# Handling Errors { #handling-errors }

There are many situations in which you need to notify an error to a client that is using your API.

This client could be a browser with a frontend, a code from someone else, an IoT device, etc.

You could need to tell the client that:

* The client doesn't have enough privileges for that operation.
* The client doesn't have access to that resource.
* The item the client was trying to access doesn't exist.
* etc.

- **I/O Operations** (`org.codelibs.core.io`) - File handling, resource management, stream utilities, and traversal utilities for efficient resource processing
- **Reflection** (`org.codelibs.core.lang`) - Class loading, method/field access, type introspection utilities, and generics support
- **Exception Handling** (`org.codelibs.core.exception`) - Runtime exception wrappers for common checked exceptions with consistent error handling

### Modern Java 21 Support

* Decompressing gzip-compressed request bodies.
* Automatically logging all request bodies.

## Handling custom request body encodings { #handling-custom-request-body-encodings }

Let's see how to make use of a custom `Request` subclass to decompress gzip requests.

And an `APIRoute` subclass to use that custom request class.

- [ ] Implement lease break notification handling
- [ ] Modify SmbFile to support lease-based caching
- [ ] Add lease upgrade/downgrade logic
- [ ] Implement lease epoch tracking for v2 leases

#### 1.3 Integration Points
- Modify `Smb2CreateRequest` to include lease contexts
- Update `SmbFile` caching logic to use leases
- Add lease break handling in `SmbTransport`

---

### Phase 2: Persistent Handles

                    fail("Concurrent session handling failed: " + e.getMessage());
                } finally {
                    latch.countDown();
                }
            });
        }

        assertTrue(latch.await(10, TimeUnit.SECONDS));
        executor.shutdown();
    }

    @Test
    @DisplayName("Test invalid session ID handling")
    public void testInvalidSessionIdHandling() {

        System.arraycopy(outputBuffer, 50, extracted, 0, testData.length);
        assertArrayEquals(testData, extracted);
    }

    @Test
    @DisplayName("Test small data handling")
    public void testSmallDataHandling() throws CIFSException {
        byte[] smallData = new byte[100]; // Below minimum compression size

        assertNotNull(result);
        assertTrue(result.contains("3 docs"));
        // queryBuilder field is protected, so we can't directly assert it
    }

    // Test execute() method with exception handling
    public void test_execute_withException() {
        // Register a mock that throws exception
        SearchEngineClient exceptionClient = new SearchEngineClient() {
            @Override

        assertNotNull(result);
        assertTrue(result instanceof TestUser);
        assertEquals("TestUser", ((TestUser) result).name);
    }

    // Test evaluate method with error handling
    public void test_evaluate_withErrorTemplate() {
        scriptEngine = new ErrorHandlingScriptEngine();
        String template = "error";
        Map<String, Object> paramMap = new HashMap<>();

    private static SamrPolicyHandle createMockPolicyHandle() {
        return mock(SamrPolicyHandle.class);
    }

    @Nested
    @DisplayName("Constructor parameter handling")
    class ConstructorParameterHandling {

        static Stream<Arguments> provideParameters() {

///

With that you can connect the WebSocket and then send and receive messages:

<img src="/img/tutorial/websockets/image05.png">

## Handling disconnections and multiple clients { #handling-disconnections-and-multiple-clients }