node-expat-papandreou

<?xml version="1.0" encoding="iso-8859-1"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head>  <title>Expat XML Parser</title> <meta name="author" content="Clark Cooper, coopercc@netheaven.com" /> <meta http-equiv="Content-Style-Type" content="text/css" /> <link href="style.css" rel="stylesheet" type="text/css" /> </head> <body> <table cellspacing="0" cellpadding="0" width="100%"> <tr> <td class="corner"><img src="expat.png" alt="(Expat logo)" /></td> <td class="banner"><h1>The Expat XML Parser</h1></td> </tr> <tr> <td class="releaseno">Release 2.0.1</td> <td></td> </tr> </table> <div class="content"> <p>Expat is a library, written in C, for parsing XML documents. It's the underlying XML parser for the open source Mozilla project, Perl's <code>XML::Parser</code>, Python's <code>xml.parsers.expat</code>, and other open-source XML parsers.</p> <p>This library is the creation of James Clark, who's also given us groff (an nroff look-alike), Jade (an implemention of ISO's DSSSL stylesheet language for SGML), XP (a Java XML parser package), XT (a Java XSL engine). James was also the technical lead on the XML Working Group at W3C that produced the XML specification.</p> <p>This is free software, licensed under the <a href="../COPYING">MIT/X Consortium license</a>. You may download it from <a href="http://www.libexpat.org/">the Expat home page</a>. </p> <p>The bulk of this document was originally commissioned as an article by <a href="http://www.xml.com/">XML.com</a>. They graciously allowed Clark Cooper to retain copyright and to distribute it with Expat. This version has been substantially extended to include documentation on features which have been added since the original article was published, and additional information on using the original interface.</p> <hr /> <h2>Table of Contents</h2> <ul> <li><a href="#overview">Overview</a></li> <li><a href="#building">Building and Installing</a></li> <li><a href="#using">Using Expat</a></li> <li><a href="#reference">Reference</a> <ul> <li><a href="#creation">Parser Creation Functions</a> <ul> <li><a href="#XML_ParserCreate">XML_ParserCreate</a></li> <li><a href="#XML_ParserCreateNS">XML_ParserCreateNS</a></li> <li><a href="#XML_ParserCreate_MM">XML_ParserCreate_MM</a></li> <li><a href="#XML_ExternalEntityParserCreate">XML_ExternalEntityParserCreate</a></li> <li><a href="#XML_ParserFree">XML_ParserFree</a></li> <li><a href="#XML_ParserReset">XML_ParserReset</a></li> </ul> </li> <li><a href="#parsing">Parsing Functions</a> <ul> <li><a href="#XML_Parse">XML_Parse</a></li> <li><a href="#XML_ParseBuffer">XML_ParseBuffer</a></li> <li><a href="#XML_GetBuffer">XML_GetBuffer</a></li> <li><a href="#XML_StopParser">XML_StopParser</a></li> <li><a href="#XML_ResumeParser">XML_ResumeParser</a></li> <li><a href="#XML_GetParsingStatus">XML_GetParsingStatus</a></li> </ul> </li> <li><a href="#setting">Handler Setting Functions</a> <ul> <li><a href="#XML_SetStartElementHandler">XML_SetStartElementHandler</a></li> <li><a href="#XML_SetEndElementHandler">XML_SetEndElementHandler</a></li> <li><a href="#XML_SetElementHandler">XML_SetElementHandler</a></li> <li><a href="#XML_SetCharacterDataHandler">XML_SetCharacterDataHandler</a></li> <li><a href="#XML_SetProcessingInstructionHandler">XML_SetProcessingInstructionHandler</a></li> <li><a href="#XML_SetCommentHandler">XML_SetCommentHandler</a></li> <li><a href="#XML_SetStartCdataSectionHandler">XML_SetStartCdataSectionHandler</a></li> <li><a href="#XML_SetEndCdataSectionHandler">XML_SetEndCdataSectionHandler</a></li> <li><a href="#XML_SetCdataSectionHandler">XML_SetCdataSectionHandler</a></li> <li><a href="#XML_SetDefaultHandler">XML_SetDefaultHandler</a></li> <li><a href="#XML_SetDefaultHandlerExpand">XML_SetDefaultHandlerExpand</a></li> <li><a href="#XML_SetExternalEntityRefHandler">XML_SetExternalEntityRefHandler</a></li> <li><a href="#XML_SetExternalEntityRefHandlerArg">XML_SetExternalEntityRefHandlerArg</a></li> <li><a href="#XML_SetSkippedEntityHandler">XML_SetSkippedEntityHandler</a></li> <li><a href="#XML_SetUnknownEncodingHandler">XML_SetUnknownEncodingHandler</a></li> <li><a href="#XML_SetStartNamespaceDeclHandler">XML_SetStartNamespaceDeclHandler</a></li> <li><a href="#XML_SetEndNamespaceDeclHandler">XML_SetEndNamespaceDeclHandler</a></li> <li><a href="#XML_SetNamespaceDeclHandler">XML_SetNamespaceDeclHandler</a></li> <li><a href="#XML_SetXmlDeclHandler">XML_SetXmlDeclHandler</a></li> <li><a href="#XML_SetStartDoctypeDeclHandler">XML_SetStartDoctypeDeclHandler</a></li> <li><a href="#XML_SetEndDoctypeDeclHandler">XML_SetEndDoctypeDeclHandler</a></li> <li><a href="#XML_SetDoctypeDeclHandler">XML_SetDoctypeDeclHandler</a></li> <li><a href="#XML_SetElementDeclHandler">XML_SetElementDeclHandler</a></li> <li><a href="#XML_SetAttlistDeclHandler">XML_SetAttlistDeclHandler</a></li> <li><a href="#XML_SetEntityDeclHandler">XML_SetEntityDeclHandler</a></li> <li><a href="#XML_SetUnparsedEntityDeclHandler">XML_SetUnparsedEntityDeclHandler</a></li> <li><a href="#XML_SetNotationDeclHandler">XML_SetNotationDeclHandler</a></li> <li><a href="#XML_SetNotStandaloneHandler">XML_SetNotStandaloneHandler</a></li> </ul> </li> <li><a href="#position">Parse Position and Error Reporting Functions</a> <ul> <li><a href="#XML_GetErrorCode">XML_GetErrorCode</a></li> <li><a href="#XML_ErrorString">XML_ErrorString</a></li> <li><a href="#XML_GetCurrentByteIndex">XML_GetCurrentByteIndex</a></li> <li><a href="#XML_GetCurrentLineNumber">XML_GetCurrentLineNumber</a></li> <li><a href="#XML_GetCurrentColumnNumber">XML_GetCurrentColumnNumber</a></li> <li><a href="#XML_GetCurrentByteCount">XML_GetCurrentByteCount</a></li> <li><a href="#XML_GetInputContext">XML_GetInputContext</a></li> </ul> </li> <li><a href="#miscellaneous">Miscellaneous Functions</a> <ul> <li><a href="#XML_SetUserData">XML_SetUserData</a></li> <li><a href="#XML_GetUserData">XML_GetUserData</a></li> <li><a href="#XML_UseParserAsHandlerArg">XML_UseParserAsHandlerArg</a></li> <li><a