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Last active January 17, 2018 20:24
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httpuv application that listens for R commands in background
# This application will listen for local connections on port 7000 and run
# commands it receives via HTTP POST. It will run commands using the later
# packages -- that is, whenever the R call stack is empty (it is idle at the R
# prompt), or whenever later::run_now() is called. Shiny keeps calling run_now()
# when running an application, so this can run commands when a Shiny application
# is running.
# This can be useful for enabling options while a Shiny application is running.
# For example, you can use it to run `options(shiny.trace=TRUE)` without
# restarting the application.
# curl -X POST http://localhost:7000/ --data "options(shiny.trace=TRUE)"
# wget --quiet -O - http://localhost:7000/ --post-data="options(shiny.trace=TRUE)"
# Note that it requires the background-thread branch of httpuv:
# devtools::install_github('rstudio/httpuv@background-thread')
# Examples of sending R commands via POST with curl or wget:
# curl -X POST http://localhost:7000/ --data "a<-1; a+100"
# wget --quiet -O - http://localhost:7000/ --post-data="a<-1; a+100"
httpuv::startServer("", 7000,
list(call = function(req) {
txt <- req$rook.input$read_lines()
expr <- parse(text = txt)
result_txt <- capture.output({
result <- withVisible(eval(expr, envir = .GlobalEnv))
if (result$visible == TRUE) {
result_txt <- paste(result_txt, collapse = "\n")
# Print result to R console
cat(result_txt, "\n", sep = "")
# Return result to client
status = 200L,
headers = list(
'Content-Type' = 'text/plain'
body = result_txt
# To stop:
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