core: Add an option to return errors in different formats (#1071)

Bridge errors are currently included as part of the feed to
notify users about erroneous bridges (before that, bridges
silently failed).

This solution, however, can produce a high load of error
messages if servers are down (see #994 for more details).

Admins may also not want to include error messages in feeds
in order to keep those kind of problems away from users or
simply to silently fail by choice.

This commit adds a new configuration section "error" with
one option "output" which can be set to following values:

"feed": To include error messages in the feed (default)
"http": To return a HTTP header for each error
"none": To disable error reporting

Note that errors are always logged to 'error.log' independent
of the settings above.

Closes #1066

actions/DisplayAction.php

@@ -146,6 +146,7 @@ class DisplayAction extends ActionAbstract {
 			} catch(Error $e) {
 				error_log($e);
 
+				if(Configuration::getConfig('error', 'output') === 'feed') {
 					$item = new \FeedItem();
 
 					// Create "new" error message every 24 hours
@@ -178,9 +179,14 @@ class DisplayAction extends ActionAbstract {
 					$item->setContent(buildBridgeException($e, $bridge));
 
 					$items[] = $item;
+				} elseif(Configuration::getConfig('error', 'output') === 'http') {
+					header('Content-Type: text/html', true, $e->getCode());
+					die(buildTransformException($e, $bridge));
+				}
 			} catch(Exception $e) {
 				error_log($e);
 
+				if(Configuration::getConfig('error', 'output') === 'feed') {
 					$item = new \FeedItem();
 
 					// Create "new" error message every 24 hours
@@ -203,6 +209,10 @@ class DisplayAction extends ActionAbstract {
 					$item->setContent(buildBridgeException($e, $bridge));
 
 					$items[] = $item;
+				} elseif(Configuration::getConfig('error', 'output') === 'http') {
+					header('Content-Type: text/html', true, $e->getCode());
+					die(buildTransformException($e, $bridge));
+				}
 			}
 
 			// Store data in cache

config.default.ini.php

@@ -61,6 +61,15 @@ username = ""
 ; Use a strong password to prevent others from guessing your login!
 password = ""
 
+[error]
+
+; Defines how error messages are returned by RSS-Bridge
+;
+; "feed" = As part of the feed (default)
+; "http" = As HTTP error message
+; "none" = No errors are reported
+output = "feed"
+
 ; --- Cache specific configuration ---------------------------------------------
 
 [SQLiteCache]

lib/Configuration.php

@@ -201,6 +201,9 @@ final class Configuration {
 		&& !filter_var(self::getConfig('admin', 'email'), FILTER_VALIDATE_EMAIL))
 			self::reportConfigurationError('admin', 'email', 'Is not a valid email address');
 
+		if(!is_string(self::getConfig('error', 'output')))
+			self::reportConfigurationError('error', 'output', 'Is not a valid String');
+
 	}
 
 	/**