href="#XML_SetBase">XML_SetBase</a></li> <li><a href="#XML_GetBase">XML_GetBase</a></li> <li><a href="#XML_GetSpecifiedAttributeCount">XML_GetSpecifiedAttributeCount</a></li> <li><a href="#XML_GetIdAttributeIndex">XML_GetIdAttributeIndex</a></li> <li><a href="#XML_GetAttributeInfo">XML_GetAttributeInfo</a></li> <li><a href="#XML_SetEncoding">XML_SetEncoding</a></li> <li><a href="#XML_SetParamEntityParsing">XML_SetParamEntityParsing</a></li> <li><a href="#XML_SetHashSalt">XML_SetHashSalt</a></li> <li><a href="#XML_UseForeignDTD">XML_UseForeignDTD</a></li> <li><a href="#XML_SetReturnNSTriplet">XML_SetReturnNSTriplet</a></li> <li><a href="#XML_DefaultCurrent">XML_DefaultCurrent</a></li> <li><a href="#XML_ExpatVersion">XML_ExpatVersion</a></li> <li><a href="#XML_ExpatVersionInfo">XML_ExpatVersionInfo</a></li> <li><a href="#XML_GetFeatureList">XML_GetFeatureList</a></li> <li><a href="#XML_FreeContentModel">XML_FreeContentModel</a></li> <li><a href="#XML_MemMalloc">XML_MemMalloc</a></li> <li><a href="#XML_MemRealloc">XML_MemRealloc</a></li> <li><a href="#XML_MemFree">XML_MemFree</a></li> </ul> </li> </ul> </li> </ul> <hr /> <h2><a name="overview">Overview</a></h2> <p>Expat is a stream-oriented parser. You register callback (or handler) functions with the parser and then start feeding it the document. As the parser recognizes parts of the document, it will call the appropriate handler for that part (if you've registered one.) The document is fed to the parser in pieces, so you can start parsing before you have all the document. This also allows you to parse really huge documents that won't fit into memory.</p> <p>Expat can be intimidating due to the many kinds of handlers and options you can set. But you only need to learn four functions in order to do 90% of what you'll want to do with it:</p> <dl> <dt><code><a href= "#XML_ParserCreate" >XML_ParserCreate</a></code></dt> <dd>Create a new parser object.</dd> <dt><code><a href= "#XML_SetElementHandler" >XML_SetElementHandler</a></code></dt> <dd>Set handlers for start and end tags.</dd> <dt><code><a href= "#XML_SetCharacterDataHandler" >XML_SetCharacterDataHandler</a></code></dt> <dd>Set handler for text.</dd> <dt><code><a href= "#XML_Parse" >XML_Parse</a></code></dt> <dd>Pass a buffer full of document to the parser</dd> </dl> <p>These functions and others are described in the <a href="#reference">reference</a> part of this document. The reference section also describes in detail the parameters passed to the different types of handlers.</p> <p>Let's look at a very simple example program that only uses 3 of the above functions (it doesn't need to set a character handler.) The program <a href="../examples/outline.c">outline.c</a> prints an element outline, indenting child elements to distinguish them from the parent element that contains them. The start handler does all the work. It prints two indenting spaces for every level of ancestor elements, then it prints the element and attribute information. Finally it increments the global <code>Depth</code> variable.</p> <pre class="eg"> int Depth; void XMLCALL start(void *data, const char *el, const char **attr) { int i; for (i = 0; i < Depth; i++) printf(" "); printf("%s", el); for (i = 0; attr[i]; i += 2) { printf(" %s='%s'", attr[i], attr[i + 1]); } printf("\n"); Depth++; } /* End of start handler */ </pre> <p>The end tag simply does the bookkeeping work of decrementing <code>Depth</code>.</p> <pre class="eg"> void XMLCALL end(void *data, const char *el) { Depth--; } /* End of end handler */ </pre> <p>Note the <code>XMLCALL</code> annotation used for the callbacks. This is used to ensure that the Expat and the callbacks are using the same calling convention in case the compiler options used for Expat itself and the client code are different. Expat tries not to care what the default calling convention is, though it may require that it be compiled with a default convention of "cdecl" on some platforms. For code which uses Expat, however, the calling convention is specified by the <code>XMLCALL</code> annotation on most platforms; callbacks should be defined using this annotation.</p> <p>The <code>XMLCALL</code> annotation was added in Expat 1.95.7, but existing working Expat applications don't need to add it (since they are already using the "cdecl" calling convention, or they wouldn't be working). The annotation is only needed if the default calling convention may be something other than "cdecl". To use the annotation safely with older versions of Expat, you can conditionally define it <em>after</em> including Expat's header file:</p> <pre class="eg"> #include <expat.h> #ifndef XMLCALL #if defined(_MSC_EXTENSIONS) && !defined(__BEOS__) && !defined(__CYGWIN__) #define XMLCALL __cdecl #elif defined(__GNUC__) #define XMLCALL __attribute__((cdecl)) #else #define XMLCALL #endif #endif </pre> <p>After creating the parser, the main program just has the job of shoveling the document to the parser so that it can do its work.</p> <hr /> <h2><a name="building">Building and Installing Expat</a></h2> <p>The Expat distribution comes as a compressed (with GNU gzip) tar file. You may download the latest version from <a href= "http://sourceforge.net/projects/expat/" >Source Forge</a>. After unpacking this, cd into the directory. Then follow either the Win32 directions or Unix directions below.</p> <h3>Building under Win32</h3> <p>If you're using the GNU compiler under cygwin, follow the Unix directions in the next section. Otherwise if you have Microsoft's Developer Studio installed, then from Windows Explorer double-click on "expat.dsp" in the lib directory and build and install in the usual manner.</p> <p>Alternatively, you may download the Win32 binary package that contains the "expat.h" include file and a pre-built DLL.</p> <h3>Building under Unix (or GNU)</h3> <p>First you'll need to run the configure shell script in order to configure the Makefiles and headers for your system.