# crul introduction

#### Scott Chamberlain

#### 2017-03-31

`crul` is an HTTP client for R.

## Install

Stable CRAN version

    install.packages("crul")

Dev version

    devtools::install_github("ropensci/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
    #>   curl options:
    #>     timeout: 1
    #>   proxies:
    #>   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"

## do some http

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

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 43 6f 6e 6e 65 63 74 69 6f 6e 22 3a 20
    #> [139] 22 63 6c 6f 73 65 22 2c 20 0a 20 20 20 20 22 48 6f 73 74 22 3a 20 22
    #> [162] 68 74 74 70 62 69 6e 2e 6f 72 67 22 2c 20 0a 20 20 20 20 22 55 73 65
    #> [185] 72 2d 41 67 65 6e 74 22 3a 20 22 6c 69 62 63 75 72 6c 2f 37 2e 35 31
    #> [208] 2e 30 20 72 2d 63 75 72 6c 2f 32 2e 34 20 63 72 75 6c 2f 30 2e 33 2e
    #> [231] 34 22 0a 20 20 7d 2c 20 0a 20 20 22 6f 72 69 67 69 6e 22 3a 20 22 34
    #> [254] 36 2e 31 38 39 2e 36 37 2e 33 31 22 2c 20 0a 20 20 22 75 72 6c 22 3a
    #> [277] 20 22 68 74 74 70 73 3a 2f 2f 68 74 74 70 62 69 6e 2e 6f 72 67 2f 67
    #> [300] 65 74 22 0a 7d 0a

HTTP method

    res$method
    #> [1] "get"

Request headers

    res$request_headers
    #> $useragent
    #> [1] "libcurl/7.51.0 r-curl/2.4 crul/0.3.4"
    #>
    #> $a
    #> [1] "hello world"

Response headers

    res$response_headers
    #> $status
    #> [1] "HTTP/1.1 200 OK"
    #>
    #> $connection
    #> [1] "keep-alive"
    #>
    #> $server
    #> [1] "gunicorn/19.7.1"
    #>
    #> $date
    #> [1] "Fri, 31 Mar 2017 18:09:49 GMT"
    #>
    #> $`content-type`
    #> [1] "application/json"
    #>
    #> $`access-control-allow-origin`
    #> [1] "*"
    #>
    #> $`access-control-allow-credentials`
    #> [1] "true"
    #>
    #> $`content-length`
    #> [1] "305"
    #>
    #> $via
    #> [1] "1.1 vegur"

And you can parse the content with a provided function:

    res$parse()
    #> [1] "{\n  \"args\": {}, \n  \"headers\": {\n    \"A\": \"hello world\", \n    \"Accept\": \"*/*\", \n    \"Accept-Encoding\": \"gzip, deflate\", \n    \"Connection\": \"close\", \n    \"Host\": \"httpbin.org\", \n    \"User-Agent\": \"libcurl/7.51.0 r-curl/2.4 crul/0.3.4\"\n  }, \n  \"origin\": \"46.189.67.31\", \n  \"url\": \"https://httpbin.org/get\"\n}\n"
    jsonlite::fromJSON(res$parse())
    #> $args
    #> named list()
    #>
    #> $headers
    #> $headers$A
    #> [1] "hello world"
    #>
    #> $headers$Accept
    #> [1] "*/*"
    #>
    #> $headers$`Accept-Encoding`
    #> [1] "gzip, deflate"
    #>
    #> $headers$Connection
    #> [1] "close"
    #>
    #> $headers$Host
    #> [1] "httpbin.org"
    #>
    #> $headers$`User-Agent`
    #> [1] "libcurl/7.51.0 r-curl/2.4 crul/0.3.4"
    #>
    #>
    #> $origin
    #> [1] "46.189.67.31"
    #>
    #> $url
    #> [1] "https://httpbin.org/get"

