expat (3)

NAME

expat - Creates an instance of an expat parser object

SYNOPSIS

package require tdom

expat ?parsername? ?-namespace? ?arg arg ..

xml::parser ?parsername? ?-namespace? ?arg arg ..

DESCRIPTION

The parser created with expat or xml::parser (which is just another name for the same command in an own namespace) are able to parse any kind of well-formed XML. The parsers are stream oriented XML parser. This means that you register handler scripts with the parser prior to starting the parse. These handler scripts are called when the parser discovers the associated structures in the document being parsed. A start tag is an example of the kind of structures for which you may register a handler script.

The parsers do not validate the XML document. They do parse the internal DTD and, at request, external DTD and external entities, if you resolve the identifier of the external entities with the -externalentitycommand script (see there).

Additionly, the Tcl extension code that implements this command provides an API for adding C level coded handlers. Up to now, there exists the parser extension command "tdom". The handler set installed by this extension build an in memory "tDOM" DOM tree, while the parser is parsing the input.

It is possible to register an arbitrary amount of different handler scripts and C level handlers for most of the events. If the event occurs, they are called in turn.

COMMAND OPTIONS

-namespace

Enables namespace parsing. You must use this option while creating the parser with the expat or xml::parser command. You can't enable (nor disable) namespace parsing with <parserobj> configure ....

-final boolean

This option indicates whether the document data next presented to the parse method is the final part of the document. A value of "0" indicates that more data is expected. A value of "1" indicates that no more is expected. The default value is "1".

If this option is set to "0" then the parser will not report certain errors if the XML data is not well-formed upon end of input, such as unclosed or unbalanced start or end tags. Instead some data may be saved by the parser until the next call to the parse method, thus delaying the reporting of some of the data.

If this option is set to "1" then documents which are not well-formed upon end of input will generate an error.

-baseurl url

Reports the base url of the document to the parser.

-elementstartcommand script

Specifies a Tcl command to associate with the start tag of an element. The actual command consists of this option followed by at least two arguments: the element type name and the attribute list.

The attribute list is a Tcl list consisting of name/value pairs, suitable for passing to the array set Tcl command.

Example:

proc HandleStart {name attlist} {
    puts stderr "Element start ==> $name has attributes $attlist"
}

$parser configure -elementstartcommand HandleStart

$parser parse {<test id="123"></test>}

This would result in the following command being invoked:

HandleStart text {id 123}

-elementendcommand script

Specifies a Tcl command to associate with the end tag of an element. The actual command consists of this option followed by at least one argument: the element type name. In addition, if the -reportempty option is set then the command may be invoked with the -empty configuration option to indicate whether it is an empty element. See the description of the -reportempty option for an example.

Example:

proc HandleEnd {name} {
    puts stderr "Element end ==> $name"
}

$parser configure -elementendcommand HandleEnd

$parser parse {<test id="123"></test>}

This would result in the following command being invoked:

HandleEnd test

-characterdatacommand script

Specifies a Tcl command to associate with character data in the document, ie. text. The actual command consists of this option followed by one argument: the text.

It is not guaranteed that character data will be passed to the application in a single call to this command. That is, the application should be prepared to receive multiple invocations of this callback with no intervening callbacks from other features.

Example:

proc HandleText {data} {
    puts stderr "Character data ==> $data"
}

$parser configure -characterdatacommand HandleText

$parser parse {<test>this is a test document</test>}

This would result in the following command being invoked:

HandleText {this is a test document}

-processinginstructioncommand script

Specifies a Tcl command to associate with processing instructions in the document. The actual command consists of this option followed by two arguments: the PI target and the PI data.

Example:

proc HandlePI {target data} {
    puts stderr "Processing instruction ==> $target $data"
}

$parser configure -processinginstructioncommand HandlePI

$parser parse {<test><?special this is a processing instruction?></test>}

This would result in the following command being invoked:

HandlePI special {this is a processing instruction}

-notationdeclcommand script

Specifies a Tcl command to associate with notation declaration in the document. The actual command consists of this option followed by four arguments: the notation name, the base uri of the document (this means, whatever was set by the -baseurl option), the system identifier and the public identifier. The notation name is never empty, the other arguments may be.

