make_methodp - Online in the Cloud

PROGRAM:

NAME

make_method - Turn Perl code into an XML description for RPC::XML::Server

SYNOPSIS

make_method --name=system.identification --helptext='System ID string'
--signature=string --code=ident.pl --output=ident.xpl

make_method --base=methods/identification

DESCRIPTION

This is a simple tool to create the XML descriptive files for specifying methods to be
published by an RPC::XML::Server-based server.

If a server is written such that the methods it exports (or publishes) are a part of the
running code, then there is no need for this tool. However, in cases where the server may
be separate and distinct from the code (such as an Apache-based RPC server), specifying
the routines and filling in the supporting information can be cumbersome.

One solution that the RPC::XML::Server package offers is the means to load publishable
code from an external file. The file is in a simple XML dialect that clearly delinates the
externally-visible name, the method signatures, the help text and the code itself. These
files may be created manually, or this tool may be used as an aide.

REQUIRED ARGUMENTS

There are no required arguments, but if there are not sufficient options passed you will
be told by an error message.

OPTIONS

The tool recognizes the following options:

--help
Prints a short summary of the options.

--name=STRING
Specifies the published name of the method being encoded. This is the name by which it
will be visible to clients of the server.

--namespace=STRING
Specifies a namespace that the code of the method will be evaluated in, when the XPL
file is loaded by a server instance.

--type=STRING
Specify the type for the resulting file. "Type" here refers to whether the container
tag used in the resulting XML will specify a procedure or a method. The default is
method. The string is treated case-independant, and only the first character ("m" or
"p") is actually regarded.

--version=STRING
Specify a version stamp for the code routine.

--hidden
If this is passe, the resulting file will include a tag that tells the server daemon
to not make the routine visible through any introspection interfaces.

--signature=STRING [ --signature=STRING ... ]
Specify one or more signatures for the method. Signatures should be the type names as
laid out in the documentation in RPC::XML, with the elements separated by a colon. You
may also separate them with spaces, if you quote the argument. This option may be
specified more than once, as some methods may have several signatures.

--helptext=STRING
Specify the help text for the method as a simple string on the command line. Not
suited for terribly long help strings.

--helpfile=FILE
Read the help text for the method from the file specified.

--code=FILE
Read the actual code for the routine from the file specified. If this option is not
given, the code is read from the standard input file descriptor.

--output=FILE
Write the resulting XML representation to the specified file. If this option is not
given, then the output goes to the standard output file descriptor.

--base=NAME
This is a special, "all-in-one" option. If passed, all other options are ignored.

The value is used as the base element for reading information from a file named
BASE.base. This file will contain specification of the name, version, hidden status,
signatures and other method information. Each line of the file should look like one of
the following:

Name: STRING
Specify the name of the routine being published. If this line does not appear,
then the value of the --base argument with all directory elements removed will be
used.

Version: STRING
Provide a version stamp for the function. If no line matching this pattern is
present, no version tag will be written.

Hidden: STRING
If present, STRING should be either "yes" or "no" (case not important). If it is
"yes", then the method is marked to be hidden from any introspection API.

Signature: STRING
This line may appear more than once, and is treated cumulatively. Other options
override previous values if they appear more than once. The portion following the
"Signature:" part is taken to be a published signature for the method, with
elements separated by whitespace. Each method must have at least one signature, so
a lack of any will cause an error.

Helpfile: STRING
Specifies the file from which to read the help text. It is not an error if no help
text is specified.

Codefile: STRING
Specifies the file from which to read the code. Code is assumed to be Perl, and
will be tagged as such in the resulting file.

Codefile[lang]: string
Specifies the file from which to read code, while also identifying the language
that the code is in. This allows for the creation of a XPL file that includes
multiple language implementations of the given method or procedure.

Any other lines than the above patterns are ignored.

If no code has been read, then the tool will exit with an error message.

The output is written to BASE.xpl, preserving the path information so that the
resulting file is right alongside the source files. This allows constructs such as:

make_method --base=methods/introspection

FILE FORMAT AND DTD

The file format for these published routines is a very simple XML dialect. This is less
due to XML being an ideal format than it is the availability of the parser, given that the
RPC::XML::Server class will already have the parser code in core. Writing a completely new
format would not have gained anything.

The Document Type Declaration for the format can be summarized by:

<!ELEMENT proceduredef (name, namespace?, version?, hidden?,
signature+, help?, code)>
<!ELEMENT methoddef (name, namespace?, version?, hidden?,
signature+, help?, code)>
<!ELEMENT functiondef (name, namespace?, version?, hidden?,
signature+, help?, code)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT namespace (#PCDATA)>
<!ELEMENT version (#PCDATA)>
<!ELEMENT hidden EMPTY>
<!ELEMENT signature (#PCDATA)>
<!ELEMENT help (#PCDATA)>
<!ELEMENT code (#PCDATA)>
<!ATTLIST code language (#PCDATA)>

The file "rpc-method.dtd" that comes with the distribution has some commentary in addition
to the actual specification.

A file is (for now) limited to one definition. This is started by the one of the opening
tags "<methoddef>", "<functiondef>" or "<proceduredef>". This is followed by exactly one
"<name>" container specifying the method name, an optional version stamp, an optional
hide-from-introspection flag, one or more "<signature>" containers specifying signatures,
an optional "<help>" container with the help text, then the "<code>" container with the
actual program code. All text should use entity encoding for the symbols:

& C<&amp;> (ampersand)
E<lt> C<&lt;> (less-than)
E<gt> C<&gt;> (greater-than)

The parsing process within the server class will decode the entities. To make things
easier, the tool scans all text elements and encodes the above entities before writing the
file.

The Specification of Code
This is not "Programming 101", nor is it "Perl for the Somewhat Dim". The code that is
passed in via one of the "*.xpl" files gets passed to "eval" with next to no modification
(see below). Thus, badly-written or malicious code can very well wreak havoc on your
server. This is not the fault of the server code. The price of the flexibility this system
offers is the responsibility on the part of the developer to ensure that the code is
tested and safe.

Code itself is treated as verbatim as possible. Some edits may occur on the server-side,
as it make the code suitable for creating an anonymous subroutine from. The make_method
tool will attempt to use a "CDATA" section to embed the code within the XML document, so
that there is no need to encode entities or such. This allows for the resulting *.xpl
files to be syntax-testable with "perl -cx". You can aid this by ensuring that the code
does not contain either of the two following character sequences:

]]>

__DATA__

The first is the "CDATA" terminator. If it occurs naturally in the code, it would trigger
the end-of-section in the parser. The second is the familiar Perl token, which is inserted
so that the remainder of the XML document does not clutter up the Perl parser.

EXAMPLES

The RPC::XML distribution comes with a number of default methods in a subdirectory called
(cryptically enough) "methods". Each of these is expressed as a set of ("*.base",
"*.code", "*.help") files. The Makefile.PL file configures the resulting Makefile such
that these are used to create "*.xpl" files using this tool, and then install them.

DIAGNOSTICS

Most problems come out in the form of error messages followed by an abrupt exit.

EXIT STATUS

The tool exits with a status of 0 upon success, and 255 otherwise.

CAVEATS

I don't much like this approach to specifying the methods, but I liked my other ideas even
less.

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