Curb - Libcurl bindings for Ruby

Curb (probably CUrl-RuBy or something) provides Ruby-language bindings for the libcurl(3), a fully-featured client-side URL transfer library. cURL and libcurl live at .

Curb is a work-in-progress, and currently only supports libcurl's easy and multi modes.


Curb is copyright (c) 2006 Ross Bamford, and released under the terms of the Ruby license. See the LICENSE file for the gory details.

Easy mode

GET request

  res = Curl.get("") {|http|
    http.timeout = 10 # raise exception if request/response not handled within 10 seconds
  puts res.code
  puts res.head
  puts res.body

POST request

  res ="", {post: "this"}.to_json) {|http|
    http.headers["Content-Type"] = "application/json"
  puts res.code
  puts res.head
  puts res.body

You will need

  • A working Ruby installation (2.0.0+ will work but 2.1+ preferred) (it's possible it still works with 1.8.7 but you'd have to tell me if not...)
  • A working libcurl development installation (Ideally one of the versions listed in the compatibility chart below that maps to your curb version)
  • A sane build environment (e.g. gcc, make)

Version Compatibility chart

A non-exhaustive set of compatibility versions of the libcurl library with this gem are as follows. (Note that these are only the ones that have been tested and reported to work across a variety of platforms / rubies)

Gem Version Release Date libcurl versions
1.0.5 Jan 2023 7.58 - 7.87
1.0.4 Jan 2023 7.58 - 7.87
1.0.3* Dec 2022 7.58 - 7.87
1.0.2* Dec 2022 7.58 - 7.87
1.0.1 Apr 2022 7.58 - 7.87
1.0.0 Jan 2022 7.58 - 7.87
0.9.8 Jan 2019 7.58 - 7.81
0.9.7 Nov 2018 7.56 - 7.60
0.9.6 May 2018 7.51 - 7.59
0.9.5 May 2018 7.51 - 7.59
0.9.4 Aug 2017 7.41 - 7.58
0.9.3 Apr 2016 7.26 - 7.58

*avoid using these version are known to have issues with segmentation faults


... will usually be as simple as:

$ gem install curb

On Windows, make sure you're using the DevKit and the development version of libcurl. Unzip, then run this in your command line (alter paths to your curl location, but remember to use forward slashes):

gem install curb --platform=ruby -- --with-curl-lib=C:/curl-7.39.0-devel-mingw32/lib --with-curl-include=C:/curl-7.39.0-devel-mingw32/include

Note that with Windows moving from one method of compiling to another as of Ruby 2.4 (DevKit -> MYSYS2), the usage of Ruby 2.4+ with this gem on windows is unlikely to work. It is advised to use the latest version of Ruby 2.3 available HERE

Or, if you downloaded the archive:

$ rake compile && rake install

If you have a weird setup, you might need extconf options. In this case, pass them like so:

$ rake compile EXTCONF_OPTS='--with-curl-dir=/path/to/libcurl --prefix=/what/ever' && rake install

Curb is tested only on GNU/Linux x86 and Mac OSX - YMMV on other platforms. If you do use another platform and experience problems, or if you can expand on the above instructions, please report the issue at

On Ubuntu, the dependencies can be satisfied by installing the following packages:

18.04 and onwards

$ sudo apt-get install libcurl4 libcurl3-gnutls libcurl4-openssl-dev

< 18.04

$ sudo apt-get install libcurl3 libcurl3-gnutls libcurl4-openssl-dev

On RedHat:

$ sudo yum install ruby-devel libcurl-devel openssl-devel

Curb has fairly extensive RDoc comments in the source. You can build the documentation with:

$ rake doc

Usage & examples

Curb provides two classes:

  • Curl::Easy - simple API, for day-to-day tasks.
  • Curl::Multi - more advanced API, for operating on multiple URLs simultaneously.

To use either, you will need to require the curb gem:

require 'curb'

Super simple API (less typing)

http = Curl.get("")
puts http.body

http ="", {:foo => "bar"})
puts http.body

http = Curl.get("") do |http|
  http.headers['Cookie'] = 'foo=1;bar=2'
puts http.body

Simple fetch via HTTP:

c = Curl::Easy.perform("")
puts c.body

Same thing, more manual:

c ="")
puts c.body

Additional config:

http = Curl::Easy.perform("") do |curl|
  curl.headers["User-Agent"] = "myapp-0.0"
  curl.verbose = true

Same thing, more manual:

c ="") do |curl|
  curl.headers["User-Agent"] = "myapp-0.0"
  curl.verbose = true


HTTP basic authentication:

c ="")
c.http_auth_types = :basic
c.username = 'foo'
c.password = 'bar'

HTTP "insecure" SSL connections (like curl -k, --insecure) to avoid Curl::Err::SSLCACertificateError:

c ="")
c.ssl_verify_peer = false

Supplying custom handlers:

c ="")

c.on_body { |data| print(data) }
c.on_header { |data| print(data) }


Reusing Curls:

c =

["", ""].map do |url|
  c.url = url


c = Curl::Easy.http_post("",
                         Curl::PostField.content('thing[name]', 'box'),
                         Curl::PostField.content('thing[type]', 'storage'))

HTTP POST file upload:

c ="")
c.multipart_form_post = true
c.http_post(Curl::PostField.file('thing[file]', 'myfile.rb'))

Using HTTP/2

c ="")
c.set(:HTTP_VERSION, Curl::HTTP_2_0)

puts (c.body_str.include? "You are using HTTP/2 right now!") ? "HTTP/2" : "HTTP/1.x"

Multi Interface (Basic HTTP GET):

# make multiple GET requests
easy_options = {:follow_location => true}
# Use Curl::CURLPIPE_MULTIPLEX for HTTP/2 multiplexing
multi_options = {:pipeline => Curl::CURLPIPE_HTTP1}

Curl::Multi.get(['url1','url2','url3','url4','url5'], easy_options, multi_options) do|easy|
  # do something interesting with the easy response
  puts easy.last_effective_url

Multi Interface (Basic HTTP POST):

# make multiple POST requests
easy_options = {:follow_location => true, :multipart_form_post => true}
multi_options = {:pipeline => Curl::CURLPIPE_HTTP1}

url_fields = [
  { :url => 'url1', :post_fields => {'f1' => 'v1'} },
  { :url => 'url2', :post_fields => {'f1' => 'v1'} },
  { :url => 'url3', :post_fields => {'f1' => 'v1'} }
], easy_options, multi_options) do|easy|
  # do something interesting with the easy response
  puts easy.last_effective_url

Multi Interface (Advanced):

responses = {}
requests = ["", ""]
m =
# add a few easy handles
requests.each do |url|
  responses[url] = ""
  c = do|curl|
    curl.follow_location = true
    curl.on_body{|data| responses[url] << data; data.size }
    curl.on_success {|easy| puts "success, add more easy handles" }

m.perform do
  puts "idling... can do some work here"

requests.each do|url|
  puts responses[url]

Easy Callbacks

  • on_success is called when the response code is 2xx
  • on_redirect is called when the response code is 3xx
  • on_missing is called when the response code is 4xx
  • on_failure is called when the response code is 5xx
  • on_complete is called in all cases.