plumber

Plumber allows you to create a web API by merely decorating your existing R source code with roxygen2-like comments. Take a look at an example.

# plumber.R

#* Echo back the input
#* @param msg The message to echo
#* @get /echo
function(msg="") {
  list(msg = paste0("The message is: '", msg, "'"))
}

#* Plot a histogram
#* @serializer png
#* @get /plot
function() {
  rand <- rnorm(100)
  hist(rand)
}

#* Return the sum of two numbers
#* @param a The first number to add
#* @param b The second number to add
#* @post /sum
function(a, b) {
  as.numeric(a) + as.numeric(b)
}

These comments allow plumber to make your R functions available as API endpoints. You can use either #* as the prefix or #', but we recommend the former since #' will collide with roxygen2.

library(plumber)
# 'plumber.R' is the location of the file shown above
pr("plumber.R") %>%
  pr_run(port=8000)

You can visit this URL using a browser or a terminal to run your R function and get the results. For instance http://localhost:8000/plot will show you a histogram, and http://localhost:8000/echo?msg=hello will echo back the 'hello' message you provided.

Here we're using curl via a Mac/Linux terminal.

$ curl "http://localhost:8000/echo"
 {"msg":["The message is: ''"]}
$ curl "http://localhost:8000/echo?msg=hello"
 {"msg":["The message is: 'hello'"]}

As you might have guessed, the request's query string parameters are forwarded to the R function as arguments (as character strings).

$ curl --data "a=4&b=3" "http://localhost:8000/sum"
 [7]

You can also send your data as JSON:

$ curl -H "Content-Type: application/json" --data '{"a":4, "b":5}' http://localhost:8000/sum
 [9]

Installation

You can install the latest stable version from CRAN using the following command:

install.packages("plumber")

If you want to try out the latest development version, you can install it from GitHub.

pak::pkg_install("rstudio/plumber")
library(plumber)

Cheat Sheet

Hosting

If you're just getting started with hosting cloud servers, the DigitalOcean integration included in plumber will be the best way to get started. You'll be able to get a server hosting your custom API in just two R commands. To deploy to DigitalOcean, check out the plumber companion package plumberDeploy.

Posit Connect is a commercial publishing platform that enables R developers to easily publish a variety of R content types, including Plumber APIs. Additional documentation is available at https://www.rplumber.io/articles/hosting.html#rstudio-connect-1.

A couple of other approaches to hosting plumber are also made available:

• PM2 - https://www.rplumber.io/articles/hosting.html#pm2-1
• Docker - https://www.rplumber.io/articles/hosting.html#docker

Related Projects

• OpenCPU - A server designed for hosting R APIs with an eye towards scientific research.
• jug - (development discontinued) an R package similar to Plumber but uses a more programmatic approach to constructing the API.