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2012-05-25 02:12 @38.107.179.236 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)
RPC::XML::Procedure(3pm) User Contributed Perl Documentation RPC::XML::Procedure(3pm)
NAME
RPC::XML::Procedure - Object encapsulation of server-side RPC procedures
SYNOPSIS
require RPC::XML::Procedure;
...
$method_1 = RPC::XML::Procedure->new({ name => 'system.identity',
code => sub { ... },
signature => [ 'string' ] });
$method_2 = RPC::XML::Procedure->new('/path/to/status.xpl');
IMPORTANT NOTE
This package is comprised of the code that was formerly RPC::XML::Method. The package was
renamed when the decision was made to support procedures and methods as functionally
different entities. It is not necessary to include both this module and RPC::XML::Method
-- this module provides the latter as an empty subclass. In time, RPC::XML::Method will be
removed from the distribution entirely.
DESCRIPTION
The RPC::XML::Procedure package is designed primarily for behind-the-scenes use by the
RPC::XML::Server class and any subclasses of it. It is documented here in case a project
chooses to sub-class it for their purposes (which would require setting the "method_class"
attribute when creating server objects, see RPC::XML::Server).
This package grew out of the increasing need to abstract the operations that related to
the methods a given server instance was providing. Previously, methods were passed around
simply as hash references. It was a small step then to move them into a package and allow
for operations directly on the objects themselves. In the spirit of the original hashes,
all the key data is kept in clear, intuitive hash keys (rather than obfuscated as the
other classes do). Thus it is important to be clear on the interface here before sub-
classing this package.
USAGE
The following methods are provided by this class:
new(FILE|HASHREF|LIST)
Creates a new object of the class, and returns a reference to it. The arguments to the
constructor are variable in nature, depending on the type:
FILE If there is exactly on argument that is not a reference, it is assumed to be a
filename from which the method is to be loaded. This is presumed to be in the
XPL format descibed below (see "XPL File Structure"). If the file cannot be
opened, or if once opened cannot be parsed, an error is raised.
HASHREF If there is exactly one argument that is a reference, it is assumed to be a
hash with the relevant information on the same keys as the object itself uses.
This is primarily to support backwards-compatibility to code written when
methods were implemented simply as hash references.
LIST If there is more than one argument in the list, then the list is assumed to be
a sort of "ersatz" hash construct, in that one of the keys ("signature") is
allowed to occur multiple times. Otherwise, each of the following is allowed,
but may only occur once:
name The name of the method, as it will be presented to clients
code A reference to a subroutine, or an anonymous subroutine, that will
receive calls for the method
signature (May appear more than once) Provides one calling-signature for the
method, as either a space-separated string of types or a list-
reference
help The help-text for a method, which is generally used as a part of
the introspection interface for a server
version The version number/string for the method
hidden A boolean (true or false) value indicating whether the method
should be hidden from introspection and similar listings
Note that all of these correspond to the values that can be changed via the
accessor methods detailed later.
If any error occurs during object creation, an error message is returned in lieu of
the object reference.
clone
Create a copy of the calling object, and return the new reference. All elements are
copied over cleanly, except for the code reference stored on the "code" hash key. The
clone will point to the same code reference as the original. Elements such as
"signature" are copied, so that changes to the clone will not impact the original.
name
Returns the name by which the server is advertising the method. Unlike the next few
accessors, this cannot be changed on an object. In order to streamline the managment
of methods within the server classes, this must persist. However, the other elements
may be used in the creation of a new object, which may then be added to the server, if
the name absolutely must change.
code([NEW])
Returns or sets the code-reference that will receive calls as marshalled by the
server. The existing value is lost, so if it must be preserved, then it should be
retrieved prior to the new value being set.
signature([NEW])
Return a list reference containing the signatures, or set it. Each element of the list
is a string of space-separated types (the first of which is the return type the method
produces in that calling context). If this is being used to set the signature, then an
array reference must be passed that contains one or more strings of this nature.
Nested list references are not allowed at this level. If the new signatures would
cause a conflict (a case in which the same set of input types are specified for
different output types), the old set is silently restored.
help([NEW])
Returns or sets the help-text for the method. As with code, the previous value is
lost.
hidden([NEW])
Returns or sets the hidden status of the method. Setting it loses the previous value.
version([NEW])
Returns or sets the version string for the method (overwriting as with the other
accessors).
is_valid
Returns a true/false value as to whether the object currently has enough content to be
a valid method for a server to publish. This entails having at the very least a name,
one or more signatures, and a code-reference to route the calls to. A server created
from the classes in this software suite will not accept a method that is not valid.
add_signature(LIST)
Add one or more signatures (which may be a list reference or a string) to the internal
tables for this method. Duplicate signatures are ignored. If the new signature would
cause a conflict (a case in which the same set of input types are specified for
different output types), the old set is restored and an error message is returned.
delete_signature(LIST)
Deletes the signature or signatures (list reference or string) from the internal
tables. Quietly ignores any signature that does not exist. If the new signature would
cause a conflict (a case in which the same set of input types are specified for
different output types), the old set is restored and an error message is returned.
match_signature(SIGNATURE)
Check that the passed-in signature is known to the method, and if so returns the type
that the method should be returning as a result of the call. Returns a zero (0)
otherwise. This differs from other signature operations in that the passed-in
signature (which may be a list-reference or a string) does not include the return
type. This method is provided so that servers may check a list of arguments against
type when marshalling an incoming call. For example, a signature of 'int int' would be
tested for by calling "$M->match_signature('int')" and expecting the return value to
be "int".
call(SERVER, PARAMLIST)
Execute the code that this object encapsulates, using the list of parameters passed in
PARAMLIST. The SERVER argument should be an object derived from the RPC::XML::Server
class. For some types of procedure objects, this becomes the first argument of the
parameter list to simulate a method call as if it were on the server object itself.
