title: R Shiny, fileInput displays "Upload Completed" a few seconds before it is actually done
body: <p>I typically need to upload large (~700MB) csv files into my shiny app. The problem is, it shows "Upload Completed" in less than 3 seconds or so, while it actually takes around 20 seconds (have also confirmed it by printing some rows of the data).</p>
  
  <p>Is there a workaround for this?  </p>
  
  <pre><code>ui &lt;- fluidPage( 
  
    titlePanel("Predictive Models"),
  
    # Sidebar layout with input and output definitions ----
    sidebarLayout(
      # Sidebar panel for inputs ----
      sidebarPanel(
        # Input: Select a file ----
        fileInput("file1", "Choose CSV File",
                  multiple = FALSE,
                  accept = c("text/csv",
                             "text/comma-separated-values,text/plain",
                             ".csv"),
                  width = "80%")
         ...
  server &lt;- function(input, output) {
  
    values &lt;- reactiveValues(df_data = NULL, station_id= NULL, station_name= NULL, station_data=NULL, processed_data=NULL,df=NULL)
  
    observeEvent(input$file1, {
      values$df_data &lt;- read.csv(input$file1$datapath);
  
      output$sum &lt;- renderPrint({
        print(head(values$df_data, 10))
      }) 
    }) 
  </code></pre>