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80 lines
2.5 KiB
Ruby
80 lines
2.5 KiB
Ruby
require 'rack/utils'
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module Rack
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# Middleware that enables conditional GET using If-None-Match and
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# If-Modified-Since. The application should set either or both of the
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# Last-Modified or Etag response headers according to RFC 2616. When
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# either of the conditions is met, the response body is set to be zero
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# length and the response status is set to 304 Not Modified.
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#
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# Applications that defer response body generation until the body's each
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# message is received will avoid response body generation completely when
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# a conditional GET matches.
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#
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# Adapted from Michael Klishin's Merb implementation:
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# https://github.com/wycats/merb/blob/master/merb-core/lib/merb-core/rack/middleware/conditional_get.rb
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class ConditionalGet
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def initialize(app)
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@app = app
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end
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def call(env)
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case env[REQUEST_METHOD]
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when "GET", "HEAD"
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status, headers, body = @app.call(env)
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headers = Utils::HeaderHash.new(headers)
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if status == 200 && fresh?(env, headers)
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status = 304
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headers.delete(CONTENT_TYPE)
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headers.delete(CONTENT_LENGTH)
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original_body = body
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body = Rack::BodyProxy.new([]) do
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original_body.close if original_body.respond_to?(:close)
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end
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end
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[status, headers, body]
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else
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@app.call(env)
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end
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end
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private
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def fresh?(env, headers)
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modified_since = env['HTTP_IF_MODIFIED_SINCE']
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none_match = env['HTTP_IF_NONE_MATCH']
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return false unless modified_since || none_match
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success = true
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success &&= modified_since?(to_rfc2822(modified_since), headers) if modified_since
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success &&= etag_matches?(none_match, headers) if none_match
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success
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end
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def etag_matches?(none_match, headers)
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etag = headers['ETag'] and etag == none_match
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end
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def modified_since?(modified_since, headers)
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last_modified = to_rfc2822(headers['Last-Modified']) and
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modified_since and
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modified_since >= last_modified
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end
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def to_rfc2822(since)
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# shortest possible valid date is the obsolete: 1 Nov 97 09:55 A
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# anything shorter is invalid, this avoids exceptions for common cases
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# most common being the empty string
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if since && since.length >= 16
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# NOTE: there is no trivial way to write this in a non execption way
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# _rfc2822 returns a hash but is not that usable
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Time.rfc2822(since) rescue nil
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else
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nil
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end
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end
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end
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end
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