util: fix inspecting of proxy objects

In certain conditions, inspecting a Proxy object can lead to a
max call stack error. Avoid that by detecting the Proxy object
and outputting information about the Proxy object itself.

Fixes: https://github.com/nodejs/node/issues/6464
PR-URL: https://github.com/nodejs/node/pull/6465
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

1 files changed, 84 insertions, 0 deletions

diff --git a/test/parallel/test-util-inspect-proxy.js b/test/parallel/test-util-inspect-proxy.js
new file mode 100644
index 0000000000..6311884b85
--- /dev/null
+++ b/test/parallel/test-util-inspect-proxy.js
@@ -0,0 +1,84 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const util = require('util');
+const processUtil = process.binding('util');
+const opts = {showProxy: true};
+
+const target = {};
+const handler = {
+  get: function() { throw new Error('Getter should not be called'); }
+};
+const proxyObj = new Proxy(target, handler);
+
+// Inspecting the proxy should not actually walk it's properties
+assert.doesNotThrow(() => util.inspect(proxyObj, opts));
+
+// getProxyDetails is an internal method, not intended for public use.
+// This is here to test that the internals are working correctly.
+const details = processUtil.getProxyDetails(proxyObj);
+assert.strictEqual(target, details[0]);
+assert.strictEqual(handler, details[1]);
+
+assert.strictEqual(util.inspect(proxyObj, opts),
+                   'Proxy [ {}, { get: [Function] } ]');
+
+// Using getProxyDetails with non-proxy returns undefined
+assert.strictEqual(processUtil.getProxyDetails({}), undefined);
+
+// This will throw because the showProxy option is not used
+// and the get function on the handler object defined above
+// is actually invoked.
+assert.throws(
+  () => util.inspect(proxyObj)
+);
+
+// Yo dawg, I heard you liked Proxy so I put a Proxy
+// inside your Proxy that proxies your Proxy's Proxy.
+const proxy1 = new Proxy({}, {});
+const proxy2 = new Proxy(proxy1, {});
+const proxy3 = new Proxy(proxy2, proxy1);
+const proxy4 = new Proxy(proxy1, proxy2);
+const proxy5 = new Proxy(proxy3, proxy4);
+const proxy6 = new Proxy(proxy5, proxy5);
+const expected0 = '{}';
+const expected1 = 'Proxy [ {}, {} ]';
+const expected2 = 'Proxy [ Proxy [ {}, {} ], {} ]';
+const expected3 = 'Proxy [ Proxy [ Proxy [ {}, {} ], {} ], Proxy [ {}, {} ] ]';
+const expected4 = 'Proxy [ Proxy [ {}, {} ], Proxy [ Proxy [ {}, {} ], {} ] ]';
+const expected5 = 'Proxy [ Proxy [ Proxy [ Proxy [Object], {} ],' +
+                  ' Proxy [ {}, {} ] ],\n  Proxy [ Proxy [ {}, {} ]' +
+                  ', Proxy [ Proxy [Object], {} ] ] ]';
+const expected6 = 'Proxy [ Proxy [ Proxy [ Proxy [Object], Proxy [Object]' +
+                  ' ],\n    Proxy [ Proxy [Object], Proxy [Object] ] ],\n' +
+                  '  Proxy [ Proxy [ Proxy [Object], Proxy [Object] ],\n' +
+                  '    Proxy [ Proxy [Object], Proxy [Object] ] ] ]';
+assert.strictEqual(util.inspect(proxy1, opts), expected1);
+assert.strictEqual(util.inspect(proxy2, opts), expected2);
+assert.strictEqual(util.inspect(proxy3, opts), expected3);
+assert.strictEqual(util.inspect(proxy4, opts), expected4);
+assert.strictEqual(util.inspect(proxy5, opts), expected5);
+assert.strictEqual(util.inspect(proxy6, opts), expected6);
+assert.strictEqual(util.inspect(proxy1), expected0);
+assert.strictEqual(util.inspect(proxy2), expected0);
+assert.strictEqual(util.inspect(proxy3), expected0);
+assert.strictEqual(util.inspect(proxy4), expected0);
+assert.strictEqual(util.inspect(proxy5), expected0);
+assert.strictEqual(util.inspect(proxy6), expected0);
+
+// Just for fun, let's create a Proxy using Arrays.
+const proxy7 = new Proxy([], []);
+const expected7 = 'Proxy [ [], [] ]';
+assert.strictEqual(util.inspect(proxy7, opts), expected7);
+assert.strictEqual(util.inspect(proxy7), '[]');
+
+// Now we're just getting silly, right?
+const proxy8 = new Proxy(Date, []);
+const proxy9 = new Proxy(Date, String);
+const expected8 = 'Proxy [ [Function: Date], [] ]';
+const expected9 = 'Proxy [ [Function: Date], [Function: String] ]';
+assert.strictEqual(util.inspect(proxy8, opts), expected8);
+assert.strictEqual(util.inspect(proxy9, opts), expected9);
+assert.strictEqual(util.inspect(proxy8), '[Function: Date]');
+assert.strictEqual(util.inspect(proxy9), '[Function: Date]');