Chapter 3 Mocking HTTP Requests
The very very short version is: webmockr helps you stub HTTP requests so you don’t have to repeat yourself.
3.1 Package documentation
Check out https://docs.ropensci.org/webmockr/ for documentation on
- Stubbing HTTP requests at low http client lib level
- Setting and verifying expectations on HTTP requests
- Matching requests based on method, URI, headers and body
- Support for
- Can be used for testing or outside of a testing context
3.3 How webmockr works in detail
webmockr what HTTP request you want to match against and if it sees a
request matching your criteria it doesn’t actually do the HTTP request. Instead,
it gives back the same object you would have gotten back with a real request, but
only with the bits it knows about. For example, we can’t give back the actual
data you’d get from a real HTTP request as the request wasn’t performed.
In addition, if you set an expectation of what
webmockr should return, we
return that. For example, if you expect a request to return a 418 error
(I’m a Teapot), then that’s what you’ll get.
What you can match against
- HTTP method (required)
Plus any single or combination of the following:
- Right now, we can match directly against URI’s, and with regex URI patterns. Eventually, we will support RFC 6570 URI templates.
- We normalize URI paths so that URL encoded things match
URL un-encoded things (e.g.
- Query parameters
- We normalize query parameter values so that URL encoded things match
URL un-encoded things (e.g.
message = hello worldto
message = hello%20world)
- We normalize query parameter values so that URL encoded things match URL un-encoded things (e.g.
- Request headers
- We normalize headers and treat all forms of same headers as equal. For
example, the following two sets of headers are equal:
list(H1 = "value1", content_length = 123, X_CuStOm_hEAder = "foo")
list(h1 = "value1", "Content-Length" = 123, "x-cuSTOM-HeAder" = "foo")
- We normalize headers and treat all forms of same headers as equal. For example, the following two sets of headers are equal:
- Request body
Real HTTP requests
There’s a few scenarios to think about when using
webmockr is loaded but not turned on. At this point
Once you turn on
webmockr will now by default not allow real HTTP requests from the http
libraries that adapters are loaded for (right now only
You can optionally allow real requests via
disallow real requests via
webmockr_disable_net_connect(). You can check
whether you are allowing real requests with
Certain kinds of real HTTP requests allowed: We don’t suppoprt this yet,
but you can allow localhost HTTP requests with the
Storing actual HTTP responses
webmockr doesn’t do that. Check out vcr
3.4 Basic usage
Stubbed request based on uri only and with the default response
#> <webmockr stub> #> method: get #> uri: https://httpbin.org/get #> with: #> query: #> body: #> request_headers: #> to_return: #> status: #> body: #> response_headers: #> should_timeout: FALSE #> should_raise: FALSE
#> <crul response> #> url: https://httpbin.org/get #> request_headers: #> User-Agent: libcurl/7.64.1 r-curl/4.3 crul/0.9.0 #> Accept-Encoding: gzip, deflate #> Accept: application/json, text/xml, application/xml, */* #> response_headers: #> status: 200