text: // 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.
  
  #ifndef NET_SPDY_SPDY_SESSION_H_
  #define NET_SPDY_SPDY_SESSION_H_
  
  #include <deque>
  #include <map>
  #include <set>
  #include <string>
  
  #include "base/basictypes.h"
  #include "base/gtest_prod_util.h"
  #include "base/memory/ref_counted.h"
  #include "base/memory/scoped_ptr.h"
  #include "base/memory/weak_ptr.h"
  #include "base/time/time.h"
  #include "net/base/io_buffer.h"
  #include "net/base/load_states.h"
  #include "net/base/net_errors.h"
  #include "net/base/net_export.h"
  #include "net/base/request_priority.h"
  #include "net/socket/client_socket_handle.h"
  #include "net/socket/client_socket_pool.h"
  #include "net/socket/next_proto.h"
  #include "net/socket/ssl_client_socket.h"
  #include "net/socket/stream_socket.h"
  #include "net/spdy/buffered_spdy_framer.h"
  #include "net/spdy/spdy_buffer.h"
  #include "net/spdy/spdy_framer.h"
  #include "net/spdy/spdy_header_block.h"
  #include "net/spdy/spdy_protocol.h"
  #include "net/spdy/spdy_session_pool.h"
  #include "net/spdy/spdy_stream.h"
  #include "net/spdy/spdy_write_queue.h"
  #include "net/ssl/ssl_config_service.h"
  #include "url/gurl.h"
  
  namespace net {
  
  // This is somewhat arbitrary and not really fixed, but it will always work
  // reasonably with ethernet. Chop the world into 2-packet chunks.  This is
  // somewhat arbitrary, but is reasonably small and ensures that we elicit
  // ACKs quickly from TCP (because TCP tries to only ACK every other packet).
  const int kMss = 1430;
  // The 8 is the size of the SPDY frame header.
  const int kMaxSpdyFrameChunkSize = (2 * kMss) - 8;
  
  // Maximum number of concurrent streams we will create, unless the server
  // sends a SETTINGS frame with a different value.
  const size_t kInitialMaxConcurrentStreams = 100;
  
  // Specifies the maxiumum concurrent streams server could send (via push).
  const int kMaxConcurrentPushedStreams = 1000;
  
  // Specifies the maximum number of bytes to read synchronously before
  // yielding.
  const int kMaxReadBytesWithoutYielding = 32 * 1024;
  
  // The initial receive window size for both streams and sessions.
  const int32 kDefaultInitialRecvWindowSize = 10 * 1024 * 1024;  // 10MB
  
  // First and last valid stream IDs. As we always act as the client,
  // start at 1 for the first stream id.
  const SpdyStreamId kFirstStreamId = 1;
  const SpdyStreamId kLastStreamId = 0x7fffffff;
  
  class BoundNetLog;
  struct LoadTimingInfo;
  class SpdyStream;
  class SSLInfo;
  
  // NOTE: There's an enum of the same name (also with numeric suffixes)
  // in histograms.xml. Be sure to add new values there also.
  enum SpdyProtocolErrorDetails {
    // SpdyFramer::SpdyError mappings.
    SPDY_ERROR_NO_ERROR = 0,
    SPDY_ERROR_INVALID_CONTROL_FRAME = 1,
    SPDY_ERROR_CONTROL_PAYLOAD_TOO_LARGE = 2,
    SPDY_ERROR_ZLIB_INIT_FAILURE = 3,
    SPDY_ERROR_UNSUPPORTED_VERSION = 4,
    SPDY_ERROR_DECOMPRESS_FAILURE = 5,
    SPDY_ERROR_COMPRESS_FAILURE = 6,
    // SPDY_ERROR_CREDENTIAL_FRAME_CORRUPT = 7, (removed).
    SPDY_ERROR_GOAWAY_FRAME_CORRUPT = 29,
    SPDY_ERROR_RST_STREAM_FRAME_CORRUPT = 30,
    SPDY_ERROR_INVALID_DATA_FRAME_FLAGS = 8,
    SPDY_ERROR_INVALID_CONTROL_FRAME_FLAGS = 9,
    SPDY_ERROR_UNEXPECTED_FRAME = 31,
    // SpdyRstStreamStatus mappings.
    // RST_STREAM_INVALID not mapped.
    STATUS_CODE_PROTOCOL_ERROR = 11,
    STATUS_CODE_INVALID_STREAM = 12,
    STATUS_CODE_REFUSED_STREAM = 13,
    STATUS_CODE_UNSUPPORTED_VERSION = 14,
    STATUS_CODE_CANCEL = 15,
    STATUS_CODE_INTERNAL_ERROR = 16,
    STATUS_CODE_FLOW_CONTROL_ERROR = 17,
    STATUS_CODE_STREAM_IN_USE = 18,
    STATUS_CODE_STREAM_ALREADY_CLOSED = 19,
    STATUS_CODE_INVALID_CREDENTIALS = 20,
    STATUS_CODE_FRAME_SIZE_ERROR = 21,
    STATUS_CODE_SETTINGS_TIMEOUT = 32,
    STATUS_CODE_CONNECT_ERROR = 33,
    STATUS_CODE_ENHANCE_YOUR_CALM = 34,
  
    // SpdySession errors
    PROTOCOL_ERROR_UNEXPECTED_PING = 22,
    PROTOCOL_ERROR_RST_STREAM_FOR_NON_ACTIVE_STREAM = 23,
    PROTOCOL_ERROR_SPDY_COMPRESSION_FAILURE = 24,
    PROTOCOL_ERROR_REQUEST_FOR_SECURE_CONTENT_OVER_INSECURE_SESSION = 25,
    PROTOCOL_ERROR_SYN_REPLY_NOT_RECEIVED = 26,
    PROTOCOL_ERROR_INVALID_WINDOW_UPDATE_SIZE = 27,
    PROTOCOL_ERROR_RECEIVE_WINDOW_VIOLATION = 28,
  
