# class Rack::Sendfile

# `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. `Rack::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-Sendfile-Type and X-Accel-Mapping headers 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://127.0.0.1:8080/;
    }

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 case-insensitive 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.

### Public Class Methods

new(app, variation = nil, mappings = []) click to toggle source

    # File lib/rack/sendfile.rb, line 118
    def initialize(app, variation = nil, mappings = [])
      @app = app
      @variation = variation
      @mappings = mappings.map do |internal, external|
        [/\A#{internal}/i, external]
      end
    end

### Public Instance Methods

call(env) click to toggle source

    # File lib/rack/sendfile.rb, line 126
    def call(env)
      status, headers, body = @app.call(env)
      if body.respond_to?(:to_path)
        case type = variation(env)
        when 'X-Accel-Redirect'
          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] = ::Rack::Utils.escape_path(url).gsub('?', '%3F')
            obody = body
            body = 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'
          path = ::File.expand_path(body.to_path)
          headers[CONTENT_LENGTH] = '0'
          headers[type] = path
          obody = body
          body = 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
      [status, headers, body]
    end

### Private Instance Methods

map_accel_path(env, path) click to toggle source

    # File lib/rack/sendfile.rb, line 177
    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#{Regexp.escape(internal)}/i, external)
          return new_path unless path == new_path
        end

        return path
      end
    end

variation(env) click to toggle source

    # File lib/rack/sendfile.rb, line 161
    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) click to toggle source

    # File lib/rack/sendfile.rb, line 167
    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