</p> <p>If you're happy with all the defaults that configure picks for you, and you have permission on your system to install into /usr/local, you can install Expat with this sequence of commands:</p> <pre class="eg"> ./configure make make install </pre> <p>There are some options that you can provide to this script, but the only one we'll mention here is the <code>--prefix</code> option. You can find out all the options available by running configure with just the <code>--help</code> option.</p> <p>By default, the configure script sets things up so that the library gets installed in <code>/usr/local/lib</code> and the associated header file in <code>/usr/local/include</code>. But if you were to give the option, <code>--prefix=/home/me/mystuff</code>, then the library and header would get installed in <code>/home/me/mystuff/lib</code> and <code>/home/me/mystuff/include</code> respectively.</p> <h3>Configuring Expat Using the Pre-Processor</h3> <p>Expat's feature set can be configured using a small number of pre-processor definitions. The definition of this symbols does not affect the set of entry points for Expat, only the behavior of the API and the definition of character types in the case of <code>XML_UNICODE_WCHAR_T</code>. The symbols are:</p> <dl class="cpp-symbols"> <dt>XML_DTD</dt> <dd>Include support for using and reporting DTD-based content. If this is defined, default attribute values from an external DTD subset are reported and attribute value normalization occurs based on the type of attributes defined in the external subset. Without this, Expat has a smaller memory footprint and can be faster, but will not load external entities or process conditional sections. This does not affect the set of functions available in the API.</dd> <dt>XML_NS</dt> <dd>When defined, support for the <cite><a href= "http://www.w3.org/TR/REC-xml-names/" >Namespaces in XML</a></cite> specification is included.</dd> <dt>XML_UNICODE</dt> <dd>When defined, character data reported to the application is encoded in UTF-16 using wide characters of the type <code>XML_Char</code>. This is implied if <code>XML_UNICODE_WCHAR_T</code> is defined.</dd> <dt>XML_UNICODE_WCHAR_T</dt> <dd>If defined, causes the <code>XML_Char</code> character type to be defined using the <code>wchar_t</code> type; otherwise, <code>unsigned short</code> is used. Defining this implies <code>XML_UNICODE</code>.</dd> <dt>XML_LARGE_SIZE</dt> <dd>If defined, causes the <code>XML_Size</code> and <code>XML_Index</code> integer types to be at least 64 bits in size. This is intended to support processing of very large input streams, where the return values of <code><a href="#XML_GetCurrentByteIndex" >XML_GetCurrentByteIndex</a></code>, <code><a href="#XML_GetCurrentLineNumber" >XML_GetCurrentLineNumber</a></code> and <code><a href="#XML_GetCurrentColumnNumber" >XML_GetCurrentColumnNumber</a></code> could overflow. It may not be supported by all compilers, and is turned off by default.</dd> <dt>XML_CONTEXT_BYTES</dt> <dd>The number of input bytes of markup context which the parser will ensure are available for reporting via <code><a href= "#XML_GetInputContext" >XML_GetInputContext</a></code>. This is normally set to 1024, and must be set to a positive interger. If this is not defined, the input context will not be available and <code><a href= "#XML_GetInputContext" >XML_GetInputContext</a></code> will always report NULL. Without this, Expat has a smaller memory footprint and can be faster.</dd> <dt>XML_STATIC</dt> <dd>On Windows, this should be set if Expat is going to be linked statically with the code that calls it; this is required to get all the right MSVC magic annotations correct. This is ignored on other platforms.</dd> <dt>XML_ATTR_INFO</dt> <dd>If defined, makes the the additional function <code><a href= "#XML_GetAttributeInfo" >XML_GetAttributeInfo</a></code> available for reporting attribute byte offsets.</dd> </dl> <hr /> <h2><a name="using">Using Expat</a></h2> <h3>Compiling and Linking Against Expat</h3> <p>Unless you installed Expat in a location not expected by your compiler and linker, all you have to do to use Expat in your programs is to include the Expat header (<code>#include <expat.h></code>) in your files that make calls to it and to tell the linker that it needs to link against the Expat library. On Unix systems, this would usually be done with the <code>-lexpat</code> argument. Otherwise, you'll need to tell the compiler where to look for the Expat header and the linker where to find the Expat library. You may also need to take steps to tell the operating system where to find this library at run time.</p> <p>On a Unix-based system, here's what a Makefile might look like when Expat is installed in a standard location:</p> <pre class="eg"> CC=cc LDFLAGS= LIBS= -lexpat xmlapp: xmlapp.o $(CC) $(LDFLAGS) -o xmlapp xmlapp.o $(LIBS) </pre> <p>If you installed Expat in, say, <code>/home/me/mystuff</code>, then the Makefile would look like this:</p> <pre class="eg"> CC=cc CFLAGS= -I/home/me/mystuff/include LDFLAGS= LIBS= -L/home/me/mystuff/lib -lexpat xmlapp: xmlapp.o $(CC) $(LDFLAGS) -o xmlapp xmlapp.o $(LIBS) </pre> <p>You'd also have to set the environment variable <code>LD_LIBRARY_PATH</code> to <code>/home/me/mystuff/lib</code> (or to <code>${LD_LIBRARY_PATH}:/home/me/mystuff/lib</code> if LD_LIBRARY_PATH already has some directories in it) in order to run your application.</p> <h3>Expat Basics</h3> <p>As we saw in the example in the overview, the first step in parsing an XML document with Expat is to create a parser object. There are <a href="#creation">three functions</a> in the Expat API for creating a parser object. However, only two of these (<code><a href= "#XML_ParserCreate" >XML_ParserCreate</a></code> and <code><a href= "#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>) can be used for constructing a parser for a top-level document. The object returned by these functions is an opaque pointer (i.e. "expat.h" declares it as void *) to data with further internal structure. In order to free the memory associated with this object you must call <code><a href= "#XML_ParserFree" >XML_ParserFree</a></code>. Note that if you have provided any <a href="#userdata">user data</a> that gets stored in the parser, then your application is responsible for freeing it prior to calling <code>XML_ParserFree</code>.