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This commit fixes some defects in the backend's xml.c, found upon inspection of the internals of libxml2: - xmlEncodeSpecialChars() can fail on malloc(), returning NULL back to the caller. xmltext() assumed that this could never happen. Like other code paths, a TRY/CATCH block is added there, covering also the fact that cstring_to_text_with_len() could fail a memory allocation, where the backend would miss to free the buffer allocated by xmlEncodeSpecialChars(). - Some libxml2 routines called in xmlelement() can return NULL, like xmlAddChildList() or xmlTextWriterStartElement(). Dedicated errors are added for them. - xml_xmlnodetoxmltype() missed that xmlXPathCastNodeToString() can fail on an allocation failure. In this case, the call can just be moved to the existing TRY/CATCH block. All these code paths would cause the server to crash. As this is unlikely a problem in practice, no backpatch is done. Jim and I have caught these defects, not sure who has scored the most. The contrib module xml2/ has similar defects, which will be addressed in a separate change. Reported-by: Jim Jones <jim.jones@uni-muenster.de> Reviewed-by: Jim Jones <jim.jones@uni-muenster.de> Discussion: https://postgr.es/m/aEEingzOta_S_Nu7@paquier.xyz