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XML (eXtensible Markup Language) is a data format for structured
document interchange on the Web. It is a standard defined by
The World Wide Web consortium (W3C). Information about XML and
related technologies can be found at http://www.w3.org/XML/.
This extension uses expat, which can
be found at http://www.jclark.com/xml/. The
Makefile that comes with expat does not build a library by
default, you can use this make rule for that:
Note that if you are using Apache-1.3.7 or later, you already
have the required expat library. Simply configure PHP using
--with-xml (without any
additional path) and it will automatically use the expat library
built into Apache.
On UNIX, run configure with the --with-xml option. The
expat library should be installed
somewhere your compiler can find it. If you compile PHP as a
module for Apache 1.3.9 or later, PHP will automatically use the
bundled expat library from Apache.
You may need to set CPPFLAGS and
LDFLAGS in your environment before running
configure if you have installed expat somewhere exotic.
This PHP extension implements support for James Clark's
expat in PHP. This toolkit lets you
parse, but not validate, XML documents. It supports three
source character encodings
also provided by PHP: US-ASCII,
ISO-8859-1 and UTF-8.
UTF-16 is not supported.
This extension lets you create XML parsers
and then define handlers for different XML
events. Each XML parser also has a few parameters you
can adjust.
Character data is roughly all the non-markup contents of
XML documents, including whitespace between tags. Note
that the XML parser does not add or remove any whitespace,
it is up to the application (you) to decide whether
whitespace is significant.
PHP programmers should be familiar with processing
instructions (PIs) already. <?php ?> is a processing
instruction, where php is called
the "PI target". The handling of these are
application-specific, except that all PI targets starting
with "XML" are reserved.
This handler is called when the XML parser finds a
reference to an external parsed general entity. This can
be a reference to a file or URL, for example. See the external entity
example for a demonstration.
The element handler functions may get their element names
case-folded. Case-folding is defined by
the XML standard as "a process applied to a sequence of
characters, in which those identified as non-uppercase are
replaced by their uppercase equivalents". In other words, when
it comes to XML, case-folding simply means uppercasing.
By default, all the element names that are passed to the handler
functions are case-folded. This behaviour can be queried and
controlled per XML parser with the
xml_parser_get_option() and
xml_parser_set_option() functions,
respectively.
PHP's XML extension supports the Unicode character set through
different character encodings. There are
two types of character encodings, source
encoding and target encoding.
PHP's internal representation of the document is always encoded
with UTF-8.
Source encoding is done when an XML document is parsed. Upon creating an XML
parser, a source encoding can be specified (this encoding
can not be changed later in the XML parser's lifetime). The
supported source encodings are ISO-8859-1,
US-ASCII and UTF-8. The
former two are single-byte encodings, which means that each
character is represented by a single byte.
UTF-8 can encode characters composed by a
variable number of bits (up to 21) in one to four bytes. The
default source encoding used by PHP is
ISO-8859-1.
Target encoding is done when PHP passes data to XML handler
functions. When an XML parser is created, the target encoding
is set to the same as the source encoding, but this may be
changed at any point. The target encoding will affect character
data as well as tag names and processing instruction targets.
If the XML parser encounters characters outside the range that
its source encoding is capable of representing, it will return
an error.
If PHP encounters characters in the parsed XML document that can
not be represented in the chosen target encoding, the problem
characters will be "demoted". Currently, this means that such
characters are replaced by a question mark.
This example maps tags in an XML document directly to HTML
tags. Elements not found in the "map array" are ignored. Of
course, this example will only work with a specific XML
document type.
$file = "data.xml";
$map_array = array(
"BOLD" => "B",
"EMPHASIS" => "I",
"LITERAL" => "TT"
);
function startElement($parser, $name, $attrs) {
global $map_array;
if ($htmltag = $map_array[$name]) {
print "<$htmltag>";
}
}
function endElement($parser, $name) {
global $map_array;
if ($htmltag = $map_array[$name]) {
print "</$htmltag>";
}
}
function characterData($parser, $data) {
print $data;
}
$xml_parser = xml_parser_create();
// use case-folding so we are sure to find the tag in $map_array
xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, true);
xml_set_element_handler($xml_parser, "startElement", "endElement");
xml_set_character_data_handler($xml_parser, "characterData");
if (!($fp = fopen($file, "r"))) {
die("could not open XML input");
}
while ($data = fread($fp, 4096)) {
if (!xml_parse($xml_parser, $data, feof($fp))) {
die(sprintf("XML error: %s at line %d",
xml_error_string(xml_get_error_code($xml_parser)),
xml_get_current_line_number($xml_parser)));
}
}
xml_parser_free($xml_parser);
This example highlights XML code. It illustrates how to use an
external entity reference handler to include and parse other
documents, as well as how PIs can be processed, and a way of
determining "trust" for PIs containing code.
