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From "Nicko Cadell (JIRA)" <j...@apache.org>
Subject [jira] Created: (LOG4NET-22) XmlLayout allows output of invalid control characters
Date Sun, 10 Apr 2005 18:42:22 GMT
XmlLayout allows output of invalid control characters 
------------------------------------------------------

         Key: LOG4NET-22
         URL: http://issues.apache.org/jira/browse/LOG4NET-22
     Project: Log4net
        Type: Bug
  Components: Appenders  
    Versions: 1.2.9    
    Reporter: Nicko Cadell


XmlLayout allows output of invalid control characters.

Reported by Mike Blake-Knox with additional comments from Curt Arnold.


The XmlLayout encodes the character 0x1e as &#x1E; using the standard XML numeric character
reference.

This character code is in a range which is not allowed to appear in XML 1.0 either as a un-encoded
value or as a numeric character reference.

The valid character ranges are defined here in the XML recommendation:
http://www.w3.org/TR/REC-xml/#charsets

They are:

#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]

Numeric character references are not able to express characters from outside these ranges.

The System.Xml.XmlTextWriter does not verify if the unicode character is valid in XML, but
it does encode it as a numeric character reference if it cannot be expressed in the output
encoding.

To complicate matters further XML 1.1 does allow further, so called restricted characters,
to be included in the output if they are encoded as numeric character references. These ranges
are:

[#x1-#x8] | [#xB-#xC] | [#xE-#x1F] | [#x7F-#x84] | [#x86-#x9F]

See http://www.w3.org/TR/2004/REC-xml11-20040204/#charsets for details.

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