</p> <p>The objects returned by the parser creation functions are good for parsing only one XML document or external parsed entity. If your application needs to parse many XML documents, then it needs to create a parser object for each one. The best way to deal with this is to create a higher level object that contains all the default initialization you want for your parser objects.</p> <p>Walking through a document hierarchy with a stream oriented parser will require a good stack mechanism in order to keep track of current context. For instance, to answer the simple question, "What element does this text belong to?" requires a stack, since the parser may have descended into other elements that are children of the current one and has encountered this text on the way out.</p> <p>The things you're likely to want to keep on a stack are the currently opened element and it's attributes. You push this information onto the stack in the start handler and you pop it off in the end handler.</p> <p>For some tasks, it is sufficient to just keep information on what the depth of the stack is (or would be if you had one.) The outline program shown above presents one example. Another such task would be skipping over a complete element. When you see the start tag for the element you want to skip, you set a skip flag and record the depth at which the element started. When the end tag handler encounters the same depth, the skipped element has ended and the flag may be cleared. If you follow the convention that the root element starts at 1, then you can use the same variable for skip flag and skip depth.</p> <pre class="eg"> void init_info(Parseinfo *info) { info->skip = 0; info->depth = 1; /* Other initializations here */ } /* End of init_info */ void XMLCALL rawstart(void *data, const char *el, const char **attr) { Parseinfo *inf = (Parseinfo *) data; if (! inf->skip) { if (should_skip(inf, el, attr)) { inf->skip = inf->depth; } else start(inf, el, attr); /* This does rest of start handling */ } inf->depth++; } /* End of rawstart */ void XMLCALL rawend(void *data, const char *el) { Parseinfo *inf = (Parseinfo *) data; inf->depth--; if (! inf->skip) end(inf, el); /* This does rest of end handling */ if (inf->skip == inf->depth) inf->skip = 0; } /* End rawend */ </pre> <p>Notice in the above example the difference in how depth is manipulated in the start and end handlers. The end tag handler should be the mirror image of the start tag handler. This is necessary to properly model containment. Since, in the start tag handler, we incremented depth <em>after</em> the main body of start tag code, then in the end handler, we need to manipulate it <em>before</em> the main body. If we'd decided to increment it first thing in the start handler, then we'd have had to decrement it last thing in the end handler.</p> <h3 id="userdata">Communicating between handlers</h3> <p>In order to be able to pass information between different handlers without using globals, you'll need to define a data structure to hold the shared variables. You can then tell Expat (with the <code><a href= "#XML_SetUserData" >XML_SetUserData</a></code> function) to pass a pointer to this structure to the handlers. This is the first argument received by most handlers. In the <a href="#reference" >reference section</a>, an argument to a callback function is named <code>userData</code> and have type <code>void *</code> if the user data is passed; it will have the type <code>XML_Parser</code> if the parser itself is passed. When the parser is passed, the user data may be retrieved using <code><a href="#XML_GetUserData" >XML_GetUserData</a></code>.</p> <p>One common case where multiple calls to a single handler may need to communicate using an application data structure is the case when content passed to the character data handler (set by <code><a href= "#XML_SetCharacterDataHandler" >XML_SetCharacterDataHandler</a></code>) needs to be accumulated. A common first-time mistake with any of the event-oriented interfaces to an XML parser is to expect all the text contained in an element to be reported by a single call to the character data handler. Expat, like many other XML parsers, reports such data as a sequence of calls; there's no way to know when the end of the sequence is reached until a different callback is made. A buffer referenced by the user data structure proves both an effective and convenient place to accumulate character data.</p>  <h3>XML Version</h3> <p>Expat is an XML 1.0 parser, and as such never complains based on the value of the <code>version</code> pseudo-attribute in the XML declaration, if present.</p> <p>If an application needs to check the version number (to support alternate processing), it should use the <code><a href= "#XML_SetXmlDeclHandler" >XML_SetXmlDeclHandler</a></code> function to set a handler that uses the information in the XML declaration to determine what to do. This example shows how to check that only a version number of <code>"1.0"</code> is accepted:</p> <pre class="eg"> static int wrong_version; static XML_Parser parser; static void XMLCALL xmldecl_handler(void *userData, const XML_Char *version, const XML_Char *encoding, int standalone) { static const XML_Char Version_1_0[] = {'1', '.', '0', 0}; int i; for (i = 0; i < (sizeof(Version_1_0) / sizeof(Version_1_0[0])); ++i) { if (version[i] != Version_1_0[i]) { wrong_version = 1; /* also clear all other handlers: */ XML_SetCharacterDataHandler(parser, NULL); ... return; } } ... } </pre> <h3>Namespace Processing</h3> <p>When the parser is created using the <code><a href= "#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>, function, Expat performs namespace processing. Under namespace processing, Expat consumes <code>xmlns</code> and <code>xmlns:...