Allow HEAD requests on collections

GCDWebDAVServer/GCDWebDAVServer.m

@@ -88,13 +88,15 @@ static inline BOOL _IsMacFinder(GCDWebServerRequest* request) {
   if (![absolutePath hasPrefix:_uploadDirectory] || ![[NSFileManager defaultManager] fileExistsAtPath:absolutePath isDirectory:&isDirectory]) {
     return [GCDWebServerErrorResponse responseWithClientError:kGCDWebServerHTTPStatusCode_NotFound message:@"\"%@\" does not exist", relativePath];
   }
-  if (isDirectory) {
-    return [GCDWebServerErrorResponse responseWithClientError:kGCDWebServerHTTPStatusCode_BadRequest message:@"\"%@\" is not a file", relativePath];
+  
+  NSString* itemName = [absolutePath lastPathComponent];
+  if (([itemName hasPrefix:@"."] && !_showHidden) || (!isDirectory && ![self _checkFileExtension:itemName])) {
+    return [GCDWebServerErrorResponse responseWithClientError:kGCDWebServerHTTPStatusCode_Forbidden message:@"Downlading item name \"%@\" is not allowed", itemName];
   }
   
-  NSString* fileName = [absolutePath lastPathComponent];
-  if (([fileName hasPrefix:@"."] && !_showHidden) || ![self _checkFileExtension:fileName]) {
-    return [GCDWebServerErrorResponse responseWithClientError:kGCDWebServerHTTPStatusCode_Forbidden message:@"Downlading file name \"%@\" is not allowed", fileName];
+  // Because HEAD requests are mapped to GET ones, we need to handle directories but it's OK to return nothing per http://webdav.org/specs/rfc4918.html#rfc.section.9.4
+  if (isDirectory) {
+    return [GCDWebServerResponse response];
   }
   
   if ([_delegate respondsToSelector:@selector(davServer:didDownloadFileAtPath:)]) {