path: root/rpc++/rpc++.texi

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@setfilename rpc++.info
@settitle A C++ Interface to Remote Procedure Calls
@setchapternewpage on
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@ifinfo
This file documents a C++ interface to Sun remote procedure calls.

Copyright @copyright{} 1992 Michael N. Lipp
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through @TeX{} and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU Library General Public License'' is included exactly as
in the original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU Library General Public License'' and
this permission notice may be included in translations approved by the
Free Software Foundation instead of in the original English.
@end ifinfo

@titlepage

@title A C++ Interface
@title to Sun Remote Procedure Calls
@sp 1
@subtitle @authorfont{by Michael N. Lipp}
@sp 20
@subtitle{for version 2.2}
@subtitle{Technische Hochschule Darmstadt, Institut f@"ur Datentechnik}

@comment  The following two commands start the copyright page.
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1992 Michael N. Lipp

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU Library General Public License'' is included exactly as
in the original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU Library General Public License'' may be
included in a translation approved by the author instead of in the original
English.
@end titlepage

@node Top, Overview, (dir), (dir)

@menu
* Overview::                    Overview
* Installation::                Installation
* Classes::                     The Classes
* Caveats::                     Caveats
* References::                  References
* Copying::                     GNU LIBRARY GENERAL PUBLIC LICENSE
* Data Type Index::             Data Type Index
* Function Index::              Function and Method Index
* Concept Index::               Concept Index

 --- The Detailed Node Listing ---

The classes

* XdrInfo::                     @code{XdrInfo}
* RpcRequest::                  @code{RpcRequest}
* Callbacks::                   @code{Callbacks}
* RpcService::                  @code{RpcService}
* RpcStub::                     @code{RpcStub}

Callbacks

* RpcCallback::                 @code{RpcCallback}
* RpcMethodCall::               @code{RpcMethodCall}
* Calling Conventions::         @code{Calling Conventions}

Caveats

* Global objects::              Global objects
* Destruction rules::           Destruction rules
* Matching server and clients::  Matching server and clients
@end menu

@node    Overview, Installation, Top, Top
@comment node-name,     next,           previous, up
@chapter Overview
@cindex Overview

This document describes my C++ interface to Sun Remote Procedure Calls.
It is based on sources from Peter Bersen that I got from some newsgroup,
though I don't remember which one. I liked the basic idea but disliked
several aspects of the interface details. So I adapted it to my likes. I
intended some minor changes but soon found myself renaming classes,
changing method parameters, introducing new classes, etc. The result is
by no way compatible with the original version. It is, I hope,
nevertheless useful.

Basically, the interface defines six class: @code{XdrInfo},
@code{RpcRequest}, @code{RpcCallback}/@code{RpcMethodCall},
@code{RpcService} and @code{RpcStub}.

@code{XdrInfo} objects describe the external data representation of a
type. There are predefined @code{XdrInfo}s for the basic types.
@code{RpcRequest} objects describe the available procedure calls. They
are constructed from a unique request number, the @code{XdrInfo}s of the
procedure's arguments and its return type. @code{RpcCallback} is an
object that holds a pointer to a function and information about the
number of its arguments. @code{RpcMethodCall} is a template that in a
similar way holds a pointer to an object and one of its methods and
Information about the number of its arguments.

An @code{RpcRequest} and its matching @code{RpcCallback} or
@code{RpcMethodCall} may be registered with an @code{RpcService}.
Exactly one object of type @code{RpcService} may be instantiated in a
program that implements an RPC server. Method @code{Provide ()} is a
loop that waits for requests and dispatches them.

A client program instantiates an object of type @code{RpcStub}.  The
constructor establishes a connection to the server specified by its
arguments. Procedures of the server may be invoked using method
@code{Call (@dots{})}.

@node    Installation, Classes, Overview, Top
@comment node-name,     next,           previous, up
@chapter Installation
@cindex Installation

The rpc++ library has successfully been tested using a patched gcc-2.2.2
on a SparcStation running SunOS 4.1.[12] and a 386 system running
Interactive Unix (a SYSV 3.2). Patching gcc-2.2.2 was necessary because
the unpatched version can't handle typedefs that are local to templates.
The bug report with patches can be found in the source directory in file
@code{gcc-2.2.2.fix}.