</code> attributes, which declare namespaces for the scope of the element in which they occur. This means that your start handler will not see these attributes. Your application can still be informed of these declarations by setting namespace declaration handlers with <a href= "#XML_SetNamespaceDeclHandler" ><code>XML_SetNamespaceDeclHandler</code></a>.</p> <p>Element type and attribute names that belong to a given namespace are passed to the appropriate handler in expanded form. By default this expanded form is a concatenation of the namespace URI, the separator character (which is the 2nd argument to <code><a href= "#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>), and the local name (i.e. the part after the colon). Names with undeclared prefixes are not well-formed when namespace processing is enabled, and will trigger an error. Unprefixed attribute names are never expanded, and unprefixed element names are only expanded when they are in the scope of a default namespace.</p> <p>However if <code><a href= "#XML_SetReturnNSTriplet" >XML_SetReturnNSTriplet</a></code> has been called with a non-zero <code>do_nst</code> parameter, then the expanded form for names with an explicit prefix is a concatenation of: URI, separator, local name, separator, prefix.</p> <p>You can set handlers for the start of a namespace declaration and for the end of a scope of a declaration with the <code><a href= "#XML_SetNamespaceDeclHandler" >XML_SetNamespaceDeclHandler</a></code> function. The StartNamespaceDeclHandler is called prior to the start tag handler and the EndNamespaceDeclHandler is called after the corresponding end tag that ends the namespace's scope. The namespace start handler gets passed the prefix and URI for the namespace. For a default namespace declaration (xmlns='...'), the prefix will be null. The URI will be null for the case where the default namespace is being unset. The namespace end handler just gets the prefix for the closing scope.</p> <p>These handlers are called for each declaration. So if, for instance, a start tag had three namespace declarations, then the StartNamespaceDeclHandler would be called three times before the start tag handler is called, once for each declaration.</p> <h3>Character Encodings</h3> <p>While XML is based on Unicode, and every XML processor is required to recognized UTF-8 and UTF-16 (1 and 2 byte encodings of Unicode), other encodings may be declared in XML documents or entities. For the main document, an XML declaration may contain an encoding declaration:</p> <pre> <?xml version="1.0" encoding="ISO-8859-2"?> </pre> <p>External parsed entities may begin with a text declaration, which looks like an XML declaration with just an encoding declaration:</p> <pre> <?xml encoding="Big5"?> </pre> <p>With Expat, you may also specify an encoding at the time of creating a parser. This is useful when the encoding information may come from a source outside the document itself (like a higher level protocol.)</p> <p><a name="builtin_encodings"></a>There are four built-in encodings in Expat:</p> <ul> <li>UTF-8</li> <li>UTF-16</li> <li>ISO-8859-1</li> <li>US-ASCII</li> </ul> <p>Anything else discovered in an encoding declaration or in the protocol encoding specified in the parser constructor, triggers a call to the <code>UnknownEncodingHandler</code>. This handler gets passed the encoding name and a pointer to an <code>XML_Encoding</code> data structure. Your handler must fill in this structure and return <code>XML_STATUS_OK</code> if it knows how to deal with the encoding. Otherwise the handler should return <code>XML_STATUS_ERROR</code>. The handler also gets passed a pointer to an optional application data structure that you may indicate when you set the handler.</p> <p>Expat places restrictions on character encodings that it can support by filling in the <code>XML_Encoding</code> structure. include file:</p> <ol> <li>Every ASCII character that can appear in a well-formed XML document must be represented by a single byte, and that byte must correspond to it's ASCII encoding (except for the characters $@\^'{}~)</li> <li>Characters must be encoded in 4 bytes or less.</li> <li>All characters encoded must have Unicode scalar values less than or equal to 65535 (0xFFFF)<em>This does not apply to the built-in support for UTF-16 and UTF-8</em></li> <li>No character may be encoded by more that one distinct sequence of bytes</li> </ol> <p><code>XML_Encoding</code> contains an array of integers that correspond to the 1st byte of an encoding sequence. If the value in the array for a byte is zero or positive, then the byte is a single byte encoding that encodes the Unicode scalar value contained in the array. A -1 in this array indicates a malformed byte. If the value is -2, -3, or -4, then the byte is the beginning of a 2, 3, or 4 byte sequence respectively. Multi-byte sequences are sent to the convert function pointed at in the <code>XML_Encoding</code> structure. This function should return the Unicode scalar value for the sequence or -1 if the sequence is malformed.</p> <p>One pitfall that novice Expat users are likely to fall into is that although Expat may accept input in various encodings, the strings that it passes to the handlers are always encoded in UTF-8 or UTF-16 (depending on how Expat was compiled). Your application is responsible for any translation of these strings into other encodings.</p> <h3>Handling External Entity References</h3> <p>Expat does not read or parse external entities directly. Note that any external DTD is a special case of an external entity. If you've set no <code>ExternalEntityRefHandler</code>, then external entity references are silently ignored. Otherwise, it calls your handler with the information needed to read and parse the external entity.