assert: prevent OOM when generating diff for large objects

lib/internal/assert/assertion_error.js

@@ -12,12 +12,14 @@ const {
   ObjectPrototypeHasOwnProperty,
   SafeSet,
   String,
+  StringPrototypeEndsWith,
   StringPrototypeRepeat,
   StringPrototypeSlice,
   StringPrototypeSplit,
 } = primordials;
 
 const { isError } = require('internal/util');
+const { totalmem } = require('os');
 
 const { inspect } = require('internal/util/inspect');
 const colors = require('internal/util/colors');
@@ -42,6 +44,16 @@ const kReadableOperator = {
 
 const kMaxShortStringLength = 12;
 const kMaxLongStringLength = 512;
+// Truncation limit for inspect output to prevent OOM during diff generation.
+// Scaled to system memory: 512KB under 1GB, 1MB under 2GB, 2MB otherwise.
+const kGB = 1024 ** 3;
+const kMB = 1024 ** 2;
+const totalMem = totalmem();
+const kMaxInspectOutputLength =
+  totalMem < kGB ? kMB / 2 :
+  totalMem < 2 * kGB ? kMB :
+  2 * kMB;
+const kTruncatedByteMarker = '\n... [truncated]';
 
 const kMethodsWithCustomMessageDiff = new SafeSet()
   .add('deepStrictEqual')
@@ -72,7 +84,7 @@ 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 +97,17 @@ 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 +212,12 @@ 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);

lib/internal/assert/myers_diff.js

@@ -2,7 +2,13 @@
 
 const {
   ArrayPrototypePush,
+  ArrayPrototypeSlice,
   Int32Array,
+  MathFloor,
+  MathMax,
+  MathMin,
+  MathRound,
+  RegExpPrototypeExec,
   StringPrototypeEndsWith,
 } = primordials;
 
@@ -14,7 +20,11 @@ const {
 
 const colors = require('internal/util/colors');
 
+const kChunkSize = 512;
 const kNopLinesToCollapse = 5;
+// Lines that are just structural characters make poor alignment anchors
+// because they appear many times and don't uniquely identify a position.
+const kTrivialLinePattern = /^\s*[{}[\],]+\s*$/;
 const kOperations = {
   DELETE: -1,
   NOP: 0,
@@ -31,19 +41,11 @@ function areLinesEqual(actual, expected, checkCommaDisparity) {
   return false;
 }
 
-function myersDiff(actual, expected, checkCommaDisparity = false) {
+function myersDiffInternal(actual, expected, checkCommaDisparity) {
   const actualLength = actual.length;
   const expectedLength = expected.length;
   const max = actualLength + expectedLength;
 
-  if (max > 2 ** 31 - 1) {
-    throw new ERR_OUT_OF_RANGE(
-      'myersDiff input size',
-      '< 2^31',
-      max,
-    );
-  }
-
   const v = new Int32Array(2 * max + 1);
   const trace = [];
 
@@ -124,6 +126,170 @@ function backtrack(trace, actual, expected, checkCommaDisparity) {
   return result;
 }
 
