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Turning vcr on and off

2024-10-25

Source: vignettes/lightswitch.Rmd
lightswitch.Rmd

Sometimes you may need to turn off vcr, either for individual function calls, individual test blocks, whole test files, or for the entire package. The following attempts to break down all the options.

vcr has the following four exported functions:

  • turned_off() - Turns vcr off for the duration of a code block
  • turn_off() - Turns vcr off completely, so that it no longer handles every HTTP request
  • turn_on() - turns vcr on; the opposite of turn_off()
  • turned_on() - Asks if vcr is turned on, returns a boolean

Instead of using the above four functions, you could use environment variables to achieve the same thing. This way you could enable/disable vcr in non-interactive environments such as continuous integration, Docker containers, or running R non-interactively from the command line. The full set of environment variables vcr uses, all of which accept only TRUE or FALSE:

  • VCR_TURN_OFF: turn off vcr altogether; set to TRUE to skip any vcr usage; default: FALSE
  • VCR_TURNED_OFF: set the turned_off internal package setting; this does not turn off vcr completely as does VCR_TURN_OFF does, but rather is looked at together with VCR_IGNORE_CASSETTES
  • VCR_IGNORE_CASSETTES: set the ignore_cassettes internal package setting; this is looked at together with VCR_TURNED_OFF

turned_off

turned_off() lets you temporarily make a real HTTP request without completely turning vcr off, unloading it, etc.

What happens internally is we turn off vcr, run your code block, then on exit turn vcr back on - such that vcr is only turned off for the duration of your code block. Even if your code block errors, vcr will be turned back on due to use of on.exit(turn_on())

library(vcr)
library(crul)
turned_off({
  con <- HttpClient$new(url = "https://httpbin.org/get")
  con$get()
})
#> <crul response>
#>   url: https://httpbin.org/get
#>   request_headers:
#>     User-Agent: libcurl/7.54.0 r-curl/4.3 crul/0.9.0
#>     Accept-Encoding: gzip, deflate
#>     Accept: application/json, text/xml, application/xml, */*
#>   response_headers:
#>     status: HTTP/1.1 200 OK
#>     date: Fri, 14 Feb 2020 19:44:46 GMT
#>     content-type: application/json
#>     content-length: 365
#>     connection: keep-alive
#>     server: gunicorn/19.9.0
#>     access-control-allow-origin: *
#>     access-control-allow-credentials: true
#>   status: 200

turn_off/turn_on

turn_off() is different from turned_off() in that turn_off() is not aimed at a single call block, but rather it turns vcr off for the entire package. turn_off() does check first before turning vcr off that there is not currently a cassette in use. turn_off() is meant to make R ignore vcr::insert_cassette() and vcr::use_cassette() blocks in your test suite - letting the code in the block run as if they were not wrapped in vcr code - so that all you have to do to run your tests with cached requests/responses AND with real HTTP requests is toggle a single R function or environment variable.

library(vcr)
vcr_configure(dir = tempdir())
# real HTTP request works - vcr is not engaged here
crul::HttpClient$new(url = "https://eu.httpbin.org/get")$get()
# wrap HTTP request in use_cassette() - vcr is engaged here
use_cassette("foo_bar", {
  crul::HttpClient$new(url = "https://eu.httpbin.org/get")$get()
})
# turn off & ignore cassettes - use_cassette is ignored, real HTTP request made
turn_off(ignore_cassettes = TRUE)
use_cassette("foo_bar", {
  crul::HttpClient$new(url = "https://eu.httpbin.org/get")$get()
})
# if you turn off and don't ignore cassettes, error thrown
turn_off(ignore_cassettes = FALSE)
use_cassette("foo_bar", {
  res2=crul::HttpClient$new(url = "https://eu.httpbin.org/get")$get()
})
# vcr back on - now use_cassette behaves as before
turn_on()
use_cassette("foo_bar3", {
  res2=crul::HttpClient$new(url = "https://eu.httpbin.org/get")$get()
})

turned_on

turned_on() does what it says on the tin - it tells you if vcr is turned on or not.

library(vcr)
turn_on()
turned_on()
#> [1] TRUE
turn_off()
#> vcr turned off; see ?turn_on to turn vcr back on
turned_on()
#> [1] FALSE

Environment variables

The VCR_TURN_OFF environment variable can be used within R or on the command line to turn off vcr. For example, you can run tests for a package that uses vcr, but ignore any use_cassette/insert_cassette usage, by running this on the command line in the root of your package:

VCR_TURN_OFF=true Rscript -e "devtools::test()"

Or, similarly within R:

Sys.setenv(VCR_TURN_OFF = TRUE)
devtools::test()

The VCR_TURNED_OFF and VCR_IGNORE_CASSETTES environment variables can be used in combination to achieve the same thing as VCR_TURN_OFF:

VCR_TURNED_OFF=true VCR_IGNORE_CASSETTES=true Rscript -e "devtools::test()"