Callback reasons

Every LWS_CALLBACK_* reason is exposed as an integer constant on the lws module and as a camelCased name (via getCallbackName). Use the named handlers on your protocol descriptor for clarity:

{
  name: 'http',
  onHttp(wsi, uri) { … },
  onClosedHttp(wsi) { … },
}

The list below mirrors lws_callback_names[] in lws.c and documents the JS arguments after wsi.

WebSocket server

Constant	Handler	Arguments
`LWS_CALLBACK_ESTABLISHED`	`onEstablished`	`(sslPtrString, len)`
`LWS_CALLBACK_RECEIVE`	`onReceive`	`(data, len [, frame])`
`LWS_CALLBACK_RECEIVE_PONG`	`onReceivePong`	`(data, len)`
`LWS_CALLBACK_SERVER_WRITEABLE`	`onServerWriteable`	`()`
`LWS_CALLBACK_CLOSED`	`onClosed`	`()`
`LWS_CALLBACK_WS_PEER_INITIATED_CLOSE`	`onWsPeerInitiatedClose`	`(code, reasonString)`
`LWS_CALLBACK_WS_SERVER_BIND_PROTOCOL`	`onWsServerBindProtocol`	`()`
`LWS_CALLBACK_WS_SERVER_DROP_PROTOCOL`	`onWsServerDropProtocol`	`()`
`LWS_CALLBACK_FILTER_PROTOCOL_CONNECTION`	`onFilterProtocolConnection`	`(data, len)`
`LWS_CALLBACK_CONFIRM_EXTENSION_OKAY`	`onConfirmExtensionOkay`	`(name)`
`LWS_CALLBACK_WS_EXT_DEFAULTS`	`onWsExtDefaults`	`()`

WebSocket client

Constant	Handler	Arguments
`LWS_CALLBACK_CLIENT_ESTABLISHED`	`onClientEstablished`	`()`
`LWS_CALLBACK_CLIENT_CONNECTION_ERROR`	`onClientConnectionError`	`(message, errno)`
`LWS_CALLBACK_CLIENT_FILTER_PRE_ESTABLISH`	`onClientFilterPreEstablish`	`(data, len)`
`LWS_CALLBACK_CLIENT_RECEIVE`	`onClientReceive`	`(data, len [, frame])`
`LWS_CALLBACK_CLIENT_RECEIVE_PONG`	`onClientReceivePong`	`(data, len)`
`LWS_CALLBACK_CLIENT_WRITEABLE`	`onClientWriteable`	`()`
`LWS_CALLBACK_CLIENT_CLOSED`	`onClientClosed`	`()`
`LWS_CALLBACK_CLIENT_APPEND_HANDSHAKE_HEADER`	`onClientAppendHandshakeHeader`	`(buf, lenArray)`
`LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED`	`onClientConfirmExtensionSupported`	`(name)`
`LWS_CALLBACK_WS_CLIENT_BIND_PROTOCOL`	`onWsClientBindProtocol`	`()`
`LWS_CALLBACK_WS_CLIENT_DROP_PROTOCOL`	`onWsClientDropProtocol`	`()`

The frame argument to onReceive/onClientReceive is only present for multi-fragment messages. It is a `{ multifragment: true, first, final }` descriptor — use it to reassemble big frames.

