[I] MultiprocessRollingFileAppender error "Can't cast writer to FileOutputStream" [logging-log4cxx]

[via GitHub]

BigMichi1 opened a new issue, #439:
URL: https://github.com/apache/logging-log4cxx/issues/439

   when adding a `MultiprocessRollingFileAppender` to `log4cxx.xml` like in the 
following snippet
   
   ```xml
   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
   <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/";>
   
     <appender name="multi" 
class="org.apache.log4j.rolling.MultiprocessRollingFileAppender">
       <param name="file" value="log/logfile.log"/>
       <rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy">
         <param name="FileNamePattern" 
value="log/logfile.%d{yyyy-MM-dd}.log.gz"/>
       </rollingPolicy>
       <triggeringPolicy 
class="org.apache.log4j.rolling.SizeBasedTriggeringPolicy">
         <param name="MaxFileSize" value="100MB"/>
       </triggeringPolicy>
       <layout class="org.apache.log4j.PatternLayout">
         <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss}] %c 
%-5p - %m%n"/>
       </layout>
     </appender>
   
     <root>
       <priority value ="debug" />
       <appender-ref ref="multi" />
     </root>
     
   </log4j:configuration>
   ```
   
   and in my `main.cpp`
   
   ```cpp
     LogLog::setInternalDebugging(true);
     DOMConfigurator::configure("log4cxx.xml");
     auto root = Logger::getRootLogger();
   
     LOG4CXX_DEBUG(root, "Foo Bar");
   ```
   
   i receive an error
   
   ```plain
   log4cxx: DOMConfigurator configuring file log4cxx.xml...
   log4cxx: Loading configuration file [log4cxx.xml].
   log4cxx: debug attribute= "".
   log4cxx: Ignoring internalDebug attribute.
   log4cxx: Threshold ="".
   log4cxx: Class name: 
[org.apache.log4j.rolling.MultiprocessRollingFileAppender]
   log4cxx: Setting option name=[file], value=[log/logfile.log]
   log4cxx: Parsing rolling policy of class: 
"org.apache.log4j.rolling.TimeBasedRollingPolicy"
   log4cxx: Setting option name=[FileNamePattern], 
value=[log/logfile.%d{yyyy-MM-dd}.log.gz]
   log4cxx: Parsing triggering policy of class: 
"org.apache.log4j.rolling.SizeBasedTriggeringPolicy"
   log4cxx: Setting option name=[MaxFileSize], value=[100MB]
   log4cxx: Parsing layout of class: "org.apache.log4j.PatternLayout"
   log4cxx: Setting option name=[ConversionPattern], value=[[%d{yyyy-MM-dd 
HH:mm:ss}] %c %-5p - %m%n]
   log4cxx: Adding appender named [multi] to logger [root].
   log4cxx: Can't cast writer to FileOutputStream
   ```
   
   as far as i understand the code it is caused by the cast in 
https://github.com/apache/logging-log4cxx/blob/master/src/main/cpp/multiprocessrollingfileappender.cpp#L508
   
   a quick and dirty implementation change which fixed the issue is instead of 
   
   ```cpp
   const FileOutputStreamPtr fos = LOG4CXX_NS::cast<FileOutputStream>( writer );
   ```
   
   something like this must be used to retrieve the `FileOutputStream` from the 
`WriterPtr`
   
   ```cpp
       const OutputStreamWriterPtr oswptr = 
static_pointer_cast<OutputStreamWriter>(writer);
       const OutputStreamPtr osptr = oswptr->getOutputStreamPtr();
       const CountingOutputStreamPtr cos = 
static_pointer_cast<CountingOutputStream>(osptr);
       const OutputStream *ptr = &(cos->getFileOutPutStreamPtr());
       const FileOutputStream *fos = dynamic_cast<const FileOutputStream 
*>(ptr);
   ```


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