    // Next free value.
    NUM_SPDY_PROTOCOL_ERROR_DETAILS = 35,
  };
  SpdyProtocolErrorDetails NET_EXPORT_PRIVATE
      MapFramerErrorToProtocolError(SpdyFramer::SpdyError error);
  Error NET_EXPORT_PRIVATE MapFramerErrorToNetError(SpdyFramer::SpdyError error);
  SpdyProtocolErrorDetails NET_EXPORT_PRIVATE
      MapRstStreamStatusToProtocolError(SpdyRstStreamStatus status);
  SpdyGoAwayStatus NET_EXPORT_PRIVATE MapNetErrorToGoAwayStatus(Error err);
  
  // If these compile asserts fail then SpdyProtocolErrorDetails needs
  // to be updated with new values, as do the mapping functions above.
  COMPILE_ASSERT(12 == SpdyFramer::LAST_ERROR,
                 SpdyProtocolErrorDetails_SpdyErrors_mismatch);
  COMPILE_ASSERT(15 == RST_STREAM_NUM_STATUS_CODES,
                 SpdyProtocolErrorDetails_RstStreamStatus_mismatch);
  
  // Splits pushed |headers| into request and response parts. Request headers are
  // the headers specifying resource URL.
  void NET_EXPORT_PRIVATE
      SplitPushedHeadersToRequestAndResponse(const SpdyHeaderBlock& headers,
                                             SpdyMajorVersion protocol_version,
                                             SpdyHeaderBlock* request_headers,
                                             SpdyHeaderBlock* response_headers);
  
  // A helper class used to manage a request to create a stream.
  class NET_EXPORT_PRIVATE SpdyStreamRequest {
   public:
    SpdyStreamRequest();
    // Calls CancelRequest().
    ~SpdyStreamRequest();
  
    // Starts the request to create a stream. If OK is returned, then
    // ReleaseStream() may be called. If ERR_IO_PENDING is returned,
    // then when the stream is created, |callback| will be called, at
    // which point ReleaseStream() may be called. Otherwise, the stream
    // is not created, an error is returned, and ReleaseStream() may not
    // be called.
    //
    // If OK is returned, must not be called again without
    // ReleaseStream() being called first. If ERR_IO_PENDING is
    // returned, must not be called again without CancelRequest() or
    // ReleaseStream() being called first. Otherwise, in case of an
    // immediate error, this may be called again.
    int StartRequest(SpdyStreamType type,
                     const base::WeakPtr<SpdySession>& session,
                     const GURL& url,
                     RequestPriority priority,
                     const BoundNetLog& net_log,
                     const CompletionCallback& callback);
  
    // Cancels any pending stream creation request. May be called
    // repeatedly.
    void CancelRequest();
  
    // Transfers the created stream (guaranteed to not be NULL) to the
    // caller. Must be called at most once after StartRequest() returns
    // OK or |callback| is called with OK. The caller must immediately
    // set a delegate for the returned stream (except for test code).
    base::WeakPtr<SpdyStream> ReleaseStream();
  
   private:
    friend class SpdySession;
  
    // Called by |session_| when the stream attempt has finished
    // successfully.
    void OnRequestCompleteSuccess(const base::WeakPtr<SpdyStream>& stream);
  
    // Called by |session_| when the stream attempt has finished with an
    // error. Also called with ERR_ABORTED if |session_| is destroyed
    // while the stream attempt is still pending.
    void OnRequestCompleteFailure(int rv);
  
    // Accessors called by |session_|.
    SpdyStreamType type() const { return type_; }
    const GURL& url() const { return url_; }
    RequestPriority priority() const { return priority_; }
    const BoundNetLog& net_log() const { return net_log_; }
  
    void Reset();
  
    SpdyStreamType type_;
    base::WeakPtr<SpdySession> session_;
    base::WeakPtr<SpdyStream> stream_;
    GURL url_;
    RequestPriority priority_;
    BoundNetLog net_log_;
    CompletionCallback callback_;
  
    base::WeakPtrFactory<SpdyStreamRequest> weak_ptr_factory_;
  
    DISALLOW_COPY_AND_ASSIGN(SpdyStreamRequest);
  };
  
  class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
                                 public SpdyFramerDebugVisitorInterface,
                                 public HigherLayeredPool {
   public:
    // TODO(akalin): Use base::TickClock when it becomes available.
    typedef base::TimeTicks (*TimeFunc)(void);
  
    // How we handle flow control (version-dependent).
    enum FlowControlState {
      FLOW_CONTROL_NONE,
      FLOW_CONTROL_STREAM,
      FLOW_CONTROL_STREAM_AND_SESSION
    };
  
    // Create a new SpdySession.
    // |spdy_session_key| is the host/port that this session connects to, privacy
    // and proxy configuration settings that it's using.
    // |session| is the HttpNetworkSession.  |net_log| is the NetLog that we log
    // network events to.
    SpdySession(const SpdySessionKey& spdy_session_key,
                const base::WeakPtr<HttpServerProperties>& http_server_properties,
                bool verify_domain_authentication,
                bool enable_sending_initial_data,
                bool enable_compression,
                bool enable_ping_based_connection_checking,
                NextProto default_protocol,
                size_t stream_initial_recv_window_size,
                size_t initial_max_concurrent_streams,
                size_t max_concurrent_streams_limit,
                TimeFunc time_func,
                const HostPortPair& trusted_spdy_proxy,
                NetLog* net_log);
  
    virtual ~SpdySession();
  
    const HostPortPair& host_port_pair() const {
      return spdy_session_key_.host_port_proxy_pair().first;
    }
    const HostPortProxyPair& host_port_proxy_pair() const {
      return spdy_session_key_.host_port_proxy_pair();
    }
    const SpdySessionKey& spdy_session_key() const {
      return spdy_session_key_;
    }
    // Get a pushed stream for a given |url|.  If the server initiates a
    // stream, it might already exist for a given path.  The server
    // might also not have initiated the stream yet, but indicated it
    // will via X-Associated-Content.  Returns OK if a stream was found
    // and put into |spdy_stream|, or if one was not found but it is
    // okay to create a new stream (in which case |spdy_stream| is
    // reset).  Returns an error (not ERR_IO_PENDING) otherwise, and
    // resets |spdy_stream|.
    int GetPushStream(
        const GURL& url,
        base::WeakPtr<SpdyStream>* spdy_stream,
        const BoundNetLog& stream_net_log);
  
