Cache for mDNS records

net/dns/mdns_cache.h

+// 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 <string>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+class ParsedDnsRecord;
+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:
+  typedef base::Callback<void(const RecordParsed*)> RecordRemovedCallback;
+
+  enum UpdateType {
+    RecordAdded,
+    RecordChanged,
+    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(scoped_ptr<const RecordParsed> record);
+
+  // Return records with type |type| and name |name|. Expired records will not
+  // be returned. If |name| is empty, return all records with type |type|.
+  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_; }
+
+  void Clear();
+
+ private:
+  // 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_; }
+
+   private:
+     unsigned type_;
+     std::string name_;
+     std::string optional_;
+  };
+
+  typedef std::map<Key, 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.
+  base::Time GetEffectiveExpiration(const RecordParsed* entry) const;
+
+  // 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.
+  std::string GetOptionalFieldForRecord(const RecordParsed* record) const;
+
+  RecordMap mdns_cache_;
+
+  base::Time next_expiration_;
+
+  DISALLOW_COPY_AND_ASSIGN(MDnsCache);
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_MDNS_CACHE_H_