</p> <p>Your handler isn't actually responsible for parsing the entity, but it is responsible for creating a subsidiary parser with <code><a href= "#XML_ExternalEntityParserCreate" >XML_ExternalEntityParserCreate</a></code> that will do the job. This returns an instance of <code>XML_Parser</code> that has handlers and other data structures initialized from the parent parser. You may then use <code><a href= "#XML_Parse" >XML_Parse</a></code> or <code><a href= "#XML_ParseBuffer">XML_ParseBuffer</a></code> calls against this parser. Since external entities my refer to other external entities, your handler should be prepared to be called recursively.</p> <h3>Parsing DTDs</h3> <p>In order to parse parameter entities, before starting the parse, you must call <code><a href= "#XML_SetParamEntityParsing" >XML_SetParamEntityParsing</a></code> with one of the following arguments:</p> <dl> <dt><code>XML_PARAM_ENTITY_PARSING_NEVER</code></dt> <dd>Don't parse parameter entities or the external subset</dd> <dt><code>XML_PARAM_ENTITY_PARSING_UNLESS_STANDALONE</code></dt> <dd>Parse parameter entites and the external subset unless <code>standalone</code> was set to "yes" in the XML declaration.</dd> <dt><code>XML_PARAM_ENTITY_PARSING_ALWAYS</code></dt> <dd>Always parse parameter entities and the external subset</dd> </dl> <p>In order to read an external DTD, you also have to set an external entity reference handler as described above.</p> <h3 id="stop-resume">Temporarily Stopping Parsing</h3> <p>Expat 1.95.8 introduces a new feature: its now possible to stop parsing temporarily from within a handler function, even if more data has already been passed into the parser. Applications for this include</p> <ul> <li>Supporting the <a href= "http://www.w3.org/TR/xinclude/" >XInclude</a> specification.</li> <li>Delaying further processing until additional information is available from some other source.</li> <li>Adjusting processor load as task priorities shift within an application.</li> <li>Stopping parsing completely (simply free or reset the parser instead of resuming in the outer parsing loop). This can be useful if a application-domain error is found in the XML being parsed or if the result of the parse is determined not to be useful after all.</li> </ul> <p>To take advantage of this feature, the main parsing loop of an application needs to support this specifically. It cannot be supported with a parsing loop compatible with Expat 1.95.7 or earlier (though existing loops will continue to work without supporting the stop/resume feature).</p> <p>An application that uses this feature for a single parser will have the rough structure (in pseudo-code):</p> <pre class="pseudocode"> fd = open_input() p = create_parser() if parse_xml(p, fd) { /* suspended */ int suspended = 1; while (suspended) { do_something_else() if ready_to_resume() { suspended = continue_parsing(p, fd); } } } </pre> <p>An application that may resume any of several parsers based on input (either from the XML being parsed or some other source) will certainly have more interesting control structures.</p> <p>This C function could be used for the <code>parse_xml</code> function mentioned in the pseudo-code above:</p> <pre class="eg"> #define BUFF_SIZE 10240 /* Parse a document from the open file descriptor 'fd' until the parse is complete (the document has been completely parsed, or there's been an error), or the parse is stopped. Return non-zero when the parse is merely suspended. */ int parse_xml(XML_Parser p, int fd) { for (;;) { int last_chunk; int bytes_read; enum XML_Status status; void *buff = XML_GetBuffer(p, BUFF_SIZE); if (buff == NULL) { /* handle error... */ return 0; } bytes_read = read(fd, buff, BUFF_SIZE); if (bytes_read < 0) { /* handle error... */ return 0; } status = XML_ParseBuffer(p, bytes_read, bytes_read == 0); switch (status) { case XML_STATUS_ERROR: /* handle error... */ return 0; case XML_STATUS_SUSPENDED: return 1; } if (bytes_read == 0) return 0; } } </pre> <p>The corresponding <code>continue_parsing</code> function is somewhat simpler, since it only need deal with the return code from <code><a href= "#XML_ResumeParser">XML_ResumeParser</a></code>; it can delegate the input handling to the <code>parse_xml</code> function:</p> <pre class="eg"> /* Continue parsing a document which had been suspended. The 'p' and 'fd' arguments are the same as passed to parse_xml(). Return non-zero when the parse is suspended. */ int continue_parsing(XML_Parser p, int fd) { enum XML_Status status = XML_ResumeParser(p); switch (status) { case XML_STATUS_ERROR: /* handle error... */ return 0; case XML_ERROR_NOT_SUSPENDED: /* handle error... */ return 0;. case XML_STATUS_SUSPENDED: return 1; } return parse_xml(p, fd); } </pre> <p>Now that we've seen what a mess the top-level parsing loop can become, what have we gained? Very simply, we can now use the <code><a href= "#XML_StopParser" >XML_StopParser</a></code> function to stop parsing, without having to go to great lengths to avoid additional processing that we're expecting to ignore. As a bonus, we get to stop parsing <em>temporarily</em>, and come back to it when we're ready.</p> <p>To stop parsing from a handler function, use the <code><a href= "#XML_StopParser" >XML_StopParser</a></code> function. This function takes two arguments; the parser being stopped and a flag indicating whether the parse can be resumed in the future.