text: /*
   * Copyright 2010 Google Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  // Author: jmarantz@google.com (Joshua Marantz)
  
  #ifndef NET_INSTAWEB_REWRITER_PUBLIC_CACHE_EXTENDER_H_
  #define NET_INSTAWEB_REWRITER_PUBLIC_CACHE_EXTENDER_H_
  
  #include "net/instaweb/rewriter/public/resource.h"  // for ResourcePtr
  #include "net/instaweb/rewriter/public/resource_slot.h"
  #include "net/instaweb/rewriter/public/rewrite_filter.h"
  #include "net/instaweb/rewriter/public/rewrite_options.h"
  #include "net/instaweb/rewriter/public/rewrite_result.h"
  #include "net/instaweb/rewriter/public/server_context.h"
  #include "pagespeed/kernel/base/basictypes.h"
  #include "pagespeed/kernel/base/string_util.h"
  
  namespace net_instaweb {
  
  class CachedResult;
  class HtmlElement;
  class ResponseHeaders;
  class RewriteContext;
  class RewriteDriver;
  class Statistics;
  class Variable;
  
  // Rewrites resources without changing their content -- just their
  // URLs and headers.  The original intent of this filter was limited
  // to cache extension.  However, its scope has been expanded to include
  // domain sharding and moving static resources to cookieless domains or
  // CDNs.
  //
  // TODO(jmarantz): rename this class to something more generic, like
  // RenameUrlFilter or ProxyUrlFilter.
  class CacheExtender : public RewriteFilter {
   public:
    static const char kCacheExtensions[];
    static const char kNotCacheable[];
  
    explicit CacheExtender(RewriteDriver* driver);
    virtual ~CacheExtender();
  
    static void InitStats(Statistics* statistics);
  
    virtual void StartDocumentImpl() {}
    virtual void StartElementImpl(HtmlElement* element);
    virtual void EndElementImpl(HtmlElement* element) {}
  
    virtual const char* Name() const { return "CacheExtender"; }
    virtual const char* id() const { return RewriteOptions::kCacheExtenderId; }
  
    // Creates a nested rewrite for given parent and slot, and returns it.
    // The result is not registered with the parent.
    RewriteContext* MakeNestedContext(RewriteContext* parent,
                                      const ResourceSlotPtr& slot);
  
   protected:
    virtual bool ComputeOnTheFly() const;
    virtual RewriteContext* MakeRewriteContext();
  
   private:
    class Context;
    friend class Context;
  
    RewriteResult RewriteLoadedResource(const ResourcePtr& input_resource,
                                        const OutputResourcePtr& output_resource,
                                        CachedResult* result);
  
    bool ShouldRewriteResource(
        const ResponseHeaders* headers, int64 now_ms,
        const ResourcePtr& input_resource, const StringPiece& url,
        CachedResult* result) const;
  
    Variable* extension_count_;
    Variable* not_cacheable_count_;
  
    DISALLOW_COPY_AND_ASSIGN(CacheExtender);
  };
  
  }  // namespace net_instaweb
  
  #endif  // NET_INSTAWEB_REWRITER_PUBLIC_CACHE_EXTENDER_H_
  