XML documents that can be used for this example are found below
the example (xmltest.xml and
xmltest2.xml.)
Example 3. External Entity Example
$file = "xmltest.xml";
function trustedFile($file) {
// only trust local files owned by ourselves
if (!eregi("^([a-z]+)://", $file)
&& fileowner($file) == getmyuid()) {
return true;
}
return false;
}
function startElement($parser, $name, $attribs) {
print "<<font color=\"#0000cc\">$name</font>";
if (sizeof($attribs)) {
while (list($k, $v) = each($attribs)) {
print " <font color=\"#009900\">$k</font>=\"<font
color=\"#990000\">$v</font>\"";
}
}
print ">";
}
function endElement($parser, $name) {
print "</<font color=\"#0000cc\">$name</font>>";
}
function characterData($parser, $data) {
print "<b>$data</b>";
}
function PIHandler($parser, $target, $data) {
switch (strtolower($target)) {
case "php":
global $parser_file;
// If the parsed document is "trusted", we say it is safe
// to execute PHP code inside it. If not, display the code
// instead.
if (trustedFile($parser_file[$parser])) {
eval($data);
} else {
printf("Untrusted PHP code: <i>%s</i>",
htmlspecialchars($data));
}
break;
}
}
function defaultHandler($parser, $data) {
if (substr($data, 0, 1) == "&" && substr($data, -1, 1) == ";") {
printf('<font color="#aa00aa">%s</font>',
htmlspecialchars($data));
} else {
printf('<font size="-1">%s</font>',
htmlspecialchars($data));
}
}
function externalEntityRefHandler($parser, $openEntityNames, $base, $systemId,
$publicId) {
if ($systemId) {
if (!list($parser, $fp) = new_xml_parser($systemId)) {
printf("Could not open entity %s at %s\n", $openEntityNames,
$systemId);
return false;
}
while ($data = fread($fp, 4096)) {
if (!xml_parse($parser, $data, feof($fp))) {
printf("XML error: %s at line %d while parsing entity %s\n",
xml_error_string(xml_get_error_code($parser)),
xml_get_current_line_number($parser), $openEntityNames);
xml_parser_free($parser);
return false;
}
}
xml_parser_free($parser);
return true;
}
return false;
}
function new_xml_parser($file) {
global $parser_file;
$xml_parser = xml_parser_create();
xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, 1);
xml_set_element_handler($xml_parser, "startElement", "endElement");
xml_set_character_data_handler($xml_parser, "characterData");
xml_set_processing_instruction_handler($xml_parser, "PIHandler");
xml_set_default_handler($xml_parser, "defaultHandler");
xml_set_external_entity_ref_handler($xml_parser, "externalEntityRefHandler");
if (!($fp = @fopen($file, "r"))) {
return false;
}
if (!is_array($parser_file)) {
settype($parser_file, "array");
}
$parser_file[$xml_parser] = $file;
return array($xml_parser, $fp);
}
if (!(list($xml_parser, $fp) = new_xml_parser($file))) {
die("could not open XML input");
}
print "<pre>";
while ($data = fread($fp, 4096)) {
if (!xml_parse($xml_parser, $data, feof($fp))) {
die(sprintf("XML error: %s at line %d\n",
xml_error_string(xml_get_error_code($xml_parser)),
xml_get_current_line_number($xml_parser)));
}
}
print "</pre>";
print "parse complete\n";
xml_parser_free($xml_parser);
?>
Example 4. xmltest.xml
<?xml version='1.0'?>
<!DOCTYPE chapter SYSTEM "/just/a/test.dtd" [
<!ENTITY plainEntity "FOO entity">
<!ENTITY systemEntity SYSTEM "xmltest2.xml">
]>
<chapter>
<TITLE>Title &plainEntity;</TITLE>
<para>
<informaltable>
<tgroup cols="3">
<tbody>
<row><entry>a1</entry><entry morerows="1">b1</entry><entry>c1</entry></row>
<row><entry>a2</entry><entry>c2</entry></row>
<row><entry>a3</entry><entry>b3</entry><entry>c3</entry></row>
</tbody>
</tgroup>
</informaltable>
</para>
&systemEntity;
<sect1 id="about">
<title>About this Document</title>
<para>
<!-- this is a comment -->
<?php print 'Hi! This is PHP version '.phpversion(); ?>
</para>
</sect1>
</chapter>
This file is included from xmltest.xml:
Example 5. xmltest2.xml
<?xml version="1.0"?>
<!DOCTYPE foo [
<!ENTITY testEnt "test entity">
]>
<foo>
<element attrib="value"/>
&testEnt;
<?php print "This is some more PHP code being executed."; ?>
</foo>
