HTTP streaming and Server-Sent Events in R with nanonext

sse.R

# pak::pak("r-lib/nanonext")
library(nanonext)

conns <- list()
handlers <- list(
  handler_stream("/stream",
    on_request = function(conn, req) {
      conn$set_header("Content-Type", "application/x-ndjson")
      conns[[as.character(conn$id)]] <<- conn
      conn$send('{"status":"connected"}\n')
    },
    on_close = function(conn) {
      conns[[as.character(conn$id)]] <<- NULL
    }
  ),
  # POST endpoint triggers broadcast to all streaming clients
  handler("/broadcast", function(req) {
    msg <- paste0('{"msg":"', rawToChar(req$body), '"}\n')
    lapply(conns, function(c) c$send(msg))
    list(status = 200L, body = "sent")
  }, method = "POST")
)

server <- http_server(
  url = "http://127.0.0.1:8080",
  handlers = handlers
)
server$start()
server$url

# Open in two terminals
# curl -X GET http://127.0.0.1:8080/stream
# curl -X GET http://127.0.0.1:8080/stream

# Send in another terminal
# curl -X POST http://127.0.0.1:8080/broadcast -H "Content-Type: application/json" -d 'hello world'

# Both clients recieve the message