// Copyright (c) 2012 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.
//
// A server side dispatcher which dispatches a given client's data to their
// stream.

#ifndef NET_TOOLS_QUIC_QUIC_DISPATCHER_H_
#define NET_TOOLS_QUIC_QUIC_DISPATCHER_H_

#include <vector>

#include "base/containers/hash_tables.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "net/base/ip_endpoint.h"
#include "net/base/linked_hash_map.h"
#include "net/quic/quic_blocked_writer_interface.h"
#include "net/quic/quic_connection.h"
#include "net/quic/quic_protocol.h"
#include "net/tools/quic/quic_server_session_base.h"
#include "net/tools/quic/quic_time_wait_list_manager.h"

namespace net {

class QuicConfig;
class QuicCryptoServerConfig;
class QuicServerSessionBase;

namespace tools {

namespace test {
class QuicDispatcherPeer;
}  // namespace test

class ProcessPacketInterface {
 public:
  virtual ~ProcessPacketInterface() {}
  virtual void ProcessPacket(const IPEndPoint& server_address,
                             const IPEndPoint& client_address,
                             const QuicEncryptedPacket& packet) = 0;
};

class QuicDispatcher : public QuicServerSessionVisitor,
                       public ProcessPacketInterface,
                       public QuicBlockedWriterInterface {
 public:
  // Ideally we'd have a linked_hash_set: the  boolean is unused.
  typedef linked_hash_map<QuicBlockedWriterInterface*, bool> WriteBlockedList;

  // Due to the way delete_sessions_closure_ is registered, the Dispatcher must
  // live until server Shutdown. |supported_versions| specifies the std::list
  // of supported QUIC versions. Takes ownership of |packet_writer_factory|,
  // which is used to create per-connection writers.
  QuicDispatcher(const QuicConfig& config,
                 const QuicCryptoServerConfig* crypto_config,
                 const QuicVersionVector& supported_versions,
                 QuicConnectionHelperInterface* helper);

  ~QuicDispatcher() override;

  // Takes ownership of |writer|.
  void InitializeWithWriter(QuicPacketWriter* writer);

  // Process the incoming packet by creating a new session, passing it to
  // an existing session, or passing it to the time wait list.
  void ProcessPacket(const IPEndPoint& server_address,
                     const IPEndPoint& client_address,
                     const QuicEncryptedPacket& packet) override;

  // Called when the socket becomes writable to allow queued writes to happen.
  void OnCanWrite() override;

  // Returns true if there's anything in the blocked writer list.
  virtual bool HasPendingWrites() const;

  // Sends ConnectionClose frames to all connected clients.
  void Shutdown();

  // QuicServerSessionVisitor interface implementation:
  // Ensure that the closed connection is cleaned up asynchronously.
  void OnConnectionClosed(QuicConnectionId connection_id,
                          QuicErrorCode error) override;

  // Queues the blocked writer for later resumption.
  void OnWriteBlocked(QuicBlockedWriterInterface* blocked_writer) override;

  // Called whenever the time wait list manager adds a new connection to the
  // time-wait list.
  void OnConnectionAddedToTimeWaitList(QuicConnectionId connection_id) override;

  // Called whenever the time wait list manager removes an old connection from
  // the time-wait list.
  void OnConnectionRemovedFromTimeWaitList(
      QuicConnectionId connection_id) override;

  typedef base::hash_map<QuicConnectionId, QuicServerSessionBase*> SessionMap;

  const SessionMap& session_map() const { return session_map_; }

  // Deletes all sessions on the closed session list and clears the list.
  void DeleteSessions();

  // The largest packet number we expect to receive with a connection
  // ID for a connection that is not established yet.  The current design will
  // send a handshake and then up to 50 or so data packets, and then it may
  // resend the handshake packet up to 10 times.  (Retransmitted packets are
  // sent with unique packet numbers.)
  static const QuicPacketNumber kMaxReasonableInitialPacketNumber = 100;
  static_assert(kMaxReasonableInitialPacketNumber >=
                    kInitialCongestionWindow + 10,
                "kMaxReasonableInitialPacketNumber is unreasonably small "
                "relative to kInitialCongestionWindow.");

 protected:
  virtual QuicServerSessionBase* CreateQuicSession(
      QuicConnectionId connection_id,
      const IPEndPoint& client_address);

  // Called by |framer_visitor_| when the public header has been parsed.
  virtual bool OnUnauthenticatedPublicHeader(
      const QuicPacketPublicHeader& header);

