source: vbox/trunk/src/libs/libxml2-2.9.14/os400/README400@ 103850

Implementation notes:

  This is a true OS/400 implementation, not a PASE implementation (for PASE,
use an AIX implementation).

  The biggest problem with OS/400 is EBCDIC. The current libxml2 implementation
uses UTF-8 internally. To ease encoding conversion between the calling
applications and libxml2, supplementary "convert and latch" functions are
provided (See below). To bind the EBCDIC OS/400 system calls and libxml2,
an ASCII run-time environment (QADRT) has been used and wrapper functions have
been designed.

Other problems are:
- Source code line length: to be stored in DB2 members, source files may not
  have lines longer than 100 characters. Some header and documentation files
  have been modified accordingly.
- va_list dereferencing: the OS/400 implementation of va_list type is an array
  but the compiler forbids explicit array dereferencing. Source files have
  been updated accordingly.
- Depending on the compilation/execution environment, it is possible that
  stdin/stdout/stderr are not associated with a file descriptor; as a side
  effect, open() may return a file descriptor value 0, 1 or 2 that is NOT
  a C standard file. Thus using such a number may be inaccurate.
- iconv_open() arguments: OS/400 uses non-standard encoding names and does not
  support standard names. For this reason, a name wrapper has been designed.
- dlopen() (support for xmodule): the function and its corollaries are not
  provided by the OS/400 library. However a local implementation is provided.


Compiling on OS/400:

_ As a prerequisite, QADRT development environment must be installed.
_ Install the libxml2 source directory in IFS.
_ Enter shell (QSH)
_ Change current directory to the libxml2 installation directory
_ Change current directory to ./os400
_ Edit file iniscript.sh. You may want to change tunable configuration
  parameters, like debug info generation, optimisation level, listing option,
  target library, zlib availability, etc.
_ Copy any file in the current directory to makelog (i.e.:
  cp initscript.sh makelog): this is intended to create the makelog file with
  an ASCII CCSID!
_ Enter the command "sh make.sh >makelog 2>&1'
_ Examine the makelog file to check for compilation errors.

  Leaving file initscript.sh unchanged, this will produce the following
OS/400 objects:
_ Library LIBXML2. All other objects will be stored in this library.
_ Modules for all libxml2 units, with full debug info and no code optimization.
_ Binding directory LIBXML2_A, to be used at calling program link time for
  statically binding the modules (specify BNDSRVPGM(QADRTTS QGLDCLNT QGLDBRDR)
  when creating a program using LIBXML2_A).
_ Service program LIBXML2. To be used at calling program run-time
  when this program has dynamically bound libxml2 at link time.
_ Binding directory LIBXML2. To be used to dynamically bind libxml2 when
  linking a calling program.
_ Source file LIBXML. It contains all the header members needed to compile a
  C/C++ module using libxml2.
_ Standard and additional C/C++ libxml2 header members (possibly renamed) in
  file LIBXML.
_ IFS directory /libxml2 with subdirectory include/libxml containing all
  C/C++ header files for IFS-based compilation.
_ Source file LIBXMLRPG. It contains all the include members needed to compile a
  ILE/RPG module/program using libxml2 (ILE/RPG binding).
_ ILE/RPG binding include members (possibly renamed) in file LIBXMLRPG.
_ IFS subdirectory /libxml2/include/libxmlrpg containing all ILE/RPG include
  files for IFS-based compilation.


Renamed header files in DB2 members:
  DB2 member names are limited to 10 characters, thus the following C/C++
header members are renamed as:
  parserInternals.h     -->     PARSERINTE
  schemasInternals.h    -->     SCHEMASINT
  xmlautomata.h         -->     XMLAUTOMAT
  xmlschemastype.h      -->     SCHMTYPES
  xpathInternals.h      -->     XPATHINTER
IFS header files are NOT renamed.
ILE/RPG headers are processed likewise.


Special programming consideration:

QADRT being used, the following points must be considered:
_ If static binding is used, service program QADRTTS must be linked too.
_ The EBCDIC CCSID used by QADRT is 37 by default, NOT THE JOB'S CCSID. If
  another EBCDIC CCSID is required, it must be set via a locale through a call
  to setlocale_a (QADRT's setlocale() ASCII wrapper) with category LC_ALL or
  LC_CTYPE, or by setting environment variable QADRT_ENV_LOCALE to the locale
  object path before executing the program.
_ Always use *IFSIO or *IFS64IO to compile calling programs.



