[Mono-bugs] [Bug 74704][Wis] New - XmlTextReader: handling of xml:base causes exception

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Changed by heath@pointedstick.net.

http://bugzilla.ximian.com/show_bug.cgi?id=74704

--- shadow/74704	2005-04-23 15:56:44.000000000 -0400
+++ shadow/74704.tmp.11705	2005-04-23 15:56:44.000000000 -0400
@@ -0,0 +1,81 @@
+Bug#: 74704
+Product: Mono: Class Libraries
+Version: 1.0
+OS: 
+OS Details: Fedora Core 3 x86
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Wishlist
+Component: Sys.XML
+AssignedTo: mono-bugs@ximian.com                            
+ReportedBy: heath@pointedstick.net               
+QAContact: mono-bugs@ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: XmlTextReader: handling of xml:base causes exception
+
+Please fill in this template when reporting a bug, unless you know what you
+are doing.
+Description of Problem:
+In the ReadStartTag() method, XmlTextReader tries to use the BaseURI
+variable to construct a URI without checking if it's empty.  This can cause
+a UriFormatException.
+
+Apparently, this was noticed and changed in Mono 1.1, because XmlTextReader
+in Mono 1.1 checks for this condition.
+
+Code from Mono 1.0.6 (XmlTextReader.cs, line 1333):
+
+string baseUri = GetAttribute ("xml:base");
+if (baseUri != null) {
+    parsercontext.BaseURI = 
+      resolver.ResolveUri (new Uri(BaseURI), value).ToString();
+else
+    parsercontext.BaseURI = baseUri;
+
+The problem comes in using the Uri constructor when BaseURI == String.Empty.
+
+The equivalent code in Mono 1.1.6 (XmlTextReader.cs, line 1323):
+
+case "base":
+    if (this.resolver != null) {
+        Uri buri = BaseURI != String.Empty ?
+                   new Uri (BaseURI) : null;
+        Uri uri  = resolver.ResolveUri (buri, value);
+        parsercontext.BaseURI = 
+                   uri != null ? 
+                   uri.ToString () :
+                   String.Empty;
+    }
+    else
+        parsercontext.BaseURI = value;
+
+
+
+Steps to reproduce the problem:
+1. Read an XML file containing xml:base attributes (in my case, an 
+    Atom feed) with an XmlTextReader.
+2. Watch XmlTextReader.ReadStartTag() throw UriFormatException.
+ 
+
+Actual Results:
+UriFormatException.
+
+Expected Results:
+No UriFormatException, same as Mono 1.1.
+
+How often does this happen? 
+Always, in my experience, but from the look of the code it's possible that
+it wouldn't happen under other circumstances.
+
+Additional Information:
+I discovered this by writing a patch for Imendio Blam! that adds Atom feed
+support using Atom.NET (atomnet.sourceforge.net).  The constructor for the
+AtomReader class is throwing this exception, but only on Mono 1.0.X.  The
+AtomReader constructor creates an XPathDocument from a stream, which
+creates an XmlTextReader, which reads through the feed and throws the
+UriFormatException.  Again, this does not happen on Mono 1.1.
+
+I have a short patch that fixes the problem, attached shortly.