As a prerequisite to using RPCs with C++ you need ANSI-C/C++ conformant
header files for RPC. I have provided such files in the directory
@code{StdHdrs/rpc} of the source tree. To avoid any copyright conflicts,
they are derived from the public available RPC source code rather than
from the files that come with SunOS 4.1.X. The differences are minor.
The SunOS 4.1.X files define some additional functions. You have to
either copy the files from @code{StdHdrs/rpc} or patched files from your
@code{/usr/include/rpc} to a directory where gcc can find them. If you
don't want to install them globally in gcc's include directory, you can
include them by using an additional ``@code{-I}'' flag during
compilation.

In SunOS you can simply type `@code{make install INSTROOT=@dots{}}'
which will make the library and install it in @code{INSTROOT/lib} and
the header files in @code{INSTROOT/include/rpc++}.  Other Unices will
probably have problems with the `install' command. Type only `make' and
copy the resulting @code{librpc++.a} to your local library directory and
the files @code{rpc++/*} to an @code{rpc++}-subdirectory of your local
include directory.

@node    Classes, Caveats, Installation, Top
@comment node-name,     next,           previous,	up
@chapter The classes

@menu
* XdrInfo::                     @code{XdrInfo}
* RpcRequest::                  @code{RpcRequest}
* Callbacks::                   @code{Callbacks}
* RpcService::                  @code{RpcService}
* RpcStub::                     @code{RpcStub}
@end menu

@node    XdrInfo, RpcRequest,  , Classes
@comment node-name,     next,           previous, up
@section @code{XdrInfo}
@cindex @code{XdrInfo}

Declared in: @code{"rpc++/xdr++.h"}

@deftp Class XdrInfo
Class XdrInfo describes serializers. It combines the xdrproc_t with the
size info (the size of the data to be converted) usually needed if you
want to apply a serializer.
@end deftp

There is only one constructor for @code{XdrInfo}:

@deftypefn Constructor {} XdrInfo (xdrproc_t @var{t}, size_t @var{s})
Construct an @code{XdrInfo} for a type. The type can be converted to an
external data representation (serielized) with function @var{t}. Its
size (in bytes, from @code{sizeof (type)}), is @var{s}.
@end deftypefn

The methods query the information given to the constructor:

@deftypefn Method xdrproc_t Proc () const
Return the conversion function stored in an @code{XdrInfo}.
@end deftypefn

@deftypefn Method size_t Size () const
Return the size of the type described by the @code{XdrInfo}.
@end deftypefn

There are a number of predefined @code{XdrInfo}s. They are defined as
static members of a class @code{Xdr} for scoping reasons.

@defvr XdrInfo Xdr::Xchar
The conversion and size information for a character.
@end defvr

@defvr XdrInfo Xdr::Xshort
The conversion and size information for a short integer.
@end defvr

@defvr XdrInfo Xdr::Xint
The conversion and size information for an integer.
@end defvr

@defvr XdrInfo Xdr::Xlong
The conversion and size information for a long integer.
@end defvr

@defvr XdrInfo Xdr::Xuchar
The conversion and size information for an unsigned character.
@end defvr

@defvr XdrInfo Xdr::Xushort
The conversion and size information for an unsigned short integer.
@end defvr

@defvr XdrInfo Xdr::Xulong
The conversion and size information for an unsigned long integer.
@end defvr

@defvr XdrInfo Xdr::Xfloat
The conversion and size information for a float.
@end defvr

@defvr XdrInfo Xdr::Xdouble
The conversion and size information for a double.
@end defvr

@defvr XdrInfo Xdr::Xenum_t
The conversion and size information for any enumeration type.
@end defvr

@defvr XdrInfo Xdr::Xbool_t
The conversion and size information for a bool.
@end defvr

@defvr XdrInfo Xdr::Xvoid
A special @code{XdrInfo} for the return type of a procedure that returns
nothing.
@end defvr

@defvr XdrInfo Xdr::Xnull
A special @code{XdrInfo} for the return type of a procedure that is to
be executed batched or asynchronously (@pxref{RpcRequest}).
@end defvr

@page
@node    RpcRequest, Callbacks, XdrInfo, Classes
@comment node-name,     next,           previous, up
@section @code{RpcRequest}
@cindex @code{RpcRequest}

Declared in: @code{"rpc++/request.h"}

@deftp Class RpcRequest
RpcRequest is a class that specifies a request for a procedure that is
part of (registered with) a service.
@end deftp

There are several constructors for @code{RpcRequest}. They vary in the
number of @code{XdrInfo}s used to describe the input parameters of the
procedure.