-externalentitycommand script

Specifies a Tcl command to associate with references to external entities in the document. The actual command consists of this option followed by three arguments: the base uri, the system identifier of the entity and the public identifier of the entity. The base uri and the public identifier may be the empty list.

This handler script has to return a tcl list consisting of three elements. The first element of this list signals, how the external entity is returned to the processor. At the moment, the three allowed types are "string", "channel" and "filename". The second element of the list has to be the (absolute) base URI of the external entity to be parsed. The third element of the list are data, either the already read data out of the external entity as string in the case of type "string", or the name of a tcl channel, in the case of type "channel", or the path to the external entity to be read in case of type "filename". Behind the scene, the external entity referenced by the returned Tcl channel, string or file name will be parsed with an expat external entity parser with the same handler sets as the main parser. If parsing of the external entity fails, the whole parsing is stopped with an error message. If a Tcl command registered as externalentitycommand isn't able to resolve an external entity it is allowed to return TCL_CONTINUE. In this case, the wrapper give the next registered externalentitycommand a try. If no externalentitycommand is able to handle the external entity parsing stops with an error.

Example:

proc externalEntityRefHandler {base systemId publicId} {
    if {![regexp {^[a-zA-Z]+:/} $systemId]}  {
        regsub {^[a-zA-Z]+:} $base {} base
        set basedir [file dirname $base]
        set systemId "[set basedir]/[set systemId]"
    } else {
        regsub {^[a-zA-Z]+:} $systemId systemId
    }
    if {[catch {set fd [open $systemId]}]} {
        return -code error \
                -errorinfo "Failed to open external entity $systemId"
    }
    return [list channel $systemId $fd]
}

set parser [expat -externalentitycommand externalEntityRefHandler \
                  -baseurl "file:///local/doc/doc.xml" \
                  -paramentityparsing notstandalone]
$parser parse {<?xml version='1.0'?>
<!DOCTYPE test SYSTEM "test.dtd">
<test/>}

This would result in the following command being invoked:

externalEntityRefHandler file:///local/doc/doc.xml test.dtd {}

External entities are only tried to resolve via this handler script, if necessary. This means, external parameter entities triggers this handler only, if -paramentityparsing is used with argument "always" or if -paramentityparsing is used with argument "notstandalone" and the document isn't marked as standalone.

-unknownencodingcommand script

Not implemented at Tcl level.

-startnamespacedeclcommand script

Specifies a Tcl command to associate with start scope of namespace declarations in the document. The actual command consists of this option followed by two arguments: the namespace prefix and the namespace URI. For an xmlns attribute, prefix will be the empty list. For an xmlns="" attribute, uri will be the empty list. The call to the start and end element handlers occur between the calls to the start and end namespace declaration handlers.

-endnamespacedeclcommand script

Specifies a Tcl command to associate with end scope of namespace declarations in the document. The actual command consists of this option followed by the namespace prefix as argument. In case of an xmlns attribute, prefix will be the empty list. The call to the start and end element handlers occur between the calls to the start and end namespace declaration handlers.

-commentcommand script

Specifies a Tcl command to associate with comments in the document. The actual command consists of this option followed by one argument: the comment data.

Example:

proc HandleComment {data} {
    puts stderr "Comment ==> $data"
}

$parser configure -commentcommand HandleComment

$parser parse {<test><!-- this is <obviously> a comment --></test>}

This would result in the following command being invoked:

HandleComment { this is <obviously> a comment }

-notstandalonecommand script

This Tcl command is called, if the document is not standalone (it has an external subset or a reference to a parameter entity, but does not have standalone="yes"). It is called with no additional arguments.

-startcdatasectioncommand script

Specifies a Tcl command to associate with the start of a CDATA section. It is called with no additional arguments.

-endcdatasectioncommand script

Specifies a Tcl command to associate with the end of a CDATA section. It is called with no additional arguments.

