context.rb in rack-cache-0.4

- old
+ new
@@ -1,95 +1,233 @@
-require 'rack/cache/config'
 require 'rack/cache/options'
-require 'rack/cache/core'
 require 'rack/cache/request'
 require 'rack/cache/response'
 require 'rack/cache/storage'
 
 module Rack::Cache
   # Implements Rack's middleware interface and provides the context for all
-  # cache logic. This class includes the Options, Config, and Core modules
-  # to provide much of its core functionality.
-
+  # cache logic, including the core logic engine.
   class Context
     include Rack::Cache::Options
-    include Rack::Cache::Config
-    include Rack::Cache::Core
 
+    # Array of trace Symbols
+    attr_reader :trace
+
     # The Rack application object immediately downstream.
     attr_reader :backend
 
-    def initialize(backend, options={}, &block)
-      @errors = nil
-      @env = nil
+    def initialize(backend, options={})
       @backend = backend
+      @trace = []
+
       initialize_options options
-      initialize_core
-      initialize_config(&block)
+      yield self if block_given?
+
+      @private_header_keys =
+        private_headers.map { |name| "HTTP_#{name.upcase.tr('-', '_')}" }
     end
 
-    # The call! method is invoked on the duplicate context instance.
-    # process_request is defined in Core.
-    alias_method :call!, :process_request
-    protected :call!
+    # The configured MetaStore instance. Changing the rack-cache.metastore
+    # value effects the result of this method immediately.
+    def metastore
+      uri = options['rack-cache.metastore']
+      storage.resolve_metastore_uri(uri)
+    end
 
-    # The Rack call interface. The receiver acts as a prototype and runs each
-    # request in a duplicate object, unless the +rack.run_once+ variable is set
-    # in the environment.
+    # The configured EntityStore instance. Changing the rack-cache.entitystore
+    # value effects the result of this method immediately.
+    def entitystore
+      uri = options['rack-cache.entitystore']
+      storage.resolve_entitystore_uri(uri)
+    end
+
+    # The Rack call interface. The receiver acts as a prototype and runs
+    # each request in a dup object unless the +rack.run_once+ variable is
+    # set in the environment.
     def call(env)
       if env['rack.run_once']
         call! env
       else
         clone.call! env
       end
     end
 
-  public
-    # IO-like object that receives log, warning, and error messages;
-    # defaults to the rack.errors environment variable.
-    def errors
-      @errors || (@env && (@errors = @env['rack.errors'])) || STDERR
+    # The real Rack call interface. The caching logic is performed within
+    # the context of the receiver.
+    def call!(env)
+      @trace = []
+      @env = @default_options.merge(env)
+      @request = Request.new(@env.dup.freeze)
+
+      response =
+        if @request.get? || @request.head?
+          if !@env['HTTP_EXPECT']
+            lookup
+          else
+            pass
+          end
+        else
+          invalidate
+        end
+
+      # log trace and set X-Rack-Cache tracing header
+      trace = @trace.join(', ')
+      response.headers['X-Rack-Cache'] = trace
+
+      # write log message to rack.errors
+      if verbose?
+        message = "cache: [%s %s] %s\n" %
+          [@request.request_method, @request.fullpath, trace]
+        @env['rack.errors'].write(message)
+      end
+
+      # tidy up response a bit
+      response.not_modified! if not_modified?(response)
+      response.body = [] if @request.head?
+      response.to_a
     end
 
-    # Set the output stream for log messages, warnings, and errors.
-    def errors=(ioish)
-      fail "stream must respond to :write" if ! ioish.respond_to?(:write)
-      @errors = ioish
+  private
+
+    # Record that an event took place.
+    def record(event)
+      @trace << event
     end
 
-    # The configured MetaStore instance. Changing the rack-cache.metastore
-    # environment variable effects the result of this method immediately.
-    def metastore
-      uri = options['rack-cache.metastore']
-      storage.resolve_metastore_uri(uri)
+    # Does the request include authorization or other sensitive information
+    # that should cause the response to be considered private by default?
+    # Private responses are not stored in the cache.
+    def private_request?
+      @private_header_keys.any? { |key| @env.key?(key) }
     end
 
