WebSocket Communication between R Server and Chrome Client

Complete example showing how to:
1. Set up a WebSocket server in R
2. Continuously collect data from a URL
3. Process the data and store results in a dataframe
4. Send the data to a Chrome client
5. Display the data as a chart in the browser

R Server Side Code
library(websocket)
library(httr)
library(jsonlite)

# Create a dataframe to store results
results_df <- data.frame(
  timestamp = character(),
  value = numeric(),
  stringsAsFactors = FALSE
)

# Function to fetch and process data from URL
fetch_data <- function() {
  # Example: Fetch random data from an API
  # Replace with your actual data source
  response <- GET("https://api.coingecko.com/api/v3/simple/price?ids=bitcoin&vs_currencies=usd")
  data <- content(response, "parsed")
  
  # Process the data
  current_time <- format(Sys.time(), "%Y-%m-%d %H:%M:%S")
  value <- data$bitcoin$usd
  
  # Add to dataframe
  new_row <- data.frame(timestamp = current_time, value = value)
  results_df <<- rbind(results_df, new_row)
  
  # Keep only last 100 entries
  if (nrow(results_df) > 100) {
    results_df <<- tail(results_df, 100)
  }
  
  # Return latest data point
  list(timestamp = current_time, value = value, all_data = results_df)
}

# WebSocket server
start_websocket_server <- function() {
  ws_server <- WebSocket$new("127.0.0.1", 8080)
  
  ws_server$onConnection(function(ws) {
    cat("Client connected\n")
    
    # Send initial data
    data <- fetch_data()
    ws$send(toJSON(data))
    
    # Set up a timer to send updates every 2 seconds
    timer <- later::later(
      function() {
        if (ws$readyState() == 1) {  # 1 = OPEN
          data <- fetch_data()
          ws$send(toJSON(data))
          timer <<- later::later(repeatable, 2)
        }
      },
      2
    )
    
    repeatable <- function() {
      if (ws$readyState() == 1) {
        data <- fetch_data()
        ws$send(toJSON(data))
        timer <<- later::later(repeatable, 2)
      }
    }
    
    ws$onClose(function() {
      cat("Client disconnected\n")
      if (!is.null(timer)) later::destroy(timer)
    })
  })
  
  cat("WebSocket server running on ws://127.0.0.1:8080\n")
  later::run_now()
}

# Start the server
start_websocket_server()

Chrome Client Side Code (HTML/JavaScript)



How to Run This Example
1. Save the R code to a file (e.g., `websocket_server.R`)
2. Run the R script: `Rscript websocket_server.R`
3. Save the HTML code to `client.html`
4. Open `client.html` in Chrome
5. You should see a real-time chart updating every 2 seconds with data from the R server

Key Features

1. R Server Side:
- Uses `websocket` package to create a WebSocket server
- Fetches data from a URL (Bitcoin price API in this example)
- Stores historical data in a dataframe
- Sends both latest data point and all historical data to client

2. Chrome Client Side:
- Connects to the R server via WebSocket
- Uses Chart.js to visualize the data
- Updates the chart in real-time as new data arrives

You can modify the `fetch_data()` function to collect data from any URL or API you need. The example shows Bitcoin prices, but you can replace it with any data source.