Stubbing and Setting Expectations on HTTP Requests • webmockr

R library for stubbing and setting expectations on HTTP requests.

Port of the Ruby gem webmock

How it works in detail

The very very short version is: webmockr helps you stub HTTP requests so you don’t have to repeat yourself.

More details

You tell 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:

URI
- 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. hello world to hello%20world)
Query parameters
- We normalize query parameter values so that URL encoded things match URL un-encoded things (e.g. message = hello world to message = hello%20world)
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")
Request body

Real HTTP requests

There’s a few scenarios to think about when using webmockr:

After doing

library(webmockr)

webmockr is loaded but not turned on. At this point webmockr doesn’t change anythning.

Once you turn on webmockr like

webmockr::enable()

webmockr will now by default not allow real HTTP requests from the http libraries that adapters are loaded for (right now only crul).

You can optionally allow real requests via webmockr_allow_net_connect(), and disallow real requests via webmockr_disable_net_connect(). You can check whether you are allowing real requests with webmockr_net_connect_allowed().

Certain kinds of real HTTP requests allowed: We don’t suppoprt this yet, but you can allow localhost HTTP requests with the allow_localhost parameter in the webmockr_configure() function.

Storing actual HTTP responses

webmockr doesn’t do that. Check out vcr

Features

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 testthat via vcr
Can be used for testing or outside of a testing context

Supported HTTP libraries

crul
httr

Install

from cran

install.packages("webmockr")

Dev version

remotes::install_github("ropensci/webmockr")

library(webmockr)

Enable webmockr

webmockr::enable()
#> CrulAdapter enabled!
#> HttrAdapter enabled!

Inside a test framework

library(crul)
library(testthat)

# make a stub
stub_request("get", "https://httpbin.org/get") %>%
   to_return(body = "success!", status = 200)
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get
#>   with: 
#>     query: 
#>     body: 
#>     request_headers: 
#>   to_return: 
#>   - status: 200
#>     body: success!
#>     response_headers: 
#>     should_timeout: FALSE
#>     should_raise: FALSE

# check that it's in the stub registry
stub_registry()
#> <webmockr stub registry> 
#>  Registered Stubs
#>    GET: https://httpbin.org/get   | to_return:   with body "success!"  with status 200

# make the request
z <- crul::HttpClient$new(url = "https://httpbin.org")$get("get")

# run tests (nothing returned means it passed)
expect_is(z, "HttpResponse")
expect_equal(z$status_code, 200)
expect_equal(z$parse("UTF-8"), "success!")

Outside a test framework

library(crul)

Stubbed request based on uri only and with the default response

stub_request("get", "https://httpbin.org/get")
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get
#>   with: 
#>     query: 
#>     body: 
#>     request_headers: 
#>   to_return:

x <- HttpClient$new(url = "https://httpbin.org")
x$get('get')
#> <crul response> 
#>   url: https://httpbin.org/get
#>   request_headers: 
#>     User-Agent: libcurl/7.79.1 r-curl/5.0.0 crul/1.3
#>     Accept-Encoding: gzip, deflate
#>     Accept: application/json, text/xml, application/xml, */*
#>   response_headers: 
#>   status: 200

set return objects

stub_request("get", "https://httpbin.org/get") %>%
  wi_th(
    query = list(hello = "world")) %>%
    to_return(status = 418)
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get
#>   with: 
#>     query: hello=world
#>     body: 
#>     request_headers: 
#>   to_return: 
#>   - status: 418
#>     body: 
#>     response_headers: 
#>     should_timeout: FALSE
#>     should_raise: FALSE

x$get('get', query = list(hello = "world"))
#> <crul response> 
#>   url: https://httpbin.org/get
#>   request_headers: 
#>     User-Agent: libcurl/7.79.1 r-curl/5.0.0 crul/1.3
#>     Accept-Encoding: gzip, deflate
#>     Accept: application/json, text/xml, application/xml, */*
#>   response_headers: 
#>   status: 418

Stubbing requests based on method, uri and query params

stub_request("get", "https://httpbin.org/get") %>%
  wi_th(query = list(hello = "world"), 
        headers = list('User-Agent' = 'libcurl/7.51.0 r-curl/2.6 crul/0.3.6', 
                       'Accept-Encoding' = "gzip, deflate"))
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get
#>   with: 
#>     query: hello=world
#>     body: 
#>     request_headers: User-Agent=libcurl/7.51.0 r-cur..., Accept-Encoding=gzip, deflate
#>   to_return:

stub_registry()
#> <webmockr stub registry> 
#>  Registered Stubs
#>    GET: https://httpbin.org/get 
#>    GET: https://httpbin.org/get?hello=world   | to_return:    with status 418 
#>    GET: https://httpbin.org/get?hello=world   with headers {"User-Agent":"libcurl/7.51.0 r-curl/2.6 crul/0.3.6","Accept-Encoding":"gzip, deflate"}

x <- HttpClient$new(url = "https://httpbin.org")
x$get('get', query = list(hello = "world"))
#> <crul response> 
#>   url: https://httpbin.org/get
#>   request_headers: 
#>     User-Agent: libcurl/7.79.1 r-curl/5.0.0 crul/1.3
#>     Accept-Encoding: gzip, deflate
#>     Accept: application/json, text/xml, application/xml, */*
#>   response_headers: 
#>   status: 418