    // Initialize the session with the given connection. |is_secure|
    // must indicate whether |connection| uses an SSL socket or not; it
    // is usually true, but it can be false for testing or when SPDY is
    // configured to work with non-secure sockets.
    //
    // |pool| is the SpdySessionPool that owns us.  Its lifetime must
    // strictly be greater than |this|.
    //
    // |certificate_error_code| must either be OK or less than
    // ERR_IO_PENDING.
    //
    // The session begins reading from |connection| on a subsequent event loop
    // iteration, so the SpdySession may close immediately afterwards if the first
    // read of |connection| fails.
    void InitializeWithSocket(scoped_ptr<ClientSocketHandle> connection,
                              SpdySessionPool* pool,
                              bool is_secure,
                              int certificate_error_code);
  
    // Returns the protocol used by this session. Always between
    // kProtoSPDYMinimumVersion and kProtoSPDYMaximumVersion.
    NextProto protocol() const { return protocol_; }
  
    // Check to see if this SPDY session can support an additional domain.
    // If the session is un-authenticated, then this call always returns true.
    // For SSL-based sessions, verifies that the server certificate in use by
    // this session provides authentication for the domain and no client
    // certificate or channel ID was sent to the original server during the SSL
    // handshake.  NOTE:  This function can have false negatives on some
    // platforms.
    // TODO(wtc): rename this function and the Net.SpdyIPPoolDomainMatch
    // histogram because this function does more than verifying domain
    // authentication now.
    bool VerifyDomainAuthentication(const std::string& domain);
  
    // Pushes the given producer into the write queue for
    // |stream|. |stream| is guaranteed to be activated before the
    // producer is used to produce its frame.
    void EnqueueStreamWrite(const base::WeakPtr<SpdyStream>& stream,
                            SpdyFrameType frame_type,
                            scoped_ptr<SpdyBufferProducer> producer);
  
    // Creates and returns a SYN frame for |stream_id|.
    scoped_ptr<SpdyFrame> CreateSynStream(
        SpdyStreamId stream_id,
        RequestPriority priority,
        SpdyControlFlags flags,
        const SpdyHeaderBlock& headers);
  
    // Creates and returns a SpdyBuffer holding a data frame with the
    // given data. May return NULL if stalled by flow control.
    scoped_ptr<SpdyBuffer> CreateDataBuffer(SpdyStreamId stream_id,
                                            IOBuffer* data,
                                            int len,
                                            SpdyDataFlags flags);
  
    // Close the stream with the given ID, which must exist and be
    // active. Note that that stream may hold the last reference to the
    // session.
    void CloseActiveStream(SpdyStreamId stream_id, int status);
  
    // Close the given created stream, which must exist but not yet be
    // active. Note that |stream| may hold the last reference to the
    // session.
    void CloseCreatedStream(const base::WeakPtr<SpdyStream>& stream, int status);
  
    // Send a RST_STREAM frame with the given status code and close the
    // stream with the given ID, which must exist and be active. Note
    // that that stream may hold the last reference to the session.
    void ResetStream(SpdyStreamId stream_id,
                     SpdyRstStreamStatus status,
                     const std::string& description);
  
    // Check if a stream is active.
    bool IsStreamActive(SpdyStreamId stream_id) const;
  
    // The LoadState is used for informing the user of the current network
    // status, such as "resolving host", "connecting", etc.
    LoadState GetLoadState() const;
  
    // Fills SSL info in |ssl_info| and returns true when SSL is in use.
    bool GetSSLInfo(SSLInfo* ssl_info,
                    bool* was_npn_negotiated,
                    NextProto* protocol_negotiated);
  
    // Fills SSL Certificate Request info |cert_request_info| and returns
    // true when SSL is in use.
    bool GetSSLCertRequestInfo(SSLCertRequestInfo* cert_request_info);
  
    // Send a WINDOW_UPDATE frame for a stream. Called by a stream
    // whenever receive window size is increased.
    void SendStreamWindowUpdate(SpdyStreamId stream_id,
                                uint32 delta_window_size);
  
    // Accessors for the session's availability state.
    bool IsAvailable() const { return availability_state_ == STATE_AVAILABLE; }
    bool IsGoingAway() const { return availability_state_ == STATE_GOING_AWAY; }
    bool IsDraining() const { return availability_state_ == STATE_DRAINING; }
  
    // Closes this session. This will close all active streams and mark
    // the session as permanently closed. Callers must assume that the
    // session is destroyed after this is called. (However, it may not
    // be destroyed right away, e.g. when a SpdySession function is
    // present in the call stack.)
    //
    // |err| should be < ERR_IO_PENDING; this function is intended to be
    // called on error.
    // |description| indicates the reason for the error.
    void CloseSessionOnError(Error err, const std::string& description);
  
    // Mark this session as unavailable, meaning that it will not be used to
    // service new streams. Unlike when a GOAWAY frame is received, this function
    // will not close any streams.
    void MakeUnavailable();
  
    // Closes all active streams with stream id's greater than
    // |last_good_stream_id|, as well as any created or pending
    // streams. Must be called only when |availability_state_| >=
    // STATE_GOING_AWAY. After this function, DcheckGoingAway() will
    // pass. May be called multiple times.
    void StartGoingAway(SpdyStreamId last_good_stream_id, Error status);
  