-    # The configured EntityStore instance. Changing the rack-cache.entitystore
-    # environment variable effects the result of this method immediately.
-    def entitystore
-      uri = options['rack-cache.entitystore']
-      storage.resolve_entitystore_uri(uri)
+    # Determine if the #response validators (ETag, Last-Modified) matches
+    # a conditional value specified in #request.
+    def not_modified?(response)
+      response.etag_matches?(@request.env['HTTP_IF_NONE_MATCH']) ||
+        response.last_modified_at?(@request.env['HTTP_IF_MODIFIED_SINCE'])
     end
 
-  protected
-    # Write a log message to the errors stream. +level+ is a symbol
-    # such as :error, :warn, :info, or :trace.
-    def log(level, message=nil, *params)
-      errors.write("[cache] #{level}: #{message}\n" % params)
-      errors.flush
+    # Whether the cache entry is "fresh enough" to satisfy the request.
+    def fresh_enough?(entry)
+      if entry.fresh?
+        if allow_revalidate? && max_age = @request.cache_control.max_age
+          max_age > 0 && max_age >= entry.age
+        else
+          true
+        end
+      end
     end
 
-    def info(*message, &bk)
-      log :info, *message, &bk
+    # Delegate the request to the backend and create the response.
+    def forward
+      Response.new(*backend.call(@env))
     end
 
-    def warn(*message, &bk)
-      log :warn, *message, &bk
+    # The request is sent to the backend, and the backend's response is sent
+    # to the client, but is not entered into the cache.
+    def pass
+      record :pass
+      forward
     end
 
-    def trace(*message, &bk)
-      return unless verbose?
-      log :trace, *message, &bk
+    # Invalidate POST, PUT, DELETE and all methods not understood by this cache
+    # See RFC2616 13.10
+    def invalidate
+      record :invalidate
+      metastore.invalidate(@request, entitystore)
+      pass
     end
-  end
 
+    # Try to serve the response from cache. When a matching cache entry is
+    # found and is fresh, use it as the response without forwarding any
+    # request to the backend. When a matching cache entry is found but is
+    # stale, attempt to #validate the entry with the backend using conditional
+    # GET. When no matching cache entry is found, trigger #miss processing.
+    def lookup
+      if @request.no_cache? && allow_reload?
+        record :reload
+        fetch
+      elsif entry = metastore.lookup(@request, entitystore)
+        if fresh_enough?(entry)
+          record :fresh
+          entry.headers['Age'] = entry.age.to_s
+          entry
+        else
+          record :stale
+          validate(entry)
+        end
+      else
+        record :miss
+        fetch
+      end
+    end
+
+    # Validate that the cache entry is fresh. The original request is used
+    # as a template for a conditional GET request with the backend.
+    def validate(entry)
+      # send no head requests because we want content
+      @env['REQUEST_METHOD'] = 'GET'
+
+      # add our cached validators to the environment
+      @env['HTTP_IF_MODIFIED_SINCE'] = entry.last_modified
+      @env['HTTP_IF_NONE_MATCH'] = entry.etag
+
+      backend_response = forward
+
+      response =
+        if backend_response.status == 304
+          record :valid
+          entry = entry.dup
+          entry.headers.delete('Date')
+          %w[Date Expires Cache-Control ETag Last-Modified].each do |name|
+            next unless value = backend_response.headers[name]
+            entry.headers[name] = value
+          end
+          entry
+        else
+          record :invalid
+          backend_response
+        end
+
+      store(response) if response.cacheable?
+
+      response
+    end
+
+    # The cache missed or a reload is required. Forward the request to the
+    # backend and determine whether the response should be stored.
+    def fetch
+      # send no head requests because we want content
+      @env['REQUEST_METHOD'] = 'GET'
+
+      # avoid that the backend sends no content
+      @env.delete('HTTP_IF_MODIFIED_SINCE')
+      @env.delete('HTTP_IF_NONE_MATCH')
+
+      response = forward
+
+      # Mark the response as explicitly private if any of the private
+      # request headers are present and the response was not explicitly
+      # declared public.
+      if private_request? && !response.cache_control.public?
+        response.private = true
+      elsif default_ttl > 0 && response.ttl.nil? && !response.cache_control.must_revalidate?
+        # assign a default TTL for the cache entry if none was specified in
+        # the response; the must-revalidate cache control directive disables
+        # default ttl assigment.
+        response.ttl = default_ttl
+      end
+
+      store(response) if response.cacheable?
+
+      response
+    end
+
+    # Write the response to the cache.
+    def store(response)
+      record :store
+      metastore.store(@request, response, entitystore)
+      response.headers['Age'] = response.age.to_s
+    end
+  end
 end