Stubbing requests and set expectation of a timeout

stub_request("post", "https://httpbin.org/post") %>% to_timeout()
#> <webmockr stub> 
#>   method: post
#>   uri: https://httpbin.org/post
#>   with: 
#>     query: 
#>     body: 
#>     request_headers: 
#>   to_return: 
#>   - status: 
#>     body: 
#>     response_headers: 
#>     should_timeout: TRUE
#>     should_raise: FALSE
x <- HttpClient$new(url = "https://httpbin.org")
x$post('post')
#> Error: Request Timeout (HTTP 408).
#>  - The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.

Stubbing requests and set HTTP error expectation

library(fauxpas)
stub_request("get", "https://httpbin.org/get?a=b") %>% to_raise(HTTPBadRequest)
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get?a=b
#>   with: 
#>     query: 
#>     body: 
#>     request_headers: 
#>   to_return: 
#>   - status: 
#>     body: 
#>     response_headers: 
#>     should_timeout: FALSE
#>     should_raise: HTTPBadRequest
x <- HttpClient$new(url = "https://httpbin.org")
x$get('get', query = list(a = "b"))
#> Error: Bad Request (HTTP 400).
#>  - The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.

httr integration

library(webmockr)
library(httr)
#> 
#> Attaching package: 'httr'
#> The following object is masked from 'package:crul':
#> 
#>     handle

# turn on httr mocking
httr_mock()

# no stub found
GET("https://httpbin.org/get")
#> Error: Real HTTP connections are disabled.
#> Unregistered request:
#>   GET https://httpbin.org/get   with headers {Accept: application/json, text/xml, application/xml, */*}
#> 
#> You can stub this request with the following snippet:
#> 
#>    stub_request('get', uri = 'https://httpbin.org/get') %>%
#>      wi_th(
#>        headers = list('Accept' = 'application/json, text/xml, application/xml, */*')
#>      )
#> ============================================================

make a stub

stub_request('get', uri = 'https://httpbin.org/get') %>%
  wi_th(
    headers = list('Accept' = 'application/json, text/xml, application/xml, */*')
  ) %>%
  to_return(status = 418, body = "I'm a teapot!!!", headers = list(im_a = "teapot"))
#> <webmockr stub> 
#>   method: get
#>   uri: https://httpbin.org/get
#>   with: 
#>     query: 
#>     body: 
#>     request_headers: Accept=application/json, te...
#>   to_return: 
#>   - status: 418
#>     body: I'm a teapot!!!
#>     response_headers: im_a=teapot
#>     should_timeout: FALSE
#>     should_raise: FALSE

now returns mocked response

(res <- GET("https://httpbin.org/get"))
res$status_code
#> [1] 418
res$headers
#> $im_a
#> [1] "teapot"

Writing to disk

Write to a file before mocked request

## make a temp file
f <- tempfile(fileext = ".json")
## write something to the file
cat("{\"hello\":\"world\"}\n", file = f)
readLines(f)
#> [1] "{\"hello\":\"world\"}"
## make the stub
invisible(stub_request("get", "https://httpbin.org/get") %>% 
  to_return(body = file(f)))
## make a request
out <- HttpClient$new("https://httpbin.org/get")$get(disk = f)
readLines(file(f))
#> [1] "{\"hello\":\"world\"}"

OR - you can use mock_file() to have webmockr handle file and contents

g <- tempfile(fileext = ".json")
## make the stub
invisible(stub_request("get", "https://httpbin.org/get") %>% 
  to_return(body = mock_file(g, "{\"hello\":\"mars\"}\n")))
## make a request
out <- crul::HttpClient$new("https://httpbin.org/get")$get(disk = g)
readLines(out$content)
#> [1] "{\"hello\":\"world\"}"

Writing to disk is supported in both crul and httr

Many requests in a row

e.g., many redirects, then a final successful request

webmockr::enable()
library(crul)
library(fauxpas)

z <- stub_request("get", "https://httpbin.org/get")
to_return(z, status = 200, body = "foobar", headers = list(a = 5))
to_return(z, status = 200, body = "bears", headers = list(b = 6))
to_raise(z, HTTPBadRequest)
z

con <- crul::HttpClient$new(url = "https://httpbin.org")
# the first to_return()
first <- con$get("get")
first
first$parse("UTF-8")
# the second to_return()
second <- con$get("get")
second
second$parse("UTF-8")
# the third to_return() - fails as specified
third <- con$get("get")

Note that subsequent requests past the number of responses given with to_return()/etc. simply gives the last response you specified. Although if you set a to_timeout or to_raise this feature won’t happen since you fail out.

webmockr