Can't update reactive value from download handler

[bhu]

When attempting to update a reactive value from within a download handler, the value is either not updated until modified by another action button:
Shinylive example

Or the value is not updated at all when separately registering a side effect:
Shinylive example

Is this the intended behavior (implicit asynchrony for the download handler)? Or would there be a way to properly modify reactive values from within download handlers?

[cpsievert]

Can confirm this does seem like a real issue/bug -- here's an R/Shiny app that demonstrates the desired behavior:

library(shiny)

ui <- fluidPage(
    h3("Sample Data"),
    tableOutput("data_table"),
    
    br(),
    
    downloadButton("downloadData", "Download CSV"),
    
    br(), br(),
    
    h4("Download Status:"),
    textOutput("status")
)


server <- function(input, output, session) {
  
  # Sample data
  sample_data <- data.frame(
    Name = c("Alice", "Bob", "Charlie", "Diana"),
    Age = c(25, 30, 35, 28),
    Score = c(85, 92, 78, 88)
  )
  
  # Create a reactive value to track downloads
  download_trigger <- reactiveVal(0)
  
  # Display the data
  output$data_table <- renderTable({
    sample_data
  })
  
  # Download handler
  output$downloadData <- downloadHandler(
    filename = function() {
      paste("data-", Sys.Date(), ".csv", sep = "")
    },
    content = function(file) {
      write.csv(sample_data, file, row.names = FALSE)
      # Increment the trigger after successful download
      download_trigger(download_trigger() + 1)
    }
  )
  
  # Observer that responds to downloads
  observeEvent(download_trigger(), {
    if (download_trigger() > 0) {
      # Your post-download logic here
      showNotification("Download completed successfully!")
    }
  })
  
  # Display download count
  output$status <- renderText({
    if (download_trigger() == 0) {
      "No downloads yet"
    } else {
      paste("Downloads completed:", download_trigger())
    }
  })
}

# Run the app
shinyApp(ui = ui, server = server)