    // Must be called only when going away (i.e., DcheckGoingAway()
    // passes). If there are no more active streams and the session
    // isn't closed yet, close it.
    void MaybeFinishGoingAway();
  
    // Retrieves information on the current state of the SPDY session as a
    // Value.  Caller takes possession of the returned value.
    base::Value* GetInfoAsValue() const;
  
    // Indicates whether the session is being reused after having successfully
    // used to send/receive data in the past or if the underlying socket was idle
    // before being used for a SPDY session.
    bool IsReused() const;
  
    // Returns true if the underlying transport socket ever had any reads or
    // writes.
    bool WasEverUsed() const {
      return connection_->socket()->WasEverUsed();
    }
  
    // Returns the load timing information from the perspective of the given
    // stream.  If it's not the first stream, the connection is considered reused
    // for that stream.
    //
    // This uses a different notion of reuse than IsReused().  This function
    // sets |socket_reused| to false only if |stream_id| is the ID of the first
    // stream using the session.  IsReused(), on the other hand, indicates if the
    // session has been used to send/receive data at all.
    bool GetLoadTimingInfo(SpdyStreamId stream_id,
                           LoadTimingInfo* load_timing_info) const;
  
    // Returns true if session is not currently active
    bool is_active() const {
      return !active_streams_.empty() || !created_streams_.empty();
    }
  
    // Access to the number of active and pending streams.  These are primarily
    // available for testing and diagnostics.
    size_t num_active_streams() const { return active_streams_.size(); }
    size_t num_unclaimed_pushed_streams() const {
        return unclaimed_pushed_streams_.size();
    }
    size_t num_created_streams() const { return created_streams_.size(); }
  
    size_t pending_create_stream_queue_size(RequestPriority priority) const {
      DCHECK_GE(priority, MINIMUM_PRIORITY);
      DCHECK_LE(priority, MAXIMUM_PRIORITY);
      return pending_create_stream_queues_[priority].size();
    }
  
    // Returns the (version-dependent) flow control state.
    FlowControlState flow_control_state() const {
      return flow_control_state_;
    }
  
    // Returns the current |stream_initial_send_window_size_|.
    int32 stream_initial_send_window_size() const {
      return stream_initial_send_window_size_;
    }
  
    // Returns the current |stream_initial_recv_window_size_|.
    int32 stream_initial_recv_window_size() const {
      return stream_initial_recv_window_size_;
    }
  
    // Returns true if no stream in the session can send data due to
    // session flow control.
    bool IsSendStalled() const {
      return
          flow_control_state_ == FLOW_CONTROL_STREAM_AND_SESSION &&
          session_send_window_size_ == 0;
    }
  
    const BoundNetLog& net_log() const { return net_log_; }
  
    int GetPeerAddress(IPEndPoint* address) const;
    int GetLocalAddress(IPEndPoint* address) const;
  
    // Adds |alias| to set of aliases associated with this session.
    void AddPooledAlias(const SpdySessionKey& alias_key);
  
    // Returns the set of aliases associated with this session.
    const std::set<SpdySessionKey>& pooled_aliases() const {
      return pooled_aliases_;
    }
  
    SpdyMajorVersion GetProtocolVersion() const;
  
    size_t GetDataFrameMinimumSize() const {
      return buffered_spdy_framer_->GetDataFrameMinimumSize();
    }
  
    size_t GetControlFrameHeaderSize() const {
      return buffered_spdy_framer_->GetControlFrameHeaderSize();
    }
  
    size_t GetFrameMinimumSize() const {
      return buffered_spdy_framer_->GetFrameMinimumSize();
    }
  
    size_t GetFrameMaximumSize() const {
      return buffered_spdy_framer_->GetFrameMaximumSize();
    }
  
    size_t GetDataFrameMaximumPayload() const {
      return buffered_spdy_framer_->GetDataFrameMaximumPayload();
    }
  
    // https://http2.github.io/http2-spec/#TLSUsage mandates minimum security
    // standards for TLS.
    bool HasAcceptableTransportSecurity() const;
  
    // Must be used only by |pool_|.
    base::WeakPtr<SpdySession> GetWeakPtr();
  
    // HigherLayeredPool implementation:
    virtual bool CloseOneIdleConnection() OVERRIDE;
  
   private:
    friend class base::RefCounted<SpdySession>;
    friend class SpdyStreamRequest;
    friend class SpdySessionTest;
  
    // Allow tests to access our innards for testing purposes.
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, ClientPing);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, FailedPing);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, GetActivePushStream);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, DeleteExpiredPushStreams);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, ProtocolNegotiation);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, ClearSettings);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, AdjustRecvWindowSize);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, AdjustSendWindowSize);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, SessionFlowControlInactiveStream);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, SessionFlowControlNoReceiveLeaks);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, SessionFlowControlNoSendLeaks);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, SessionFlowControlEndToEnd);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, StreamIdSpaceExhausted);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, UnstallRacesWithStreamCreation);
    FRIEND_TEST_ALL_PREFIXES(SpdySessionTest, GoAwayOnSessionFlowControlError);
  
    typedef std::deque<base::WeakPtr<SpdyStreamRequest> >
        PendingStreamRequestQueue;
  
    struct ActiveStreamInfo {
      ActiveStreamInfo();
      explicit ActiveStreamInfo(SpdyStream* stream);
      ~ActiveStreamInfo();
  
      SpdyStream* stream;
      bool waiting_for_syn_reply;
    };
    typedef std::map<SpdyStreamId, ActiveStreamInfo> ActiveStreamMap;
  
    struct PushedStreamInfo {
      PushedStreamInfo();
      PushedStreamInfo(SpdyStreamId stream_id, base::TimeTicks creation_time);
      ~PushedStreamInfo();
  
