ESP WebSocket Client

Overview

The ESP WebSocket client is an implementation of WebSocket protocol client for ESP32

Features

Supports WebSocket over TCP, TLS with mbedtls

Easy to setup with URI

Multiple instances (Multiple clients in one application)

Configuration

URI

Supports ws, wss schemes
WebSocket samples:
- ws://echo.websocket.org: WebSocket over TCP, default port 80
- wss://echo.websocket.org: WebSocket over SSL, default port 443

Minimal configurations:

const esp_websocket_client_config_t ws_cfg = {
    .uri = "ws://echo.websocket.org",
};

The WebSocket client supports the use of both path and query in the URI. Sample:

const esp_websocket_client_config_t ws_cfg = {
    .uri = "ws://echo.websocket.org/connectionhandler?id=104",
};

If there are any options related to the URI in esp_websocket_client_config_t, the option defined by the URI will be overridden. Sample:

const esp_websocket_client_config_t ws_cfg = {
    .uri = "ws://echo.websocket.org:123",
    .port = 4567,
};
//WebSocket client will connect to websocket.org using port 4567

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 default to 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.

Application Example

A simple WebSocket example that uses esp_websocket_client to establish a websocket connection and send/receive data with the websocket.org server can be found here: example

Sending Text Data

The WebSocket client supports sending data as a text data frame, which informs the application layer that the payload data is text data encoded as UTF-8. Example:

esp_websocket_client_send_text(client, data, len, portMAX_DELAY);

API Reference

Header File

../components/esp_websocket_client/include/esp_websocket_client.h

Functions

esp_websocket_client_handle_t esp_websocket_client_init(const esp_websocket_client_config_t *config)

Start a Websocket session This function must be the first function to call, and it returns a esp_websocket_client_handle_t that you must use as input to other functions in the interface. This call MUST have a corresponding call to esp_websocket_client_destroy when the operation is complete.

Parameters

config – [in] The configuration

Returns

esp_websocket_client_handle_t
NULL if any errors

esp_err_t esp_websocket_client_set_uri(esp_websocket_client_handle_t client, const char *uri)

Set URL for client, when performing this behavior, the options in the URL will replace the old ones Must stop the WebSocket client before set URI if the client has been connected.

Parameters

client – [in] The client
uri – [in] The uri

Returns

esp_err_t

esp_err_t esp_websocket_client_set_headers(esp_websocket_client_handle_t client, const char *headers)

Set additional websocket headers for the client, when performing this behavior, the headers will replace the old ones.

This API should be used after the WebSocket client connection has succeeded (i.e., once the transport layer is initialized).
If you wish to set or append headers before the WebSocket client connection is established(before handshake), consider the following options:
1. Input headers directly into the config options, terminating each item with [CR][LF]. This approach will replace any previous headers. Example: websocket_cfg.headers = “Sec-WebSocket-Key: my_key\r\nPassword: my_pass\r\n”;
2. Use the esp_websocket_client_append_header API to append a single header to the current set.

Pre

Must stop the WebSocket client before set headers if the client has been connected

Parameters

client – [in] The WebSocket client handle
headers – [in] Additional header strings each terminated with [CR][LF]

Returns

esp_err_t

esp_err_t esp_websocket_client_append_header(esp_websocket_client_handle_t client, const char *key, const char *value)

Appends a new key-value pair to the headers of a WebSocket client.

Parameters

client – [in] The WebSocket client handle
key – [in] The header key to append
value – [in] The associated value for the given key

Pre

Ensure that this function is called before starting the WebSocket client.

Returns

esp_err_t

esp_err_t esp_websocket_client_start(esp_websocket_client_handle_t client)

Open the WebSocket connection.

Parameters: client – [in] The client
Returns: esp_err_t

esp_err_t esp_websocket_client_stop(esp_websocket_client_handle_t client)

Stops the WebSocket connection without websocket closing handshake.

This API stops ws client and closes TCP connection directly without sending close frames. It is a good practice to close the connection in a clean way using esp_websocket_client_close().

Notes:

Cannot be called from the websocket event handler

Parameters: client – [in] The client
Returns: esp_err_t

esp_err_t esp_websocket_client_destroy(esp_websocket_client_handle_t client)

Destroy the WebSocket connection and free all resources. This function must be the last function to call for an session. It is the opposite of the esp_websocket_client_init function and must be called with the same handle as input that a esp_websocket_client_init call returned. This might close all connections this handle has used.

Notes:

Cannot be called from the websocket event handler

Parameters: client – [in] The client
Returns: esp_err_t

esp_err_t esp_websocket_client_destroy_on_exit(esp_websocket_client_handle_t client)

If this API called, WebSocket client will destroy and free all resources at the end of event loop.

