[libxml2] Improve buffer allocation scheme

[Nick Wellnhofer <nwellnhof src gnome org>]

commit d99ddd9bd57a08fad891795de3b3f7910e4aec55
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Mar 5 21:46:40 2022 +0100

    Improve buffer allocation scheme
    
    In most places, we really need the double-it scheme to avoid quadratic
    behavior. The hybrid scheme still can cause many reallocations and the
    bounded scheme doesn't seem to provide meaningful protection in
    xmlreader.c.

 parser.c    |  1 +
 runsuite.c  |  3 +++
 tree.c      |  7 +++++--
 xmlIO.c     |  5 +----
 xmlreader.c | 13 +++++++++----
 xmlsave.c   |  4 ++++
 6 files changed, 23 insertions(+), 10 deletions(-)
---
diff --git a/parser.c b/parser.c
index f4707cbb..712328ca 100644
--- a/parser.c
+++ b/parser.c
@@ -8068,6 +8068,7 @@ xmlLoadEntityContent(xmlParserCtxtPtr ctxt, xmlEntityPtr entity) {
                    "xmlLoadEntityContent parameter error");
         return(-1);
     }
+    xmlBufferSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
 
     input = xmlNewEntityInputStream(ctxt, entity);
     if (input == NULL) {
diff --git a/runsuite.c b/runsuite.c
index f7957ce1..483490a2 100644
--- a/runsuite.c
+++ b/runsuite.c
@@ -325,6 +325,7 @@ xsdIncorrectTestCase(xmlNodePtr cur) {
         fprintf(stderr, "out of memory !\n");
        fatalError();
     }
+    xmlBufferSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlNodeDump(buf, test->doc, test, 0, 0);
     pctxt = xmlRelaxNGNewMemParserCtxt((const char *)buf->content, buf->use);
     xmlRelaxNGSetParserErrors(pctxt, testErrorHandler, testErrorHandler,
@@ -363,6 +364,7 @@ installResources(xmlNodePtr tst, const xmlChar *base) {
         fprintf(stderr, "out of memory !\n");
        fatalError();
     }
+    xmlBufferSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlNodeDump(buf, tst->doc, tst, 0, 0);
 
     while (tst != NULL) {
@@ -458,6 +460,7 @@ xsdTestCase(xmlNodePtr tst) {
         fprintf(stderr, "out of memory !\n");
        fatalError();
     }
+    xmlBufferSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlNodeDump(buf, test->doc, test, 0, 0);
     pctxt = xmlRelaxNGNewMemParserCtxt((const char *)buf->content, buf->use);
     xmlRelaxNGSetParserErrors(pctxt, testErrorHandler, testErrorHandler,
diff --git a/tree.c b/tree.c
index 583a7ea7..e4425f10 100644
--- a/tree.c
+++ b/tree.c
@@ -1284,7 +1284,7 @@ xmlStringLenGetNodeList(const xmlDoc *doc, const xmlChar *value, int len) {
 
     buf = xmlBufCreateSize(0);
     if (buf == NULL) return(NULL);
-    xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_HYBRID);
+    xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
 
     q = cur;
     while ((cur < end) && (*cur != 0)) {
@@ -1505,7 +1505,7 @@ xmlStringGetNodeList(const xmlDoc *doc, const xmlChar *value) {
 
     buf = xmlBufCreateSize(0);
     if (buf == NULL) return(NULL);
-    xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_HYBRID);
+    xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
 
     q = cur;
     while (*cur != 0) {
@@ -5559,6 +5559,7 @@ xmlNodeGetContent(const xmlNode *cur)
                 buf = xmlBufCreateSize(64);
                 if (buf == NULL)
                     return (NULL);
+                xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
                xmlBufGetNodeContent(buf, cur);
                 ret = xmlBufDetach(buf);
                 xmlBufFree(buf);
@@ -5584,6 +5585,7 @@ xmlNodeGetContent(const xmlNode *cur)
                 buf = xmlBufCreate();
                 if (buf == NULL)
                     return (NULL);
+                xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
 
                 xmlBufGetNodeContent(buf, cur);
 
@@ -5606,6 +5608,7 @@ xmlNodeGetContent(const xmlNode *cur)
            buf = xmlBufCreate();
            if (buf == NULL)
                return (NULL);
+            xmlBufSetAllocationScheme(buf, XML_BUFFER_ALLOC_DOUBLEIT);
 
            xmlBufGetNodeContent(buf, (xmlNodePtr) cur);
 
diff --git a/xmlIO.c b/xmlIO.c
index a80ef11f..172044a5 100644
--- a/xmlIO.c
+++ b/xmlIO.c
@@ -2389,10 +2389,7 @@ xmlAllocOutputBuffer(xmlCharEncodingHandlerPtr encoder) {
         xmlFree(ret);
        return(NULL);
     }
-
-    /* try to avoid a performance problem with Windows realloc() */
-    if (xmlBufGetAllocationScheme(ret->buffer) == XML_BUFFER_ALLOC_EXACT)
-        xmlBufSetAllocationScheme(ret->buffer, XML_BUFFER_ALLOC_DOUBLEIT);
+    xmlBufSetAllocationScheme(ret->buffer, XML_BUFFER_ALLOC_DOUBLEIT);
 
