Re: [xml] xmlNodeDumpOutputInternal segfault when usingt '/' as xpath expr

Daniel Veillard wrote:

On Mon, Jul 05, 2004 at 08:36:43AM -0700, Joel McConaughy wrote:
I get the following segfault when using '/' as an xpath expression:

  Program received signal SIGSEGV, Segmentation fault.
  [Switching to Thread 1024 (LWP 6946)]
  0x400d5cb8 in xmlNodeDumpOutputInternal (ctxt=0xbffff640, cur=0x804d438)
      at xmlsave.c:737
  737        if ((cur->ns != NULL) && (cur->ns->prefix != NULL)) {

I have modified the xpath2.c sample to dump the results of an xpath expression using xmlNodeDumpOutput. The problem can be reproduced by

 xpath2.c is used to modify the target nodes to change their value.
if You do that on / you would modify the Document Root node. This won't

The only change I made to the sample was to replace update_xpath_nodes() with get_xpath_nodes(). The code is pretty simple and I can't see any problems however pilot error is always a possibility. Help would be greatly appreciated. Thanks.

there is no get_xpath_nodes() in xpath2.c . Using "/" as an XPath expression is used all the time, especially in XSLT
on top of libxml2. I don't see this being an xpath error. It likely to be
an error handling the XML_DOCUMENT_NODE nore returned from the query.
Never assume that a node is of a given type before processing it. Always
test node->type first.


Thanks for the quick response. I'm not changing the doc in this code. I removed the update_xpath_nodes() function and replaced with the following which walks the xmlNodeSetPtr array and calls xmlNodeDumpOutput() for each element. The node that causes the segfault is type=9, name=null.

static char *
get_xpath_nodes(xmlDocPtr doc, xmlNodeSetPtr nodes) {
   int size;
   int i;
   xmlOutputBufferPtr outbuf;
   char *s = calloc(1,1);
size = (nodes) ? nodes->nodeNr : 0;
   for(i = 0; i < size; i++) {
       outbuf = xmlAllocOutputBuffer(NULL);

       xmlNodeDumpOutput(outbuf, doc, nodes->nodeTab[i], 0, 0, NULL);

       s = realloc(s, strlen(s) + outbuf->buffer->use + 1);
       strncat(s, outbuf->buffer->content, outbuf->buffer->use);


   return s;

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