Bug fixes to reduce logging-related crashes

* Provide a method for plugins to report failure to initialise
* Check plugins initialised properly before adding to list of logging
backends
* Check the logger is available before trying to log a message
(might cause bugs if errors are logged very early in initialisation)

source/lib/SihnonFramework/Log/Plugin/FlatFile.class.php

@@ -18,6 +18,9 @@ class SihnonFramework_Log_Plugin_FlatFile extends SihnonFramework_Log_PluginBase
         $this->filename = $filename;
         $this->format   = $format;
         
+        // Verify the given log file can be written to
+        $this->verifyLogfile();
+        
         $this->fp = fopen($this->filename, 'a');
     }
     
@@ -32,6 +35,26 @@ class SihnonFramework_Log_Plugin_FlatFile extends SihnonFramework_Log_PluginBase
         return new self($instance, $filename, $format);
     }
     
+    protected function verifyLogfile() {
+        // Check that the file exists, or can be created
+        $file_ok = false;
+        
+        if (preg_match('#php://(stderr|stdout)#', $this->filename)) {
+            $file_ok = true;
+        } else if (file_exists($this->filename) && is_writable($this->filename)) {
+            $file_ok = true;
+        } else {
+            $directory = dirname($this->filename);
+            if (file_exists($directory) && is_writeable($directory)) {
+                $file_ok = true;
+            }
+        }
+        
+        if (!$file_ok) {
+            throw new SihnonFramework_Exception_LogFileNotWriteable($this->filename);
+        }
+    }
+    
     /**
      * Records a new entry in the storage backend used by this logging plugin
      *