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

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

@@ -25,15 +25,14 @@ 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: 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

@@ -1,6 +1,9 @@
 # learnr (development version)
 
+-   Added a new option, `tutorial.exercise.throttle`, to slow down successive exercise execution. This option should be set to the number of seconds a user will have to wait between performing code executions. The option defaults to 1 second to deter rapid code executions. To disable submission throttling, call `options(tutorial.exercise.throttle = 0)` within your setup chunk. (@internaut, #818)
+
 -   Removed dependency on ellipsis (@olivroy, #809)
+
 -   Added Norwegian translation contributed by @jonovik. (#806)
 
 # learnr 0.11.5

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)
 
+  # throttle option to slow down successive exercise execution requests
+  throttle_s <- getOption("tutorial.exercise.throttle", 1) # in seconds
+  if (is.numeric(throttle_s) && throttle_s > 0) {
+    exercise_rx <- throttle(exercise_rx, throttle_s * 1000) # in milliseconds
+  }
   # observe input
   observeEvent(exercise_rx(), {
-
     # get exercise from app
     exercise <- exercise_rx()
     # Add tutorial information

vignettes/articles/exercises.Rmd

@@ -80,6 +80,20 @@ This option can also be set either globally or per-chunk:
 insert_snippet("exerciseeval")
 ```
 
+To prevent server overload caused by users rapidly clicking the "Run Code" button, you can set a delay between exercise code submissions using the `tutorial.exercise.throttle` option (in seconds). This will ensure that the same user can only start the evaluation of the same exercise per `tutorial.exercise.throttle` seconds. This option is set globally and the default is a throttle of of 1 second.
+
+```{r snippet-exercisethrottle, eval = FALSE}
+# Set exercise submission throttle time to 5 seconds
+options("tutorial.exercise.throttle" = 5)
+```
+
+To disable of this behavior, you can set the option to 0:
+
+```{r snippet-exercisethrottleoff, eval = FALSE}
+# Disable exercise submission throttle
+options("tutorial.exercise.throttle" = 0)
+```
+
 ## Exercise Setup {#exercise-setup}
 
 Code chunks with `exercise=TRUE` are evaluated within standalone environments.