Catch exceptions from ::isWriteMode in ApiMain::sendCacheHeaders

Why:
* Modules that extend ApiQueryBase are loaded using the ApiQuery
  module. This defines an override to the ApiBase::isWriteMode
  method that loads the modules.
* Using the mModule when $isError is true could lead to the
  exception that was thrown in ::executeAction being thrown again.
* Therefore, ApiMain::sendCacheHeaders should only call the
  ApiBase::isWriteMode method if the request did not fail
  with an error that caused $isError to be true.
* Without this fix, ApiUsageExceptions appear in logstash as
  exceptions, as described in T363133.

What:
* Only interact with $this->mModule if the $isError argument
  is false. If $isError is true, assume that ::isWriteMode
  would return true. Assuming this will also avoid error
  responses being marked as fresh for any amount of time, as
  the error may be temporary.
* Add a test that verifies that the method does not throw if
  ApiBase::isWriteMode throws an ApiUsageException.

Bug: T363133
Change-Id: I41d869c257878b8a94d6c40332e2028405de8729

1 files changed, 1 insertions, 1 deletions

diff --git a/includes/api/ApiMain.php b/includes/api/ApiMain.php
index 7d38d740801f..4773d9b7d2a1 100644
--- a/includes/api/ApiMain.php
+++ b/includes/api/ApiMain.php
@@ -1243,7 +1243,7 @@ class ApiMain extends ApiBase {
 		$maxage = 0;
 		if ( isset( $this->mCacheControl['max-age'] ) ) {
 			$maxage = $this->mCacheControl['max-age'];
-		} elseif ( ( $this->mModule && !$this->mModule->isWriteMode() ) ||
+		} elseif ( ( !$isError && $this->mModule && !$this->mModule->isWriteMode() ) ||
 			$this->mCacheMode !== 'private'
 		) {
 			$maxage = $this->getParameter( 'maxage' );