Notes:

After event loop finished, client handle would be dangling and should never be used

Parameters: client – [in] The client
Returns: esp_err_t

int esp_websocket_client_send_bin(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)

Write binary data to the WebSocket connection (data send with WS OPCODE=02, i.e. binary)

Parameters

client – [in] The client
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_bin_partial(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)

Write binary data to the WebSocket connection and sends it without setting the FIN flag(data send with WS OPCODE=02, i.e. binary)

Notes:

To send continuation frame, you should use ‘esp_websocket_client_send_cont_msg(…)’ API.
To mark the end of fragmented data, you should use the ‘esp_websocket_client_send_fin(…)’ API. This sends a FIN frame.

Parameters

client – [in] The client
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_text(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)

Write textual data to the WebSocket connection (data send with WS OPCODE=01, i.e. text)

Parameters

client – [in] The client
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_text_partial(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)

Write textual data to the WebSocket connection and sends it without setting the FIN flag(data send with WS OPCODE=01, i.e. text)

Notes:

To send continuation frame, you should use ‘esp_websocket_client_send_cont_mgs(…)’ API.
To mark the end of fragmented data, you should use the ‘esp_websocket_client_send_fin(…)’ API. This sends a FIN frame.

Parameters

client – [in] The client
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_cont_msg(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)

Write textual data to the WebSocket connection and sends it as continuation frame (OPCODE=0x0)

Notes:

Continuation frames have an opcode of 0x0 and do not explicitly signify whether they are continuing a text or a binary message.
You determine the type of message (text or binary) being continued by looking at the opcode of the initial frame in the sequence of fragmented frames.
To mark the end of fragmented data, you should use the ‘esp_websocket_client_send_fin(…)’ API. This sends a FIN frame.

Parameters

client – [in] The client
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_fin(esp_websocket_client_handle_t client, TickType_t timeout)

Sends FIN frame.

Parameters

client – [in] The client
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

int esp_websocket_client_send_with_opcode(esp_websocket_client_handle_t client, ws_transport_opcodes_t opcode, const uint8_t *data, int len, TickType_t timeout)

Write opcode data to the WebSocket connection.

Notes:

In order to send a zero payload, data and len should be set to NULL/0
This API sets the FIN bit on the last fragment of message

Parameters

client – [in] The client
opcode – [in] The opcode
data – [in] The data
len – [in] The length
timeout – [in] Write data timeout in RTOS ticks

Returns

Number of data was sent
(-1) if any errors

esp_err_t esp_websocket_client_close(esp_websocket_client_handle_t client, TickType_t timeout)

Close the WebSocket connection in a clean way.

Sequence of clean close initiated by client:

Client sends CLOSE frame
Client waits until server echos the CLOSE frame
Client waits until server closes the connection
Client is stopped the same way as by the esp_websocket_client_stop()

Notes:
- Cannot be called from the websocket event handler

Parameters

client – [in] The client
timeout – [in] Timeout in RTOS ticks for waiting

Returns

esp_err_t

esp_err_t esp_websocket_client_close_with_code(esp_websocket_client_handle_t client, int code, const char *data, int len, TickType_t timeout)

Close the WebSocket connection in a clean way with custom code/data Closing sequence is the same as for esp_websocket_client_close()

Notes:

Cannot be called from the websocket event handler

Parameters

client – [in] The client
code – [in] Close status code as defined in RFC6455 section-7.4
data – [in] Additional data to closing message
len – [in] The length of the additional data
timeout – [in] Timeout in RTOS ticks for waiting

Returns

esp_err_t

bool esp_websocket_client_is_connected(esp_websocket_client_handle_t client)

Check the WebSocket client connection state.

Parameters

client – [in] The client handle

Returns

true
false

size_t esp_websocket_client_get_ping_interval_sec(esp_websocket_client_handle_t client)

Get the ping interval sec for client.

Parameters: client – [in] The client
Returns: The ping interval in sec

esp_err_t esp_websocket_client_set_ping_interval_sec(esp_websocket_client_handle_t client, size_t ping_interval_sec)

Set new ping interval sec for client.

Parameters

client – [in] The client
ping_interval_sec – [in] The new interval

Returns

esp_err_t

esp_err_t esp_websocket_register_events(esp_websocket_client_handle_t client, esp_websocket_event_id_t event, esp_event_handler_t event_handler, void *event_handler_arg)

Register the Websocket Events.

Parameters

client – The client handle
event – The event id
event_handler – The callback function
event_handler_arg – User context

Returns

esp_err_t

Structures

struct esp_websocket_error_codes_t

Websocket error code structure to be passed as a contextual information into ERROR event.

Public Members

esp_err_t esp_tls_last_esp_err: last esp_err code reported from esp-tls component

int esp_tls_stack_err: tls specific error code reported from underlying tls stack

int esp_tls_cert_verify_flags: tls flags reported from underlying tls stack during certificate verification

int esp_ws_handshake_status_code: http status code of the websocket upgrade handshake

int esp_transport_sock_errno: errno from the underlying socket

struct esp_websocket_event_data_t

Websocket event data.

