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WebSocket Server and Client for Arduino Build Status

a WebSocket Server and Client for Arduino based on RFC6455.

Supported features of RFC6455
  • text frame
  • binary frame
  • connection close
  • ping
  • pong
  • continuation frame
  • max input length is limited to the ram size and the WEBSOCKETS_MAX_DATA_SIZE define
  • max output length has no limit (the hardware is the limit)
  • Client send big frames with mask 0x00000000 (on AVR all frames)
  • continuation frame reassembly need to be handled in the application code
Limitations for Async
  • Functions called from within the context of the websocket event might not honor yield() and/or delay(). See this issue for more info and a potential workaround.
  • wss / SSL is not possible.
Supported Hardware
  • ESP8266 Arduino for ESP8266
  • ESP32 Arduino for ESP32
  • ESP31B
  • Particle with STM32 ARM Cortex M3
  • ATmega328 with Ethernet Shield (ATmega branch)
  • ATmega328 with enc28j60 (ATmega branch)
  • ATmega2560 with Ethernet Shield (ATmega branch)
  • ATmega2560 with enc28j60 (ATmega branch)

version 2.0.0 and up is not compatible with AVR/ATmega, check ATmega branch.

version 2.3.0 has API changes for the ESP8266 BareSSL (may brakes existing code)

Arduino for AVR not supports std namespace of c++.

wss / SSL

supported for:

  • wss client on the ESP8266
  • wss / SSL is not natively supported in WebSocketsServer however it is possible to achieve secure websockets by running the device behind an SSL proxy. See Nginx for a sample Nginx server configuration file to enable this.


This libary can run in Async TCP mode on the ESP.

The mode can be activated in the WebSockets.h (see WEBSOCKETS_NETWORK_TYPE define).

ESPAsyncTCP libary is required.

High Level Client API

  • begin : Initiate connection sequence to the websocket host.
void begin(const char *host, uint16_t port, const char * url = "/", const char * protocol = "arduino");
void begin(String host, uint16_t port, String url = "/", String protocol = "arduino");
  • onEvent: Callback to handle for websocket events
void onEvent(WebSocketClientEvent cbEvent);
  • WebSocketClientEvent: Handler for websocket events
void (*WebSocketClientEvent)(WStype_t type, uint8_t * payload, size_t length)

Where WStype_t type is defined as:

typedef enum {
} WStype_t;


Submit issues to:

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License and credits

The library is licensed under LGPLv2.1

libb64 written by Chris Venter. It is distributed under Public Domain see LICENSE.

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