The Specification of Code

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.

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.

--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 the RPC::XML manpage, 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 specifed. 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, version?, hidden?, signature+,
                             help?, code)>
    <!ELEMENT  methoddef  (name, version?, hidden?, signature+,
                           help?, code)>
    <!ELEMENT  functiondef (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 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.

CAVEATS

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

CREDITS

LICENSE

This module is licensed under the terms of the Artistic License that covers Perl itself. See <http://language.perl.com/misc/Artistic.html> for the license itself.

AUTHOR

Randy J. Ray <rjray@blackperl.com>