-elementdeclcommand script

Specifies a Tcl command to associate with element declarations. The actual command consists of this option followed by two arguments: the name of the element and the content model. The content model arg is a tcl list of four elements. The first list element specifies the type of the XML element; the six different possible types are reported as "MIXED", "NAME", "EMPTY", "CHOICE", "SEQ" or "ANY". The second list element reports the quantifier to the content model in XML Syntax ("?", "*" or "+") or is the empty list. If the type is "MIXED", then the quantifier will be "{}", indicating an PCDATA only element, or "*", with the allowed elements to intermix with PCDATA as tcl list as the fourth argument. If the type is "NAME", the name is the third arg; otherwise the third argument is the empty list. If the type is "CHOICE" or "SEQ" the fourth argument will contain a list of content models build like this one. The "EMPTY", "ANY", and "MIXED" types will only occur at top level.

Examples:

proc elDeclHandler {name content} {
     puts "$name $content"
}

set parser [expat -elementdeclcommand elDeclHandler]
$parser parse {<?xml version='1.0'?>
<!DOCTYPE test [
<!ELEMENT test (#PCDATA)> 
]>
<test>foo</test>}

This would result in the following command being invoked:

test {MIXED {} {} {}}

$parser reset
$parser parse {<?xml version='1.0'?>
<!DOCTYPE test [
<!ELEMENT test (a|b)>
]>
<test><a/></test>}

This would result in the following command being invoked:

elDeclHandler test {CHOICE {} {} {{NAME {} a {}} {NAME {} b {}}}}

-attlistdeclcommand script

Specifies a Tcl command to associate with attlist declarations. The actual command consists of this option followed by five arguments. The Attlist declaration handler is called for *each* attribute. So a single Attlist declaration with multiple attributes declared will generate multiple calls to this handler. The arguments are the element name this attribute belongs to, the name of the attribute, the type of the attribute, the default value (may be the empty list) and a required flag. If this flag is true and the default value is not the empty list, then this is a "#FIXED" default.

Example:

proc attlistHandler {elname name type default isRequired} {
    puts "$elname $name $type $default $isRequired"
}

set parser [expat -attlistdeclcommand attlistHandler]
$parser parse {<?xml version='1.0'?>
<!DOCTYPE test [
<!ELEMENT test EMPTY>
<!ATTLIST test
          id      ID      #REQUIRED
          name    CDATA   #IMPLIED>
]>
<test/>}

This would result in the following commands being invoked:

attlistHandler test id ID {} 1
attlistHandler test name CDATA {} 0

-startdoctypedeclcommand script

Specifies a Tcl command to associate with the start of the DOCTYPE declaration. This command is called before any DTD or internal subset is parsed. The actual command consists of this option followed by four arguments: the doctype name, the system identifier, the public identifier and a boolean, that shows if the DOCTYPE has an internal subset.

-enddoctypedeclcommand script

Specifies a Tcl command to associate with the end of the DOCTYPE declaration. This command is called after processing any external subset. It is called with no additional arguments.

-paramentityparsing never|notstandalone|always

"never" disables expansion of parameter entities, "always" expands always and "notstandalone" only, if the document isn't "standalone='no'". The default ist "never"

-entitydeclcommand script

Specifies a Tcl command to associate with any entity declaration. The actual command consists of this option followed by seven arguments: the entity name, a boolean identifying parameter entities, the value of the entity, the base uri, the system identifier, the public identifier and the notation name. According to the type of entity declaration some of this arguments may be the empty list.

-ignorewhitecdata boolean

If this flag is set, element content which contain only whitespaces isn't reported with the -characterdatacommand.

-ignorewhitespace boolean

Another name for -ignorewhitecdata; see there.

-handlerset name

This option sets the Tcl handler set scope for the configure options. Any option value pair following this option in the same call to the parser are modifying the named Tcl handler set. If you don't use this option, you are modifying the default Tcl handler set, named "default".

