assert: prevent OOM when generating diff for large objects

lib/internal/assert/assertion_error.js

@@ -12,6 +12,7 @@ const {
   ObjectPrototypeHasOwnProperty,
   SafeSet,
   String,
+  StringPrototypeEndsWith,
   StringPrototypeRepeat,
   StringPrototypeSlice,
   StringPrototypeSplit,
@@ -42,6 +43,11 @@ const kReadableOperator = {
 
 const kMaxShortStringLength = 12;
 const kMaxLongStringLength = 512;
+// Maximum size for inspect output before truncation to prevent OOM.
+// Objects with many converging paths can produce exponential growth in
+// util.inspect output at high depths, leading to OOM during diff generation.
+const kMaxInspectOutputLength = 2 * 1024 * 1024; // 2MB
+const kTruncatedByteMarker = '\n... [truncated]';
 
 const kMethodsWithCustomMessageDiff = new SafeSet()
   .add('deepStrictEqual')
@@ -72,7 +78,7 @@ function copyError(source) {
 function inspectValue(val) {
   // The util.inspect default values could be changed. This makes sure the
   // error messages contain the necessary information nevertheless.
-  return inspect(val, {
+  const result = inspect(val, {
     compact: false,
     customInspect: false,
     depth: 1000,
@@ -85,6 +91,17 @@ function inspectValue(val) {
     // Inspect getters as we also check them when comparing entries.
     getters: true,
   });
+
+  // Truncate if the output is too large to prevent OOM during diff generation.
+  // Objects with deeply nested structures can produce exponentially large
+  // inspect output that causes memory exhaustion when passed to the diff
+  // algorithm.
+  if (result.length > kMaxInspectOutputLength) {
+    return StringPrototypeSlice(result, 0, kMaxInspectOutputLength) +
+      kTruncatedByteMarker;
+  }
+
+  return result;
 }
 
 function getErrorMessage(operator, message) {
@@ -189,6 +206,12 @@ function createErrDiff(actual, expected, operator, customMessage, diffType = 'si
   let message = '';
   const inspectedActual = inspectValue(actual);
   const inspectedExpected = inspectValue(expected);
+
+  // Check if either value was truncated due to size limits
+  if (StringPrototypeEndsWith(inspectedActual, kTruncatedByteMarker) ||
+      StringPrototypeEndsWith(inspectedExpected, kTruncatedByteMarker)) {
+    skipped = true;
+  }
   const inspectedSplitActual = StringPrototypeSplit(inspectedActual, '\n');
   const inspectedSplitExpected = StringPrototypeSplit(inspectedExpected, '\n');
   const showSimpleDiff = isSimpleDiff(actual, inspectedSplitActual, expected, inspectedSplitExpected);

test/parallel/test-assert-large-object-diff-oom.js

@@ -0,0 +1,91 @@
+// Flags: --max-old-space-size=512
+'use strict';
+
+// Regression test: assert.strictEqual should not OOM when comparing objects
+// with many converging paths to shared objects. Such objects cause exponential
+// growth in util.inspect output, which previously led to OOM during error
+// message generation.
+
+require('../common');
+const assert = require('assert');
+
+// Test: should throw AssertionError, not OOM
+{
+  const { doc1, doc2 } = createTestObjects();
+
+  assert.throws(
+    () => assert.strictEqual(doc1, doc2),
+    (err) => {
+      assert.ok(err instanceof assert.AssertionError);
+      // Message should be bounded (fix truncates inspect output at 2MB)
+      assert.ok(err.message.length < 5 * 1024 * 1024);
+      return true;
+    }
+  );
+}
+
+// Creates objects where many paths converge on shared objects, causing
+// exponential growth in util.inspect output at high depths.
+function createTestObjects() {
+  const base = createBase();
+
+  const s1 = createSchema(base, 's1');
+  const s2 = createSchema(base, 's2');
+  base.schemas.s1 = s1;
+  base.schemas.s2 = s2;
+
+  const doc1 = createDoc(s1, base);
+  const doc2 = createDoc(s2, base);
+
+  // Populated refs create additional converging paths
+  for (let i = 0; i < 2; i++) {
+    const ps = createSchema(base, 'p' + i);
+    base.schemas['p' + i] = ps;
+    doc1.$__.pop['r' + i] = { value: createDoc(ps, base), opts: { base, schema: ps } };
+  }
+
+  // Cross-link creates more converging paths
+  doc1.$__.pop.r0.value.$__parent = doc2;
+
+  return { doc1, doc2 };
+}
+
+function createBase() {
+  const base = { types: {}, schemas: {} };
+  for (let i = 0; i < 4; i++) {
+    base.types['t' + i] = {
+      base,
+      caster: { base },
+      opts: { base, validators: [{ base }, { base }] }
+    };
+  }
+  return base;
+}
+
+function createSchema(base, name) {
+  const schema = { name, base, paths: {}, children: [] };
+  for (let i = 0; i < 6; i++) {
+    schema.paths['f' + i] = {
+      schema, base,
+      type: base.types['t' + (i % 4)],
+      caster: base.types['t' + (i % 4)].caster,
+      opts: { schema, base, validators: [{ schema, base }] }
+    };
+  }
+  for (let i = 0; i < 2; i++) {
+    const child = { name: name + '_c' + i, base, parent: schema, paths: {} };
+    for (let j = 0; j < 3; j++) {
+      child.paths['cf' + j] = { schema: child, base, type: base.types['t' + (j % 4)] };
+    }
+    schema.children.push(child);
+  }
+  return schema;
+}
+
+function createDoc(schema, base) {
+  const doc = { schema, base, $__: { scopes: {}, pop: {} } };
+  for (let i = 0; i < 6; i++) {
+    doc.$__.scopes['p' + i] = { schema, base, type: base.types['t' + (i % 4)] };
+  }
+  return doc;
+}