libxml2: Attribute decoding patch (was: Re: xmlstarlet ignores XML attributes)

[David Stacey]

On 30/09/2017 16:25, Kay Ulbrich wrote:
> on a current Cygwin-installation, xmlstarlet fails to validate a valid
> XML document against an XML schema (XSD).
>
> [snip]
>
> I found a quite recent similar bug report for Debian, there seems to be
> a problem with certain versions of libxml:
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=832602

Yaakov, please could you consider taking the patch attached, which is 
from Debian Stretch [1]. Or you may prefer to update to libxml2-2.9.5, 
as the patch has been incorporated upstream. Either should address the 
problem reported above.

Dave.

[1] - https://packages.debian.org/stretch/libxml2

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From 256366ed60f8795279b25f7b7b55e8089b4c6ff4 Mon Sep 17 00:00:00 2001
From: Alex Henrie <alexhenrie24@gmail.com>
Date: Thu, 26 May 2016 17:38:35 -0600
Subject: [PATCH] Fix attribute decoding during XML schema validation

For https://bugzilla.gnome.org/show_bug.cgi?id=766834

vctxt->parserCtxt is always NULL in xmlSchemaSAXHandleStartElementNs,
so this function can't call xmlStringLenDecodeEntities to decode the
entities.
---
 xmlschemas.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/xmlschemas.c b/xmlschemas.c
index e1b3a4f..59535e5 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -27391,6 +27391,7 @@ xmlSchemaSAXHandleStartElementNs(void *ctx,
     * attributes yet.
     */
     if (nb_attributes != 0) {
+	int valueLen, k, l;
 	xmlChar *value;
 
         for (j = 0, i = 0; i < nb_attributes; i++, j += 5) {
@@ -27400,12 +27401,31 @@ xmlSchemaSAXHandleStartElementNs(void *ctx,
 	    * libxml2 differs from normal SAX here in that it escapes all ampersands
 	    * as & instead of delivering the raw converted string. Changing the
 	    * behavior at this point would break applications that use this API, so
-	    * we are forced to work around it. There is no danger of accidentally
-	    * decoding some entity other than & in this step because without
-	    * unescaped ampersands there can be no other entities in the string.
+	    * we are forced to work around it.
 	    */
-	    value = xmlStringLenDecodeEntities(vctxt->parserCtxt, attributes[j+3],
-		attributes[j+4] - attributes[j+3], XML_SUBSTITUTE_REF, 0, 0, 0);
+	    valueLen = attributes[j+4] - attributes[j+3];
+	    value = xmlMallocAtomic(valueLen + 1);
+	    if (value == NULL) {
+		xmlSchemaVErrMemory(vctxt,
+		    "allocating string for decoded attribute",
+		    NULL);
+		goto internal_error;
+	    }
+	    for (k = 0, l = 0; k < valueLen; l++) {
+		if (k < valueLen - 4 &&
+		    attributes[j+3][k+0] == '&' &&
+		    attributes[j+3][k+1] == '#' &&
+		    attributes[j+3][k+2] == '3' &&
+		    attributes[j+3][k+3] == '8' &&
+		    attributes[j+3][k+4] == ';') {
+		    value[l] = '&';
+		    k += 5;
+		} else {
+		    value[l] = attributes[j+3][k];
+		    k++;
+		}
+	    }
+	    value[l] = '\0';
 	    /*
 	    * TODO: Set the node line.
 	    */
-- 
2.8.3

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