With the `HttpClient` object, which holds any configuration stuff we set, we can make other HTTP verb requests. For example, a `HEAD` request:

    x$post(
      path = "post",
      body = list(hello = "world")
    )
    #> <crul response>
    #>   url: https://httpbin.org/post
    #>   request_headers:
    #>     useragent: libcurl/7.51.0 r-curl/2.4 crul/0.3.4
    #>     a: hello world
    #>   response_headers:
    #>     status: HTTP/1.1 200 OK
    #>     connection: keep-alive
    #>     server: gunicorn/19.7.1
    #>     date: Fri, 31 Mar 2017 18:09:49 GMT
    #>     content-type: application/json
    #>     access-control-allow-origin: *
    #>     access-control-allow-credentials: true
    #>     content-length: 549
    #>     via: 1.1 vegur
    #>   status: 200

## write to disk

    x <- HttpClient$new(url = "https://httpbin.org")
    f <- tempfile()
    res <- x$get(disk = f)
    # when using write to disk, content is a path
    res$content
    #> [1] "/var/folders/gs/4khph0xs0436gmd2gdnwsg080000gn/T//Rtmp2MSXqe/file78287b7cd6c9"

Read lines

    readLines(res$content, n = 10)
    #>  [1] "<!DOCTYPE html>"
    #>  [2] "<html>"
    #>  [3] "<head>"
    #>  [4] "  <meta http-equiv='content-type' value='text/html;charset=utf8'>"
    #>  [5] "  <meta name='generator' value='Ronn/v0.7.3 (http://github.com/rtomayko/ronn/tree/0.7.3)'>"
    #>  [6] "  <title>httpbin(1): HTTP Client Testing Service</title>"
    #>  [7] "  <style type='text/css' media='all'>"
    #>  [8] "  /* style: man */"
    #>  [9] "  body#manpage {margin:0}"
    #> [10] "  .mp {max-width:100ex;padding:0 9ex 1ex 4ex}"

## stream data

    (x <- HttpClient$new(url = "https://httpbin.org"))
    #> <crul connection>
    #>   url: https://httpbin.org
    #>   curl options:
    #>   proxies:
    #>   headers:
    res <- x$get('stream/5', stream = function(x) cat(rawToChar(x)))
    #> {"headers": {"Host": "httpbin.org", "Accept-Encoding": "gzip, deflate", "User-Agent": "libcurl/7.51.0 r-curl/2.4 crul/0.3.4", "Connection": "close", "Accept": "*/*"}, "url": "https://httpbin.org/stream/5", "args": {}, "id": 0, "origin": "46.189.67.31"}
    #> {"headers": {"Host": "httpbin.org", "Accept-Encoding": "gzip, deflate", "User-Agent": "libcurl/7.51.0 r-curl/2.4 crul/0.3.4", "Connection": "close", "Accept": "*/*"}, "url": "https://httpbin.org/stream/5", "args": {}, "id": 1, "origin": "46.189.67.31"}
    #> {"headers": {"Host": "httpbin.org", "Accept-Encoding": "gzip, deflate", "User-Agent": "libcurl/7.51.0 r-curl/2.4 crul/0.3.4", "Connection": "close", "Accept": "*/*"}, "url": "https://httpbin.org/stream/5", "args": {}, "id": 2, "origin": "46.189.67.31"}
    #> {"headers": {"Host": "httpbin.org", "Accept-Encoding": "gzip, deflate", "User-Agent": "libcurl/7.51.0 r-curl/2.4 crul/0.3.4", "Connection": "close", "Accept": "*/*"}, "url": "https://httpbin.org/stream/5", "args": {}, "id": 3, "origin": "46.189.67.31"}
    #> {"headers": {"Host": "httpbin.org", "Accept-Encoding": "gzip, deflate", "User-Agent": "libcurl/7.51.0 r-curl/2.4 crul/0.3.4", "Connection": "close", "Accept": "*/*"}, "url": "https://httpbin.org/stream/5", "args": {}, "id": 4, "origin": "46.189.67.31"}
    # when streaming, content is NULL
    res$content
    #> NULL