      SpdyStreamId stream_id;
      base::TimeTicks creation_time;
    };
    typedef std::map<GURL, PushedStreamInfo> PushedStreamMap;
  
    typedef std::set<SpdyStream*> CreatedStreamSet;
  
    enum AvailabilityState {
      // The session is available in its socket pool and can be used
      // freely.
      STATE_AVAILABLE,
      // The session can process data on existing streams but will
      // refuse to create new ones.
      STATE_GOING_AWAY,
      // The session is draining its write queue in preparation of closing.
      // Further writes will not be queued, and further reads will not be issued
      // (though the remainder of a current read may be processed). The session
      // will be destroyed by its write loop once the write queue is drained.
      STATE_DRAINING,
    };
  
    enum ReadState {
      READ_STATE_DO_READ,
      READ_STATE_DO_READ_COMPLETE,
    };
  
    enum WriteState {
      // There is no in-flight write and the write queue is empty.
      WRITE_STATE_IDLE,
      WRITE_STATE_DO_WRITE,
      WRITE_STATE_DO_WRITE_COMPLETE,
    };
  
    // Checks whether a stream for the given |url| can be created or
    // retrieved from the set of unclaimed push streams. Returns OK if
    // so. Otherwise, the session is closed and an error <
    // ERR_IO_PENDING is returned.
    Error TryAccessStream(const GURL& url);
  
    // Called by SpdyStreamRequest to start a request to create a
    // stream. If OK is returned, then |stream| will be filled in with a
    // valid stream. If ERR_IO_PENDING is returned, then
    // |request->OnRequestComplete{Success,Failure}()| will be called
    // when the stream is created (unless it is cancelled). Otherwise,
    // no stream is created and the error is returned.
    int TryCreateStream(const base::WeakPtr<SpdyStreamRequest>& request,
                        base::WeakPtr<SpdyStream>* stream);
  
    // Actually create a stream into |stream|. Returns OK if successful;
    // otherwise, returns an error and |stream| is not filled.
    int CreateStream(const SpdyStreamRequest& request,
                     base::WeakPtr<SpdyStream>* stream);
  
    // Called by SpdyStreamRequest to remove |request| from the stream
    // creation queue.
    void CancelStreamRequest(const base::WeakPtr<SpdyStreamRequest>& request);
  
    // Returns the next pending stream request to process, or NULL if
    // there is none.
    base::WeakPtr<SpdyStreamRequest> GetNextPendingStreamRequest();
  
    // Called when there is room to create more streams (e.g., a stream
    // was closed). Processes as many pending stream requests as
    // possible.
    void ProcessPendingStreamRequests();
  
    bool TryCreatePushStream(SpdyStreamId stream_id,
                             SpdyStreamId associated_stream_id,
                             SpdyPriority priority,
                             const SpdyHeaderBlock& headers);
  
    // Close the stream pointed to by the given iterator. Note that that
    // stream may hold the last reference to the session.
    void CloseActiveStreamIterator(ActiveStreamMap::iterator it, int status);
  
    // Close the stream pointed to by the given iterator. Note that that
    // stream may hold the last reference to the session.
    void CloseCreatedStreamIterator(CreatedStreamSet::iterator it, int status);
  
    // Calls EnqueueResetStreamFrame() and then
    // CloseActiveStreamIterator().
    void ResetStreamIterator(ActiveStreamMap::iterator it,
                             SpdyRstStreamStatus status,
                             const std::string& description);
  
    // Send a RST_STREAM frame with the given parameters. There should
    // either be no active stream with the given ID, or that active
    // stream should be closed shortly after this function is called.
    //
    // TODO(akalin): Rename this to EnqueueResetStreamFrame().
    void EnqueueResetStreamFrame(SpdyStreamId stream_id,
                                 RequestPriority priority,
                                 SpdyRstStreamStatus status,
                                 const std::string& description);
  
    // Calls DoReadLoop. Use this function instead of DoReadLoop when
    // posting a task to pump the read loop.
    void PumpReadLoop(ReadState expected_read_state, int result);
  
    // Advance the ReadState state machine. |expected_read_state| is the
    // expected starting read state.
    //
    // This function must always be called via PumpReadLoop().
    int DoReadLoop(ReadState expected_read_state, int result);
    // The implementations of the states of the ReadState state machine.
    int DoRead();
    int DoReadComplete(int result);
  
    // Calls DoWriteLoop. If |availability_state_| is STATE_DRAINING and no
    // writes remain, the session is removed from the session pool and
    // destroyed.
    //
    // Use this function instead of DoWriteLoop when posting a task to
    // pump the write loop.
    void PumpWriteLoop(WriteState expected_write_state, int result);
  
    // Iff the write loop is not currently active, posts a callback into
    // PumpWriteLoop().
    void MaybePostWriteLoop();
  
    // Advance the WriteState state machine. |expected_write_state| is
    // the expected starting write state.
    //
    // This function must always be called via PumpWriteLoop().
    int DoWriteLoop(WriteState expected_write_state, int result);
    // The implementations of the states of the WriteState state machine.
    int DoWrite();
    int DoWriteComplete(int result);
  
    // TODO(akalin): Rename the Send* and Write* functions below to
    // Enqueue*.
  
    // Send initial data. Called when a connection is successfully
    // established in InitializeWithSocket() and
    // |enable_sending_initial_data_| is true.
    void SendInitialData();
  
    // Helper method to send a SETTINGS frame.
    void SendSettings(const SettingsMap& settings);
  
    // Handle SETTING.  Either when we send settings, or when we receive a
    // SETTINGS control frame, update our SpdySession accordingly.
    void HandleSetting(uint32 id, uint32 value);
  
    // Adjust the send window size of all ActiveStreams and PendingStreamRequests.
    void UpdateStreamsSendWindowSize(int32 delta_window_size);
  
    // Send the PING (preface-PING) frame.
    void SendPrefacePingIfNoneInFlight();
  
    // Send PING if there are no PINGs in flight and we haven't heard from server.
    void SendPrefacePing();
  
    // Send a single WINDOW_UPDATE frame.
    void SendWindowUpdateFrame(SpdyStreamId stream_id, uint32 delta_window_size,
                               RequestPriority priority);
  
