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Class: Rack::Sendfile

Relationships & Source Files
Inherits: Object
Defined in: lib/rack/sendfile.rb

Overview

Sendfile

The Sendfile middleware intercepts responses whose body is being served from a file and replaces it with a server specific x-sendfile header. The web server is then responsible for writing the file contents to the client. This can dramatically reduce the amount of work required by the Ruby backend and takes advantage of the web server’s optimized file delivery code.

In order to take advantage of this middleware, the response body must respond to to_path and the request must include an x-sendfile-type header. Files and other components implement to_path so there’s rarely anything you need to do in your application. The x-sendfile-type header is typically set in your web servers configuration. The following sections attempt to document

Nginx

Nginx supports the x-accel-redirect header. This is similar to x-sendfile but requires parts of the filesystem to be mapped into a private URL hierarchy.

The following example shows the Nginx configuration required to create a private “/files/” area, enable x-accel-redirect, and pass the special x-accel-mapping header to the backend:

location ~ /files/(.*) {
  internal;
  alias /var/www/$1;
}

location / {
  proxy_redirect     off;

  proxy_set_header   Host                $host;
  proxy_set_header   X-Real-IP           $remote_addr;
  proxy_set_header   X-Forwarded-For     $proxy_add_x_forwarded_for;

  proxy_set_header   x-accel-mapping     /var/www/=/files/;

  proxy_pass         http://127.0:8080/;
}

The x-accel-mapping header should specify the location on the file system, followed by an equals sign (=), followed name of the private URL pattern that it maps to. The middleware performs a simple substitution on the resulting path.

To enable x-accel-redirect, you must configure the middleware explicitly:

use Rack::Sendfile, "x-accel-redirect"

For security reasons, the x-sendfile-type header from requests is ignored. The sendfile variation must be set via the middleware constructor.

See Also: www.nginx.com/resources/wiki/start/topics/examples/xsendfile

lighttpd

Lighttpd has supported some variation of the x-sendfile header for some time, although only recent version support x-sendfile in a reverse proxy configuration.

$HTTP["host"] == "example.com" {
   proxy-core.protocol = "http"
   proxy-core.balancer = "round-robin"
   proxy-core.backends = (
     "127.0.0.1:8000",
     "127.0.0.1:8001",
     #...
   )

   proxy-core.allow-x-sendfile = "enable"
   proxy-core.rewrite-request = (
     "x-sendfile-type" => (".*" => "x-sendfile")
   )
 }

See Also: redmine.lighttpd.net/wiki/lighttpd/Docs:ModProxyCore

Apache

x-sendfile is supported under Apache 2.x using a separate module:

tn123.org/mod_xsendfile/

Once the module is compiled and installed, you can enable it using XSendFile config directive:

RequestHeader Set x-sendfile-type x-sendfile
ProxyPassReverse / http://localhost:8001/
XSendFile on
Mapping parameter

The third parameter allows for an overriding extension of the x-accel-mapping header. Mappings should be provided in tuples of internal to external. The internal values may contain regular expression syntax, they will be matched with case indifference.

When x-accel-redirect is explicitly enabled via the variation parameter, and no application-level mappings are provided, the middleware will read the x-accel-mapping header from the proxy. This allows nginx to control the path mapping without requiring application-level configuration.

Security

For security reasons, the x-sendfile-type header from HTTP requests is ignored. The sendfile variation must be explicitly configured via the middleware constructor to prevent information disclosure vulnerabilities where attackers could bypass proxy restrictions.

Class Method Summary

Instance Method Summary

Constructor Details

.new(app, variation = nil, mappings = []) ⇒ Sendfile

[ GitHub ] 

  


# File 'lib/rack/sendfile.rb', line 122



def initialize(app, variation = nil, mappings = [])
  @app = app
  @variation = variation
  @mappings = mappings.map do |internal, external|
    [/\A#{internal}/i, external]
  end
end


  







Instance Method Details



  

    #call(env)  
  

  [ GitHub ]


  

  


# File 'lib/rack/sendfile.rb', line 130



def call(env)
  _, headers, body = response = @app.call(env)

  if body.respond_to?(:to_path)
    case type = variation(env)
    when /x-accel-redirect/i
      path = ::File.expand_path(body.to_path)
      if url = map_accel_path(env, path)
        headers[CONTENT_LENGTH] = '0'
        # '?' must be percent-encoded because it is not query string but a part of path
        headers[type.downcase] = ::Rack::Utils.escape_path(url).gsub('?', '%3F')
        obody = body
        response[2] = Rack::BodyProxy.new([]) do
          obody.close if obody.respond_to?(:close)
        end
      else
        env[RACK_ERRORS].puts "x-accel-mapping header missing"
      end
    when /x-sendfile|x-lighttpd-send-file/i
      path = ::File.expand_path(body.to_path)
      headers[CONTENT_LENGTH] = '0'
      headers[type.downcase] = path
      obody = body
      response[2] = Rack::BodyProxy.new([]) do
        obody.close if obody.respond_to?(:close)
      end
    when '', nil
    else
      env[RACK_ERRORS].puts "Unknown x-sendfile variation: #{type.inspect}"
    end
  end
  response
end


  








  

    #map_accel_path(env, path)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rack/sendfile.rb', line 182



def map_accel_path(env, path)
  if mapping = @mappings.find { |internal, _| internal =~ path }
    return path.sub(*mapping)
  elsif mapping = x_accel_mapping(env)
    # Safe to use header: explicit config + no app mappings:
    mapping.split(',').map(&:strip).each do |m|
      internal, external = m.split('=', 2).map(&:strip)
      new_path = path.sub(/\A#{internal}/i, external)
      return new_path unless path == new_path
    end

    return path
  end
end


  








  

    #variation(env)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rack/sendfile.rb', line 166



def variation(env)
  # Note: HTTP_X_SENDFILE_TYPE is intentionally NOT read for security reasons.
  # Attackers could use this header to enable x-accel-redirect and bypass proxy restrictions.
  @variation || env['sendfile.type']
end


  








  

    #x_accel_mapping(env)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rack/sendfile.rb', line 172



def x_accel_mapping(env)
  # Only allow header when:
  # 1. `x-accel-redirect` is explicitly enabled via constructor.
  # 2. No application-level mappings are configured.
  return nil unless @variation =~ /x-accel-redirect/i
  return nil if @mappings.any?
  
  env['HTTP_X_ACCEL_MAPPING']
end