shiny progress bar linked to rmarkdown/knitr progress

app.R

library(shiny)

# custom progress function
myProgress <- function(total, labels) {
  list(update = function(i) {
        shiny::setProgress(value = i/total, message = paste0("Running chunk ", i, "/", total, ": "), detail = labels[i])
        cat(sep = "", i, "/", total, ": ", labels[i], "\n")
      }, done = function() {
        shiny::setProgress(1, message = "Done")
      })
}

# register it with knitr
op <- options(knitr.progress.fun = myProgress)

# shiny app
shinyApp(
    ui = fluidPage(
        titlePanel("Rmarkdown + Shiny Progress"),
        downloadButton("run", "Create Report")
    ), 
    server = function(input, output, session) {
      output$run <- downloadHandler(filename = "report.html",
          content = function(file) {
            withProgress(message = "Running report...", {
                  rmarkdown::render("report.Rmd", output_file = file)
                })
          })
    }
)

report.Rmd

---
title: "Rmarkdown + Shiny Progress Example"
output: html_document
---

# Header

```{r plot}
Sys.sleep(1)
plot(rnorm(100), pch = 20)
```

Some text

```{r chunk-with-table}
Sys.sleep(1)
knitr::kable(head(mtcars))
```

some more text

```{r unknown}
Sys.sleep(1)
plot(rnorm(10), pch = 20, col = sample(1:16, 10, FALSE))
```

# Conclusion

```{r final}
Sys.sleep(1)
1+1
```

end