    // Send the PING frame.
    void WritePingFrame(uint32 unique_id, bool is_ack);
  
    // Post a CheckPingStatus call after delay. Don't post if there is already
    // CheckPingStatus running.
    void PlanToCheckPingStatus();
  
    // Check the status of the connection. It calls |CloseSessionOnError| if we
    // haven't received any data in |kHungInterval| time period.
    void CheckPingStatus(base::TimeTicks last_check_time);
  
    // Get a new stream id.
    SpdyStreamId GetNewStreamId();
  
    // Pushes the given frame with the given priority into the write
    // queue for the session.
    void EnqueueSessionWrite(RequestPriority priority,
                             SpdyFrameType frame_type,
                             scoped_ptr<SpdyFrame> frame);
  
    // Puts |producer| associated with |stream| onto the write queue
    // with the given priority.
    void EnqueueWrite(RequestPriority priority,
                      SpdyFrameType frame_type,
                      scoped_ptr<SpdyBufferProducer> producer,
                      const base::WeakPtr<SpdyStream>& stream);
  
    // Inserts a newly-created stream into |created_streams_|.
    void InsertCreatedStream(scoped_ptr<SpdyStream> stream);
  
    // Activates |stream| (which must be in |created_streams_|) by
    // assigning it an ID and returns it.
    scoped_ptr<SpdyStream> ActivateCreatedStream(SpdyStream* stream);
  
    // Inserts a newly-activated stream into |active_streams_|.
    void InsertActivatedStream(scoped_ptr<SpdyStream> stream);
  
    // Remove all internal references to |stream|, call OnClose() on it,
    // and process any pending stream requests before deleting it.  Note
    // that |stream| may hold the last reference to the session.
    void DeleteStream(scoped_ptr<SpdyStream> stream, int status);
  
    // Check if we have a pending pushed-stream for this url
    // Returns the stream if found (and returns it from the pending
    // list). Returns NULL otherwise.
    base::WeakPtr<SpdyStream> GetActivePushStream(const GURL& url);
  
    // Delegates to |stream->OnInitialResponseHeadersReceived()|. If an
    // error is returned, the last reference to |this| may have been
    // released.
    int OnInitialResponseHeadersReceived(const SpdyHeaderBlock& response_headers,
                                         base::Time response_time,
                                         base::TimeTicks recv_first_byte_time,
                                         SpdyStream* stream);
  
    void RecordPingRTTHistogram(base::TimeDelta duration);
    void RecordHistograms();
    void RecordProtocolErrorHistogram(SpdyProtocolErrorDetails details);
  
    // DCHECKs that |availability_state_| >= STATE_GOING_AWAY, that
    // there are no pending stream creation requests, and that there are
    // no created streams.
    void DcheckGoingAway() const;
  
    // Calls DcheckGoingAway(), then DCHECKs that |availability_state_|
    // == STATE_DRAINING, |error_on_close_| has a valid value, and that there
    // are no active streams or unclaimed pushed streams.
    void DcheckDraining() const;
  
    // If the session is already draining, does nothing. Otherwise, moves
    // the session to the draining state.
    void DoDrainSession(Error err, const std::string& description);
  
    // Called right before closing a (possibly-inactive) stream for a
    // reason other than being requested to by the stream.
    void LogAbandonedStream(SpdyStream* stream, Error status);
  
    // Called right before closing an active stream for a reason other
    // than being requested to by the stream.
    void LogAbandonedActiveStream(ActiveStreamMap::const_iterator it,
                                  Error status);
  
    // Invokes a user callback for stream creation.  We provide this method so it
    // can be deferred to the MessageLoop, so we avoid re-entrancy problems.
    void CompleteStreamRequest(
        const base::WeakPtr<SpdyStreamRequest>& pending_request);
  
    // Remove old unclaimed pushed streams.
    void DeleteExpiredPushedStreams();
  
    // BufferedSpdyFramerVisitorInterface:
    virtual void OnError(SpdyFramer::SpdyError error_code) OVERRIDE;
    virtual void OnStreamError(SpdyStreamId stream_id,
                               const std::string& description) OVERRIDE;
    virtual void OnPing(SpdyPingId unique_id, bool is_ack) OVERRIDE;
    virtual void OnRstStream(SpdyStreamId stream_id,
                             SpdyRstStreamStatus status) OVERRIDE;
    virtual void OnGoAway(SpdyStreamId last_accepted_stream_id,
                          SpdyGoAwayStatus status) OVERRIDE;
    virtual void OnDataFrameHeader(SpdyStreamId stream_id,
                                   size_t length,
                                   bool fin) OVERRIDE;
    virtual void OnStreamFrameData(SpdyStreamId stream_id,
                                   const char* data,
                                   size_t len,
                                   bool fin) OVERRIDE;
    virtual void OnSettings(bool clear_persisted) OVERRIDE;
    virtual void OnSetting(
        SpdySettingsIds id, uint8 flags, uint32 value) OVERRIDE;
    virtual void OnWindowUpdate(SpdyStreamId stream_id,
                                uint32 delta_window_size) OVERRIDE;
    virtual void OnPushPromise(SpdyStreamId stream_id,
                               SpdyStreamId promised_stream_id,
                               const SpdyHeaderBlock& headers) OVERRIDE;
    virtual void OnSynStream(SpdyStreamId stream_id,
                             SpdyStreamId associated_stream_id,
                             SpdyPriority priority,
                             bool fin,
                             bool unidirectional,
                             const SpdyHeaderBlock& headers) OVERRIDE;
    virtual void OnSynReply(
        SpdyStreamId stream_id,
        bool fin,
        const SpdyHeaderBlock& headers) OVERRIDE;
    virtual void OnHeaders(
        SpdyStreamId stream_id,
        bool fin,
        const SpdyHeaderBlock& headers) OVERRIDE;
  
