Ensure BoringSSL error queue is cleared

lib/src/impl_ffi/impl_ffi.utils.dart

@@ -93,6 +93,7 @@ void _checkOp(bool condition, {String? message, String? fallback}) {
     message ??= err ?? fallback ?? 'unknown error';
     throw operationError(message);
   }
+  ssl.ERR_clear_error();
 }
 
 /// Throw [OperationError] if [retval] is not `1`.
@@ -113,6 +114,7 @@ void _checkData(bool condition, {String? message, String? fallback}) {
     message ??= err ?? fallback ?? 'unknown error';
     throw FormatException(message);
   }
+  ssl.ERR_clear_error();
 }
 
 /// Throw [FormatException] if [retval] is `1`.
@@ -270,6 +272,7 @@ class _Scope implements Allocator {
       return await fn(scope);
     } finally {
       scope._release();
+      ssl.ERR_clear_error();
     }
   }
 
@@ -281,6 +284,7 @@ class _Scope implements Allocator {
       yield* fn(scope);
     } finally {
       scope._release();
+      ssl.ERR_clear_error();
     }
   }
 
@@ -294,6 +298,7 @@ class _Scope implements Allocator {
       return fn(scope);
     } finally {
       scope._release();
+      ssl.ERR_clear_error();
     }
   }
 }
@@ -428,10 +433,10 @@ Future<bool> _verifyStream(
       signature.length,
     );
     if (result != 1) {
-      // TODO: We should always clear errors, when returning from any
-      //       function that uses BoringSSL.
-      // Note: In this case we could probably assert that error is just
-      //       signature related.
+      // Always clear errors, so we don't leak anything from the error queue.
+      ssl.ERR_clear_error();
+    } else {
+      // Also clear errors on success, just in case.
       ssl.ERR_clear_error();
     }
     return result == 1;

test/thread_local_error_test.dart

@@ -0,0 +1,85 @@
+@TestOn('vm')
+library thread_local_error_test;
+
+import 'dart:typed_data';
+
+import 'package:test/test.dart';
+import 'package:webcrypto/webcrypto.dart';
+
+// This relies on internal implementation details to check for error leaks.
+// If implementation changes significantly, this test might need updates.
+import 'package:webcrypto/src/boringssl/lookup/lookup.dart'; // Access internal ssl
+
+void main() {
+  test('BoringSSL error stack is empty after operations', () async {
+    // Helper to check error stack
+    void checkErrorStack() {
+      // We peep at the error stack to see if anything was left behind.
+      // Operations must clean up after themselves.
+      final err = ssl.ERR_peek_error();
+      if (err != 0) {
+        // Just failing with the error code is sufficient to signal a leak.
+        fail('BoringSSL error stack not empty. Error code: $err');
+      }
+    }
+
+    // Initial check to ensure clean slate
+    checkErrorStack();
+
+    // 1. Digest (SHA-256)
+    await Hash.sha256.digestBytes(Uint8List(10));
+    checkErrorStack();
+
+    // 2. HMAC Generation & Sign & Verify
+    final hmacKey = await HmacSecretKey.generateKey(Hash.sha256);
+    checkErrorStack();
+    final signature = await hmacKey.signBytes(Uint8List(10));
+    checkErrorStack();
+    final isValid = await hmacKey.verifyBytes(signature, Uint8List(10));
+    expect(isValid, isTrue);
+    checkErrorStack();
+
+    // 3. HMAC Verify Failure
+    // Flip a bit in signature to cause verification failure
+    final invalidSig = Uint8List.fromList(signature);
+    if (invalidSig.isNotEmpty) {
+      invalidSig[0] ^= 0xff;
+    }
+    final isInvalid = await hmacKey.verifyBytes(invalidSig, Uint8List(10));
+    expect(isInvalid, isFalse);
+    checkErrorStack();
+
+    // 4. AES-GCM
+    final aesKey = await AesGcmSecretKey.generateKey(256);
+    checkErrorStack();
+    final iv = Uint8List(12);
+    final encrypted = await aesKey.encryptBytes(Uint8List(10), iv);
+    checkErrorStack();
+    await aesKey.decryptBytes(encrypted, iv);
+    checkErrorStack();
+
+    // 5. ECDSA
+    final ecKey = await EcdsaPrivateKey.generateKey(EllipticCurve.p256);
+    checkErrorStack();
+    final ecSig = await ecKey.privateKey.signBytes(Uint8List(10), Hash.sha256);
+    checkErrorStack();
+    final ecValid = await ecKey.publicKey.verifyBytes(ecSig, Uint8List(10), Hash.sha256);
+    expect(ecValid, isTrue);
+    checkErrorStack();
+
+    // 6. Randomness
+    final randomBytes = Uint8List(32);
+    fillRandomBytes(randomBytes);
+    checkErrorStack();
+
+    // 7. Expected Failure (Import invalid JWK)
+    try {
+      // Missing 'k' property or invalid format
+      await AesGcmSecretKey.importJsonWebKey({'kty': 'oct', 'alg': 'A256GCM'});
+      fail('Should have thrown ArgumentError or FormatException');
+    } catch (_) {
+      // Expected exception
+      checkErrorStack();
+    }
+  });
+}