@deftypefn Constructor {} RpcRequest (u_long @var{reqid}, const XdrInfo* @var{out}, ReqType @var{t}=normal)
@end deftypefn
@deftypefn Constructor {} RpcRequest (u_long @var{reqid}, const XdrInfo* @var{out}, const XdrInfo* @var{in1}, ReqType @var{t}=normal)
@end deftypefn
@deftypefn Constructor {} RpcRequest (u_long @var{reqid}, const XdrInfo* @var{out}, const XdrInfo* @var{in1}, const XdrInfo* @var{in2}, ReqType @var{t}=normal)
These constructors construct an @code{RpcRequest} for a procedure with
zero, one or two arguments. Additional similar constructors are defined
for procedures with up to seven arguments. @var{reqid} uniquely
identifies the request (the procedure of the server). @var{reqid} may
not be 0. The @code{XdrInfo*}s following @var{reqid} specify the types of
the input parameters. They are followed by the @code{XdrInfo*} that
describes the type of the value returned by the RPC. If no value is
returned, @code{&Xdr::Xvoid} must be given as argument
(@pxref{XdrInfo}). The final optional argument @var{t} specifies the
call mode: @code{RpcRequest::normal}, @code{RpcRequest::batched} or
@code{RpcRequest::async} (see below).
@end deftypefn

@deftypefn Constructor {} RpcRequest (u_long @var{reqid}, const XdrInfo* @var{out}, const XdrInfo** @var{intypes}, ReqType @var{t}=normal)
This constructor can be used to construct an @code{RpcRequest} with an
arbitrary number of arguments. The pointers to @code{XdrInfo} are passed
in an array. The number of elements in the array must be one more than
the number of parameters and the last element must be zero.
@end deftypefn

If the request type @var{t} is @code{RpcRequest::normal}, method
@code{Call} (@pxref{RpcStub}) assembles the message to the server, sends
it, waits for a reply and returns the result.

If the request type is @code{RpcRequest::batched}, method
@code{RpcStub::Call} assembles the message to the server and puts it in
a buffer. Messages are only flushed if the buffer is full or
@code{RpcStub::Call} is used with a @code{normal} or @code{async}
request.

If the request type is @code{RpcRequest::async}, method
@code{RpcStub::Call} (@pxref{RpcStub}) assembles the message to the
server and sends it, as with @code{normal}. It does, however, not wait
for a result. Mode @code{async} is implemented by calling the underlying
RPC--function @code{clnt_call} with a timeout of zero.

As in both non--normal cases (@code{batched} and @code{async})
@code{RpcStub::Call} does not wait for a return value from the server,
the return type of the @code{RpcRequest} must be specified as
@code{&Xdr::Xnull}.

Note that requests that are registered for a service are stored in an
array using the request identification as the index, so keep ids small.

Normally, requests should be specified in a header file included by both
the server and the client program (@pxref{Matching server and clients}).

@page
@node    Callbacks, RpcService, RpcRequest, Classes
@comment node-name,     next,           previous, up
@section Callbacks
@cindex Callbacks

If a server receives a request from a client, it needs to know how a
particular procedure is to be invoked. This information is specified
using objects @code{RpcCallback} or @code{RpcMethodCall} when the
procedure resp.@ method is specified.

The class
@deftp Class AnyRpcCallback
@end deftp
serves as an abstract base class for the two kinds of callbacks.

The following sections describe the constructors for @code{RpcCallback}
and @code{RpcMethodCall} and the calling conventions for the functions
or methods called back.

@menu
* RpcCallback::                 @code{RpcCallback}
* RpcMethodCall::               @code{RpcMethodCall}
* Calling Conventions::         @code{Calling Conventions}
@end menu

@node    RpcCallback, RpcMethodCall,  , Callbacks
@comment node-name,     next,           previous, up
@subsection @code{RpcCallback}
@cindex @code{RpcCallback}

Declared in: @code{"rpc++/callback.h"}

@deftp Class RpcCallback
An @code{RpcCallback} describes a function that is to be called by the
server on request from the client.
@end deftp

@deftypefn Constructor {} RpcCallback (void* (*)() @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void*, void*) @var{proc})
Construct an @code{RpcCallback} for a function that takes zero, one or
two arguments and returns a result. Constructors for functions with
up to seven arguments are defined.
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void**) @var{proc})
Construct an @code{RpcCallback} for a function that takes an arbitrary
number of arguments and returns a result.
@end deftypefn

