回调使应用程序能够调用在另一层或级别定义的函数。 应用程序将函数参数注册为一个处理程序，该处理程序将在以后根据需要异步调用。 如果函数以异步方式指示函数成功或错误，则会调用回调。 如果作同步完成，则不调用回调。
Windows Web 服务 API 包含以下回调函数：
- WS_ABANDON_MESSAGE_CALLBACK
- WS_ABORT_CHANNEL_CALLBACK
- WS_ABORT_LISTENER_CALLBACK
- WS_ACCEPT_CHANNEL_CALLBACK
- WS_ASYNC_CALLBACK
- WS_ASYNC_FUNCTION
- WS_CERT_ISSUER_LIST_NOTIFICATION_CALLBACK
- WS_CERTIFICATE_VALIDATION_CALLBACK
- WS_CLOSE_CHANNEL_CALLBACK
- WS_CLOSE_LISTENER_CALLBACK
- WS_CREATE_CHANNEL_CALLBACK
- WS_CREATE_CHANNEL_FOR_LISTENER_CALLBACK
- WS_CREATE_DECODER_CALLBACK
- WS_CREATE_ENCODER_CALLBACK
- WS_CREATE_LISTENER_CALLBACK
- WS_DECODER_DECODE_CALLBACK
- WS_DECODER_END_CALLBACK
- WS_DECODER_GET_CONTENT_TYPE_CALLBACK
- WS_DECODER_START_CALLBACK
- WS_DURATION_COMPARISON_CALLBACK
- WS_DYNAMIC_STRING_CALLBACK
- WS_ENCODER_ENCODE_CALLBACK
- WS_ENCODER_END_CALLBACK
- WS_ENCODER_GET_CONTENT_TYPE_CALLBACK
- WS_ENCODER_START_CALLBACK
- WS_FREE_CHANNEL_CALLBACK
- WS_FREE_DECODER_CALLBACK
- WS_FREE_ENCODER_CALLBACK
- WS_FREE_LISTENER_CALLBACK
- WS_GET_CERT_CALLBACK
- WS_GET_CHANNEL_PROPERTY_CALLBACK
- WS_GET_LISTENER_PROPERTY_CALLBACK
- WS_HTTP_REDIRECT_CALLBACK
- WS_IS_DEFAULT_VALUE_CALLBACK
- WS_MESSAGE_DONE_CALLBACK
- WS_OPEN_CHANNEL_CALLBACK
- WS_OPEN_LISTENER_CALLBACK
- WS_OPERATION_CANCEL_CALLBACK
- WS_OPERATION_FREE_STATE_CALLBACK
- WS_PROXY_MESSAGE_CALLBACK
- WS_PULL_BYTES_CALLBACK
- WS_PUSH_BYTES_CALLBACK
- WS_READ_CALLBACK
- WS_READ_MESSAGE_END_CALLBACK
- WS_READ_MESSAGE_START_CALLBACK
- WS_READ_TYPE_CALLBACK
- WS_RESET_CHANNEL_CALLBACK
- WS_RESET_LISTENER_CALLBACK
- WS_SERVICE_ACCEPT_CHANNEL_CALLBACK
- WS_SERVICE_CLOSE_CHANNEL_CALLBACK
- WS_SERVICE_MESSAGE_RECEIVE_CALLBACK
- WS_SERVICE_SECURITY_CALLBACK
- WS_SERVICE_STUB_CALLBACK
- WS_SET_CHANNEL_PROPERTY_CALLBACK
- WS_SET_LISTENER_PROPERTY_CALLBACK
- WS_SHUTDOWN_SESSION_CHANNEL_CALLBACK
- WS_VALIDATE_PASSWORD_CALLBACK
- WS_VALIDATE_SAML_CALLBACK
- WS_WRITE_CALLBACK
- WS_WRITE_MESSAGE_END_CALLBACK
- WS_WRITE_MESSAGE_START_CALLBACK
- WS_WRITE_TYPE_CALLBACK