feat: Slow down successive (same) exercise execution via throttle

.github/workflows/R-CMD-check.yaml

@@ -25,15 +25,15 @@ jobs:
       fail-fast: false
       matrix:
         config:
-          - {os: macOS-latest,   r: 'release'}
-          - {os: windows-latest, r: 'release'}
-          - {os: windows-latest, r: '3.6'}
-          - {os: ubuntu-20.04,   r: 'devel', http-user-agent: 'release'}
-          - {os: ubuntu-20.04,   r: 'release'}
-          - {os: ubuntu-20.04,   r: 'oldrel-1'}
-          - {os: ubuntu-20.04,   r: 'oldrel-2'}
-          - {os: ubuntu-20.04,   r: 'oldrel-3'}
-          - {os: ubuntu-20.04,   r: 'oldrel-4'}
+          - { os: macOS-latest, r: "release" }
+          - { os: windows-latest, r: "release" }
+          # - {os: windows-latest, r: '3.6'} # Difficulty building packages on windows w/ R 3.6
+          - { os: ubuntu-20.04, r: "devel", http-user-agent: "release" }
+          - { os: ubuntu-20.04, r: "release" }
+          - { os: ubuntu-20.04, r: "oldrel-1" }
+          - { os: ubuntu-20.04, r: "oldrel-2" }
+          - { os: ubuntu-20.04, r: "oldrel-3" }
+          - { os: ubuntu-20.04, r: "oldrel-4" }
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}

DESCRIPTION

@@ -73,5 +73,5 @@ Config/Needs/coverage: covr
 Config/Needs/website: pkgdown, tidyverse/tidytemplate
 Encoding: UTF-8
 Roxygen: list(markdown = TRUE)
-RoxygenNote: 7.3.1
+RoxygenNote: 7.3.2
 SystemRequirements: pandoc (>= 1.14) - http://pandoc.org

NEWS.md

@@ -1,5 +1,6 @@
 # learnr (development version)
 
+-   Added a new option, `tutorial.exercise.debounce`, to slow down successive exercise execution. This option should be set to the number of seconds a user will have to wait before their next code execution is performed. (@internaut, #818)
 -   Removed dependency on ellipsis (@olivroy, #809)
 -   Added Norwegian translation contributed by @jonovik. (#806)
 

R/exercise.R

@@ -33,9 +33,13 @@ setup_exercise_handler <- function(exercise_rx, session) {
   # setup reactive values for return
   rv <- reactiveValues(triggered = 0, result = NULL)
 
+  # debounce option to slow down successive exercise execution requests
+  debounce_s <- getOption("tutorial.exercise.debounce", 1) # in seconds
+  if (is.numeric(debounce_s) && debounce_s > 0) {
+    exercise_rx <- debounce(exercise_rx, debounce_s * 1000) # in milliseconds
+  }
   # observe input
   observeEvent(exercise_rx(), {
-
     # get exercise from app
     exercise <- exercise_rx()
     # Add tutorial information

pkgdown/assets/snippets/exercisedebounce.md

@@ -0,0 +1,2 @@
+# Set exercise submission debounce time to 1 second
+options("tutorial.exercise.debounce" = 1)

vignettes/articles/exercises.Rmd

@@ -80,6 +80,12 @@ This option can also be set either globally or per-chunk:
 insert_snippet("exerciseeval")
 ```
 
+It may be necessary to slow down successive exercise submissions, otherwise users may overwhelm your server by running exercise code chunks in fast repetition. You can do so globally by setting the option `tutorial.exercise.debounce` to an amount of time (in seconds) that is waited before the same user's next code execution is performed:
+
+```{r snippet-exercisedebounce, echo = FALSE}
+insert_snippet("exercisedebounce")
+```
+
 ## Exercise Setup {#exercise-setup}
 
 Code chunks with `exercise=TRUE` are evaluated within standalone environments.