XML EZ_Out
Version 1.06
============
XML EZ_Out is a small set of packages intended to aid the creation of
XML-formatted output from within Ada programs. It basically wraps the
tags and data provided to it with XML syntax and writes them to a
user-supplied medium.
This medium can be any sort of writable entity, such as a file, a
memory buffer, or even a communications link, such as a socket. The
only functionality required of the medium is that it supply a
meaningful "Put" (for writing a string) and "New_Line" procedure.
Usage
=====
IMPORTANT!!
XML EZ_Out package instantiations are explicitly designed to be made
directly visible with the aid of a "use" clause! Declining to use a
"use" will make using EZ_Out inordinately verbose and awkward to use.
So use "use", and get a waiver from your programming standard if you
have to!
The key facilitator of making XML EZ_Out usage readable when
generating XML documentation is the overloading of a number of
variations of the "=" function. By doing this, a simple XML element
having no content, such as:
<player lastName="Cuddyer" firstName="Michael" team="Twins"/>
can be generated as:
Output_Tag(F,
"player",
("lastName" = "Cuddyer",
"firstName" = "Michael",
"team" = "Twins"));
To simplify the specification of the attributes, variations of "=" are
provided. Given these declarations:
Batting_Average : Float;
At_Bats : Natural;
One can directly reference the variables:
Output_Tag(F,
"stats",
("battingAvg" = Batting_Average,
"atBats" = At_Bats));
Elements that contain a number of nested sub-elements begin with a
Start_Element call and are terminated with an End_Element invocation.
Attribute/value pairs can be specified in the Start_Element call,
which is then followed by calls to Output_Tag, more
Start_Element/End_Element calls, and an Output_Content for any data
that makes up the textual body of the element.
The only functions that you really need to know to use XML EZ_Out are:
Output_XML_Header
Output_Processing_Instruction
Output_Element
Output_Tag
Start_Element
End_Element
Output_Content
The "use" of the instantiated package will take of the rest.
For an example set of intantiations and usages of the file and
buffering capabilities of XML EZ_Out, see the tmeztf.adb program.
The generic specification for EZ_Out is:
generic
type Output_Medium is limited private;
with procedure Put(F : in Output_Medium;
S : in String) is <>;
with procedure New_Line (F : in Output_Medium;
Spacing : in Ada.Text_IO.Positive_Count := 1) is <>;
-- DEPRECATED
-- Control formatting by setting the Current_Format variable in the
-- package spec.
--
-- Specify whether the XML that is created is to have indenting and
-- line breaks.
Format : Formatting_Options := Spread_Indented;
-- DEPRECATED
-- The maximum element nesting depth of an XML document
Max_Element_Nesting : Positive := 200;
package McKae.XML.EZ_Out.Generic_Medium;
Output_Medium is whatever entity is going to received the formatted
XML output. As mentioned previously, it can be a file, a stream, a
buffer, a socket, whatever. All interaction with it takes place
solely through the supplied Put and New_Line procedures, which are
obviously modeled after the Ada.Text_IO versions.
The Format parameter is now deprecated. Its functionality is now
provided by the Current_Format variable in the package specification.
The value for the generic Format parameter is now simply used as the
inital setting for Current_Format. Format may be removed in some
future release.
Format, or better yet, its replacement, Current_Format, can be set to
either Continuous_Stream or Spread_Indented. Continuous_Stream simply
produces a continuous stream of XML content, with no indentation or
line breaks. This mode reduces bandwidth and storage requirements, at
the cost of not being the easiest to read in its raw form.
Spread_Indented provides a more human-readable arrangement of the
content.
Max_Element_Nesting is used to set the size of an internal stack that
keeps track of the start and end tags of the document under
construction. Documents probably aren't going to exceed the default
200-level nesting very often, but if that happens, simply increase it.
To see the exceptions that can be raised by misusing XML EZ_Out, check
the definitions in McKae.XML.EZ_Out.
Auxiliary Packages
==================
Two auxiliary packages are provided with this distribution:
McKae.XML.EZ_Out.Text_File, and McKae.XML.EZ_Out.String_Stream.
Text_File is simply an instantiation of the core Generic_Medium
package with Ada.Text_IO.File_Type, providing a ready-to-go package
for writing XML to ordinary text files.
String_Stream uses an in-memory buffer to hold the generated XML text,
with a Get_String function for retrieving the entire generated
document as a string with one call.
Caveats
=======
Be aware that XML EZ_Out does no validation of the XML content it is
being asked to output, and it is possible to generate malformed
documents. That includes the handling of character encoding. While
XML_EZ_Out will claim the document is "UTF-8" or otherwise as set by
the application, it is up to the application to ensure that correct
content is provided in the strings that are passed to its various
subprograms. Used appropriately, though, it can provide a clear and
readable means to aid the dynamic generation of XML content by Ada
programs.
Revision History
================
Changes since 1.05:
o Fixed bug where calling Output_Content with a negative integer or
float argument would drop the leading minus sign
o Added ability to completely deallocate memory used by the
String_Stream package. [Patch provided by Xavier Grave.]
Changes since 1.04:
o Deprecated the Format generic parameter, replacing it with a
Current_Format variable in the package specification.
o Added a package variable Default_Output_Null_Attributes. If True,
attributes whose value is an empty string will be output with that
empty string as the attribute's value. If False (which is the
default), output of the attribute is omitted. [Requested by Niklas
Holsti.]
Changes since 1.03:
o Added quote and apostrophe substitution (""" and '")
within attribute values.
Changes since 1.02:
o Corrected bug in "&" for "&" substition.
Changes since 1.01:
o Added attribute specification functions ("=") for single character
values.
Changes since 1.00:
o Fixed problem with attributes being given negative numeric values.
The minus sign was being dropped.
o If an attribute value is an empty string ("") or
Null_Unbounded_String, then generation of that attribute specification
is skipped.
==================
Marc A. Criley
McKae Technologies
www.mckae.com
Last updated: 23 Sep 2006
