Rack provides a minimal, modular, and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the bridge between web servers, web frameworks, and web application into a single method call.
The exact details of this are described in the Rack Specification, which all Rack applications should conform to.
| Version | Support |
|---|---|
| 3.1.x | Bug fixes and security patches. |
| 3.0.x | Security patches only. |
| 2.2.x | Security patches only. |
| <= 2.1.x | End of support. |
Please see the Security Policy for more information.
This is the latest version of Rack. It contains bug fixes and security patches. Please check the Change Log for detailed information on specific changes.
This version of rack contains significant changes which are detailed in the Upgrade Guide. It is recommended to upgrade to Rack 3 as soon as possible to receive the latest features and security patches.
This version of Rack is receiving security patches only, and effort should be made to move to Rack 3.
Starting in Ruby 3.4 the base64 dependency will no longer be a default gem,
and may cause a warning or error about base64 being missing. To correct this,
add base64 as a dependency to your project.
Add the rack gem to your application bundle, or follow the instructions provided by a supported web framework:
# Install it generally:
$ gem install rack
# or, add it to your current application gemfile:
$ bundle add rackIf you need features from Rack::Session or bin/rackup please add those gems separately.
$ gem install rack-session rackupCreate a file called config.ru with the following contents:
run do |env|
[200, {}, ["Hello World"]]
endRun this using the rackup gem or another supported web server.
$ gem install rackup
$ rackup
# In another shell:
$ curl http://localhost:9292
Hello WorldRack is supported by a wide range of servers, including:
- Agoo
- Falcon
- Iodine
- NGINX Unit
- Phusion Passenger (which is mod_rack for Apache and for nginx)
- Pitchfork
- Puma
- Thin
- Unicorn
- uWSGI
- Lamby (for AWS Lambda)
You will need to consult the server documentation to find out what features and limitations they may have. In general, any valid Rack app will run the same on all these servers, without changing anything.
Rack provides a separate gem, rackup which is
a generic interface for running a Rack application on supported servers, which
include WEBRick, Puma, Falcon and others.
These frameworks and many others support the Rack Specification:
Between the server and the framework, Rack can be customized to your applications needs using middleware. Rack itself ships with the following middleware:
Rack::CommonLoggerfor creating Apache-style logfiles.Rack::ConditionalGetfor returning Not Modified responses when the response has not changed.Rack::Configfor modifying the environment before processing the request.Rack::ContentLengthfor setting acontent-lengthheader based on body size.Rack::ContentTypefor setting a defaultcontent-typeheader for responses.Rack::Deflaterfor compressing responses with gzip.Rack::ETagfor settingetagheader on bodies that can be buffered.Rack::Eventsfor providing easy hooks when a request is received and when the response is sent.Rack::Filesfor serving static files.Rack::Headfor returning an empty body for HEAD requests.Rack::Lintfor checking conformance to the Rack Specification.Rack::Lockfor serializing requests using a mutex.Rack::MethodOverridefor modifying the request method based on a submitted parameter.Rack::Recursivefor including data from other paths in the application, and for performing internal redirects.Rack::Reloaderfor reloading files if they have been modified.Rack::Runtimefor including a response header with the time taken to process the request.Rack::Sendfilefor working with web servers that can use optimized file serving for file system paths.Rack::ShowExceptionfor catching unhandled exceptions and presenting them in a nice and helpful way with clickable backtrace.Rack::ShowStatusfor using nice error pages for empty client error responses.Rack::Staticfor more configurable serving of static files.Rack::TempfileReaperfor removing temporary files creating during a request.
All these components use the same interface, which is described in detail in the Rack Specification. These optional components can be used in any way you wish.
If you want to develop outside of existing frameworks, implement your own ones, or develop middleware, Rack provides many helpers to create Rack applications quickly and without doing the same web stuff all over:
Rack::Requestwhich also provides query string parsing and multipart handling.Rack::Responsefor convenient generation of HTTP replies and cookie handling.Rack::MockRequestandRack::MockResponsefor efficient and quick testing of Rack application without real HTTP round-trips.Rack::Cascadefor trying additional Rack applications if an application returns a not found or method not supported response.Rack::Directoryfor serving files under a given directory, with directory indexes.Rack::MediaTypefor parsing content-type headers.Rack::Mimefor determining content-type based on file extension.Rack::RewindableInputfor making any IO object rewindable, using a temporary file buffer.Rack::URLMapto route to multiple applications inside the same process.
