Context in R Programming Language

Here’s the translation of the Go code to R, formatted in Markdown suitable for Hugo:

In R, we don’t have a direct equivalent to the context.Context concept. However, we can simulate a similar behavior using R’s event handling mechanisms and the later package for asynchronous operations. Here’s an example that mimics the functionality of the original code:

library(httpuv)
library(later)

hello <- function(req) {
  cat("server: hello handler started\n")
  on.exit(cat("server: hello handler ended\n"))

  # Simulate work
  later::later(function() {
    if (!req$cancelled) {
      req$respond(list(
        status = 200,
        headers = list('Content-Type' = 'text/plain'),
        body = "hello\n"
      ))
    }
  }, delay = 10)

  # Set up cancellation
  req$onCancel(function() {
    cat("server: request cancelled\n")
    req$respond(list(
      status = 500,
      headers = list('Content-Type' = 'text/plain'),
      body = "Internal Server Error: request cancelled"
    ))
  })

  return(list())
}

main <- function() {
  app <- list(
    call = function(req) {
      if (req$PATH_INFO == "/hello") {
        return(hello(req))
      }
      return(list(status = 404))
    }
  )

  cat("Starting server on port 8090...\n")
  httpuv::runServer("0.0.0.0", 8090, app)
}

main()

This R script sets up a simple HTTP server using the httpuv package. Here’s a breakdown of what’s happening:

1. We define a hello function that handles requests to the “/hello” endpoint.

2. Inside hello, we simulate a long-running operation using later::later(), which schedules a function to run after a 10-second delay.

3. We set up a cancellation handler using req$onCancel(). This will be called if the client cancels the request.

4. The main function sets up the server routing and starts the server on port 8090.

To run this server:

Rscript server.R

You can then simulate a client request and cancellation:

$ curl localhost:8090/hello
server: hello handler started
^C
server: request cancelled
server: hello handler ended

This example demonstrates how to handle long-running operations and request cancellations in an R web server. While it doesn’t use the exact same concepts as the original code (since R doesn’t have built-in concepts like context.Context), it achieves similar functionality using R’s asynchronous programming capabilities.