-noexpand boolean

Normally, the parser will try to expand references to entities defined in the internal subset. If this option is set to a true value this entities are not expanded, but reported literal via the default handler. Warning: If you set this option to true and doesn't install a default handler (with the -defaultcommand option) for every handler set of the parser all internal entities are silent lost for the handler sets without a default handler.

-useForeignDTD <boolen>

If <boolen> is true and the document does not have an external subset, the parser will call the -externalentitycommand script with empty values for the systemId and publicID arguments. This option must be set, before the first piece of data is parsed. Setting this option, after the parsing has started has no effect. The default is not to use a foreign DTD. The default is restored, after reseting the parser. Pleace notice, that a -paramentityparsing value of "never" (which is the default) suppresses any call to the -externalentitycommand script. Pleace notice, that, if the document also doesn't have an internal subset, the -startdoctypedeclcommand and enddoctypedeclcommand scripts, if set, are not called.

COMMAND METHODS

parser configure option value ?option value?

Sets configuration options for the parser. Every command option, except -namespace can be set or modified with this method.

parser cget ?-handlerset name? option

Return the current configuration value option for the parser.

If the -handlerset option is used, the configuration for the named handler set is returned.

parser free

Deletes the parser and the parser command. A parser cannot be freed from within one of its handler callbacks (neither directly nor indirectly) and will raise a tcl error in this case.

parser get -specifiedattributecount|-idattributeindex|-currentbytecount|-currentlinenumber|-currentcolumnnumber|-currentbyteindex

-specifiedattributecount

Returns the number of the attribute/value pairs passed in last call to the elementstartcommand that were specified in the start-tag rather than defaulted. Each attribute/value pair counts as 2; thus this corresponds to an index into the attribute list passed to the elementstartcommand.

-idattributeindex

Returns the index of the ID attribute passed in the last call to XML_StartElementHandler, or -1 if there is no ID attribute. Each attribute/value pair counts as 2; thus this corresponds to an index into the attributes list passed to the elementstartcommand.

-currentbytecount

Return the number of bytes in the current event. Returns 0 if the event is in an internal entity.

-currentlinenumber

Returns the line number of the current parse location.

-currentcolumnnumber

Returns the column number of the current parse location.

-currentbyteindex

Returns the byte index of the current parse location.

Only one value may be requested at a time.

parser parse data

Parses the XML string data. The event callback scripts will be called, as there triggering events happens. This method cannot be used from within a callback (neither directly nor indirectly) of the parser to be used and will raise an error in this case.

parser parsechannel channelID

Reads the XML data out of the tcl channel channelID (starting at the current access position, without any seek) up to the end of file condition and parses that data. The channel encoding is respected. Use the helper proc tDOM::xmlOpenFile out of the tDOM script library to open a file, if you want to use this method. This method cannot be used from within a callback (neither directly nor indirectly) of the parser to be used and will raise an error in this case.

parser parsefile filename

Reads the XML data directly out of the file with the filename filename and parses that data. This is done with low level file operations. The XML data must be in US-ASCII, ISO-8859-1, UTF-8 or UTF-16 encoding. If applicable, this is the fastest way, to parse XML data. This method cannot be used from within a callback (neither directly nor indirectly) of the parser to be used and will raise an error in this case.

parser reset

Resets the parser in preparation for parsing another document. A parser cannot be reseted from within one of its handler callbacks (neither directly nor indirectly) and will raise a tcl error in this cases.

Callback Command Return Codes

A script invoked for any of the parser callback commands, such as -elementstartcommand, -elementendcommand, etc, may return an error code other than "ok" or "error". All callbacks may in addition return "break" or "continue".

If a callback script returns an "error" error code then processing of the document is terminated and the error is propagated in the usual fashion.

If a callback script returns a "break" error code then all further processing of every handler script out of this Tcl handler set is suppressed for the further parsing. This does not influence any other handler set.

If a callback script returns a "continue" error code then processing of the current element, and its children, ceases for every handler script out of this Tcl handler set and processing continues with the next (sibling) element. This does not influence any other handler set.

SEE ALSO

expatapi, tdom

KEYWORDS

SAX