@deftypefn Constructor {} RpcCallback (void (*)() @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void*, void*) @var{proc})
Construct an @code{RpcCallback} for a function that takes zero, one or
two arguments and returns no result. Constructors for functions with
up to seven arguments are defined.
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void**) @var{proc})
Construct an @code{RpcCallback} for a function that takes an arbitrary
number of arguments and return no result.
@end deftypefn

@deftypefn Constructor {} RpcCallback (void* (*)(RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void*, RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void*, void*, RpcService*) @var{proc})
Construct an @code{RpcCallback} for a function that takes zero, one or
two arguments and returns a result. Constructors for functions with
up to seven arguments are defined. Upon invocation, a pointer to the
object of type @code{RpcService} that received the request and called
the function is passed as an additional argument.
@end deftypefn
@deftypefn Constructor {} RpcCallback (void* (*)(void**) @var{proc})
Construct an @code{RpcCallback} for a function that takes an arbitrary
number of arguments and returns a result. Upon invocation, a pointer to the
object of type @code{RpcService} that received the request and called
the function is passed as an additional argument.
@end deftypefn

@deftypefn Constructor {} RpcCallback (void (*)(RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void*, RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void*, void*, RpcService*) @var{proc})
Construct an @code{RpcCallback} for a function that takes zero, one or
two arguments and returns a result. Constructors for functions with
up to seven arguments are defined. Upon invocation, a pointer to the
object of type @code{RpcService} that received the request and called
the function is passed as an additional argument.
@end deftypefn
@deftypefn Constructor {} RpcCallback (void (*)(void**) @var{proc})
Construct an @code{RpcCallback} for a function that takes an arbitrary
number of arguments and returns a result. Upon invocation, a pointer to the
object of type @code{RpcService} that received the request and called
the function is passed as an additional argument.
@end deftypefn

@node    RpcMethodCall, Calling Conventions, RpcCallback, Callbacks
@comment node-name,     next,           previous, up
@subsection @code{RpcMethodCall}
@cindex @code{RpcMethodCall}

Declared in: @code{"rpc++/callback.h"}

@deftp Class RpcMethodCall
An @code{RpcMethodCall} describes a method of an object that is to be
called by the server on request from the client.
@end deftp

@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)() @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void*, void*) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods that
takes zero, one or two arguments and returns a result. Constructors for
methods with up to seven arguments are defined.
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void**) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes an arbitrary number of arguments and returns a result.
@end deftypefn

@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)() @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void*, void*) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes zero, one or two arguments and returns no result.
Constructors for methods with up to seven arguments are defined.
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void**) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes an arbitrary number of arguments and return no result.
@end deftypefn

@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void*, RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void*, void*, RpcService*) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes zero, one or two arguments and returns a result. Constructors
for methods with up to seven arguments are defined. Upon invocation, a
pointer to the object of type @code{RpcService} that received the
request and called the method is passed as an additional argument.
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void* (T::*)(void**) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes an arbitrary number of arguments and returns a result. Upon
invocation, a pointer to the object of type @code{RpcService} that
received the request and called the method is passed as an additional
argument.
@end deftypefn

@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void*, RpcService*) @var{proc})
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void*, void*, RpcService*) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes zero, one or two arguments and returns a result. Constructors
for methods with up to seven arguments are defined. Upon invocation, a
pointer to the object of type @code{RpcService} that received the
request and called the method is passed as an additional argument.
@end deftypefn
@deftypefn Constructor {} RpcMethodCall <class T> (void (T::*)(void**) @var{proc})
Construct an @code{RpcMethodCall} for an object and one of its methods
that takes an arbitrary number of arguments and returns a result. Upon
invocation, a pointer to the object of type @code{RpcService} that
received the request and called the method is passed as an additional
argument.
@end deftypefn

@node    Calling Conventions,  , RpcMethodCall, Callbacks
@comment node-name,     next,           previous, up
@subsection @code{Calling Conventions}
@cindex @code{calling conventions}

As could be seen from the parameter types in the constructors, functions
and methods that are called in response to a request from a client know
only about pointers to void as arguments and result values because their
real type is coded in the @code{RpcRequest} and not known at compile
time. The only way to avoid this is to implement some kind of rpcgen++.
However, I never liked this kind of tools and I'm willing to risk a bit
of type unsafeness in this case.

