R: Terminate an XML parser

xmlStopParser {XML} | R Documentation

## 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

### See Also

`xmlEventParse`

### 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))

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