Plumber: return xlsx or csv files

Created on 16 Nov 2018 · 6Comments · Source: rstudio/plumber

Hi,

My code takes in an input csv and is supposed to output another csv or xlsx. I tried using XLSX content type from https://github.com/trestletech/plumber/blob/master/R/content-types.R, but it is throwing an exception every time without any mention about the exception type. Is there a way to do this?

help wanted question

Source

Amalabdu

Most helpful comment

Thanks a lot @shrektan!! It works perfectly.

Amalabdu on 18 Nov 2018

🎉2

All 6 comments

@Amalabdu Would you mind provide a minimal reproducible example? I'm not sure what your problem is.

shrektan on 16 Nov 2018

If we have to return a PDF file then we use something like

* @serializer contentType list(type="application/pdf")

* @get /pdf

function(){
tmp <- tempfile()
pdf(tmp)
plot(1:10, type="b")
text(4, 8, "PDF from plumber!")
dev.off()

readBin(tmp, "raw", n=file.info(tmp)$size)
}

Now what if I want to return a CSV file? As in there is a model that runs and outputs a CSV. So can we output a CSV through Plumber, using XLSX or otherwise?

Amalabdu on 16 Nov 2018

@Amalabdu The example code below should solve your problem. It works for me.

BTW, using three backticks (```) to enclose the code makes your code easier to read.

The hosting code

serializer_csv <- function(){
  function(val, req, res, errorHandler){
    tryCatch({
      res$setHeader("Content-Type", "text/plain")
      res$setHeader("Content-Disposition", 'attachment; filename="xxx.csv"')
      res$body <- paste0(val, collapse="\n")
      return(res$toResponse())
    }, error=function(e){
      errorHandler(req, res, e)
    })
  }
}
plumber::addSerializer("csv", serializer_csv)
plumber::plumber$new("plumber-csv.R")$run(port = 8833)

The plumber-csv.R file

#* @serializer csv
#* @get /csv
function() {
  df <- data.frame(CHAR = letters, NUM = rnorm(length(letters)), stringsAsFactors = F)
  csv_file <- tempfile(fileext = ".csv")
  on.exit(unlink(csv_file), add = TRUE)
  write.csv(df, file = csv_file)
  readLines(csv_file)
}