GCS: Use idempotency token to identify requests (#126887)

Author: nicktindall

modules/repository-gcs/src/internalClusterTest/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageBlobStoreRepositoryTests.java

@@ -325,6 +325,8 @@ private static class GoogleCloudStorageBlobStoreHttpHandler extends GoogleCloudS
     @SuppressForbidden(reason = "this test uses a HttpServer to emulate a Google Cloud Storage endpoint")
     private static class GoogleErroneousHttpHandler extends ErroneousHttpHandler {
 
+        private static final String IDEMPOTENCY_TOKEN = "x-goog-gcs-idempotency-token";
+
         GoogleErroneousHttpHandler(final HttpHandler delegate, final int maxErrorsPerRequest) {
             super(delegate, maxErrorsPerRequest);
         }
@@ -340,6 +342,10 @@ protected String requestUniqueId(HttpExchange exchange) {
                 }
             }
 
+            if (exchange.getRequestHeaders().containsKey(IDEMPOTENCY_TOKEN)) {
+                return exchange.getRequestHeaders().getFirst(IDEMPOTENCY_TOKEN);
+            }
+
             final String range = exchange.getRequestHeaders().getFirst("Content-Range");
             return exchange.getRemoteAddress().getHostString()
                 + " "