out_es: Prevent a SIGSEGV when ctx->index is NULL

plugins/out_es/es.c

@@ -627,6 +627,11 @@ static int cb_es_init(struct flb_output_instance *ins,
         return -1;
     }
 
+    if (ctx->index == NULL && ctx->logstash_format == FLB_FALSE && ctx->generate_id == FLB_FALSE) {
+        flb_plg_error(ins, "cannot initialize plugin, index is not set and logstash_format and generate_id are both off");
+        return -1;
+    }
+
     flb_plg_debug(ctx->ins, "host=%s port=%i uri=%s index=%s type=%s",
                   ins->host.name, ins->host.port, ctx->uri,
                   ctx->index, ctx->type);
@@ -937,7 +942,7 @@ static void cb_es_flush(struct flb_event_chunk *event_chunk,
                     /*
                      * If trace_error is set, trace the actual
                      * response from Elasticsearch explaining the problem.
-                     * Trace_Output can be used to see the request. 
+                     * Trace_Output can be used to see the request.
                      */
                     if (pack_size < 4000) {
                         flb_plg_debug(ctx->ins, "error caused by: Input\n%.*s\n",

tests/runtime/out_elasticsearch.c

@@ -347,6 +347,47 @@ void flb_test_write_operation_upsert()
     flb_destroy(ctx);
 }
 
+void flb_test_null_index()
+{
+    int ret;
+    int size = sizeof(JSON_ES) - 1;
+    flb_ctx_t *ctx;
+    int in_ffd;
+    int out_ffd;
+    /* Create context, flush every second (some checks omitted here) */
+    ctx = flb_create();
+    flb_service_set(ctx, "flush", "1", "grace", "1", NULL);
+
+    /* Lib input mode */
+    in_ffd = flb_input(ctx, (char *) "lib", NULL);
+    flb_input_set(ctx, in_ffd, "tag", "test", NULL);
+
+    /* Elasticsearch output */
+    out_ffd = flb_output(ctx, (char *) "es", NULL);
+    flb_output_set(ctx, out_ffd,
+                   "match", "test",
+                   NULL);
+
+    /* Override defaults of index and type */
+    flb_output_set(ctx, out_ffd,
+                   "index", "",
+                   "type", "type_test",
+                   NULL);
+
+    /* Enable test mode */
+    ret = flb_output_set_test(ctx, out_ffd, "formatter",
+                              cb_check_index_type,
+                              NULL, NULL);
+
+    /* Start */
+    ret = flb_start(ctx);
+    TEST_CHECK(ret == -1);
+
+    sleep(2);
+    flb_stop(ctx);
+    flb_destroy(ctx);
+}
+
 void flb_test_index_type()
 {
     int ret;