Websocket Client API
Overview
The Websocket client library allows Zephyr to connect to a Websocket server. The Websocket client API can be used directly by application to establish a Websocket connection to server, or it can be used as a transport for other network protocols like MQTT.
See this Websocket Wikipedia article for a detailed overview of how Websocket works.
For more information about the protocol itself, see IETF RFC6455 The WebSocket Protocol.
Websocket Transport
The Websocket API allows it to be used as a transport for other high level
protocols like MQTT. The Zephyr MQTT client library can be configured to use
Websocket transport by enabling CONFIG_MQTT_LIB_WEBSOCKET and
CONFIG_WEBSOCKET_CLIENT Kconfig options.
First a socket needs to be created and connected to the Websocket server:
sock = socket(family, SOCK_STREAM, IPPROTO_TCP);
...
ret = connect(sock, addr, addr_len);
...
The Websocket transport socket is then created like this:
ws_sock = websocket_connect(sock, &config, timeout, user_data);
The Websocket socket can then be used to send or receive data, and the
Websocket client API will encapsulate the sent or received data to/from
Websocket packet payload. Both the websocket_xxx() API or normal
BSD socket API functions can be used to send and receive application data.
ret = websocket_send_msg(ws_sock, buf_to_send, buf_len,
WEBSOCKET_OPCODE_DATA_BINARY, true, true,
K_FOREVER);
...
ret = send(ws_sock, buf_to_send, buf_len, 0);
If normal BSD socket functions are used, then currently only TEXT data
is supported. In order to send BINARY data, the websocket_send_msg()
must be used.
When done, the Websocket transport socket must be closed. User should handle the lifecycle(close/reuse) of tcp socket after websocket_disconnect.
ret = close(ws_sock);
or
ret = websocket_disconnect(ws_sock);