    // SpdyFramerDebugVisitorInterface
    virtual void OnSendCompressedFrame(
        SpdyStreamId stream_id,
        SpdyFrameType type,
        size_t payload_len,
        size_t frame_len) OVERRIDE;
    virtual void OnReceiveCompressedFrame(
        SpdyStreamId stream_id,
        SpdyFrameType type,
        size_t frame_len) OVERRIDE;
  
    // Called when bytes are consumed from a SpdyBuffer for a DATA frame
    // that is to be written or is being written. Increases the send
    // window size accordingly if some or all of the SpdyBuffer is being
    // discarded.
    //
    // If session flow control is turned off, this must not be called.
    void OnWriteBufferConsumed(size_t frame_payload_size,
                               size_t consume_size,
                               SpdyBuffer::ConsumeSource consume_source);
  
    // Called by OnWindowUpdate() (which is in turn called by the
    // framer) to increase this session's send window size by
    // |delta_window_size| from a WINDOW_UPDATE frome, which must be at
    // least 1. If |delta_window_size| would cause this session's send
    // window size to overflow, does nothing.
    //
    // If session flow control is turned off, this must not be called.
    void IncreaseSendWindowSize(int32 delta_window_size);
  
    // If session flow control is turned on, called by CreateDataFrame()
    // (which is in turn called by a stream) to decrease this session's
    // send window size by |delta_window_size|, which must be at least 1
    // and at most kMaxSpdyFrameChunkSize.  |delta_window_size| must not
    // cause this session's send window size to go negative.
    //
    // If session flow control is turned off, this must not be called.
    void DecreaseSendWindowSize(int32 delta_window_size);
  
    // Called when bytes are consumed by the delegate from a SpdyBuffer
    // containing received data. Increases the receive window size
    // accordingly.
    //
    // If session flow control is turned off, this must not be called.
    void OnReadBufferConsumed(size_t consume_size,
                              SpdyBuffer::ConsumeSource consume_source);
  
    // Called by OnReadBufferConsume to increase this session's receive
    // window size by |delta_window_size|, which must be at least 1 and
    // must not cause this session's receive window size to overflow,
    // possibly also sending a WINDOW_UPDATE frame. Also called during
    // initialization to set the initial receive window size.
    //
    // If session flow control is turned off, this must not be called.
    void IncreaseRecvWindowSize(int32 delta_window_size);
  
    // Called by OnStreamFrameData (which is in turn called by the
    // framer) to decrease this session's receive window size by
    // |delta_window_size|, which must be at least 1 and must not cause
    // this session's receive window size to go negative.
    //
    // If session flow control is turned off, this must not be called.
    void DecreaseRecvWindowSize(int32 delta_window_size);
  
    // Queue a send-stalled stream for possibly resuming once we're not
    // send-stalled anymore.
    void QueueSendStalledStream(const SpdyStream& stream);
  
    // Go through the queue of send-stalled streams and try to resume as
    // many as possible.
    void ResumeSendStalledStreams();
  
    // Returns the next stream to possibly resume, or 0 if the queue is
    // empty.
    SpdyStreamId PopStreamToPossiblyResume();
  
    // --------------------------
    // Helper methods for testing
    // --------------------------
  
    void set_connection_at_risk_of_loss_time(base::TimeDelta duration) {
      connection_at_risk_of_loss_time_ = duration;
    }
  
    void set_hung_interval(base::TimeDelta duration) {
      hung_interval_ = duration;
    }
  
    int64 pings_in_flight() const { return pings_in_flight_; }
  
    uint32 next_ping_id() const { return next_ping_id_; }
  
    base::TimeTicks last_activity_time() const { return last_activity_time_; }
  
    bool check_ping_status_pending() const { return check_ping_status_pending_; }
  
    size_t max_concurrent_streams() const { return max_concurrent_streams_; }
  
    // Returns the SSLClientSocket that this SPDY session sits on top of,
    // or NULL, if the transport is not SSL.
    SSLClientSocket* GetSSLClientSocket() const;
  
    // Whether Do{Read,Write}Loop() is in the call stack. Useful for
    // making sure we don't destroy ourselves prematurely in that case.
    bool in_io_loop_;
  
    // The key used to identify this session.
    const SpdySessionKey spdy_session_key_;
  
    // Set set of SpdySessionKeys for which this session has serviced
    // requests.
    std::set<SpdySessionKey> pooled_aliases_;
  
    // |pool_| owns us, therefore its lifetime must exceed ours.  We set
    // this to NULL after we are removed from the pool.
    SpdySessionPool* pool_;
    const base::WeakPtr<HttpServerProperties> http_server_properties_;
  
    // The socket handle for this session.
    scoped_ptr<ClientSocketHandle> connection_;
  
    // The read buffer used to read data from the socket.
    scoped_refptr<IOBuffer> read_buffer_;
  
    SpdyStreamId stream_hi_water_mark_;  // The next stream id to use.
  
    // Queue, for each priority, of pending stream requests that have
    // not yet been satisfied.
    PendingStreamRequestQueue pending_create_stream_queues_[NUM_PRIORITIES];
  
    // Map from stream id to all active streams.  Streams are active in the sense
    // that they have a consumer (typically SpdyNetworkTransaction and regardless
    // of whether or not there is currently any ongoing IO [might be waiting for
    // the server to start pushing the stream]) or there are still network events
    // incoming even though the consumer has already gone away (cancellation).
    //
    // |active_streams_| owns all its SpdyStream objects.
    //
    // TODO(willchan): Perhaps we should separate out cancelled streams and move
    // them into a separate ActiveStreamMap, and not deliver network events to
    // them?
    ActiveStreamMap active_streams_;
  
    // (Bijective) map from the URL to the ID of the streams that have
    // already started to be pushed by the server, but do not have
    // consumers yet. Contains a subset of |active_streams_|.
    PushedStreamMap unclaimed_pushed_streams_;
  
    // Set of all created streams but that have not yet sent any frames.
    //
    // |created_streams_| owns all its SpdyStream objects.
    CreatedStreamSet created_streams_;
  
    // The write queue.
    SpdyWriteQueue write_queue_;
  
    // Data for the frame we are currently sending.
  
