DRY up the static cache

TODO

@@ -5,7 +5,6 @@ add feedback for errors to UI - esp. too long
 add about page
 make asset caching optional
 todo store buffer instead of string while grabbing contents (if possible)
-write cache to use callback instead of using non-DRY code
 
 # shared version only
 some way to do announcements easily (and use for ads)

lib/static_handler.js

@@ -35,40 +35,50 @@ StaticHandler.prototype.handle = function(incPath, response) {
   // Go to index if not found or /
   if (!this.availablePaths[incPath]) incPath = this.defaultPath;
   var filePath = this.basePath + (incPath == '/' ? this.defaultPath : incPath);
-  // And then stream the file back
-  if (StaticHandler.cache[filePath]) {
-    this.serveCached(filePath, response);
-  }
-  else {
-    this.retrieve(filePath, response);
-  }
-};
-
-// Retrieve from the file
-StaticHandler.prototype.retrieve = function(filePath, response) {
-  var _this = this;
-  fs.readFile(filePath, function(error, content) {
-    if (error) {
-      winston.error('unable to read file', { path: filePath, error: error.message });
-      response.writeHead(500, { 'content-type': 'application/json' });
-      response.end(JSON.stringify({ message: 'IO: Unable to read file' }));
-    }
-    else {
+  // And then stream the file back - either from the cache or from source
+  var cached = this.isCached(filePath);
+  var method = cached ? this.serveCached : this.retrieve;
+  // Run!
+  method(filePath, function(error, content) {
+    // Get the content
+    if (content) {
       var contentType = StaticHandler.contentTypeFor(path.extname(filePath));
       response.writeHead(200, { 'content-type': contentType });
       response.end(content, 'utf-8');
-      // Stick it in the cache
+      // Stick it in the cache if its not in there
+      if (!cached) {
         StaticHandler.cache[filePath] = content;
       }
+    }
+    // Or break down and cry
+    else {
+      winston.error('unable to read file', { path: filePath, error: error });
+      response.writeHead(500, { 'content-type': 'application/json' });
+      response.end(JSON.stringify({ message: 'IO: Unable to read file' }));
+      // If it was cached, bust the cache
+      if (cached) {
+        StaticHandler.cache[filePath] = null;
+      }
+    }
   }); 
 };
 
-// Retrieve from memory cache
-StaticHandler.prototype.serveCached = function(filePath, response) {
-  var contentType = StaticHandler.contentTypeFor(path.extname(filePath));
-  response.writeHead(200, { 'content-type': contentType });
-  response.end(StaticHandler.cache[filePath], 'utf-8');
+// Retrieve from the file
+StaticHandler.prototype.retrieve = function(filePath, callback) {
+  var _this = this;
+  fs.readFile(filePath, function(error, content) {
+    callback(error, content);
+  });    
 };
 
+// Retrieve from memory cache
+StaticHandler.prototype.serveCached = function(filePath, callback) {
+  callback(undefined, StaticHandler.cache[filePath]);
+};
+
+// Determine if a given filePath is cached or not
+StaticHandler.prototype.isCached = function(filePath) {
+  return !!StaticHandler.cache[filePath];
+};
 
 module.exports = StaticHandler;