/**
  * Builds a request to retrieve the actual content.
  *
  * @param GadgetContext $context The rendering context.
  * @param MakeRequestOptions $params Options for crafting the request.
  * @param SecurityTokenDecoder $signer A signer needed for signed requests.
  * @return RemoteContentRequest An initialized request object.
  */
 public function buildRequest(GadgetContext $context, MakeRequestOptions $params, SecurityTokenDecoder $signer = null)
 {
     // Check the protocol requested - curl doesn't really support file://
     // requests but the 'error' should be handled properly
     $protocolSplit = explode('://', $params->getHref(), 2);
     if (count($protocolSplit) < 2) {
         throw new Exception("Invalid protocol specified");
     }
     $protocol = strtoupper($protocolSplit[0]);
     if ($protocol != "HTTP" && $protocol != "HTTPS") {
         throw new Exception("Invalid protocol specified in url: " . htmlentities($protocol));
     }
     $method = $params->getHttpMethod();
     if ($method == 'POST' || $method == 'PUT') {
         // even if postData is an empty string, it will still post
         // (since RemoteContentRquest checks if its false)
         // so the request to POST is still honored
         $request = new RemoteContentRequest($params->getHref(), null, $params->getRequestBody());
     } else {
         if ($method == 'DELETE' || $method == 'GET' || $method == 'HEAD') {
             $request = new RemoteContentRequest($params->getHref());
         } else {
             throw new Exception("Invalid HTTP method.");
         }
     }
     $request->setMethod($method);
     if ($signer) {
         switch ($params->getAuthz()) {
             case 'SIGNED':
                 $request->setAuthType(RemoteContentRequest::$AUTH_SIGNED);
                 break;
             case 'OAUTH':
                 $request->setAuthType(RemoteContentRequest::$AUTH_OAUTH);
                 $request->setOAuthRequestParams($params->getOAuthRequestParameters());
                 break;
         }
         $st = $params->getSecurityTokenString();
         if ($st === false) {
             throw new Exception("A security token is required for signed requests");
         }
         $token = $context->validateToken($st, $signer);
         $request->setToken($token);
     }
     // Strip invalid request headers.  This limits the utility of the
     // MakeRequest class a little bit, but ensures that none of the invalid
     // headers are present in any request going through this class.
     $headers = $params->getRequestHeadersArray();
     if ($headers !== false) {
         $headers = $this->stripInvalidArrayKeys($headers, MakeRequest::$BAD_REQUEST_HEADERS);
         $params->setRequestHeaders($headers);
     }
     // The request expects headers to be stored as a normal header text blob.
     // ex: Content-Type: application/atom+xml
     //     Accept-Language: en-us
     $formattedHeaders = $params->getFormattedRequestHeaders();
     if ($formattedHeaders !== false) {
         $request->setHeaders($formattedHeaders);
     }
     return $request;
 }