Sun RPC

1
Sun RPC

• Ref Stevens chpt. 16

2
Outline

• Sun RPC
• Application Interface
• Pointers
• Multithreading
• XDR

3
Sun RPC

• Another example of remote procedure call
  mechanism
• Implements RPC between hosts
• You will get some practice using this in project
  3
• Language independent RPC
• Uses a separate IDL called XDR
• Same name (XDR) used for data format (External
  Data Representation)
• A simple example
• RPC specification file (foo.x)
• processed by compiler (rpcgen) to generate stub
  code
• Client program
• Server program

4
RPC Specification File

• / procedure to square a number /
• / file square.x /
• 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 / proc
  1 /
• 1 / version /
• 0x31230000 / program number-identifies
  service /

5
Program Numbers

• rpcinfo -p shows the programs currently
  registered on the system
• Program number conventions
• 0x00000000 - 0x1fffffff defined by Sun
• 0x20000000 - 0x3fffffff defined by user (you)
• 0x40000000 - 0x5fffffff transient
• 0x60000000 - 0xffffffff reserved

6
IDL Compilation

• The XDR compiler is called rpcgen
• rpcgen -C square.x
• -C forces ANSI C prototypes to be output
• Creates header files, code for client and server
  stub, main routine for server program

7
Example Client Program

• include"unpipc.h / our header /
• include"square.h / generated by rpcgen /
• int main(int argc, char argv)
• CLIENT cl / Client handle /
• square_in in
• square_out outp
• if (argc ! 3)
• err_quit("usage client lthostnamegt
  ltinteger-valuegt")
• / obtain handle to client procedure /
• cl Clnt_create(argv1,SQUARE_PROG,SQUARE_VERS,
  "tcp")
• in.arg1 atol(argv2)
• / invoke procedure RPC runtime allocates
  result struct /
• / SQUAREPROC for version 1 becomes
  squareproc_1 /
• if ((outp squareproc_1(in, cl)) NULL)
• err_quit("s", clnt_sperror(cl, argv1))
• / RPC parameter includes a pointer /
• printf("result ld\n", outp-gtres1)
• exit(0)

8
Sun RPC Pointers

• Issue Call by reference?
• Yes! Pointers are serialized
• RPC runtime on client side will traverse data
  structure, pack it into a message
• Server side receives message, unpacks it,
  recreates data structure, passes pointers to
  server procedure
• Server may modify data structures to return
  values to client

9
Example Server Program

• include"unpipc.h / our header /
• include"square.h / generated by rpcgen /
• / rpcgen program generates main() on server side
  /
• square_out
• squareproc_1_svc(square_in inp, struct svc_req
  rqstp)
• static square_out out / cannot be automatic
  variable /
• out.res1 inp-gtarg1 inp-gtarg1
• return(out)

• Procedure name append _svc to distinguish
  client procedure from server procedure
• Second parameter provides info on this invocation
  (ignore for now)
• Storage for return result allocated by server

10
Multithreading

• Above server code not thread safe need to
  eliminate static variable
• To make it thread safe, use call by reference
  (avoid server allocating storage to hold return
  result)
• By default, server not multithreaded (one thread
  handles all client requests)
• Use -M flag in rpcgen to ensure it creates thread
  safe code

11
Multithreaded Version(Client Procedure)

• include"unpipc.h / our header /
• include"square.h / generated by rpcgen /
• int main(int argc, char argv)
• CLIENT cl / Client handle /
• square_in in
• square_out outp / storage for return result
  here /
• if (argc ! 3)
• err_quit("usage client lthostnamegt
  ltinteger-valuegt")
• cl Clnt_create(argv1,SQUARE_PROG,SQUARE_VERS,
  "tcp")
• in.arg1 atol(argv2)
• if (squareproc_2(in, out, cl) ! RPC_SUCCESS)
• err_quit("s", clnt_sperror(cl, argv1))
• printf("result ld\n", outp-gtres1)
• exit(0)

12
Multithreaded Version of Server

• include"unpipc.h / our header /
• include"square.h / generated by rpcgen /
• / rpcgen program generates main() on server side
  /
• bool_t
• squareproc_2_svc(square_in inp, square_out
  outp, struct svc_req rqstp)
• / static square_out out /
• out-gtres1 inp-gtarg1 inp-gtarg1
• return(TRUE)

13
Cleaning Up Memory

• Alternatively, server procedure might allocate
  memory to hold result need a way to clean this
  up
• Also, server stub may have allocated memory need
  to clean this up too
• Must define procedure square_prog_2_freeresult
  for this purpose
• Called by server stub after (1) server procedure
  returns, and (2) result has been sent back to
  client
• Data that have been dynamically allocated by the
  XDR code (stubs) are deallocated using xdr_free
• See example in handout

14
External Data Representation(XDR)

• XDR used as IDL
• Language for describing data (and procedure
  definitions)
• XDR also refers to the rules for encoding data
• XDR uses implicit encoding
• Both sender and receiver know types and ordering
  of data (Sun RPC client and server have same
  header files)
• Data converted to a canonical representation at
  sender, decoded at receiver to desired format
• As opposed to explicit encoding, where tags are
  used in the data itself to provide type
  information

15
XDR Encoding Rules

• Rules
• All data types are encoded in multiples of 4
  bytes
• Data represented Big Endian (same as Sun
  machines) on the wire
• 2s complement integers
• IEEE format for floating point values
• Example a 5-character ASCII string represented
  as
• 4 bytes for the length (value 5)
• 5 bytes for the characters
• 3 bytes padding

16
XDR Data Types
/ procedure to square a number / / file
square.x / 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 / proc 1 / 1
/ version / 0x31230000 / program
number-identifies service /

• Specification file (.x) includes data type
  specifications (as well as procedure specs)
• These data types must be mapped to C/C
  datatypes
• So stubs, client, server code can
  generate/interpret data
• In general, mapping required for whatever
  language IDL compiler supports
• Type checking of the RPC runtime different from C
  type checking (e.g., it will enforce maximum
  string lengths)
• Prevents buffer overruns (security risk)

17
Example XDR Data Types
See Figure 16.14 Stevens for full list
18
Example
/ Please do not edit this file. It was
generated using rpcgen. / ifndef
_TEST_H_RPCGEN define _TEST_H_RPCGEN define
RPCGEN_VERSION 199506 include
ltrpc/rpc.hgt define foo 1000 struct square_in
long foo1 char foo2200
struct u_int foo3_len
char foo3_val foo3
int foo4400 struct
u_int foo5_len int foo5_val
foo5 typedef struct square_in
square_in ifdef __cplusplus extern "C" bool_t
xdr_square_in(XDR , square_in) elif
__STDC__ extern bool_t xdr_square_in(XDR ,
square_in) else / Old Style C / bool_t
xdr_square_in() endif / Old Style C / endif
/ !_TEST_H_RPCGEN /
const foo 1000 struct square_in long
foo1 opaque foo2200 opaque foo3lt300gt
int foo4400 int foo5lt500gt
rpcgen
test.x
rpcgen creates xdr_square_in() in test_xdr.c to
encode/decode data (marshal/unmarshal data)
test.h
19
Other Aspects

• Binding how to connect to a server that
  implements the required service
• User needs to know which machine has the service
  (specified in Clnt_create)
• Daemon running on machine that knows about
  available services on that machine
• Use TCP for project - UDP cannot transfer
  arbitrarily large amounts of data (e.g.,
  compressed JPEG images)
• Timeouts (TCP)
• TCP provides reliable delivery (retransmits is
  packet is lost)
• Client can set total timeout time client waits
  for server reply set via clnt_control