crul – an HTTP client

A new package crul is on CRAN. crul is another HTTP client for R, but is relatively simplified compared to httr, and is being built to link closely with webmockr and vcr. webmockr and vcr are packages ported from Ruby's webmock and vcr, respectively. They both make mocking HTTP requests really easy.

A major use case for mocking HTTP requests is for unit tests. Nearly all the packages I work on personally make HTTP requests in their test suites, so I wanted to make it really easy to mock HTTP requests. You don't have to use mocking in test suites of course.

crul is not meant to replace other HTTP R libraries, but rather to make it easy to integrate mocking.

Installation

install.packages("crul")

If binaries aren't available, try from source: install.packages("crul", type = "source") or from GitHub: devtools::install_github("ropenscilabs/crul")

library(crul)

The client

HttpClient is where to start

(x <- HttpClient$new(
  url = "https://httpbin.org",
  opts = list(
    timeout = 1
  ),
  headers = list(
    a = "hello world"
  )
))
#> <crul connection>
#>   url: https://httpbin.org
#>   options:
#>     timeout: 1
#>   headers:
#>     a: hello world

Makes a R6 class, that has all the bits and bobs you'd expect for doing HTTP requests. When it prints, it gives any defaults you've set. As you update the object you can see what's been set

x$opts
#> $timeout
#> [1] 1

x$headers
#> $a
#> [1] "hello world"

Make a request

The client object created above has http methods that you can call, and pass paths to, as well as query parameters, body values, and any other curl options.

Here, we'll do a GET request on the route /get on our base url https://httpbin.org (the full url is then https://httpbin.org/get)

res <- x$get("get")

The response from a http request is another R6 class HttpResponse, which has slots for the outputs of the request, and some functions to deal with the response:

Status code

res$status_code
#> [1] 200

Status code with the message and explanation

res$status_http()
#> <Status code: 200>
#>   Message: OK
#>   Explanation: Request fulfilled, document follows

The content

res$content
#>   [1] 7b 0a 20 20 22 61 72 67 73 22 3a 20 7b 7d 2c 20 0a 20 20 22 68 65 61
#>  [24] 64 65 72 73 22 3a 20 7b 0a 20 20 20 20 22 41 22 3a 20 22 68 65 6c 6c
#>  [47] 6f 20 77 6f 72 6c 64 22 2c 20 0a 20 20 20 20 22 41 63 63 65 70 74 22
#>  [70] 3a 20 22 2a 2f 2a 22 2c 20 0a 20 20 20 20 22 41 63 63 65 70 74 2d 45
#>  [93] 6e 63 6f 64 69 6e 67 22 3a 20 22 67 7a 69 70 2c 20 64 65 66 6c 61 74
#> [116] 65 22 2c 20 0a 20 20 20 20 22 48 6f 73 74 22 3a 20 22 68 74 74 70 62
#> [139] 69 6e 2e 6f 72 67 22 2c 20 0a 20 20 20 20 22 55 73 65 72 2d 41 67 65
#> [162] 6e 74 22 3a 20 22 6c 69 62 63 75 72 6c 2f 37 2e 34 39 2e 31 20 72 2d
#> [185] 63 75 72 6c 2f 32 2e 32 20 63 72 75 6c 2f 30 2e 31 2e 30 22 0a 20 20
#> [208] 7d 2c 20 0a 20 20 22 6f 72 69 67 69 6e 22 3a 20 22 31 35 37 2e 31 33
#> [231] 30 2e 31 37 39 2e 38 36 22 2c 20 0a 20 20 22 75 72 6c 22 3a 20 22 68
#> [254] 74 74 70 73 3a 2f 2f 68 74 74 70 62 69 6e 2e 6f 72 67 2f 67 65 74 22
#> [277] 0a 7d 0a

HTTP method

res$method
#> [1] "get"

Request headers

res$request_headers
#> $a
#> [1] "hello world"

Response headers

res$response_headers
#> [1] "HTTP/1.1 200 OK"
#> [2] "Server: nginx"
#> [3] "Date: Wed, 09 Nov 2016 19:25:14 GMT"
#> [4] "Content-Type: application/json"
#> [5] "Content-Length: 279"
#> [6] "Connection: keep-alive"
#> [7] "Access-Control-Allow-Origin: *"
#> [8] "Access-Control-Allow-Credentials: true"

And you can parse the content with a provided function:

res$parse()
#> [1] "{\n  \"args\": {}, \n  \"headers\": {\n    \"A\": \"hello world\", \n    \"Accept\": \"*/*\", \n    \"Accept-Encoding\": \"gzip, deflate\", \n    \"Host\": \"httpbin.org\", \n    \"User-Agent\": \"libcurl/7.49.1 r-curl/2.2 crul/0.1.0\"\n  }, \n  \"origin\": \"157.130.179.86\", \n  \"url\": \"https://httpbin.org/get\"\n}\n"

parse the JSON

jsonlite::fromJSON(res$parse())
#> $args
#> named list()
#>
#> $headers
#> $headers$A
#> [1] "hello world"
#>
#> $headers$Accept
#> [1] "*/*"
#>
#> $headers$`Accept-Encoding`
#> [1] "gzip, deflate"
#>
#> $headers$Host
#> [1] "httpbin.org"
#>
#> $headers$`User-Agent`
#> [1] "libcurl/7.49.1 r-curl/2.2 crul/0.1.0"
#>
#>
#> $origin
#> [1] "157.130.179.86"
#>
#> $url
#> [1] "https://httpbin.org/get"

Future work

Mocking

crul doesn't currently have mocking ability, but I am working right now on getting the first version of webmockr on CRAN. It will work together with crul so that when you use crul you can choose to turn on mocking, specify which patterns to match for mocking, and much more. webmockr is built with plugin system in mind, so that we could make a plugin for httr, RCurl, or any other http R library.

I actually started vcr first, but realized that I needed to go back and build webmockr first. So once webmockr is up on CRAN, I'll work on getting vcr on CRAN as well.

Errors

Another package I've been working on, fauxpas, is meant to be a general purpose HTTP errors package, and work with any HTTP R library. Other similar languages like Ruby and Python have a better error story, and I thought I'd try it out for R. I'll work on incorporating fauxpas into crul as well, though probably in Suggests in case users don't want to use it.