Merge pull request #232 from Expensify/neil-shouldSaveCommitCount

Save commitCount when response says to

Author: rlinoz

src/Client.php

@@ -703,12 +703,11 @@ private function receiveResponse()
             }
         } while (is_null($responseLength) || strlen($response) < $responseLength);
 
-        // We save the commitCount for future requests. This is useful if for some reason we change the bedrock node we
-        // are talking to.
-        // We only set it if process time was returned, which means we did a write. We don't care about saving the commit
-        // count for reads, since we did not change anything in the DB.
-        if (isset($responseHeaders['commitCount']) && (($responseHeaders['processTime'] ?? 0) > 0 || ($responseHeaders['upstreamProcessTime'] ?? 0) > 0)) {
-            $this->commitCount = (int) $responseHeaders['commitCount'];
+        // Save the commit count if needed.
+        // In some cases, Auth will return a header instructing the client to save the commit count. It is useful for determining if stale data was used for certain read commands.
+        // Commit counts are saved for all write commands, identified by process time being non-zero, because it can be useful for future requests if for some reason we change the bedrock node we are talking to.
+        if ($responseHeaders['shouldSaveCommitCount'] ?? false || (isset($responseHeaders['commitCount']) && (($responseHeaders['processTime'] ?? 0) > 0 || ($responseHeaders['upstreamProcessTime'] ?? 0) > 0))) {
+            $this->commitCount = (int) ($responseHeaders['commitCount'] ?? 0);
         }
 
         // We treat this '555 Timeout', which is a command timeout (not a query timeout), as a ConnectionFailure so that it gets retried regardless of if it is idempotent or not.