text: // Copyright (c) 2013 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef NET_DNS_MDNS_CACHE_H_
  #define NET_DNS_MDNS_CACHE_H_
  
  #include <map>
  #include <memory>
  #include <string>
  #include <vector>
  
  #include "base/callback.h"
  #include "base/macros.h"
  #include "base/time/time.h"
  #include "net/base/net_export.h"
  
  namespace net {
  
  class RecordParsed;
  
  // mDNS Cache
  // This is a cache of mDNS records. It keeps track of expiration times and is
  // guaranteed not to return expired records. It also has facilities for timely
  // record expiration.
  class NET_EXPORT_PRIVATE MDnsCache {
   public:
    // Key type for the record map. It is a 3-tuple of type, name and optional
    // value ordered by type, then name, then optional value. This allows us to
    // query for all records of a certain type and name, while also allowing us
    // to set records of a certain type, name and optionally value as unique.
    class Key {
     public:
      Key(unsigned type, const std::string& name, const std::string& optional);
      Key(const Key&);
      Key& operator=(const Key&);
      ~Key();
      bool operator<(const Key& key) const;
      bool operator==(const Key& key) const;
  
      unsigned type() const { return type_; }
      const std::string& name() const  { return name_; }
      const std::string& optional() const { return optional_; }
  
      // Create the cache key corresponding to |record|.
      static Key CreateFor(const RecordParsed* record);
     private:
      unsigned type_;
      std::string name_;
      std::string optional_;
    };
  
    typedef base::Callback<void(const RecordParsed*)> RecordRemovedCallback;
  
    enum UpdateType {
      RecordAdded,
      RecordChanged,
      RecordRemoved,
      NoChange
    };
  
    MDnsCache();
    ~MDnsCache();
  
    // Return value indicates whether the record was added, changed
    // (existed previously with different value) or not changed (existed
    // previously with same value).
    UpdateType UpdateDnsRecord(std::unique_ptr<const RecordParsed> record);
  
    // Check cache for record with key |key|. Return the record if it exists, or
    // NULL if it doesn't.
    const RecordParsed* LookupKey(const Key& key);
  
    // Return records with type |type| and name |name|. Expired records will not
    // be returned. If |type| is zero, return all records with name |name|.
    void FindDnsRecords(unsigned type,
                        const std::string& name,
                        std::vector<const RecordParsed*>* records,
                        base::Time now) const;
  
    // Remove expired records, call |record_removed_callback| for every removed
    // record.
    void CleanupRecords(base::Time now,
                        const RecordRemovedCallback& record_removed_callback);
  
    // Returns a time less than or equal to the next time a record will expire.
    // Is updated when CleanupRecords or UpdateDnsRecord are called. Returns
    // base::Time when the cache is empty.
    base::Time next_expiration() const { return next_expiration_; }
  
    // Remove a record from the cache.  Returns a scoped version of the pointer
    // passed in if it was removed, scoped null otherwise.
    std::unique_ptr<const RecordParsed> RemoveRecord(const RecordParsed* record);
  
    bool IsCacheOverfilled() const;
  
    void set_entry_limit_for_testing(size_t entry_limit) {
      entry_limit_ = entry_limit;
    }
  
   private:
    typedef std::map<Key, std::unique_ptr<const RecordParsed>> RecordMap;
  
    // Get the effective expiration of a cache entry, based on its creation time
    // and TTL. Does adjustments so entries with a TTL of zero will have a
    // nonzero TTL, as explained in RFC 6762 Section 10.1.
    static base::Time GetEffectiveExpiration(const RecordParsed* entry);
  
    // Get optional part of the DNS key for shared records. For example, in PTR
    // records this is the pointed domain, since multiple PTR records may exist
    // for the same name.
    static std::string GetOptionalFieldForRecord(const RecordParsed* record);
  
    RecordMap mdns_cache_;
  
    base::Time next_expiration_;
    size_t entry_limit_;
  
    DISALLOW_COPY_AND_ASSIGN(MDnsCache);
  };
  
  }  // namespace net
  
  #endif  // NET_DNS_MDNS_CACHE_H_
  