How can I send a GET request without waiting for the response

Question

I am trying to run a GET request inside a shinyApp, but I don't want to wait for the response as it would take quite a long time to process and I dont need really need the response inside the shinyApp, although a status code would be nice, but it is not obligatory.

Or is there maybe a function, that sends an async request? Like wrapping the whole GET inside a future/promise?

Currently I have this observeEvent in my shinyApp:

  observeEvent(input$import, {
    httr::GET(url = "https://someurl/that/takes/a/long/time")
  })

Is the curl_fetch_multi from the curl package suited for that task?

Answer 1

Here is a way to run GET asynchronously and in a intra-session non-blocking manner (observer returning nothing):

library(shiny)
library(future)
library(promises)
library(future.callr)
library(httr)

plan(callr)

queryGoogle <- function(queryString) {
  myResponse <- httr::GET("http://google.com/", path = "search", query = list(q = queryString))
  return(myResponse)
}

ui <- fluidPage(
  br(),
  textOutput("time_output"),
  br(),
  textInput(inputId="query_input", label = NULL, value = "", placeholder = "Search google..."),
  actionButton("import", "Query"),
  hr(),
  textOutput("query_output")
)

server <- function(input, output, session) {
  futureData <- reactiveValues(response = NULL)
  
  observeEvent(input$import, {
    myFuture <- future({
      queryGoogle(isolate(input$query_input))
    })
    
    then(
      myFuture,
      onFulfilled = function(value) {
        futureData$response <- value
      },
      onRejected = NULL
    )
    return(NULL)
  })
  
  output$query_output <- renderPrint({
    req(futureData$response)
  })
  
  time <- reactive({
    invalidateLater(500, session)
    Sys.time()
  })
  
  output$time_output <- renderText({ paste("Something running in parallel:", time()) })
}

shinyApp(ui, server)

This is a slight modification of my answer here.

Please also read Joe Cheng's related answer here carefully.