  // Values to be returned by ValidityChecks() to indicate what should be done
  // with a packet.  Fates with greater values are considered to be higher
  // priority, in that if one validity check indicates a lower-valued fate and
  // another validity check indicates a higher-valued fate, the higher-valued
  // fate should be obeyed.
  enum QuicPacketFate {
    // Process the packet normally, which is usually to establish a connection.
    kFateProcess,
    // Put the connection ID into time-wait state and send a public reset.
    kFateTimeWait,
    // Drop the packet (ignore and give no response).
    kFateDrop,
  };

  // This method is called by OnUnauthenticatedHeader on packets not associated
  // with a known connection ID.  It applies validity checks and returns a
  // QuicPacketFate to tell what should be done with the packet.
  virtual QuicPacketFate ValidityChecks(const QuicPacketHeader& header);

  // Create and return the time wait list manager for this dispatcher, which
  // will be owned by the dispatcher as time_wait_list_manager_
  virtual QuicTimeWaitListManager* CreateQuicTimeWaitListManager();

  QuicTimeWaitListManager* time_wait_list_manager() {
    return time_wait_list_manager_.get();
  }

  const QuicVersionVector& supported_versions() const {
    return supported_versions_;
  }

  const IPEndPoint& current_server_address() { return current_server_address_; }
  const IPEndPoint& current_client_address() { return current_client_address_; }
  const QuicEncryptedPacket& current_packet() { return *current_packet_; }

  const QuicConfig& config() const { return config_; }

  const QuicCryptoServerConfig* crypto_config() const { return crypto_config_; }

  QuicFramer* framer() { return &framer_; }

  QuicConnectionHelperInterface* helper() { return helper_.get(); }

  QuicPacketWriter* writer() { return writer_.get(); }

  // Creates per-connection packet writers out of the QuicDispatcher's shared
  // QuicPacketWriter. The per-connection writers' IsWriteBlocked() state must
  // always be the same as the shared writer's IsWriteBlocked(), or else the
  // QuicDispatcher::OnCanWrite logic will not work. (This will hopefully be
  // cleaned up for bug 16950226.)
  virtual QuicPacketWriter* CreatePerConnectionWriter();

  void SetLastError(QuicErrorCode error);

 private:
  class QuicFramerVisitor;
  friend class net::tools::test::QuicDispatcherPeer;

  // Called by |framer_visitor_| when the private header has been parsed
  // of a data packet that is destined for the time wait manager.
  void OnUnauthenticatedHeader(const QuicPacketHeader& header);

  // Removes the session from the session map and write blocked list, and adds
  // the ConnectionId to the time-wait list.  If |session_closed_statelessly| is
  // true, any future packets for the ConnectionId will be black-holed.
  void CleanUpSession(SessionMap::iterator it, bool session_closed_statelessly);

  bool HandlePacketForTimeWait(const QuicPacketPublicHeader& header);

  const QuicConfig& config_;

  const QuicCryptoServerConfig* crypto_config_;

  // The list of connections waiting to write.
  WriteBlockedList write_blocked_list_;

  SessionMap session_map_;

  // Entity that manages connection_ids in time wait state.
  scoped_ptr<QuicTimeWaitListManager> time_wait_list_manager_;

  // The list of closed but not-yet-deleted sessions.
  std::vector<QuicServerSessionBase*> closed_session_list_;

  // The helper used for all connections.
  scoped_ptr<QuicConnectionHelperInterface> helper_;

  // An alarm which deletes closed sessions.
  scoped_ptr<QuicAlarm> delete_sessions_alarm_;

  // The writer to write to the socket with.
  scoped_ptr<QuicPacketWriter> writer_;

  // A per-connection writer that is passed to the time wait list manager.
  scoped_ptr<QuicPacketWriter> time_wait_list_writer_;

  // This vector contains QUIC versions which we currently support.
  // This should be ordered such that the highest supported version is the first
  // element, with subsequent elements in descending order (versions can be
  // skipped as necessary).
  const QuicVersionVector supported_versions_;

  // Information about the packet currently being handled.
  IPEndPoint current_client_address_;
  IPEndPoint current_server_address_;
  const QuicEncryptedPacket* current_packet_;

  QuicFramer framer_;
  scoped_ptr<QuicFramerVisitor> framer_visitor_;

  // The last error set by SetLastError(), which is called by
  // framer_visitor_->OnError().
  QuicErrorCode last_error_;

  DISALLOW_COPY_AND_ASSIGN(QuicDispatcher);
};

}  // namespace tools
}  // namespace net

#endif  // NET_TOOLS_QUIC_QUIC_DISPATCHER_H_