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Configure vcr request matching

Scott Chamberlain

2024-12-24

Source: vignettes/request_matching.Rmd
request_matching.Rmd

Request matching

To match previously recorded requests, vcr has to try to match new HTTP requests to a previously recorded one. By default, we match on HTTP method (e.g., GET) and URI (e.g., http://foo.com), following Ruby’s VCR gem.

You can customize how we match requests with one or more of the following options, some of which are on by default, some of which can be used together, and some alone.

  • method: Use the method request matcher to match requests on the HTTP method (i.e. GET, POST, PUT, DELETE, etc). You will generally want to use this matcher. The method matcher is used (along with the uri matcher) by default if you do not specify how requests should match.
  • uri: Use the uri request matcher to match requests on the request URI. The uri matcher is used (along with the method matcher) by default if you do not specify how requests should match.
  • host: Use the host request matcher to match requests on the request host. You can use this (alone, or in combination with path) as an alternative to uri so that non-deterministic portions of the URI are not considered as part of the request matching.
  • path: Use the path request matcher to match requests on the path portion of the request URI. You can use this (alone, or in combination with host) as an alternative to uri so that non-deterministic portions of the URI
  • query: Use the query request matcher to match requests on the query string portion of the request URI. You can use this (alone, or in combination with others) as an alternative to uri so that non-deterministic portions of the URI are not considered as part of the request matching.
  • body: Use the body request matcher to match requests on the request body.
  • headers: Use the headers request matcher to match requests on the request headers.

You can set your own options by tweaking the match_requests_on parameter in use_cassette():

use_cassette(name = "foo_bar", {
    cli$post("post", body = list(a = 5))
  }, 
  match_requests_on = c('method', 'headers', 'body')
)

Matching

headers 

library(crul)
library(vcr)
cli <- crul::HttpClient$new("https://httpbin.org/get", 
  headers = list(foo = "bar"))
use_cassette(name = "nothing_new", {
    one <- cli$get()
  }, 
  match_requests_on = 'headers'
)
cli$headers$foo <- "stuff"
use_cassette(name = "nothing_new", {
    two <- cli$get()
  }, 
  match_requests_on = 'headers'
)
one$request_headers
two$request_headers

More documentation

Check out the http testing book for a lot more documentation on vcr, webmockr, and crul