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128 lines
4.8 KiB
ReStructuredText
128 lines
4.8 KiB
ReStructuredText
ESP WebSocket Client
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====================
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Overview
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--------
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The ESP WebSocket client is an implementation of `WebSocket protocol client <https://tools.ietf.org/html/rfc6455>`_ for {IDF_TARGET_NAME}
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Features
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--------
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* Supports WebSocket over TCP, TLS with mbedtls
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* Easy to setup with URI
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* Multiple instances (Multiple clients in one application)
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Configuration
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-------------
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URI
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^^^
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- Supports ``ws``, ``wss`` schemes
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- WebSocket samples:
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- ``ws://echo.websocket.org``: WebSocket over TCP, default port 80
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- ``wss://echo.websocket.org``: WebSocket over SSL, default port 443
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Minimal configurations:
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.. code:: c
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const esp_websocket_client_config_t ws_cfg = {
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.uri = "ws://echo.websocket.org",
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};
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The WebSocket client supports the use of both path and query in the URI. Sample:
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.. code:: c
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const esp_websocket_client_config_t ws_cfg = {
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.uri = "ws://echo.websocket.org/connectionhandler?id=104",
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};
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If there are any options related to the URI in
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:cpp:type:`esp_websocket_client_config_t`, the option defined by the URI will be
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overridden. Sample:
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.. code:: c
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const esp_websocket_client_config_t ws_cfg = {
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.uri = "ws://echo.websocket.org:123",
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.port = 4567,
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};
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//WebSocket client will connect to websocket.org using port 4567
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TLS
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^^^
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Configuration:
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.. code:: c
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const esp_websocket_client_config_t ws_cfg = {
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.uri = "wss://echo.websocket.org",
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.cert_pem = (const char *)websocket_org_pem_start,
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};
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.. note:: If you want to verify the server, then you need to provide a certificate in PEM format, and provide to ``cert_pem`` in :cpp:type:`websocket_client_config_t`. If no certficate is provided then the TLS connection will default to not requiring verification.
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PEM certificate for this example could be extracted from an openssl `s_client` command connecting to websocket.org.
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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).
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```
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echo "" | openssl s_client -showcerts -connect websocket.org:443 | sed -n "1,/Root/d; /BEGIN/,/END/p" | openssl x509 -outform PEM >websocket_org.pem
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```
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This command will extract the second certificate in the chain and save it as a pem-file.
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Subprotocol
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^^^^^^^^^^^
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The subprotocol field in the config struct can be used to request a subprotocol
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.. code:: c
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const esp_websocket_client_config_t ws_cfg = {
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.uri = "ws://websocket.org",
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.subprotocol = "soap",
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};
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.. note:: The client is indifferent to the subprotocol field in the server response and will accept the connection no matter what the server replies.
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For more options on :cpp:type:`esp_websocket_client_config_t`, please refer to API reference below
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Events
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------
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* `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.
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* `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.
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* `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.
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* `WEBSOCKET_EVENT_ERROR`: Not used in the current implementation of the client.
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If the client handle is needed in the event handler it can be accessed through the pointer passed to the event handler:
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.. code:: c
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esp_websocket_client_handle_t client = (esp_websocket_client_handle_t)handler_args;
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Limitations and Known Issues
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----------------------------
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* 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.
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Application Example
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-------------------
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A simple WebSocket example that uses esp_websocket_client to establish a websocket connection and send/receive data with the `websocket.org <https://websocket.org>`_ server can be found here: :example:`protocols/websocket`.
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Sending Text Data
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^^^^^^^^^^^^^^^^^
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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:
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.. code:: cpp
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esp_websocket_client_send_text(client, data, len, portMAX_DELAY);
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API Reference
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-------------
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.. include-build-file:: inc/esp_websocket_client.inc
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