# 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.

   * remove elements later. Otherwise, for non-null elements use {@link ImmutableList#of()} (for
   * varargs) or {@link ImmutableList#copyOf(Object[])} (for an array) instead. If any elements
   * might be null, or you need support for {@link List#set(int, Object)}, use {@link
   * Arrays#asList}.
   *

     * This method is called automatically when using try-with-resources statements.
     *
     * <p>The default implementation does nothing. Subclasses should override this method
     * if they need to perform cleanup operations.</p>
     *
     * @throws InvokerException if an error occurs while closing the {@link Invoker}
     */
    @Override
    default void close() throws InvokerException {}

 * <p>
 * Unlike {@link ModelSource}, this interface supports loading of parent POM(s) from the same backing store and allows
 * construction of MavenProject instances without the need to have parent POM(s) available from local or remote
 * repositories.
 * <p>
 * ModelSource2 instances are cached in {@link ModelBuildingRequest#getModelCache()}. Implementations must guarantee

### Use cases: external service { #use-cases-external-service }

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

* Add more granular permission controls with OAuth2 scopes where needed.
* ...etc.

Nevertheless, you might have a very specific use case where you really need to disable the API docs for some environment (e.g. for production) or depending on configurations from environment variables.

## Conditional OpenAPI from settings and env vars { #conditional-openapi-from-settings-and-env-vars }

		return
	}

	if err = validateConfig(ctx, cfg, subSys); err != nil {
		var validationErr ldap.Validation
		if errors.As(err, &validationErr) {
			// If we got an LDAP validation error, we need to send appropriate
			// error message back to client (likely mc).
			writeCustomErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAdminConfigLDAPValidation),
				validationErr.FormatError(), r.URL)
			return
		}

    uniqueEntries.addAll(ms.entrySet());
    assertEquals(3, uniqueEntries.size());
  }

  // Wrapper of EnumMultiset factory methods, because we need to skip create(Class).
  // create(Enum1.class) is equal to create(Enum2.class) but testEquals() expects otherwise.
  // For the same reason, we need to skip create(Iterable, Class).
  private static class EnumMultisetFactory {
    @Keep // used reflectively by testEquals

    // exponent == floor(log2(abs(x)))
    if (exponent < Long.SIZE - 1) {
      return x.longValue();
    } else if (exponent > MAX_EXPONENT) {
      return x.signum() * POSITIVE_INFINITY;
    }

    /*
     * We need the top SIGNIFICAND_BITS + 1 bits, including the "implicit" one bit. To make rounding
     * easier, we pick out the top SIGNIFICAND_BITS + 2 bits, so we have one to help us round up or

 * classes and the classes they depend on. The classes are not relocated, they all
 * remain in their original namespace. This reduces the final Gradle distribution
 * size and makes us more conscious of which parts of a library we really need.
 *
 * WARNING: if you decide to do the minification by hand, make sure that you cover all paths of loading classes:
 * reflection, dynamic loading, etc. and understand how the library works internally.