23 Advanced vcr usage

Now that we’ve covered basic vcr usage, it’s time for some more advanced usage topics.

library("vcr")

23.1 Mocking writing to disk

If you have http requests for which you write the response to disk, then use vcr_configure() to set the write_disk_path option. See more about the write_disk_path configuration option.

Here, we create a temporary directory, then set the fixtures

tmpdir <- tempdir()
vcr_configure(
  dir = file.path(tmpdir, "fixtures"),
  write_disk_path = file.path(tmpdir, "files")
)

Then pass a file path (that doesn’t exist yet) to crul’s disk parameter. vcr will take care of handling writing the response to that file in addition to the cassette.

library(crul)
## make a temp file
f <- tempfile(fileext = ".json")
## make a request
cas <- use_cassette("test_write_to_disk", {
  out <- HttpClient$new("https://httpbin.org/get")$get(disk = f)
})
file.exists(out$content)

#> [1] TRUE

out$parse()

#> [1] "{\n  \"args\": {}, \n  \"headers\": {\n    \"Accept\": \"application/json, text/xml, application/xml, */*\", \n    \"Accept-Encoding\": \"gzip, deflate\", \n    \"Host\": \"httpbin.org\", \n    \"User-Agent\": \"libcurl/8.5.0 r-curl/7.0.0 crul/1.6.0\", \n    \"X-Amzn-Trace-Id\": \"Root=1-6917c429-74a0a68a68c9ac5b7e0c0bdd\"\n  }, \n  \"origin\": \"64.236.133.176\", \n  \"url\": \"https://httpbin.org/get\"\n}\n"

This also works with httr. The only difference is that you write to disk with a function httr::write_disk(path) rather than a parameter.

Writing to disk with httr2 does not yet work with vcr – see https://github.com/ropensci/vcr/issues/270

Note that when you write to disk when using vcr, the cassette is slightly changed. Instead of holding the http response body itself, the cassette has the file path with the response body.

http_interactions:
- request:
    method: get
    uri: https://httpbin.org/get
  response:
    headers:
      status: HTTP/1.1 200 OK
      access-control-allow-credentials: 'true'
    body:
      encoding: UTF-8
      file: yes
      string: /private/var/folders/fc/n7g_vrvn0sx_st0p8lxb3ts40000gn/T/Rtmp5W4olr/files/file177e2e5d97ec.json

And the file has the response body that otherwise would have been in the string yaml field above:

{
  "args": {}, 
  "headers": {
    "Accept": "application/json, text/xml, application/xml, */*", 
    "Accept-Encoding": "gzip, deflate", 
    "Host": "httpbin.org", 
    "User-Agent": "libcurl/7.54.0 r-curl/4.3 crul/0.9.0"
  }, 
  "origin": "24.21.229.59, 24.21.229.59", 
  "url": "https://httpbin.org/get"
}