Espressif ESP32-S2 User Manual

Chapter 2. API Reference
TLS Configuration:
const esp_websocket_client_config_t ws_cfg = {
.uri = "wss://echo.websocket.org",
.cert_pem = (const char *)websocket_org_pem_start,
};
Note: If you want to verify the server, then you need to provide a certificate in PEM format, and provide to
cert_pem in websocket_client_config_t. If no certficate is provided then the TLS connection will to
default not requiring verification.
PEM certificate for this example could be extracted from an openssl s_client command connecting to websocket.org.
In case a host operating system has openssl and sed packages installed, one could execute the following command
to download and save the root or intermediate root certificate to a file (Note for Windows users: Both Linux like
environment or Windows native packages may be used). ` echo "" | openssl s_client -showcerts
-connect websocket.org:443 | sed -n "1,/Root/d; /BEGIN/,/END/p" | openssl
x509 -outform PEM >websocket_org.pem `
This command will extract the second certificate in the chain and save it as a pem-file.
Subprotocol The subprotocol field in the config struct can be used to request a subprotocol
const esp_websocket_client_config_t ws_cfg = {
.uri = "ws://websocket.org",
.subprotocol = "soap",
};
Note: The client is indifferent to the subprotocol field in the server response and will accept the connection no matter
what the server replies.
For more options on esp_websocket_client_config_t, please refer to API reference below
Events
• WEBSOCKET_EVENT_CONNECTED: The client has successfully established a connection to the server. The
client is now ready to send and receive data. Contains no event data.
• WEBSOCKET_EVENT_DISCONNECTED: The client has aborted the connection due to the transport layer
failing to read data, e.g. because the server is unavailable. Contains no event data.
• WEBSOCKET_EVENT_DATA: The client has successfully received and parsed a WebSocket frame. The event
data contains a pointer to the payload data, the length of the payload data as well as the opcode of the received
frame. A message may be fragmented into multiple events if the length exceeds the buffer size. This event will
also be posted for non-payload frames, e.g. pong or connection close frames.
• WEBSOCKET_EVENT_ERROR: Not used in the current implementation of the client.
If the client handle is needed in the event handler it can be accessed through the pointer passed to the event handler:
esp_websocket_client_handle_t client = (esp_websocket_client_handle_t)handler_args;
Limitations and Known Issues
• The client is able to request the use of a subprotocol from the server during the handshake, but does not do any
subprotocol related checks on the response from the server.
Espressif Systems 643
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Release v4.4

Espressif ESP32-S2 Specifications

General

Brand	Espressif
Model	ESP32-S2
Category	Single board computers
Language	English