Title: Reactive poll and file reader example for R Shiny

README.md

There are three main parts of the server code:

1. The first sets up an observer which writes to a log file once every second. This is just to make the example work; typically some external process will be writing to a file.

2. The second part uses a reactiveFileReader to monitor the log file for changes every 0.5 seconds.

3. The third part uses a reactivePoll to monitor the log file for changes every 4 seconds. The reactivePoll is general, and it watch for things other than file changes. It could, for example, query a database.

DESCRIPTION

Type: Shiny
Title: Reactive poll and file reader
License: MIT
Author: Winston Chang <winston@rstudio.com>
AuthorUrl: http://www.rstudio.com/
Tags: reactive-poll reactive-file-reader
DisplayMode: Showcase

server.R

shinyServer(function(input, output, session) {

  # Create a random name for the log file
  logfilename <- paste0('logfile',
                        floor(runif(1, 1e+05, 1e+06 - 1)),
                        '.txt')


  # ============================================================
  # This part of the code writes to the log file every second.
  # Writing to the file could be done by an external process.
  # In this example, we'll write to the file from inside the app.
  logwriter <- observe({
    # Invalidate this observer every second (1000 milliseconds)
    invalidateLater(1000, session)

    # Clear log file if more than 10 entries
    if (file.exists(logfilename) &&
        length(readLines(logfilename)) > 10) {
      unlink(logfilename)
    }

    # Add an entry to the log file
    cat(as.character(Sys.time()), '\n', file = logfilename,
        append = TRUE)
  })

  # When the client ends the session, suspend the observer and
  # remove the log file.
  session$onSessionEnded(function() {
    logwriter$suspend()
    unlink(logfilename)
  })

  # ============================================================
  # This part of the code monitors the file for changes once per
  # 0.5 second (500 milliseconds).
  fileReaderData <- reactiveFileReader(500, session,
                                       logfilename, readLines)

  output$fileReaderText <- renderText({
    # Read the text, and make it a consistent number of lines so
    # that the output box doesn't grow in height.
    text <- fileReaderData()
    length(text) <- 14
    text[is.na(text)] <- ""
    paste(text, collapse = '\n')
  })


  # ============================================================
  # This part of the code monitors the file for changes once
  # every four seconds.

  pollData <- reactivePoll(4000, session,
    # This function returns the time that the logfile was last
    # modified
    checkFunc = function() {
      if (file.exists(logfilename))
        file.info(logfilename)$mtime[1]
      else
        ""
    },
    # This function returns the content of the logfile
    valueFunc = function() {
      readLines(logfilename)
    }
  )

  output$pollText <- renderText({
    # Read the text, and make it a consistent number of lines so
    # that the output box doesn't grow in height.
    text <- pollData()
    length(text) <- 14
    text[is.na(text)] <- ""
    paste(text, collapse = '\n')
  })
})

ui.R

shinyUI(fluidPage(
  titlePanel("reactivePoll and reactiveFileReader"),
  fluidRow(
    column(12,
      p("This app has a log file which is appended to",
        "every second.")
    )
  ),
  fluidRow(
    column(6, wellPanel(
      "This side uses a reactiveFileReader, which is monitoring",
      "the log file for changes every 0.5 seconds.",
      verbatimTextOutput("fileReaderText")
    )),

    column(6, wellPanel(
      "This side uses a reactivePoll, which is monitoring",
      "the log file for changes every 4 seconds.",
      verbatimTextOutput("pollText")
    ))
  )
))

Hi, I'm trying to use reactiveFileReader to read from an s3 bucket that'll be updated periodically. Can't seem to get it to work. Any suggestions? Currently, my code looks like

`getFile<-function(){
my_bucket <- 'globalrss'
file <- paste0(as.character(getwd()),"/tmp")
r <- aws.s3::save_object("bodytype.csv", my_bucket, file=file)
}

shinyServer(function(input, output, session) {
fileReaderData <- reactiveFileReader(500, session,
getFile(), readLines)
output$fileReaderText <- renderText({
text <- fileReaderData()
length(text) <- 14
text[is.na(text)] <- ""
paste(text, collapse = '\n')
})
})`

It reads the s3 file correctly but does not update when the s3 file is changed. Assistance appreciated! Thanks :)