Multipart/form-data with RestRserve

Question

I would like to expose an endpoint that accepts multipart/form-data, parses the multipart content and returns a csv-file. (the multipart input contains a csv dataset and processing instructions)

I’ve done this with plumber using Rook::Multipart$parse() as suggested here. Because plumber doesn’t support parallel requests, I’d like to re-implement this with RestRserve. The following won’t work – plumber’s inputs are of class environment (which Rook::Multipart$parse() assumes) whereas RestRserve’s inputs are of class Request R6.

application = Application$new(content_type = "text/plain")
application$add_post("/echo", function(req, res) {
  multipart <- Rook::Multipart$parse(req$body)
  dta <- read_csv(multipart$dta$tempfile, trim_ws=FALSE)
  res$set_body(dta)
})

Any ideas on how to get multipart/form-data input to work with RestRserve?

Answer 1

RestRserve parses multipart body when process the incoming request. As result you have a raw request$body and metatdata in the request$files. Request object also provides a get_file method to extract body content. Let me show example for the app and request:

# load packages
library(readr)
library(callr)
library(httr)

# run RestRserve in the background
ps <- r_bg(function() {
  library(RestRserve)
  library(readr)

  app = Application$new(content_type = "text/plain")
  app$add_post(
    path = "/echo",
    FUN = function(request, response) {
      # for debug
      str(request$body)
      str(request$files)
      # extract multipart body field
      cnt <- request$get_file("csv") # 'csv' from the upload form field
      # parse CSV
      dt <- read_csv(cnt)
      # for debug
      str(dt)
      # do something with dt
      identity(dt)
      # write result to temp file
      tmp <- tempfile()
      write_csv(dt, tmp)
      # set output body
      response$set_body(c(tmpfile = tmp))
      # or simply response$set_body(format_csv(dt))
    }
  )

  backend = BackendRserve$new()
  backend$start(app, http_port = 65080)
})

# wait for up
Sys.sleep(2L)

# check is alive
ps$is_alive()

# prepare CSV to upload
tmp <- tempfile()
write_csv(head(iris, 5), tmp)

# POST request with file
rs <- POST(
  url = "http:/127.0.0.1:65080/echo",
  body = list(csv = upload_file(tmp)),
  encode = "multipart"
)
# get response content
cat(content(rs))

# read log from the RestRserve
cat(ps$read_output())

# kill background prcoess
ps$kill()

See ?Request for more details about fields and methods in this class.