HTTP server

Constant	Handler	Arguments
`LWS_CALLBACK_HTTP`	`onHttp`	`(uri)`
`LWS_CALLBACK_HTTP_BODY`	`onHttpBody`	`(data, len)`
`LWS_CALLBACK_HTTP_BODY_COMPLETION`	`onHttpBodyCompletion`	`()`
`LWS_CALLBACK_HTTP_FILE_COMPLETION`	`onHttpFileCompletion`	`()`
`LWS_CALLBACK_HTTP_WRITEABLE`	`onHttpWriteable`	`()`
`LWS_CALLBACK_HTTP_BIND_PROTOCOL`	`onHttpBindProtocol`	`()`
`LWS_CALLBACK_HTTP_DROP_PROTOCOL`	`onHttpDropProtocol`	`()`
`LWS_CALLBACK_HTTP_CONFIRM_UPGRADE`	`onHttpConfirmUpgrade`	`(typeString)`
`LWS_CALLBACK_HTTP_PMO`	`onHttpPmo`	`(data, len)`
`LWS_CALLBACK_FILTER_NETWORK_CONNECTION`	`onFilterNetworkConnection`	`(sslPtr)`
`LWS_CALLBACK_FILTER_HTTP_CONNECTION`	`onFilterHttpConnection`	`(urlString)`
`LWS_CALLBACK_CHECK_ACCESS_RIGHTS`	`onCheckAccessRights`	`(uri, authMask)` — `uri` is a read-only `ArrayBuffer`, `authMask` the mount's `authentication_mode` bitmask (not a length)
`LWS_CALLBACK_ADD_HEADERS`	`onAddHeaders`	`(buf, lenArray)`
`LWS_CALLBACK_PROCESS_HTML`	`onProcessHtml`	`(buf, lenArray)`
`LWS_CALLBACK_CLOSED_HTTP`	`onClosedHttp`	`()`
`LWS_CALLBACK_SERVER_NEW_CLIENT_INSTANTIATED`	`onServerNewClientInstantiated`	`()`
`LWS_CALLBACK_VERIFY_BASIC_AUTHORIZATION`	`onVerifyBasicAuthorization`	`(authString)`
`LWS_CALLBACK_SESSION_INFO`	`onSessionInfo`	`(buf, len)`

HTTP client

Constant	Handler	Arguments
`LWS_CALLBACK_ESTABLISHED_CLIENT_HTTP`	`onEstablishedClientHttp`	`(responseCode)`
`LWS_CALLBACK_CLIENT_HTTP_WRITEABLE`	`onClientHttpWriteable`	`()`
`LWS_CALLBACK_RECEIVE_CLIENT_HTTP`	`onReceiveClientHttp`	`()`
`LWS_CALLBACK_RECEIVE_CLIENT_HTTP_READ`	`onReceiveClientHttpRead`	`(data, len)`
`LWS_CALLBACK_COMPLETED_CLIENT_HTTP`	`onCompletedClientHttp`	`()`
`LWS_CALLBACK_CLOSED_CLIENT_HTTP`	`onClosedClientHttp`	`()`
`LWS_CALLBACK_CLIENT_HTTP_BIND_PROTOCOL`	`onClientHttpBindProtocol`	`()`
`LWS_CALLBACK_CLIENT_HTTP_DROP_PROTOCOL`	`onClientHttpDropProtocol`	`()`
`LWS_CALLBACK_CLIENT_HTTP_REDIRECT`	`onClientHttpRedirect`	`(url, status)`
`LWS_CALLBACK_WSI_TX_CREDIT_GET`	`onWsiTxCreditGet`	`()`

Raw socket

Constant	Handler	Arguments
`LWS_CALLBACK_RAW_ADOPT`	`onRawAdopt`	`()`
`LWS_CALLBACK_RAW_CONNECTED`	`onRawConnected`	`()`
`LWS_CALLBACK_RAW_RX`	`onRawRx`	`(data, len)`
`LWS_CALLBACK_RAW_WRITEABLE`	`onRawWriteable`	`()`
`LWS_CALLBACK_RAW_CLOSE`	`onRawClose`	`(errno)`
`LWS_CALLBACK_RAW_ADOPT_FILE`	`onRawAdoptFile`	`()`
`LWS_CALLBACK_RAW_RX_FILE`	`onRawRxFile`	`(data, len)`
`LWS_CALLBACK_RAW_WRITEABLE_FILE`	`onRawWriteableFile`	`()`
`LWS_CALLBACK_RAW_CLOSE_FILE`	`onRawCloseFile`	`()`
`LWS_CALLBACK_RAW_SKT_BIND_PROTOCOL`	`onRawSktBindProtocol`	`()`
`LWS_CALLBACK_RAW_SKT_DROP_PROTOCOL`	`onRawSktDropProtocol`	`()`
`LWS_CALLBACK_RAW_FILE_BIND_PROTOCOL`	`onRawFileBindProtocol`	`()`
`LWS_CALLBACK_RAW_FILE_DROP_PROTOCOL`	`onRawFileDropProtocol`	`()`
`LWS_CALLBACK_RAW_PROXY_CLI_RX`	`onRawProxyCliRx`	`(data, len)`
`LWS_CALLBACK_RAW_PROXY_SRV_RX`	`onRawProxySrvRx`	`(data, len)`
`LWS_CALLBACK_RAW_PROXY_CLI_CLOSE`	`onRawProxyCliClose`	`()`
`LWS_CALLBACK_RAW_PROXY_SRV_CLOSE`	`onRawProxySrvClose`	`()`
`LWS_CALLBACK_RAW_PROXY_CLI_WRITEABLE`	`onRawProxyCliWriteable`	`()`
`LWS_CALLBACK_RAW_PROXY_SRV_WRITEABLE`	`onRawProxySrvWriteable`	`()`
`LWS_CALLBACK_RAW_PROXY_CLI_ADOPT`	`onRawProxyCliAdopt`	`()`
`LWS_CALLBACK_RAW_PROXY_SRV_ADOPT`	`onRawProxySrvAdopt`	`()`