When a procedure (or method) is called, its arguments point to values
(the variants with an arbitrary number of arguments receive an array of
pointers to values) of the types specified in the constructor of the
@code{RpcRequest} that led to the invocation of the procedure. I
recommend to access the values and assign them to local variables of the
procedure in the first statements. E.g.:
@example
void* Add (void* s1p, void* s2p)
@{
  int s1 = *(int*)s1p;
  int s2 = *(int*)s2p;
  ...
@end example

The return value of the procedure is a pointer to the result. Therefore,
results may never be put in automatic variables. They must be global or
static. E.g.:
@example
  ...
  static int sum;
  sum = s1 + s2;
  return (void*)&sum;
@}
@end example

Note the special case of strings (defined as parameters or return values
using @code{Xdr::Xwrapstring}, @pxref{XdrInfo}). If you think of a
string as being defined as a type ``@code{typedef char* string}'', it is
obvious that a string is passed as argument or returned as result by a
@code{string*}, i.e., a @code{char**}. E.g.:
@example
void* Capitalize (void* strp)
@{
  static char* str;
  str = *(char**)strp;
  str[0] = toupper (str[0]);
  return (void*)&str;
@}
@end example

@page
@node    RpcService, RpcStub, Callbacks, Classes
@comment node-name,     next,           previous, up
@section @code{RpcService}
@cindex @code{RpcService}

Declared in: @code{"rpc++/service.h"}

@deftp Class RpcService
An object of type @code{RpcService} provides the server capabilities
within a program.
@end deftp

There are two constructors for @code{RpcService}:

@deftypefn Constructor {} RpcService (u_long @var{prog}, u_long @var{vers})
Construct an object representing the @var{vers}'th version of program
(service) number @code{prog}.
@end deftypefn
@deftypefn Constructor {} RpcService (u_long @var{vers})
Construct an object representing the @var{vers}'th version of a transient
program (service).
@end deftypefn

@deftypefn Method bool OK ()
Returns TRUE if the service is ready for operation, i.e., has successfully
been established during construction.
@end deftypefn

The number of a service, especially a transient service, can be obtained
with method @code{@w{Program ()}}:

@deftypefn Method u_long Program ()
Returns the number of the program (service). This is either the number
passed as an argument to the constructor or a number from the transient
program area.
@end deftypefn

The next step after the construction of an @code{RpcService} is to
register the requests handled by the service:

@deftypefn Method {virtual void} Register (const RpcRequest& @var{req}, const AnyRpcCallback& @var{cb})
Associate request @var{req} with the procedure or object/method pair
specified by @code{cb}. The usual way to call @code{Register} is
@example
@{
  RpcService svc (...);
  svc.register (addreq, RpcCallback (Add));
  ...
@}
@end example
@end deftypefn

After all requests have been registered, the object of type
@code{RpcService} can provide the service:
@deftypefn Method void Provide ()
Repeatedly wait for a request and handle it by calling the procedure or
method registered for it.
@end deftypefn

@deftypefn Method {virtual void*} HandleError ()
@code{HandleError} is a protected method that is called when an error
occurs. The cause of the error is stored in a protected member variable
@code{errorState}. If the default error handling (shown below) is not
appropriate for your application, derive your own class from
@code{RpcService} that implements a different error handling policy. If
you consider an error recoverable, reset @code{errorState} to
@code{RpcService::noError} in your error handler. Else, @code{OK ()}
keeps returning FALSE.
@example
void RpcService::HandleError ()
@{
  switch (errorState)
    @{
    case reconstructionAttempt:
      cerr << "rpc++: Attempt to construct another instance of RpcService.\n";
      exit (1);
    case cantCreateTCPService:
      cerr << "rpc++: can't create tcp service.\n";
      exit(1);
    case cantRegisterService:
      cerr << form ("rpc++: can't register (%d, %d, tcp).", prog, vers);
      exit(1);
    case cantSendReply:
      cerr << "rpc++: can't reply to RPC call.\n";
      break;
    case invalidResult:
      cerr << "rpc++: registered routine has return NULL pointer.\n";
      abort ();
    case notRegistered:
      cerr << "rpc++: requested RPC routine not registered.\n";
      break;
    case cantGetArgs:
      cerr << "rpc++: can't get procedure arguments.\n";
      break;
    case cantFreeArgs:
      cerr << "rpc++: can't free XDR arguments.\n";
      break;
    @}
  errorState = noError;
@}
@end example
@end deftypefn

