# Websockets for Hardware Engineers - Part 1 > Websockets are a communication protocol that allow the creation of persistent, bidirectional communication channels between client and server. - **Page** - https://iotready.com/insights/websockets-for-hardware-engineers - **Author** - Tej Pochiraju - **Published** - 2020-12-15 - **Topics** - Technology ## Before we start, what is HTTP? This is what HTTP REST looks like... ```mermaid journey title Typical Client-Server Flow section Identify Yourself! SSL Handshake: 3: Client, Server Authenticate: 5: Client Authorize: 3: Server section Make a Request Ask for data: 5: Client Send data: 3: Server ``` ```mermaid journey title A bit later... section Identify Yourself! SSL Handshake: 3: Client, Server Authenticate: 4: Client Authorize: 3: Server section Make a Request Send data: 3: Client Acknowledge: 3: Server ``` ### We noticed some issues... - Each request is preceded by an SSL handshake (if HTTPS) and authentication - This can consume significant resources (CPU, time, memory) each time The server can never send data to the client - The client needs to implement polling to request data any time it is needed. ## What are websockets? Websockets are a communication protocol that allow the creation of **persistent**, **bidirectional** communication **channels** between client and server. ```mermaid journey title A Websockets Journey section Identify Yourself! SSL Handshake: 3: Client, Server Authenticate: 5: Client Authorize: 3: Server section Make a Request Send data: 5: Client Acknowledge: 3: Server section Event on Server! Send data: 3: Server section Make a Request Get data: 5: Client Send data: 3: Server ``` ### Persistent Once established, the connection between client and server is kept-alive for a long period - No theoretical limit - Connection can be kept alive through regular pings - Disconnections are events that can be monitored to trigger reconnection ### Bidirectional Once the connection is established, the server can send information to the client at any time. - No need for the client to initiate the request - Client can also send requests to the server ### Channels Each websocket connection is actually a channel - Imagine a long pipe where information can flow both ways - Each channel is opened on a specific address, and typically, has a specific purpose - Each client can open multiple channels with the same server - Multiple clients can open channels with the same server ### Points to Note Websockets is based on TCP so the server cannot broadcast messages to all clients - Instead, on the server, maintain a list of connected clients and send them messages in a loop Each websocket connection consumes memory so close unused connections - Enforce ping based check of alive clients - if no response, close the connection! Websockets only concerns itself with the transport layer (on top of TCP) and makes no recommendation about the encoding of the data being transmitted. - You can [transmit text](https://www.websocket.org/echo.html) - Or [JSON](https://github.com/binance-exchange/binance-official-api-docs/blob/master/web-socket-streams.md) - Or [even binary files](https://techtutorialsx.com/2018/11/08/python-websocket-client-sending-binary-content/) ## Exercises ### Tools we need - [websocat](https://github.com/vi/websocat/releases) or similar command line websockets client for Exercise 1 - [NodeJS](https://nodejs.org/en/) or [Python 3](https://www.python.org/) for Exercise 2 - [ESP32](https://www.espressif.com/en/products/socs/esp32/overview) and [ESP-IDF](https://esp-idf.readthedocs.io/) for Exercise 3 ### 1. Public Websocket Server Use websocat from a terminal to connect to the [Binance websocket streams](https://github.com/binance-exchange/binance-official-api-docs/blob/master/web-socket-streams.md) These endpoints are known to work: - `wss://stream.binance.com:9443/ws/!miniTicker@arr` - `wss://stream.binance.com:9443/ws/btcusdt@depth` - `wss://stream.binance.com:9443/ws/bnbbtc@depth` - Open another terminal/tab and connect to a different stream from Binance For the really patient, check how long the connection remains open for with: ``` date; websocat wss://stream.binance.com:9443/ws/bnbbtc@depth; date ``` ### 2. Local Websocket Server #### NodeJS - Follow [this excellent tutorial](https://flaviocopes.com/websockets/) to set up a local websocket client and server #### Python - Follow [this tutorial](https://codingpointer.com/python-tutorial/python-websockets) to set up a local websocket client and server ### 3. ESP32 as a Websocket Server - [Set up ESP-IDF](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/index.html#installation-step-by-step) on your computer Build and flash the [Websocket Echo Server example](https://github.com/espressif/esp-idf/tree/master/examples/protocols/http_server/ws_echo_server) from ESP-IDF on the ESP32 - You will need to configure your WiFi settings with `idf.py menuconfig` - Once booted, the ESP32 will print its `ip_address`. You will need this. - Using websocat, connect to `ws://ip_address/ws` - Once connected, type and send any string message, e.g. `hello` Open a new terminal and repeat the websocat messaging. - What do you notice across the two clients? #### More advanced example - Try this [slightly more advanced example](https://github.com/espressif/esp-idf/tree/master/examples/protocols/websocket) ## Questions - What are the similarities and differences between HTTP and BLE? - What are the similarities and differences between Websockets and BLE? - How would you implement an API for client to request changes (e.g. switch on lights)? ## Ideas, questions or corrections? Write to us at