</p>  <hr />  <h2><a name="reference">Expat Reference</a></h2> <h3><a name="creation">Parser Creation</a></h3> <pre class="fcndec" id="XML_ParserCreate"> XML_Parser XMLCALL XML_ParserCreate(const XML_Char *encoding); </pre> <div class="fcndef"> Construct a new parser. If encoding is non-null, it specifies a character encoding to use for the document. This overrides the document encoding declaration. There are four built-in encodings: <ul> <li>US-ASCII</li> <li>UTF-8</li> <li>UTF-16</li> <li>ISO-8859-1</li> </ul> Any other value will invoke a call to the UnknownEncodingHandler. </div> <pre class="fcndec" id="XML_ParserCreateNS"> XML_Parser XMLCALL XML_ParserCreateNS(const XML_Char *encoding, XML_Char sep); </pre> <div class="fcndef"> Constructs a new parser that has namespace processing in effect. Namespace expanded element names and attribute names are returned as a concatenation of the namespace URI, <em>sep</em>, and the local part of the name. This means that you should pick a character for <em>sep</em> that can't be part of an URI. Since Expat does not check namespace URIs for conformance, the only safe choice for a namespace separator is a character that is illegal in XML. For instance, <code>'\xFF'</code> is not legal in UTF-8, and <code>'\xFFFF'</code> is not legal in UTF-16. There is a special case when <em>sep</em> is the null character <code>'\0'</code>: the namespace URI and the local part will be concatenated without any separator - this is intended to support RDF processors. It is a programming error to use the null separator with <a href= "#XML_SetReturnNSTriplet">namespace triplets</a>.</div> <pre class="fcndec" id="XML_ParserCreate_MM"> XML_Parser XMLCALL XML_ParserCreate_MM(const XML_Char *encoding, const XML_Memory_Handling_Suite *ms, const XML_Char *sep); </pre> <pre class="signature"> typedef struct { void *(XMLCALL *malloc_fcn)(size_t size); void *(XMLCALL *realloc_fcn)(void *ptr, size_t size); void (XMLCALL *free_fcn)(void *ptr); } XML_Memory_Handling_Suite; </pre> <div class="fcndef"> <p>Construct a new parser using the suite of memory handling functions specified in <code>ms</code>. If <code>ms</code> is NULL, then use the standard set of memory management functions. If <code>sep</code> is non NULL, then namespace processing is enabled in the created parser and the character pointed at by sep is used as the separator between the namespace URI and the local part of the name.</p> </div> <pre class="fcndec" id="XML_ExternalEntityParserCreate"> XML_Parser XMLCALL XML_ExternalEntityParserCreate(XML_Parser p, const XML_Char *context, const XML_Char *encoding); </pre> <div class="fcndef"> Construct a new <code>XML_Parser</code> object for parsing an external general entity. Context is the context argument passed in a call to a ExternalEntityRefHandler. Other state information such as handlers, user data, namespace processing is inherited from the parser passed as the 1st argument. So you shouldn't need to call any of the behavior changing functions on this parser (unless you want it to act differently than the parent parser). </div> <pre class="fcndec" id="XML_ParserFree"> void XMLCALL XML_ParserFree(XML_Parser p); </pre> <div class="fcndef"> Free memory used by the parser. Your application is responsible for freeing any memory associated with <a href="#userdata">user data</a>. </div> <pre class="fcndec" id="XML_ParserReset"> XML_Bool XMLCALL XML_ParserReset(XML_Parser p, const XML_Char *encoding); </pre> <div class="fcndef"> Clean up the memory structures maintained by the parser so that it may be used again. After this has been called, <code>parser</code> is ready to start parsing a new document. All handlers are cleared from the parser, except for the unknownEncodingHandler. The parser's external state is re-initialized except for the values of ns and ns_triplets. This function may not be used on a parser created using <code><a href= "#XML_ExternalEntityParserCreate" >XML_ExternalEntityParserCreate</a ></code>; it will return <code>XML_FALSE</code> in that case. Returns <code>XML_TRUE</code> on success. Your application is responsible for dealing with any memory associated with <a href="#userdata">user data</a>. </div> <h3><a name="parsing">Parsing</a></h3> <p>To state the obvious: the three parsing functions <code><a href= "#XML_Parse" >XML_Parse</a></code>, <code><a href= "#XML_ParseBuffer"> XML_ParseBuffer</a></code> and <code><a href= "#XML_GetBuffer"> XML_GetBuffer</a></code> must not be called from within a handler unless they operate on a separate parser instance, that is, one that did not call the handler. For example, it is OK to call the parsing functions from within an <code>XML_ExternalEntityRefHandler</code>, if they apply to the parser created by <code><a href= "#XML_ExternalEntityParserCreate" >XML_ExternalEntityParserCreate</a></code>.</p> <p>Note: the <code>len</code> argument passed to these functions should be considerably less than the maximum value for an integer, as it could create an integer overflow situation if the added lengths of a buffer and the unprocessed portion of the previous buffer exceed the maximum integer value. Input data at the end of a buffer will remain unprocessed if it is part of an XML token for which the end is not part of that buffer.</p> <pre class="fcndec" id="XML_Parse"> enum XML_Status XMLCALL XML_Parse(XML_Parser p, const char *s, int len, int isFinal); </pre> <pre class="signature"> enum XML_Status { XML_STATUS_ERROR = 0, XML_STATUS_OK = 1 }; </pre> <div class="fcndef"> Parse some more of the document. The string <code>s</code> is a buffer containing part (or perhaps all) of the document. The number of bytes of s that are part of the document is indicated by <code>len</code>. This means that <code>s</code> doesn't have to be null terminated. It also means that if <code>len</code> is larger than the number of bytes in the block of memory that <code>s</code> points at, then a memory fault is likely. The <code>isFinal</code> parameter informs the parser that this is the last piece of the document. Frequently, the last piece is empty (i.e. <code>len</code> is zero.) If a parse error occurred, it returns <code>XML_STATUS_ERROR</code>. Otherwise it returns <code>XML_STATUS_OK</code> value. </div> <pre class="fcndec" id="XML_ParseBuffer"> enum XML_Status XMLCALL XML_ParseBuffer(XML_Parser p, int len, int isFinal); </pre> <div class="fcndef"> This is just like <code><a href= "#XML_Parse" >XML_Parse</a></code>, except in this case Expat provides