Public Members

const char *data_ptr: Data pointer

int data_len: Data length

bool fin: Fin flag

uint8_t op_code: Received opcode

esp_websocket_client_handle_t client: esp_websocket_client_handle_t context

void *user_context: user_data context, from esp_websocket_client_config_t user_data

int payload_len: Total payload length, payloads exceeding buffer will be posted through multiple events

int payload_offset: Actual offset for the data associated with this event

esp_websocket_error_codes_t error_handle: esp-websocket error handle including esp-tls errors as well as internal websocket errors

struct esp_websocket_client_config_t

Websocket client setup configuration.

Public Members

const char *uri: Websocket URI, the information on the URI can be overrides the other fields below, if any

const char *host: Domain or IP as string

int port: Port to connect, default depend on esp_websocket_transport_t (80 or 443)

const char *username: Using for Http authentication, only support basic auth now

const char *password: Using for Http authentication

const char *path: HTTP Path, if not set, default is /

bool disable_auto_reconnect: Disable the automatic reconnect function when disconnected

void *user_context: HTTP user data context

int task_prio: Websocket task priority

const char *task_name: Websocket task name

int task_stack: Websocket task stack

int buffer_size: Websocket buffer size

const char *cert_pem: Pointer to certificate data in PEM or DER format for server verify (with SSL), default is NULL, not required to verify the server. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in cert_len.

size_t cert_len: Length of the buffer pointed to by cert_pem. May be 0 for null-terminated pem

const char *client_cert: Pointer to certificate data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also client_key has to be provided. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in client_cert_len.

size_t client_cert_len: Length of the buffer pointed to by client_cert. May be 0 for null-terminated pem

const char *client_key: Pointer to private key data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also client_cert has to be provided. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in client_key_len

size_t client_key_len: Length of the buffer pointed to by client_key_pem. May be 0 for null-terminated pem

esp_websocket_transport_t transport: Websocket transport type, see `esp_websocket_transport_t

const char *subprotocol: Websocket subprotocol

const char *user_agent: Websocket user-agent

const char *headers: Websocket additional headers

int pingpong_timeout_sec: Period before connection is aborted due to no PONGs received

bool disable_pingpong_discon: Disable auto-disconnect due to no PONG received within pingpong_timeout_sec

bool use_global_ca_store: Use a global ca_store for all the connections in which this bool is set.

esp_err_t (*crt_bundle_attach)(void *conf): Function pointer to esp_crt_bundle_attach. Enables the use of certification bundle for server verification, MBEDTLS_CERTIFICATE_BUNDLE must be enabled in menuconfig. Include esp_crt_bundle.h, and use esp_crt_bundle_attach here to include bundled CA certificates.

bool skip_cert_common_name_check: Skip any validation of server certificate CN field

bool keep_alive_enable: Enable keep-alive timeout

int keep_alive_idle: Keep-alive idle time. Default is 5 (second)

int keep_alive_interval: Keep-alive interval time. Default is 5 (second)

int keep_alive_count: Keep-alive packet retry send count. Default is 3 counts

int reconnect_timeout_ms: Reconnect after this value in miliseconds if disable_auto_reconnect is not enabled (defaults to 10s)

int network_timeout_ms: Abort network operation if it is not completed after this value, in milliseconds (defaults to 10s)

size_t ping_interval_sec: Websocket ping interval, defaults to 10 seconds if not set

struct ifreq *if_name: The name of interface for data to go through. Use the default interface without setting

Type Definitions

typedef struct esp_websocket_client *esp_websocket_client_handle_t

Enumerations

enum esp_websocket_event_id_t

Websocket Client events id.

Values:

enumerator WEBSOCKET_EVENT_ANY

enumerator WEBSOCKET_EVENT_ERROR: This event occurs when there are any errors during execution

enumerator WEBSOCKET_EVENT_CONNECTED: Once the Websocket has been connected to the server, no data exchange has been performed

enumerator WEBSOCKET_EVENT_DISCONNECTED: The connection has been disconnected

enumerator WEBSOCKET_EVENT_DATA: When receiving data from the server, possibly multiple portions of the packet

enumerator WEBSOCKET_EVENT_CLOSED: The connection has been closed cleanly

enumerator WEBSOCKET_EVENT_BEFORE_CONNECT: The event occurs before connecting

enumerator WEBSOCKET_EVENT_MAX

enum esp_websocket_error_type_t

Websocket connection error codes propagated via ERROR event.

Values:

enumerator WEBSOCKET_ERROR_TYPE_NONE

enumerator WEBSOCKET_ERROR_TYPE_TCP_TRANSPORT

enumerator WEBSOCKET_ERROR_TYPE_PONG_TIMEOUT

enumerator WEBSOCKET_ERROR_TYPE_HANDSHAKE

enum esp_websocket_transport_t

Websocket Client transport.

Values:

enumerator WEBSOCKET_TRANSPORT_UNKNOWN: Transport unknown

enumerator WEBSOCKET_TRANSPORT_OVER_TCP: Transport over tcp

enumerator WEBSOCKET_TRANSPORT_OVER_SSL: Transport over ssl

ESP WebSocket Client

Overview

Features

Configuration

URI

TLS

Subprotocol

Events

Limitations and Known Issues

Application Example

Sending Text Data

API Reference

Header File

Functions

Structures

Type Definitions

Enumerations