -
0x1fffffff defined by SUN 0x20000000 -
0x3fffffff defined by system mng. 0x40000000 -
0x5fffffff customer written appl. 0x60000000 -
0xffffffff 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)

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RPC Mapping

• 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

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PORT MAPPER, RPCBIND

• Uses a database of dynamic port mapping. (TCP/UDP
  port 111)
• Starts in multiuser mode.

• Servers 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.

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PORT MAPPER, RPCBIND
V2 ? historical (just TCP UDP) v3,4 ? newer
protocols
Uses /etc/rpc
Solaris rpcinfo -p program vers proto port se
rvice 100000 4 tcp 111 rpcbind 100000
3 tcp 111 rpcbind 100000 2 tcp 111 rpcbind 1000
00 4 udp 111 rpcbind 100000 3 udp 111 rpcbind
100000 2 udp 111 rpcbind .... 824377344
1 udp 42972 server 824377344 1 tcp 40849 server
Solaris rpcinfo -d sprayd 1 ... unregisters
sprayd demon. Solaris pkill -HUP inetd ...
inetd reads the /etc/inetd.conf file and
registers sprayd again.
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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.

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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

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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
• Reply received Exactly Once
• No reply At most once

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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

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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
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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.

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RPC Example
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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 /
• 0x31230000 / program number /

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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 lthostnamegt
  ltinteger-valuegt")
• cl clnt_create(argv1, SQUARE_PROG,
  SQUARE_VERS, "tcp")
• in.arg1 atol(argv2)
• if ( (outp squareproc_1(in, cl)) NULL)
• err_quit("s", clnt_sperror(cl, argv1))
• printf("result ld\n", outp-gtres1)
• exit(0)

Client handle
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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-gtarg1 inp-gtarg1
• return(out)

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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
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RPC Example