Supplementary (non libxml2 standard) support procedures for OS/400.

  As cited above, there are some procedures to ease encoding conversion of
libxml2 function arguments and results: the mechanism is based on
dictionaries. The functions convert a string, latch the result in a dictionary
to ensure its persistence and return its address. It is the caller's
responsibility to clean the dictionary when it becomes too big or disappears.

The procedures are:

#include <libxml/transcode.h>

const char *  xmlTranscodeResult(const xmlChar * s,
                                 const char * encoding,
                                 xmlDictPtr * dict,
                                 void (*freeproc)(const void *));

const xmlChar * xmlTranscodeString(const char * s,
                                   const char * encoding,
                                   xmlDictPtr * dict);

const xmlChar * xmlTranscodeWString(const char * s,
                                    const char * encoding,
                                    xmlDictPtr * dict);

const xmlChar * xmlTranscodeWString(const char * s,
                                    const char * encoding,
                                    xmlDictPtr * dict);

where:
s               is the string to translate.
encoding        is the alternate character encoding. If null, the current job's
                encoding (CCSID) is used.
dict            is the address of the latching directory. If NULL, the procedure
                functions as a simple non-latching encoding converter and
                its result value should be freed by the caller.
freeproc        is a procedure to release the original string, or NULL.

xmlTranscodeResult()  converts from UTF-8 to the given alternate encoding.
xmlTranscodeString()  converts from the given 8-bit encoding to UTF-8 (note that
                      UTF-8 itself is considered as a 8-bit encoding).
xmlTranscodeWString() converts from the given 16-bit encoding to UTF-8.
xmlTranscodeHString() converts from the given 32-bit encoding to UTF-8.


To shorten statements using these functions, shorthands are defined:

xmlTR for xmlTranscodeResult
xmlTS for xmlTranscodeString
xmlTW for xmlTranscodeWString
xmlTH for xmlTranscodeHstring

These shorthands may be disabled by defining XML_NO_SHORT_NAMES before
libxml/transcode.h inclusion.

A directory pointer must be preset to NULL before the first call using it to
one of the above procedure.

To release a latching directory, use function

void          xmlZapDict(xmlDictPtr * dict);


Example:

#include <libxml/transcode.h>
#include <libxml/tree.h>

xmlDocPtr mySimpleXMLDoc(char * element, char * text)
{
        xmlDocPtr doc;
        xmlNodePtr node;
        xmlDictPtr dict = NULL;

        /* element and text are encoded in the current job's encoding. */

        doc = xmlNewDoc();
        xmlNewTextChild((xmlNodePtr) doc, NULL, xmlTS(element, NULL,
                               &dict), xmlTS(text, NULL, &dict));
        xmlZapDict(&dict);
        return doc;
}


Additionally, a formatter into latched/dynamic storage is provided:

const char *    xmlVasprintf(xmlDictPtr * dict,
                             const char * encoding,
                             const xmlChar * fmt,
                             va_list args);


xmllint and xmlcatalog programs:

  These programs are fully implemented at the qshell level, with standard
command line options. Links to these are installed in sub-directory bin of
the IFS installation directory.
  CL command interfaces to these programs are also provided with limited
support. In particular, interactive mode is not supported and argument count
and lengths are limited by the CL command syntax.


ILE/RPG binding:

  All standard types and procedures are provided. Since ILE/RPG does not
support macros, they have not been ported. However some of them are emulated
as functions: these are the more useful ones (xmlXPathNodeSetGetLength,
xmlXPathNodeSetItem, xmlXPathNodeSetIsEmpty, htmlDefaultSubelement,
htmlElementAllowedHereDesc, htmlRequiredAttrs) and the global/threaded
variables access macros. These variables can be read with function
get_xxx(void), where xxxx is the name of the variable; they may be set by
calling function set_xxxx(value), where value is of the same type as the
variable.

  The C va_list is not implemented as such in ILE/RPG. Functions implementing
va_list and associated methods are provided:

      /include "libxmlrpg/xmlstdarg"

     d xmlVaStart      pr
     d  list                               like(xmlVaList)
     d  lastargaddr                    *   value
     d  lastargsize                  10u 0 value

     d xmlVaArg        pr
     d  list                               like(xmlVaList)
     d  dest                           *   value
     d  argsize                      10i 0 value

     d xmlVaEnd        pr
     d  list                               like(xmlVaList)