The return value should be a data object (possibly a RPC::XML::fault), but may not
always be pre-encoded. Errors trapped in $@ are converted to fault objects. This
method is generally used in the "dispatch" method of the server class, where the
return value is subsequently wrapped within a RPC::XML::response object.
reload
Instruct the object to reload itself from the file it originally was loaded from,
assuming that it was loaded from a file to begin with. Returns an error if the method
was not originally loaded from a file, or if an error occurs during the reloading
operation.
Additional Hash Data
In addition to the attributes managed by the accessors documented earlier, the following
hash keys are also available for use. These are also not strongly protected, and the same
care should be taken before altering any of them:
file
When the method was loaded from a file, this key contains the path to the file used.
mtime
When the method was loaded from a file, this key contains the modification-time of the
file, as a UNIX-style "time" value. This is used to check for changes to the file the
code was originally read from.
called
When the method is being used by one of the server classes provided in this software
suite, this key is incremented each time the server object dispatches a request to the
method. This can later be checked to provide some indication of how frequently the
method is being invoked.
XPL File Structure
This section focuses on the way in which methods are expressed in these files, referred to
here as "XPL files" due to the "*.xpl" filename extension (which stands for "XML Procedure
Layout"). This mini-dialect, based on XML, is meant to provide a simple means of
specifying method definitions separate from the code that comprises the application
itself. Thus, methods may theoretically be added, removed, debugged or even changed
entirely without requiring that the server application itself be rebuilt (or, possibly,
without it even being restarted).
The XML-based file structure
The XPL Procedure Layout dialect is a very simple application of XML to the problem of
expressing the method in such a way that it could be useful to other packages than
this one, or useful in other contexts than this one.
The lightweight DTD for the layout can be summarized as:
<!ELEMENT proceduredef (name, version?, hidden?, signature+,
help?, code)>
<!ELEMENT methoddef (name, version?, hidden?, signature+,
help?, code)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT version (#PCDATA)>
<!ELEMENT hidden EMPTY>
<!ELEMENT signature (#PCDATA)>
<!ELEMENT help (#PCDATA)>
<!ELEMENT code (#PCDATA)>
<!ATTLIST code language (#PCDATA)>
The containing tag is always one of "<methoddef>" or "<proceduredef>". The tags that
specify name, signatures and the code itself must always be present. Some optional
information may also be supplied. The "help" text, or what an introspection API would
expect to use to document the method, is also marked as optional. Having some degree
of documentation for all the methods a server provides is a good rule of thumb,
however.
The default methods that this package provides are turned into XPL files by the
make_method tool (see make_method). The final forms of these may serve as direct
examples of what the file should look like.
Information used only for book-keeping
Some of the information in the XPL file is only for book-keeping: the version stamp of
a method is never involved in the invocation. The server also keeps track of the last-
modified time of the file the method is read from, as well as the full directory path
to that file. The "<hidden />" tag is used to identify those methods that should not
be exposed to the outside world through any sort of introspection/documentation API.
They are still available and callable, but the client must possess the interface
information in order to do so.
The information crucial to the method
The name, signatures and code must be present for obvious reasons. The "<name>" tag
tells the server what external name this procedure is known by. The "<signature>" tag,
which may appear more than once, provides the definition of the interface to the
function in terms of what types and quantity of arguments it will accept, and for a
given set of arguments what the type of the returned value is. Lastly is the "<code>"
tag, without which there is no procedure to remotely call.
Why the <code> tag allows multiple languages
Note that the "<code>" tag is the only one with an attribute, in this case "language".
This is designed to allow for one XPL file to provide a given method in multiple
languages. Why, one might ask, would there be a need for this?
It is the hope behind this package that collections of RPC suites may one day be made
available as separate entities from this specific software package. Given this hope,
it is not unreasonable to suggest that such a suite of code might be implemented in
more than one language (each of Perl, Python, Ruby and Tcl, for example). Languages
which all support the means by which to take new code and add it to a running process
on demand (usually through an ""eval"" keyword or something similar). If the file
A.xpl is provided with implementations in all four of the above languages, the name,
help text, signature and even hidden status would likely be identical. So, why not
share the non-language-specific elements in the spirit of re-use?
The "make_method" utility
The utility script "make_method" is provided as a part of this software suite. It
allows for the automatic creation of XPL files from either command-line information or
from template files. It has a wide variety of features and options, and is out of the
scope of this particular manual page. The package Makefile.PL features an example of
engineering the automatic generation of XPL files and their delivery as a part of the
normal Perl module build process. Using this tool is highly recommended over managing
XPL files directly. For the full details, see make_method.
DIAGNOSTICS
Unless otherwise noted in the individual documentation sections, all methods return the
object reference on success, or a (non-reference) text string containing the error message
upon failure.
CAVEATS
Moving the method management to a separate class adds a good deal of overhead to the
general system. The trade-off in reduced complexity and added maintainability should
offset this.
LICENSE
This module and the code within are released under the terms of the Artistic License 2.0
(http://www.opensource.org/licenses/artistic-license-2.0.php). This code may be
redistributed under either the Artistic License or the GNU Lesser General Public License
(LGPL) version 2.1 (http://www.opensource.org/licenses/lgpl-license.php).
SEE ALSO
RPC::XML::Server, make_method
AUTHOR
Randy J. Ray <rjray AT blackperl.com>
perl v5.10.0 2008-04-09 RPC::XML::Procedure(3pm)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2012-05-25 02:12 @38.107.179.236 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)