3 packages:
crul, webmockr, vcr

rOpenSci has a lot of pkgs that do http requests

giving rise to the tools presented here

crul - a new http client

ropensci/crul

crul - features

• asynchronous requests

• pagination

• supports mocking and caching

• writing to disk + streaming

• request + response hooks




• does not have: OAuth

• not something I need ...

crul - lots of example usage

Mocking/caching

webmockr & vcr:
forked from another language (Ruby)

we can take advantage of all they've learned

& both general purpose
work with current and future http pkgs

Other langs

keep an eye out for other languages

what good ideas can we adopt in R land

webmockr - mock http requests

arose: because needed to make vcr

ropensci/webmockr

webmockr - what does it do?

set what you want to match against & what to return

make a request

if it matches you get what you set to return

if it doesn't match: error

webmockr - huh?

webmockr hooks into crul, hijacking the normal request

constructing a response that matches a real response

based on what you told webmockr to respond with

& vcr builds on webmockr ...

vcr - record and replay HTTP requests/responses

arose: observing other language communities &
need to improve testing in many API clients

ropensci/vcr

vcr - hardest software project I've worked on

vcr - how does it work?

I thought vcr worked by listening for requests in R

realized it most definitely did not

it modifies an HTTP request & looks for a match

so had to make webmockr first

vcr - what does it do?

HTTP requests in a test suite as usual

w/o making real HTTP requests

so you test your package

not the remote service

(p.s. great for rate-limited services)

vcr - no monkey patching in R!

Allowed in Ruby, but not in R

in R we can use

But not allowed on CRAN

vcr - in the works

• JSON cassettes

• testthat reporter for cassette usage

• dates   

• data security , always more to do

• responses written to disk

• docs: http testing book - bit.ly/http-testing

• many more ...

help appreciated!

further reading

HTTP Testing Book:
bit.ly/http-testing

crul/webmockr/vcr in detail
w/ caveats/edge cases/etc.