more robust error handling when API not available (#26)

R/api.R

@@ -4,11 +4,32 @@
 #  for CSV responses (get_measurements) the readr package is a hidden dependency
 # ==============================================================================
 
+default_api = 'https://api.opensensemap.org'
+
 #' Get the default openSenseMap API endpoint
 #' @export
 #' @return A character string with the HTTP URL of the openSenseMap API
-osem_endpoint = function() {
-  'https://api.opensensemap.org'
+osem_endpoint = function() default_api
+
+#' Check if the given openSenseMap API endpoint is available
+#' @param endpoint The API base URL to check, defaulting to \code{\link{osem_endpoint}}
+#' @return \code{TRUE} if the API is available, otherwise \code{stop()} is called.
+osem_ensure_api_available = function(endpoint = osem_endpoint()) {
+  code = FALSE
+  try({
+    code = httr::status_code(httr::GET(endpoint, path='stats'))
+  }, silent = TRUE)
+  
+  if (code == 200)
+    return(TRUE)
+  
+  errtext = paste('The API at', endpoint, 'is currently not available.')
+  if (code != FALSE)
+    errtext = paste0(errtext, ' (HTTP code ', code, ')')
+  if (endpoint == default_api)
+    errtext = c(errtext, 'If the issue persists, please check back at https://status.sensebox.de/778247404 and notify support@sensebox.de')
+  stop(paste(errtext, collapse='\n  '), call. = FALSE)
+  FALSE
 }
 
 get_boxes_ = function (..., endpoint) {
@@ -81,7 +102,7 @@ osem_get_resource = function (host, path, ..., type = 'parsed', progress = T, ca
   }
 
   res = osem_request_(host, path, query, type, progress)
-  if (!is.na(cache)) saveRDS(res, filename)
+  if (!is.na(res) && !is.na(cache)) saveRDS(res, filename)
   res
 }
 
@@ -115,6 +136,9 @@ osem_clear_cache = function (location = tempdir()) {
 }
 
 osem_request_ = function (host, path, query = list(), type = 'parsed', progress = TRUE) {
+  # stop() if API is not available
+  osem_ensure_api_available(host)
+  
   progress = if (progress && !is_non_interactive()) httr::progress() else NULL
   res = httr::GET(host, progress, path = path, query = query)
 

tests/testthat/test_api.R

@@ -0,0 +1,7 @@
+context('API error handling')
+
+test_that('unavailable API yields informative error message', {
+  expect_error({
+    osem_boxes(endpoint = 'example.zip')
+  }, 'The API at example.zip is currently not available')
+})

tests/testthat/test_archive.R

@@ -18,6 +18,7 @@ test_that('osem_box_to_archive_name does the correct character replacements', {
 })
 
 test_that('osem_box_to_archive_name works for one box', {
+  check_api()
   if (is.null(box)) skip('no box data could be fetched')
 
   archivename = opensensmapr:::osem_box_to_archivename(box)
@@ -26,6 +27,7 @@ test_that('osem_box_to_archive_name works for one box', {
 })
 
 test_that('osem_box_to_archive_name works for multiple boxes', {
+  check_api()
   if (is.null(boxes)) skip('no box data available')
 
   archivename = opensensmapr:::osem_box_to_archivename(boxes)
@@ -36,6 +38,7 @@ test_that('osem_box_to_archive_name works for multiple boxes', {
 context('osem_measurements_archive()')
 
 test_that('osem_measurements_archive works for one box', {
+  check_api()
   if (is.null(box)) skip('no box data could be fetched')
 
   m = osem_measurements_archive(box, as.POSIXlt('2018-08-08'))
@@ -44,6 +47,7 @@ test_that('osem_measurements_archive works for one box', {
 })
 
 test_that('osem_measurements_archive fails for multiple boxes', {
+  check_api()
   if (is.null(boxes)) skip('no box data available')
 
   expect_error(

tests/testthat/test_box.R

@@ -19,6 +19,8 @@ test_that('a single box can be retrieved by ID', {
 })
 
 test_that('required box attributes are correctly parsed', {
+  check_api()
+  
   expect_is(box$X_id, 'character')
   expect_is(box$name, 'character')
   expect_is(box$exposure, 'character')
@@ -29,6 +31,8 @@ test_that('required box attributes are correctly parsed', {
 })
 
 test_that('optional box attributes are correctly parsed', {
+  check_api()
+  
   completebox = osem_box('5a676e49411a790019290f94') # all fields populated
   expect_is(completebox$description, 'character')
   expect_is(completebox$grouptag, 'character')
@@ -65,6 +69,8 @@ test_that('[.sensebox maintains attributes', {
 })
 
 test_that("print.sensebox filters important attributes for a single box", {
+  check_api()
+  
   msg = capture.output({
     print(box)
   })
@@ -72,6 +78,8 @@ test_that("print.sensebox filters important attributes for a single box", {
 })
 
 test_that("summary.sensebox outputs all metrics for a single box", {
+  check_api()
+  
   msg = capture.output({
     summary(box)
   })

tests/testthat/test_measurements.R

@@ -123,6 +123,7 @@ test_that('[.osem_measurements maintains attributes', {
 })
 
 test_that('data.frame can be converted to measurements data.frame', {
+  check_api()
   m = osem_measurements('Windrichtung')
   df = osem_as_measurements(data.frame(c(1, 2), c('a', 'b')))
   expect_equal(class(df), class(m))

tests/testthat/test_phenomena.R

@@ -25,6 +25,8 @@ test_that('phenomena from boxes has all phenomena', {
 })
 
 test_that('phenomena from a not sensebox data.frame returns error', {
+  check_api()
+  
   expect_error(osem_phenomena(list()), 'no applicable method')
   expect_error(osem_phenomena(data.frame()), 'no applicable method')
   boxes_df = boxes