Rack exposes several configuration parameters to control various features of the implementation.
Rack::Utils.param_depth_limit = 32 # defaultThe maximum amount of nesting allowed in parameters. For example, if set to 3, this query string would be allowed:
?a[b][c]=d
but this query string would not be allowed:
?a[b][c][d]=e
Limiting the depth prevents a possible stack overflow when parsing parameters.
Rack::Utils.multipart_file_limit = 128 # defaultThe maximum number of parts with a filename a request can contain. Accepting too many parts can lead to the server running out of file handles.
The default is 128, which means that a single request can't upload more than 128 files at once. Set to 0 for no limit.
Can also be set via the RACK_MULTIPART_FILE_LIMIT environment variable.
(This is also aliased as multipart_part_limit and RACK_MULTIPART_PART_LIMIT for compatibility)
The maximum total number of parts a request can contain of any type, including both file and non-file form fields.
The default is 4096, which means that a single request can't contain more than 4096 parts.
Set to 0 for no limit.
Can also be set via the RACK_MULTIPART_TOTAL_PART_LIMIT environment variable.
See CHANGELOG.md.
See CONTRIBUTING.md for specific details about how to make a contribution to Rack.
Please post bugs, suggestions and patches to GitHub Issues.
Please check our Security Policy for responsible disclosure and security bug reporting process. Due to wide usage of the library, it is strongly preferred that we manage timing in order to provide viable patches at the time of disclosure. Your assistance in this matter is greatly appreciated.
The plethora of useful middleware created the need for a project that collects
fresh Rack middleware. rack-contrib includes a variety of add-on components
for Rack and it is easy to contribute new modules.
Provides convenient session management for Rack.
The Rack Core Team, consisting of
- Aaron Patterson tenderlove
- Samuel Williams ioquatix
- Jeremy Evans jeremyevans
- Eileen Uchitelle eileencodes
- Matthew Draper matthewd
- Rafael França rafaelfranca
and the Rack Alumni
- Ryan Tomayko rtomayko
- Scytrin dai Kinthra scytrin
- Leah Neukirchen leahneukirchen
- James Tucker raggi
- Josh Peek josh
- José Valim josevalim
- Michael Fellinger manveru
- Santiago Pastorino spastorino
- Konstantin Haase rkh
would like to thank:
- Adrian Madrid, for the LiteSpeed handler.
- Christoffer Sawicki, for the first Rails adapter and
Rack::Deflater. - Tim Fletcher, for the HTTP authentication code.
- Luc Heinrich for the Cookie sessions, the static file handler and bugfixes.
- Armin Ronacher, for the logo and racktools.
- Alex Beregszaszi, Alexander Kahn, Anil Wadghule, Aredridel, Ben Alpert, Dan Kubb, Daniel Roethlisberger, Matt Todd, Tom Robinson, Phil Hagelberg, S. Brent Faulkner, Bosko Milekic, Daniel Rodríguez Troitiño, Genki Takiuchi, Geoffrey Grosenbach, Julien Sanchez, Kamal Fariz Mahyuddin, Masayoshi Takahashi, Patrick Aljordm, Mig, Kazuhiro Nishiyama, Jon Bardin, Konstantin Haase, Larry Siden, Matias Korhonen, Sam Ruby, Simon Chiang, Tim Connor, Timur Batyrshin, and Zach Brock for bug fixing and other improvements.
- Eric Wong, Hongli Lai, Jeremy Kemper for their continuous support and API improvements.
- Yehuda Katz and Carl Lerche for refactoring rackup.
- Brian Candler, for
Rack::ContentType. - Graham Batty, for improved handler loading.
- Stephen Bannasch, for bug reports and documentation.
- Gary Wright, for proposing a better
Rack::Responseinterface. - Jonathan Buch, for improvements regarding
Rack::Response. - Armin Röhrl, for tracking down bugs in the Cookie generator.
- Alexander Kellett for testing the Gem and reviewing the announcement.
- Marcus Rückert, for help with configuring and debugging lighttpd.
- The WSGI team for the well-done and documented work they've done and Rack builds up on.
- All bug reporters and patch contributors not mentioned above.
Rack is released under the MIT License.
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