assert: cap large assertion diffs

benchmark/assert/strict-equal-buffer-array.js

@@ -0,0 +1,23 @@
+'use strict';
+const common = require('../common.js');
+const assert = require('assert');
+
+const bench = common.createBenchmark(main, {
+  n: [100],
+  size: [1000, 8000],
+});
+
+function main({ n, size }) {
+  const buffer = Buffer.alloc(size);
+
+  bench.start();
+  for (let i = 0; i < n; ++i) {
+    new assert.AssertionError({
+      actual: buffer,
+      expected: [buffer],
+      operator: 'strictEqual',
+      stackStartFunction: () => {},
+    });
+  }
+  bench.end(n);
+}

lib/internal/assert/assertion_error.js

@@ -42,6 +42,7 @@ const kReadableOperator = {
 
 const kMaxShortStringLength = 12;
 const kMaxLongStringLength = 512;
+const kMaxDiffInputLines = 1000;
 
 const kMethodsWithCustomMessageDiff = new SafeSet()
   .add('deepStrictEqual')
@@ -215,17 +216,27 @@ function createErrDiff(actual, expected, operator, customMessage, diffType = 'si
     header = '';
   } else {
     const checkCommaDisparity = actual != null && typeof actual === 'object';
-    const diff = myersDiff(inspectedSplitActual, inspectedSplitExpected, checkCommaDisparity);
+    if (
+      diffType !== 'full' &&
+      (inspectedSplitActual.length > kMaxDiffInputLines ||
+        inspectedSplitExpected.length > kMaxDiffInputLines)
+    ) {
+      message = `\n${colors.green}+${colors.white} ${addEllipsis(inspectedActual)}\n` +
+        `${colors.red}-${colors.white} ${addEllipsis(inspectedExpected)}`;
+      skipped = true;
+    } else {
+      const diff = myersDiff(inspectedSplitActual, inspectedSplitExpected, checkCommaDisparity);
 
-    const myersDiffMessage = printMyersDiff(diff, operator);
-    message = myersDiffMessage.message;
+      const myersDiffMessage = printMyersDiff(diff, operator);
+      message = myersDiffMessage.message;
 
-    if (operator === 'partialDeepStrictEqual') {
-      header = `${colors.gray}${colors.hasColors ? '' : '+ '}actual${colors.white} ${colors.red}- expected${colors.white}`;
-    }
+      if (operator === 'partialDeepStrictEqual') {
+        header = `${colors.gray}${colors.hasColors ? '' : '+ '}actual${colors.white} ${colors.red}- expected${colors.white}`;
+      }
 
-    if (myersDiffMessage.skipped) {
-      skipped = true;
+      if (myersDiffMessage.skipped) {
+        skipped = true;
+      }
     }
   }
 
@@ -241,7 +252,7 @@ function addEllipsis(string) {
     lines.length = 10;
     return `${ArrayPrototypeJoin(lines, '\n')}\n...`;
   } else if (string.length > kMaxLongStringLength) {
-    return `${StringPrototypeSlice(string, kMaxLongStringLength)}...`;
+    return `${StringPrototypeSlice(string, 0, kMaxLongStringLength)}...`;
   }
   return string;
 }

test/parallel/test-assert.js

@@ -559,6 +559,16 @@ test('Output that extends beyond 10 lines should also be truncated for display',
   });
 });
 
+test('Large strictEqual object diffs are truncated for display', () => {
+  const buffer = Buffer.alloc(1001);
+  const err = assert.throws(() => assert.strictEqual(buffer, [buffer]));
+
+  assert.strictEqual(err.code, 'ERR_ASSERTION');
+  assert.match(err.message, /\.\.\. Skipped lines/);
+  assert.ok(err.message.includes('<Buffer'));
+  assert.ok(err.message.split('\n').length < 40);
+});
+
 test('Bad args to AssertionError constructor should throw TypeError.', () => {
   const args = [1, true, false, '', null, Infinity, Symbol('test'), undefined];
   for (const input of args) {