If the program that provides the service has other things to do as well,
i.e., does not only handle requests, it usually has its own main loop
that handles events. This loop must be extended to handle RPC events,
i.e., if anything happens on the RPC file descriptors, it must call
@code{svc_getreqset} just as @code{Provide ()} does.
@example
void RpcService::Provide ()
@{
  int dtbsz = getdtablesize();
  fd_set readfds;

  for(;;)
    @{
      readfds = svc_fdset;
      switch(select (dtbsz, &readfds, 0, 0, 0))
        @{
        case -1:
          if (errno != EBADF)
            continue;
          cerr << "PRC++: select: " << sys_errlist[errno] << '\n';
          return;
          break;
        case 0:
          continue;
        default:
          svc_getreqset (&readfds);
          break;
        @}
    @}
@}
@end example

The following methods are only available during the execution of a
callback, i.e., they can be applied to @code{RpcService} if a pointer to
the invoking object has been declared as last parameter of a callback
routine.

@deftypefn Method {struct sockaddr_in*} Caller ()
Return the socket address information of the calling host.
@end deftypefn

@deftypefn Method char* CallerName ()
Return the name of the calling host.
@end deftypefn

@deftypefn Method void Reply ()
@end deftypefn
@deftypefn Method void Reply (void* @var{res})
Normally, a request to the server terminates when the callback completes
(either with or without returning a value, depending on the return
type). In some cases it is desirable to reply to the client before all
the actions related to the request have been completed. This allows the
client to resume execution. The result (if any) must of course not
depend on the functions still to be executed.
@end deftypefn

@deftypefn Method void Interrupt ()
This is the proper way to terminate the loop entered by calling
@code{Provide()}. After return from the callback that invoked
@code{Interrupt()} method @code{Provide()} will return.
@end deftypefn

@page
@node    RpcStub,  , RpcService, Classes
@comment node-name,     next,           previous, up
@section @code{RpcStub}
@cindex @code{RpcStub}

Declared in: @code{"rpc++/stub.h"}

@deftp Class RpcStub
An @code{RpcStub} represents the client side of a connection.
@end deftp

There are two constructors for @code{RpcStub} that vary in the position
of their arguments only:

@deftypefn Constructor {} RpcStub (u_long @code{prognum}, u_long @code{versnum}, char* @var{hostname}="localhost", timeval @var{timeout}=defaultTimeout, bool @var{connect}=TRUE)
@end deftypefn
@deftypefn Constructor {} RpcStub (u_long @code{prognum}, u_long @code{versnum}, char* @var{hostname}="localhost", bool @var{connect}=TRUE, timeval @var{timeout}=defaultTimeout)
Construct an @code{RpcStub} that connects to the @var{versnum}'th
version of program (service) @var{prognum} on host @var{hostname}. The
timeout for successful completion of communication operations is
@var{timeout} which defaults to 25 seconds. Unless @var{connect} is
false, the constructor makes a connection attempt.
@end deftypefn

There are various methods:

@deftypefn Method void Reconnect ()
Connect to the server. Usually this method is called if the connection
was not to be established by the constructor or if the connection
attempt failed and is to be repeated.
@end deftypefn

@deftypefn Method bool OK ()
Returns TRUE if the stub is ready for operation, i.e., connected to a
server.
@end deftypefn

@deftypefn Method CLIENT* Service ()
Access to the standard RPC level. Returns the handle that identifies the
server.
@end deftypefn

@deftypefn Method timeval GetTimeout () const
Returns the default timeout for network operations.
@end deftypefn

@deftypefn Method void SetTimeout (timeval& @var{timo})
Sets the default timeout for network operations
@end deftypefn

@deftypefn Method void* Call (RpcRequest& @var{req}, bool @var{handle_errors}=TRUE)
@end deftypefn
@deftypefn Method void* Call (RpcRequest& @var{req}, void* @var{in1}, bool @var{handle_errors}=TRUE)
@end deftypefn
@deftypefn Method void* Call (RpcRequest& @var{req}, void* @var{in1}, @var{in2} bool @var{handle_errors}=TRUE)
Request the operation specified by @var{req} from the server, passing
zero, one or two arguments. There are declarations of this method for up
two seven arguments. Arguments are passed as pointers to the argument
values. The value returned by @code{Call} is a pointer to the result
returned by the server. The result is valid until @code{Call} is called
again. If @var{handle_errors} is FALSE and an error occurs, @code{Call}
simply returns 0. Else, it calls method @code{HandleError} (see below).
@end deftypefn
@deftypefn Method void* Call (RpcRequest& @var{req}, void** @var{invals}, bool @var{handle_errors}=TRUE)
The variant of @code{Call} that handles an arbitrary number of
arguments.  Pointers to the arguments are passed in an array in
parameter @var{invals}. The size of the array must match the number of
arguments given to the constructor of @var{req}.
@end deftypefn

