util: limit inspection output size to 128 MB

The maximum hard limit that `util.inspect()` could theoretically handle
is the maximum string size. That is ~2 ** 28 on 32 bit systems and
~2 ** 30 on 64 bit systems.

Due to the recursive algorithm a complex object could easily exceed
that limit without throwing an error right away and therefore
crashing the application by exceeding the heap limit.

`util.inspect()` is fast enough to compute 128 MB of data below one
second on an Intel(R) Core(TM) i7-5600U CPU. This hard limit allows
to inspect arbitrary big objects from now on without crashing the
application or blocking the event loop significantly.

PR-URL: https://github.com/nodejs/node/pull/22756
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/test/parallel/test-util-inspect-long-running.js b/test/parallel/test-util-inspect-long-running.js
new file mode 100644
index 0000000000..167f72ba64
--- /dev/null
+++ b/test/parallel/test-util-inspect-long-running.js
@@ -0,0 +1,20 @@
+'use strict';
+
+require('../common');
+
+// Test that huge objects don't crash due to exceeding the maximum heap size.
+
+const util = require('util');
+
+// Create a difficult to stringify object. Without the artificial limitation
+// this would crash or throw an maximum string size error.
+let last = {};
+const obj = last;
+
+for (let i = 0; i < 1000; i++) {
+  last.next = { circular: obj, last, obj: { a: 1, b: 2, c: true } };
+  last = last.next;
+  obj[i] = last;
+}
+
+util.inspect(obj, { depth: Infinity });