CGI / TLS / MQTT misc

Constant	Handler	Arguments
`LWS_CALLBACK_CGI`	`onCgi`	`(data, len)`
`LWS_CALLBACK_CGI_TERMINATED`	`onCgiTerminated`	`()`
`LWS_CALLBACK_CGI_STDIN_DATA`	`onCgiStdinData`	`(data, len)`
`LWS_CALLBACK_CGI_STDIN_COMPLETED`	`onCgiStdinCompleted`	`()`
`LWS_CALLBACK_CGI_PROCESS_ATTACH`	`onCgiProcessAttach`	`(pid)`
`LWS_CALLBACK_CONNECTING`	`onConnecting`	`(fd)`
`LWS_CALLBACK_PROTOCOL_INIT`	`onProtocolInit`	`()`
`LWS_CALLBACK_PROTOCOL_DESTROY`	`onProtocolDestroy`	`()`
`LWS_CALLBACK_WSI_CREATE`	`onWsiCreate`	`()`
`LWS_CALLBACK_WSI_DESTROY`	`onWsiDestroy`	`()`
`LWS_CALLBACK_OPENSSL_LOAD_EXTRA_CLIENT_VERIFY_CERTS`	`onOpensslLoadExtraClientVerifyCerts`	`(sslPtr)`
`LWS_CALLBACK_OPENSSL_LOAD_EXTRA_SERVER_VERIFY_CERTS`	`onOpensslLoadExtraServerVerifyCerts`	`(sslPtr)`
`LWS_CALLBACK_OPENSSL_PERFORM_CLIENT_CERT_VERIFICATION`	`onOpensslPerformClientCertVerification`	`(sslPtr, preverifyOk)`
`LWS_CALLBACK_OPENSSL_PERFORM_SERVER_CERT_VERIFICATION`	`onOpensslPerformServerCertVerification`	`(sslPtr, preverifyOk)`
`LWS_CALLBACK_SSL_INFO`	`onSslInfo`	`(data, len)`
`LWS_CALLBACK_VHOST_CERT_AGING`	`onVhostCertAging`	`(daysLeft)`
`LWS_CALLBACK_VHOST_CERT_UPDATE`	`onVhostCertUpdate`	`()`
`LWS_CALLBACK_TIMER`	`onTimer`	`()`
`LWS_CALLBACK_GET_THREAD_ID`	`onGetThreadId`	`()`
`LWS_CALLBACK_EVENT_WAIT_CANCELLED`	`onEventWaitCancelled`	`()`
`LWS_CALLBACK_GS_EVENT`	`onGsEvent`	`(data, len)`
`LWS_CALLBACK_CHILD_CLOSING`	`onChildClosing`	`()`
`LWS_CALLBACK_MQTT_*`	`onMqtt*`	varies

Reasons handled internally (you usually don't write them)

ADD_POLL_FD, DEL_POLL_FD, CHANGE_MODE_POLL_FD, LOCK_POLL, UNLOCK_POLL — see event-loop.md.

#Callback reasons

#WebSocket server

#WebSocket client

#HTTP server

#HTTP client

#Raw socket

#CGI / TLS / MQTT misc

#Reasons handled internally (you usually don't write them)