@deftypefn Method {virtual void*} HandleError ()
@code{HandleError} is a protected method that is called when an error
occurs. The cause of the error is stored in a protected member variable
@code{errorState}. If the default error handling policy (shown below) is
not appropriate for your application, derive your own class from
@code{RpcStub} that implements a different one. If you consider an error
recoverable, reset @code{errorState} to @code{RpcStub::noError} in your
error handler. Else, @code{OK ()} keeps returning FALSE.  If an error
occurs during a @code{Call} and parameter @var{handle_errors} is TRUE,
@code{Call} invokes @code{HandleError} and returns its result as result
of the call.
@example
void* RpcStub::HandleError ()
@{
  switch (errorState)
    @{
    case notConnected:
      cerr << "rpc++: Stub has not been connected to server.\n";
    case cantCreate:
      cerr << clnt_spcreateerror ("rpc++") << '\n';
      break;
    case cantCall:
      cerr << clnt_sperror (svc, "rpc++") << '\n';
      exit (1);
    @}
  return 0;
@}
@end example
@end deftypefn

While no or little improvement of coding quality can be gained from
deriving a service specific class from @code{RpcService}, the opposite
is true for @code{RpcStub}.  A service specific derivation may define
methods that have the ``real'' argument lists instead of pointers to
void. These methods are simply implemented by casting the arguments and
(inline) calling one of the @code{Call}--methods. Apart from better
type checking, this has the advantage of keeping details like the
available @code{RpcRequest}s local to the definition of the derived
class (see the example in the @code{example}--directory).

@node Caveats, References, Classes, Top
@comment  node-name,  next,  previous,  up
@chapter Caveats
@cindex Caveats

@menu
* Global objects::              Global objects
* Destruction rules::           Destruction rules
* Matching server and clients::  Matching server and clients
@end menu

@node Global objects, Destruction rules,  , Caveats
@comment  node-name,  next,  previous,  up
@section Global objects
@cindex Global objects

As a general C++ rule, be careful with global objects. The sequence of
constructor invocations for global objects is not defined. This is the
reason, why @code{RpcRequests} are constructed from pointers to
@code{XdrInfo}s rather than from @code{XdrInfo}s.

Both @code{XdrInfo}s and @code{RpcRequest}s tend to be instantiated as
global objects or static member variables. If the constructor of
@code{RpcRequest} received @code{XdrInfo}s instead of pointers and
copied the information contained in the @code{XdrInfo} (the solution I
had preferred), it may happen that the @code{XdrInfo} has not been
constructed yet and thus contains invalid data.

The same problem occurs if you want to define a global
``alias--@code{XdrInfo}'' matching a ``@code{typedef int myint}''.
Don't use @code{XdrInfo Xmyint (Xdr::Xint)} as this may copy the
uninitialized @code{Xdr::Xint}. Use @code{XdrInfo& Xmyint = Xdr::Xint}
instead.

@node Destruction rules, Matching server and clients, Global objects, Caveats
@comment  node-name,  next,  previous,  up
@section Destruction rules
@cindex Destruction rules

Objects of type @code{XdrInfo} are resources that can be used more than
once, i.e., in different @code{RpcRequest}s. If they were handled
properly, references to @code{XdrInfo} would be counted and the
@code{XdrInfo} destructed automatically if the last reference is
removed (unless it is the @code{XdrInfo} of a predefined type).

Such a resource management for @code{XdrInfo}s has been considered
unnecessary as @code{XdrInfo}s will rarely be dynamic objects. If the
user allocates an @code{XdrInfo} on the stack or the heap, it is his
responsibility to assure that the object is valid until the last
@code{RpcResource} that uses it has been destructed.

@node Matching server and clients,  , Destruction rules, Caveats
@comment  node-name,  next,  previous,  up
@section Matching server and clients

In order to make sure that the server and the clients agree about the
protocol, all @code{RpcRequest}s for a service should be declared in a
header file and instantiated in a corresponding source file. The header
file and the compiled source file make the ``library'' that provides the
service. Thus a server consists of three files: the server executable, a
header file defining the service that is to be included in client
sources and an object file which must be linked to the client
executable.