    // The buffer we're currently writing.
    scoped_ptr<SpdyBuffer> in_flight_write_;
    // The type of the frame in |in_flight_write_|.
    SpdyFrameType in_flight_write_frame_type_;
    // The size of the frame in |in_flight_write_|.
    size_t in_flight_write_frame_size_;
    // The stream to notify when |in_flight_write_| has been written to
    // the socket completely.
    base::WeakPtr<SpdyStream> in_flight_write_stream_;
  
    // Flag if we're using an SSL connection for this SpdySession.
    bool is_secure_;
  
    // Certificate error code when using a secure connection.
    int certificate_error_code_;
  
    // Spdy Frame state.
    scoped_ptr<BufferedSpdyFramer> buffered_spdy_framer_;
  
    // The state variables.
    AvailabilityState availability_state_;
    ReadState read_state_;
    WriteState write_state_;
  
    // If the session is closing (i.e., |availability_state_| is STATE_DRAINING),
    // then |error_on_close_| holds the error with which it was closed, which
    // may be OK (upon a polite GOAWAY) or an error < ERR_IO_PENDING otherwise.
    // Initialized to OK.
    Error error_on_close_;
  
    // Limits
    size_t max_concurrent_streams_;  // 0 if no limit
    size_t max_concurrent_streams_limit_;
  
    // Some statistics counters for the session.
    int streams_initiated_count_;
    int streams_pushed_count_;
    int streams_pushed_and_claimed_count_;
    int streams_abandoned_count_;
  
    // |total_bytes_received_| keeps track of all the bytes read by the
    // SpdySession. It is used by the |Net.SpdySettingsCwnd...| histograms.
    int total_bytes_received_;
  
    bool sent_settings_;      // Did this session send settings when it started.
    bool received_settings_;  // Did this session receive at least one settings
                              // frame.
    int stalled_streams_;     // Count of streams that were ever stalled.
  
    // Count of all pings on the wire, for which we have not gotten a response.
    int64 pings_in_flight_;
  
    // This is the next ping_id (unique_id) to be sent in PING frame.
    uint32 next_ping_id_;
  
    // This is the last time we have sent a PING.
    base::TimeTicks last_ping_sent_time_;
  
    // This is the last time we had activity in the session.
    base::TimeTicks last_activity_time_;
  
    // This is the length of the last compressed frame.
    size_t last_compressed_frame_len_;
  
    // This is the next time that unclaimed push streams should be checked for
    // expirations.
    base::TimeTicks next_unclaimed_push_stream_sweep_time_;
  
    // Indicate if we have already scheduled a delayed task to check the ping
    // status.
    bool check_ping_status_pending_;
  
    // Whether to send the (HTTP/2) connection header prefix.
    bool send_connection_header_prefix_;
  
    // The (version-dependent) flow control state.
    FlowControlState flow_control_state_;
  
    // Initial send window size for this session's streams. Can be
    // changed by an arriving SETTINGS frame. Newly created streams use
    // this value for the initial send window size.
    int32 stream_initial_send_window_size_;
  
    // Initial receive window size for this session's streams. There are
    // plans to add a command line switch that would cause a SETTINGS
    // frame with window size announcement to be sent on startup. Newly
    // created streams will use this value for the initial receive
    // window size.
    int32 stream_initial_recv_window_size_;
  
    // Session flow control variables. All zero unless session flow
    // control is turned on.
    int32 session_send_window_size_;
    int32 session_recv_window_size_;
    int32 session_unacked_recv_window_bytes_;
  
    // A queue of stream IDs that have been send-stalled at some point
    // in the past.
    std::deque<SpdyStreamId> stream_send_unstall_queue_[NUM_PRIORITIES];
  
    BoundNetLog net_log_;
  
    // Outside of tests, these should always be true.
    bool verify_domain_authentication_;
    bool enable_sending_initial_data_;
    bool enable_compression_;
    bool enable_ping_based_connection_checking_;
  
    // The SPDY protocol used. Always between kProtoSPDYMinimumVersion and
    // kProtoSPDYMaximumVersion.
    NextProto protocol_;
  
    // |connection_at_risk_of_loss_time_| is an optimization to avoid sending
    // wasteful preface pings (when we just got some data).
    //
    // If it is zero (the most conservative figure), then we always send the
    // preface ping (when none are in flight).
    //
    // It is common for TCP/IP sessions to time out in about 3-5 minutes.
    // Certainly if it has been more than 3 minutes, we do want to send a preface
    // ping.
    //
    // We don't think any connection will time out in under about 10 seconds. So
    // this might as well be set to something conservative like 10 seconds. Later,
    // we could adjust it to send fewer pings perhaps.
    base::TimeDelta connection_at_risk_of_loss_time_;
  
    // The amount of time that we are willing to tolerate with no activity (of any
    // form), while there is a ping in flight, before we declare the connection to
    // be hung. TODO(rtenneti): When hung, instead of resetting connection, race
    // to build a new connection, and see if that completes before we (finally)
    // get a PING response (http://crbug.com/127812).
    base::TimeDelta hung_interval_;
  
    // This SPDY proxy is allowed to push resources from origins that are
    // different from those of their associated streams.
    HostPortPair trusted_spdy_proxy_;
  
    TimeFunc time_func_;
  
    // Used for posting asynchronous IO tasks.  We use this even though
    // SpdySession is refcounted because we don't need to keep the SpdySession
    // alive if the last reference is within a RunnableMethod.  Just revoke the
    // method.
    base::WeakPtrFactory<SpdySession> weak_factory_;
  };
  
  }  // namespace net
  
  #endif  // NET_SPDY_SPDY_SESSION_H_
  