the buffer. By obtaining the buffer from Expat with the <code><a href= "#XML_GetBuffer" >XML_GetBuffer</a></code> function, the application can avoid double copying of the input. </div> <pre class="fcndec" id="XML_GetBuffer"> void * XMLCALL XML_GetBuffer(XML_Parser p, int len); </pre> <div class="fcndef"> Obtain a buffer of size <code>len</code> to read a piece of the document into. A NULL value is returned if Expat can't allocate enough memory for this buffer. This has to be called prior to every call to <code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code>. A typical use would look like this: <pre class="eg"> for (;;) { int bytes_read; void *buff = XML_GetBuffer(p, BUFF_SIZE); if (buff == NULL) { /* handle error */ } bytes_read = read(docfd, buff, BUFF_SIZE); if (bytes_read < 0) { /* handle error */ } if (! XML_ParseBuffer(p, bytes_read, bytes_read == 0)) { /* handle parse error */ } if (bytes_read == 0) break; } </pre> </div> <pre class="fcndec" id="XML_StopParser"> enum XML_Status XMLCALL XML_StopParser(XML_Parser p, XML_Bool resumable); </pre> <div class="fcndef"> <p>Stops parsing, causing <code><a href= "#XML_Parse" >XML_Parse</a></code> or <code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code> to return. Must be called from within a call-back handler, except when aborting (when <code>resumable</code> is <code>XML_FALSE</code>) an already suspended parser. Some call-backs may still follow because they would otherwise get lost, including <ul> <li> the end element handler for empty elements when stopped in the start element handler,</li> <li> the end namespace declaration handler when stopped in the end element handler,</li> <li> the character data handler when stopped in the character data handler while making multiple call-backs on a contiguous chunk of characters,</li> </ul> and possibly others.</p> <p>This can be called from most handlers, including DTD related call-backs, except when parsing an external parameter entity and <code>resumable</code> is <code>XML_TRUE</code>. Returns <code>XML_STATUS_OK</code> when successful, <code>XML_STATUS_ERROR</code> otherwise. The possible error codes are:</p> <dl> <dt><code>XML_ERROR_SUSPENDED</code></dt> <dd>when suspending an already suspended parser.</dd> <dt><code>XML_ERROR_FINISHED</code></dt> <dd>when the parser has already finished.</dd> <dt><code>XML_ERROR_SUSPEND_PE</code></dt> <dd>when suspending while parsing an external PE.</dd> </dl> <p>Since the stop/resume feature requires application support in the outer parsing loop, it is an error to call this function for a parser not being handled appropriately; see <a href= "#stop-resume" >Temporarily Stopping Parsing</a> for more information.</p> <p>When <code>resumable</code> is <code>XML_TRUE</code> then parsing is <em>suspended</em>, that is, <code><a href= "#XML_Parse" >XML_Parse</a></code> and <code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code> return <code>XML_STATUS_SUSPENDED</code>. Otherwise, parsing is <em>aborted</em>, that is, <code><a href= "#XML_Parse" >XML_Parse</a></code> and <code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code> return <code>XML_STATUS_ERROR</code> with error code <code>XML_ERROR_ABORTED</code>.</p> <p><strong>Note:</strong> This will be applied to the current parser instance only, that is, if there is a parent parser then it will continue parsing when the external entity reference handler returns. It is up to the implementation of that handler to call <code><a href= "#XML_StopParser" >XML_StopParser</a></code> on the parent parser (recursively), if one wants to stop parsing altogether.</p> <p>When suspended, parsing can be resumed by calling <code><a href= "#XML_ResumeParser" >XML_ResumeParser</a></code>.</p> <p>New in Expat 1.95.8.</p> </div> <pre class="fcndec" id="XML_ResumeParser"> enum XML_Status XMLCALL XML_ResumeParser(XML_Parser p); </pre> <div class="fcndef"> <p>Resumes parsing after it has been suspended with <code><a href= "#XML_StopParser" >XML_StopParser</a></code>. Must not be called from within a handler call-back. Returns same status codes as <code><a href= "#XML_Parse">XML_Parse</a></code> or <code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code>. An additional error code, <code>XML_ERROR_NOT_SUSPENDED</code>, will be returned if the parser was not currently suspended.</p> <p><strong>Note:</strong> This must be called on the most deeply nested child parser instance first, and on its parent parser only after the child parser has finished, to be applied recursively until the document entity's parser is restarted. That is, the parent parser will not resume by itself and it is up to the application to call <code><a href= "#XML_ResumeParser" >XML_ResumeParser</a></code> on it at the appropriate moment.</p> <p>New in Expat 1.95.8.</p> </div> <pre class="fcndec" id="XML_GetParsingStatus"> void XMLCALL XML_GetParsingStatus(XML_Parser p, XML_ParsingStatus *status); </pre> <pre class="signature"> enum XML_Parsing { XML_INITIALIZED, XML_PARSING, XML_FINISHED, XML_SUSPENDED }; typedef struct { enum XML_Parsing parsing; XML_Bool finalBuffer; } XML_ParsingStatus; </pre> <div class="fcndef"> <p>Returns status of parser with respect to being initialized, parsing, finished, or suspended, and whether the final buffer is being processed. The <code>status</code> parameter <em>must not</em> be NULL.</p> <p>New in Expat 1.95.8.</p> </div> <h3><a name="setting">Handler Setting</a></h3> <p>Although handlers are typically set prior to parsing and left alone, an application may choose to set or change the handler for a parsing event while the parse is in progress. For instance, your application may choose to ignore all text not descended from a <code>para</code> element. One way it could do this is to set the character handler when a para start tag is seen, and unset it for the corresponding end tag.</p> <p>A handler may be <em>unset</em> by providing a NULL pointer to the appropriate handler sett