downloadHandler: File Downloads
In tomkuipers1402/shiny: Web Application Framework for R

Allows content from the Shiny application to be made available to the user as file downloads (for example, downloading the currently visible data as a CSV file). Both filename and contents can be calculated dynamically at the time the user initiates the download. Assign the return value to a slot on output in your server function, and in the UI use downloadButton() or downloadLink() to make the download available.

1	downloadHandler(filename, content, contentType = NA, outputArgs = list())

`filename`	A string of the filename, including extension, that the user's web browser should default to when downloading the file; or a function that returns such a string. (Reactive values and functions may be used from this function.)
`content`	A function that takes a single argument `file` that is a file path (string) of a nonexistent temp file, and writes the content to that file path. (Reactive values and functions may be used from this function.)
`contentType`	A string of the download's content type, for example `"text/csv"` or `"image/png"`. If `NULL` or `NA`, the content type will be guessed based on the filename extension, or `application/octet-stream` if the extension is unknown.
`outputArgs`	A list of arguments to be passed through to the implicit call to `downloadButton()` when `downloadHandler` is used in an interactive R Markdown document.

## Only run examples in interactive R sessions
if (interactive()) {

ui <- fluidPage(
  downloadLink("downloadData", "Download")
)

server <- function(input, output) {
  # Our dataset
  data <- mtcars

  output$downloadData <- downloadHandler(
    filename = function() {
      paste("data-", Sys.Date(), ".csv", sep="")
    },
    content = function(file) {
      write.csv(data, file)
    }
  )
}

shinyApp(ui, server)
}