src: expose BROTLI_DECODER_ERROR_FORMAT_BLOCK_SWITCH

Signed-off-by: Antoine du Hamel <duhamelantoine1995@gmail.com>
PR-URL: nodejs-private/node-private#1002
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
CVE-ID: CVE-2026-111497

Author: aduh95

src/node_zlib.cc

@@ -2268,6 +2268,7 @@ void DefineZlibConstants(Local<Object> target) {
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_FORMAT_PADDING_1);
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_FORMAT_PADDING_2);
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_FORMAT_DISTANCE);
+  NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_FORMAT_BLOCK_SWITCH);
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_DICTIONARY_NOT_SET);
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_INVALID_ARGUMENTS);
   NODE_DEFINE_CONSTANT(target, BROTLI_DECODER_ERROR_ALLOC_CONTEXT_MODES);

test/parallel/test-zlib-invalid-input.js

@@ -89,6 +89,33 @@ Object.defineProperty(spoofedLength, 'byteLength', { get: () => 5000 });
   deflate.close();
 }
 
+{
+  // A block switch is invalid when the stream declares only one block type.
+  const invalidBlockSwitch = Buffer.from(
+    '200010414141fcffff07002228f00b60f7f41f000000',
+    'hex',
+  );
+  const expectedError = {
+    code: 'ERR__ERROR_FORMAT_BLOCK_SWITCH',
+    errno: zlib.constants.BROTLI_DECODER_ERROR_FORMAT_BLOCK_SWITCH,
+  };
+
+  assert.strictEqual(expectedError.errno, -17);
+  assert.throws(
+    () => zlib.brotliDecompressSync(invalidBlockSwitch),
+    expectedError,
+  );
+
+  const brotli = zlib.createBrotliDecompress();
+  brotli.resume();
+  brotli.on('error', common.expectsError(expectedError));
+  brotli.on('end', common.mustNotCall());
+  for (let i = 0; i < invalidBlockSwitch.length; i++) {
+    brotli.write(invalidBlockSwitch.subarray(i, i + 1));
+  }
+  brotli.end();
+}
+
 unzips.forEach(common.mustCall((uz, i) => {
   uz.on('error', common.mustCall());
   uz.on('end', common.mustNotCall());