Slightly better error messages on reading AudioProperties

spec/taglibSpec.js

@@ -59,6 +59,30 @@ vows.describe('taglib bindings')
     }
   },
 
+  'reading AudioProperties from non-existent file': {
+    topic: function() {
+        return function() {
+          return new Taglib.AudioProperties('thisfileobviouslyshouldnot.exist');
+        }
+    },
+
+    'should throw an exception': function(topic) {
+        assert.throws(topic, /readable/);
+    }
+  },
+
+  'reading AudioProperties from a non-audio file': {
+    topic: function() {
+        return function() {
+          return new Taglib.AudioProperties(__filename);
+        }
+    },
+
+    'should throw an exception': function(topic) {
+        assert.throws(topic, /extract audio properties/);
+    }
+  },
+
   'writing Tags to File': {
     topic: function() {
       var filename = __dirname+'/sample-write.mp3';

src/audioproperties.cc

@@ -56,12 +56,16 @@ Handle<Value> AudioProperties::New(const Arguments &args) {
 
     String::Utf8Value path(args[0]->ToString());
 
+    if (!TagLib::File::isReadable(*path)) {
+        std::string err = "File " + std::string(*path) + " is not readable";
+        return ThrowException(String::New(err.c_str(), err.length()));
+    }
+
     TagLib::FileRef * f = new TagLib::FileRef(*path);
     if ( f->isNull() || !f->audioProperties() )
     {
-        std::string err = "Error while reading data from ";
-        err = err + std::string(*path);
-        return ThrowException( String::New( err.c_str(), err.length() ) );
+        std::string err = "Failed to extract audio properties from " + std::string(*path);
+        return ThrowException(String::New(err.c_str(),err.length()));
     }
 
     AudioProperties * properties = new AudioProperties(f);