XML: xmlStopParser – R documentation

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xmlStopParser

Terminate an XML parser

Description

This function allows an R-level function to terminate an XML parser before it completes the processing of the XML content. This might be useful, for example, in event-driven parsing with xmlEventParse when we want to read through an XML file until we find a record of interest. Then, having retrieved the necessary information, we want to terminate the parsing rather than let it pointlessly continue. Instead of raising an error in our handler function, we can call xmlStopParser and return. The parser will then take control again and terminate and return back to the original R function from which it was invoked.

The only argument to this function is a reference to internal C-level which identifies the parser. This is passed by the R-XML parser mechanism to a function invoked by the parser if that function inherits (in the S3 sense) from the class XMLParserContextFunction.

Usage

xmlStopParser(parser)

Arguments

parser

an object of class XMLParserContext which must have been obtained by via an XMLParserContextFunction function called by the parser. This is just a handler function whose class includes XMLParserContextFunction

Value

TRUE if it succeeded and an error is raised if the parser object is not valid.

Author(s)

Duncan Temple Lang

References

libxml2 http://xmlsoft.org

Examples

############################################
  # Stopping the parser mid-way and an example of using XMLParserContextFunction.

  startElement =
  function(ctxt, name, attrs, ...)  {
    print(ctxt)
      print(name)
      if(name == "rewriteURI") {
           cat("Terminating parser\n")
	   xmlStopParser(ctxt)
      }
  }
  class(startElement) = "XMLParserContextFunction"  
  endElement =
  function(name, ...) 
    cat("ending", name, "\n")

  fileName = system.file("exampleData", "catalog.xml", package = "XML")
  xmlEventParse(fileName, handlers = list(startElement = startElement, endElement = endElement))

XML

Tools for Parsing and Generating XML Within R and S-Plus

v3.99-0.10

BSD_3_clause + file LICENSE

Authors

CRAN Team [ctb, cre] (de facto maintainer since 2013), Duncan Temple Lang [aut] (<https://orcid.org/0000-0003-0159-1546>), Tomas Kalibera [ctb]

Initial release