     ret->encoder = encoder;
     if (encoder != NULL) {
diff --git a/xmlreader.c b/xmlreader.c
index 5d2250a6..ba95813b 100644
--- a/xmlreader.c
+++ b/xmlreader.c
@@ -1180,6 +1180,7 @@ xmlTextReaderCollectSiblings(xmlNodePtr node)
     buffer = xmlBufferCreate();
     if (buffer == NULL)
        return NULL;
+    xmlBufferSetAllocationScheme(buffer, XML_BUFFER_ALLOC_DOUBLEIT);
 
     for ( ; node != NULL; node = node->next) {
        switch (node->type) {
@@ -1633,11 +1634,14 @@ xmlTextReaderReadInnerXml(xmlTextReaderPtr reader ATTRIBUTE_UNUSED)
     buff = xmlBufferCreate();
     if (buff == NULL)
         return NULL;
+    xmlBufferSetAllocationScheme(buff, XML_BUFFER_ALLOC_DOUBLEIT);
     for (cur_node = reader->node->children; cur_node != NULL;
          cur_node = cur_node->next) {
         /* XXX: Why is the node copied? */
         node = xmlDocCopyNode(cur_node, doc, 1);
+        /* XXX: Why do we need a second buffer? */
         buff2 = xmlBufferCreate();
+        xmlBufferSetAllocationScheme(buff2, XML_BUFFER_ALLOC_DOUBLEIT);
         if (xmlNodeDump(buff2, doc, node, 0, 0) == -1) {
             xmlFreeNode(node);
             xmlBufferFree(buff2);
@@ -1687,6 +1691,7 @@ xmlTextReaderReadOuterXml(xmlTextReaderPtr reader ATTRIBUTE_UNUSED)
                node = xmlDocCopyNode(node, doc, 1);
        }
     buff = xmlBufferCreate();
+    xmlBufferSetAllocationScheme(buff, XML_BUFFER_ALLOC_DOUBLEIT);
     if (xmlNodeDump(buff, doc, node, 0, 0) == -1) {
         xmlFreeNode(node);
         xmlBufferFree(buff);
@@ -2017,7 +2022,7 @@ xmlNewTextReader(xmlParserInputBufferPtr input, const char *URI) {
     }
     /* no operation on a reader should require a huge buffer */
     xmlBufSetAllocationScheme(ret->buffer,
-                             XML_BUFFER_ALLOC_BOUNDED);
+                             XML_BUFFER_ALLOC_DOUBLEIT);
     ret->sax = (xmlSAXHandler *) xmlMalloc(sizeof(xmlSAXHandler));
     if (ret->sax == NULL) {
        xmlBufFree(ret->buffer);
@@ -3555,7 +3560,7 @@ xmlTextReaderConstValue(xmlTextReaderPtr reader) {
                         return (NULL);
                     }
                    xmlBufSetAllocationScheme(reader->buffer,
-                                             XML_BUFFER_ALLOC_BOUNDED);
+                                             XML_BUFFER_ALLOC_DOUBLEIT);
                 } else
                     xmlBufEmpty(reader->buffer);
                xmlBufGetNodeContent(reader->buffer, node);
@@ -3565,7 +3570,7 @@ xmlTextReaderConstValue(xmlTextReaderPtr reader) {
                    xmlBufFree(reader->buffer);
                    reader->buffer = xmlBufCreateSize(100);
                    xmlBufSetAllocationScheme(reader->buffer,
-                                             XML_BUFFER_ALLOC_BOUNDED);
+                                             XML_BUFFER_ALLOC_DOUBLEIT);
                    ret = BAD_CAST "";
                }
                return(ret);
@@ -5079,7 +5084,7 @@ xmlTextReaderSetup(xmlTextReaderPtr reader,
     }
     /* no operation on a reader should require a huge buffer */
     xmlBufSetAllocationScheme(reader->buffer,
-                             XML_BUFFER_ALLOC_BOUNDED);
+                             XML_BUFFER_ALLOC_DOUBLEIT);
     if (reader->sax == NULL)
        reader->sax = (xmlSAXHandler *) xmlMalloc(sizeof(xmlSAXHandler));
     if (reader->sax == NULL) {
diff --git a/xmlsave.c b/xmlsave.c
index 3addd652..7b557494 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -474,6 +474,7 @@ xmlBufDumpNotationTable(xmlBufPtr buf, xmlNotationTablePtr table) {
          */
         return;
     }
+    xmlBufferSetAllocationScheme(buffer, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlDumpNotationTable(buffer, table);
     xmlBufMergeBuffer(buf, buffer);
 }
@@ -497,6 +498,7 @@ xmlBufDumpElementDecl(xmlBufPtr buf, xmlElementPtr elem) {
          */
         return;
     }
+    xmlBufferSetAllocationScheme(buffer, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlDumpElementDecl(buffer, elem);
     xmlBufMergeBuffer(buf, buffer);
 }
@@ -520,6 +522,7 @@ xmlBufDumpAttributeDecl(xmlBufPtr buf, xmlAttributePtr attr) {
          */
         return;
     }
+    xmlBufferSetAllocationScheme(buffer, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlDumpAttributeDecl(buffer, attr);
     xmlBufMergeBuffer(buf, buffer);
 }
@@ -542,6 +545,7 @@ xmlBufDumpEntityDecl(xmlBufPtr buf, xmlEntityPtr ent) {
          */
         return;
     }
+    xmlBufferSetAllocationScheme(buffer, XML_BUFFER_ALLOC_DOUBLEIT);
     xmlDumpEntityDecl(buffer, ent);
     xmlBufMergeBuffer(buf, buffer);
 }