Added ReaderWriter::fileExists() method to help enable querrying of existing of files on servers using the curl plugin

include/osgDB/Options

@@ -142,7 +142,7 @@ class OSGDB_EXPORT Options : public osg::Object
         void setPluginStringData(const std::string& s, const std::string& v) const { _pluginStringData[s] = v; }
 
         /** Get a string from the PluginStrData */
-        std::string getPluginStringData(const std::string& s) { return _pluginStringData[s]; }
+        std::string& getPluginStringData(const std::string& s) { return _pluginStringData[s]; }
 
         /** Get a value from the PluginData */
         const std::string getPluginStringData(const std::string& s) const

include/osgDB/ReaderWriter

@@ -200,6 +200,10 @@ class OSGDB_EXPORT ReaderWriter : public osg::Object
 
         typedef osgDB::Options Options;
 
+        /** determine if a file exists, normally the default implementation will be approrpiate for local file access
+         *  but with plugins like the libcurl based on it will return true if the file is accessible a server.*/
+        virtual bool fileExists(const std::string& filename, const Options* options) const;
+
         /** open an archive for reading, writing, or to create an empty archive for writing to.*/ 
         virtual ReadResult openArchive(const std::string& /*fileName*/,ArchiveStatus, unsigned int =4096, const Options* =NULL) const { return ReadResult(ReadResult::NOT_IMPLEMENTED); }
 

src/osgDB/ReaderWriter.cpp

@@ -117,3 +117,12 @@ ReaderWriter::FeatureList ReaderWriter::featureAsString(ReaderWriter::Features f
     }
     return result;
 }
+
+bool ReaderWriter::fileExists(const std::string& filename, const Options* /*options*/) const
+{
+#ifdef OSG_USE_UTF8_FILENAME
+    return _waccess( OSGDB_STRING_TO_FILENAME(filename).c_str(), F_OK ) == 0;
+#else
+    return access( filename.c_str(), F_OK ) == 0;
+#endif
+}