@c ======================================================================

@node References, Copying, Caveats, Top
@comment  node-name,  next,  previous,  up
@unnumbered References

Margaret A. Ellis, @cite{The Annotated C++ Reference Manual},
Addison-Wesley, 1990.

Stanley B. Lippmann, @cite{A C++ Primer}, Addison-Wesley, 1989.

Bjarne Stroustrup, @cite{The C++ Programming Language}, Addison-Wesley,
1986.

Sun Microsystems, @cite{Network Programming}, March 1990.

@c ======================================================================

@node Copying, Data Type Index, References, Top
@appendix GNU LIBRARY GENERAL PUBLIC LICENSE
@center Version 2, June 1991

@display
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Everyone is permitted to copy and distribute verbatim copies
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@end display

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@iftex
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.

@item
If the distribution and/or use of the Library is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Library under this License may add
an explicit geographical distribution limitation excluding those countries,
so that distribution is permitted only in or among countries not thus
excluded.  In such case, this License incorporates the limitation as if
written in the body of this License.

@item
The Free Software Foundation may publish revised and/or new
versions of the Library General Public License from time to time.
Such new versions will be similar in spirit to the present version,
but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number.  If the Library
specifies a version number of this License which applies to it and
``any later version'', you have the option of following the terms and
conditions either of that version or of any later version published by
the Free Software Foundation.  If the Library does not specify a
license version number, you may choose any version ever published by
the Free Software Foundation.

@item
If you wish to incorporate parts of the Library into other free
programs whose distribution conditions are incompatible with these,
write to the author to ask for permission.  For software which is
copyrighted by the Free Software Foundation, write to the Free
Software Foundation; we sometimes make exceptions for this.  Our
decision will be guided by the two goals of preserving the free status
of all derivatives of our free software and of promoting the sharing
and reuse of software generally.

@iftex
@heading NO WARRANTY
@end iftex
@ifinfo
@center NO WARRANTY
@end ifinfo

@item
BECAUSE THE LIBRARY IS LICENSED FREE OF CHARGE, THERE IS NO
WARRANTY FOR THE LIBRARY, TO THE EXTENT PERMITTED BY APPLICABLE LAW.
EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR
OTHER PARTIES PROVIDE THE LIBRARY ``AS IS'' WITHOUT WARRANTY OF ANY
KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE
LIBRARY IS WITH YOU.  SHOULD THE LIBRARY PROVE DEFECTIVE, YOU ASSUME
THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

@item
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY
AND/OR REDISTRIBUTE THE LIBRARY AS PERMITTED ABOVE, BE LIABLE TO YOU
FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
LIBRARY (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A
FAILURE OF THE LIBRARY TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES.
@end enumerate

@iftex
@heading END OF TERMS AND CONDITIONS
@end iftex
@ifinfo
@center END OF TERMS AND CONDITIONS
@end ifinfo

@page
@unnumberedsec How to Apply These Terms to Your New Libraries

  If you develop a new library, and you want it to be of the greatest
possible use to the public, we recommend making it free software that
everyone can redistribute and change.  You can do so by permitting
redistribution under these terms (or, alternatively, under the terms of the
ordinary General Public License).

  To apply these terms, attach the following notices to the library.  It is
safest to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least the
``copyright'' line and a pointer to where the full notice is found.

@smallexample
@var{one line to give the library's name and a brief idea of what it does.}
Copyright (C) @var{year}  @var{name of author}

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free
Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
@end smallexample

Also add information on how to contact you by electronic and paper mail.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the library, if
necessary.  Here is a sample; alter the names:

@example
Yoyodyne, Inc., hereby disclaims all copyright interest in the
library `Frob' (a library for tweaking knobs) written by James Random Hacker.

@var{signature of Ty Coon}, 1 April 1990
Ty Coon, President of Vice
@end example

That's all there is to it!

@c ========================================================================

@page
@node    Data Type Index, Function Index, Copying, Top
@comment node-name,     next, previous,		up
@unnumbered Data Type Index

@printindex tp

@node  Function Index, Concept Index, Data Type Index, Top
@comment  node-name,  next,  previous,  up
@unnumbered Function and Method Index

@printindex fn

@node    Concept Index,  , Function Index, Top
@comment node-name,     next, previous,      up
@unnumbered Concept Index

@printindex cp

@contents
@bye