+function myersDiff(actual, expected, checkCommaDisparity = false) {
+  const actualLength = actual.length;
+  const expectedLength = expected.length;
+  const max = actualLength + expectedLength;
+
+  if (max > 2 ** 31 - 1) {
+    throw new ERR_OUT_OF_RANGE(
+      'myersDiff input size',
+      '< 2^31',
+      max,
+    );
+  }
+
+  // For small inputs, run the algorithm directly
+  if (actualLength <= kChunkSize && expectedLength <= kChunkSize) {
+    return myersDiffInternal(actual, expected, checkCommaDisparity);
+  }
+
+  const boundaries = findAlignedBoundaries(
+    actual, expected, checkCommaDisparity,
+  );
+
+  // Process chunks and concatenate results (last chunk first for reversed order)
+  const result = [];
+  for (let i = boundaries.length - 2; i >= 0; i--) {
+    const actualStart = boundaries[i].actualIdx;
+    const actualEnd = boundaries[i + 1].actualIdx;
+    const expectedStart = boundaries[i].expectedIdx;
+    const expectedEnd = boundaries[i + 1].expectedIdx;
+
+    const actualChunk = ArrayPrototypeSlice(actual, actualStart, actualEnd);
+    const expectedChunk = ArrayPrototypeSlice(expected, expectedStart, expectedEnd);
+
+    if (actualChunk.length === 0 && expectedChunk.length === 0) continue;
+
+    if (actualChunk.length === 0) {
+      for (let j = expectedChunk.length - 1; j >= 0; j--) {
+        ArrayPrototypePush(result, [kOperations.DELETE, expectedChunk[j]]);
+      }
+      continue;
+    }
+
+    if (expectedChunk.length === 0) {
+      for (let j = actualChunk.length - 1; j >= 0; j--) {
+        ArrayPrototypePush(result, [kOperations.INSERT, actualChunk[j]]);
+      }
+      continue;
+    }
+
+    const chunkDiff = myersDiffInternal(actualChunk, expectedChunk, checkCommaDisparity);
+    for (let j = 0; j < chunkDiff.length; j++) {
+      ArrayPrototypePush(result, chunkDiff[j]);
+    }
+  }
+
+  return result;
+}
+
+function findAlignedBoundaries(actual, expected, checkCommaDisparity) {
+  const actualLen = actual.length;
+  const expectedLen = expected.length;
+  const boundaries = [{ actualIdx: 0, expectedIdx: 0 }];
+  const searchRadius = kChunkSize / 2;
+
+  const numTargets = MathMax(
+    MathFloor((actualLen - 1) / kChunkSize),
+    1,
+  );
+
+  for (let i = 1; i <= numTargets; i++) {
+    const targetActual = MathMin(i * kChunkSize, actualLen);
+    if (targetActual >= actualLen) {
+      break;
+    }
+
+    const targetExpected = MathMin(
+      MathRound(targetActual * expectedLen / actualLen),
+      expectedLen - 1,
+    );
+    const prevBoundary = boundaries[boundaries.length - 1];
+
+    const anchor = findAnchorNear(
+      actual, expected, targetActual, targetExpected,
+      prevBoundary, searchRadius, checkCommaDisparity,
+    );
+
+    if (anchor !== undefined) {
+      ArrayPrototypePush(boundaries, anchor);
+    } else {
+      // Fallback: use proportional position, ensuring strictly increasing
+      const fallbackActual = MathMax(targetActual, prevBoundary.actualIdx + 1);
+      const fallbackExpected = MathMax(targetExpected, prevBoundary.expectedIdx + 1);
+      if (fallbackActual < actualLen && fallbackExpected < expectedLen) {
+        ArrayPrototypePush(boundaries, { actualIdx: fallbackActual, expectedIdx: fallbackExpected });
+      }
+    }
+  }
+
+  ArrayPrototypePush(boundaries, { actualIdx: actualLen, expectedIdx: expectedLen });
+  return boundaries;
+}
+
+// Search outward from targetActual and targetExpected for a non-trivial
+// line that matches in both arrays, with adjacent context verification.
+function findAnchorNear(actual, expected, targetActual, targetExpected,
+                        prevBoundary, searchRadius, checkCommaDisparity) {
+  const actualLen = actual.length;
+  const expectedLen = expected.length;
+
+  for (let offset = 0; offset <= searchRadius; offset++) {
+    const candidates = offset === 0 ? [targetActual] : [targetActual + offset, targetActual - offset];
+
+    for (let i = 0; i < candidates.length; i++) {
+      const actualIdx = candidates[i];
+      if (actualIdx <= prevBoundary.actualIdx || actualIdx >= actualLen) {
+        continue;
+      }
+
+      const line = actual[actualIdx];
+      if (isTrivialLine(line)) {
+        continue;
+      }
+
+      const searchStart = MathMax(prevBoundary.expectedIdx + 1, targetExpected - searchRadius);
+      const searchEnd = MathMin(expectedLen - 1, targetExpected + searchRadius);
+
+      for (let j = 0; j <= searchRadius; j++) {
+        const offsets = j === 0 ? [0] : [j, -j];
+        for (let k = 0; k < offsets.length; k++) {
+          const expectedIdx = targetExpected + offsets[k];
+          if (expectedIdx < searchStart || expectedIdx > searchEnd || expectedIdx <= prevBoundary.expectedIdx) {
+            continue;
+          }
+
+          if (
+              areLinesEqual(line, expected[expectedIdx], checkCommaDisparity) &&
+              hasAdjacentMatch(actual, expected, actualIdx, expectedIdx, checkCommaDisparity)
+            ) {
+            return { actualIdx, expectedIdx };
+          }
+        }
+      }
+    }
+  }
+
+  return undefined;
+}
+
+function hasAdjacentMatch(actual, expected, actualIdx, expectedIdx, checkCommaDisparity) {
+  if (actualIdx > 0 && expectedIdx > 0 &&
+      areLinesEqual(actual[actualIdx - 1], expected[expectedIdx - 1], checkCommaDisparity)) {
+    return true;
+  }
+  if (actualIdx < actual.length - 1 && expectedIdx < expected.length - 1 &&
+      areLinesEqual(actual[actualIdx + 1], expected[expectedIdx + 1], checkCommaDisparity)) {
+    return true;
+  }
+  return false;
+}
+
+function isTrivialLine(line) {
+  return RegExpPrototypeExec(kTrivialLinePattern, line) !== null;
+}
+
 function printSimpleMyersDiff(diff) {
   let message = '';
 

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

@@ -0,0 +1,99 @@
+// 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.
+
+const common = require('../common');
+const os = require('os');
+const assert = require('assert');
+
+// This test creates objects with exponential inspect output that requires
+// significant memory. Skip on systems with less than 1GB total memory.
+const totalMemMB = os.totalmem() / 1024 / 1024;
+if (totalMemMB < 1024) {
+  common.skip(`insufficient system memory (${Math.round(totalMemMB)}MB, need 1024MB)`);
+}
+
+// Test: should throw AssertionError, not OOM
+{
+  const { doc1, doc2 } = createTestObjects();
+
+  assert.throws(
+    () => assert.strictEqual(doc1, doc2),
+    (err) => {
+      assert.ok(err instanceof assert.AssertionError);
+      // Message should be bounded (fix truncates inspect output at 2MB)
+      assert.ok(err.message.length < 5 * 1024 * 1024);
+      return true;
+    }
+  );
+}
+
+// Creates objects where many paths converge on shared objects, causing
+// exponential growth in util.inspect output at high depths.
+function createTestObjects() {
+  const base = createBase();
+
+  const s1 = createSchema(base, 's1');
+  const s2 = createSchema(base, 's2');
+  base.schemas.s1 = s1;
+  base.schemas.s2 = s2;
+
+  const doc1 = createDoc(s1, base);
+  const doc2 = createDoc(s2, base);
+
+  // Populated refs create additional converging paths
+  for (let i = 0; i < 2; i++) {
+    const ps = createSchema(base, 'p' + i);
+    base.schemas['p' + i] = ps;
+    doc1.$__.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;
+}