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 QUICHE_QUIC_CORE_QUIC_CONSTANTS_H_
  #define QUICHE_QUIC_CORE_QUIC_CONSTANTS_H_
  
  #include <stddef.h>
  
  #include <cstdint>
  #include <limits>
  
  #include "quic/core/quic_types.h"
  #include "quic/platform/api/quic_export.h"
  
  // Definitions of constant values used throughout the QUIC code.
  
  namespace quic {
  
  // Simple time constants.
  const uint64_t kNumSecondsPerMinute = 60;
  const uint64_t kNumSecondsPerHour = kNumSecondsPerMinute * 60;
  const uint64_t kNumSecondsPerWeek = kNumSecondsPerHour * 24 * 7;
  const uint64_t kNumMillisPerSecond = 1000;
  const uint64_t kNumMicrosPerMilli = 1000;
  const uint64_t kNumMicrosPerSecond = kNumMicrosPerMilli * kNumMillisPerSecond;
  
  // Default number of connections for N-connection emulation.
  const uint32_t kDefaultNumConnections = 2;
  // Default initial maximum size in bytes of a QUIC packet.
  const QuicByteCount kDefaultMaxPacketSize = 1350;
  // Default initial maximum size in bytes of a QUIC packet for servers.
  const QuicByteCount kDefaultServerMaxPacketSize = 1000;
  // Maximum transmission unit on Ethernet.
  const QuicByteCount kEthernetMTU = 1500;
  // The maximum packet size of any QUIC packet over IPv6, based on ethernet's max
  // size, minus the IP and UDP headers. IPv6 has a 40 byte header, UDP adds an
  // additional 8 bytes.  This is a total overhead of 48 bytes.  Ethernet's
  // max packet size is 1500 bytes,  1500 - 48 = 1452.
  const QuicByteCount kMaxV6PacketSize = 1452;
  // The maximum packet size of any QUIC packet over IPv4.
  // 1500(Ethernet) - 20(IPv4 header) - 8(UDP header) = 1472.
  const QuicByteCount kMaxV4PacketSize = 1472;
  // The maximum incoming packet size allowed.
  const QuicByteCount kMaxIncomingPacketSize = kMaxV4PacketSize;
  // The maximum outgoing packet size allowed.
  const QuicByteCount kMaxOutgoingPacketSize = kMaxV6PacketSize;
  // ETH_MAX_MTU - MAX(sizeof(iphdr), sizeof(ip6_hdr)) - sizeof(udphdr).
  const QuicByteCount kMaxGsoPacketSize = 65535 - 40 - 8;
  // The maximal IETF DATAGRAM frame size we'll accept. Choosing 2^16 ensures
  // that it is greater than the biggest frame we could ever fit in a QUIC packet.
  const QuicByteCount kMaxAcceptedDatagramFrameSize = 65536;
  // Default value of the max_packet_size transport parameter if it is not
  // transmitted.
  const QuicByteCount kDefaultMaxPacketSizeTransportParam = 65527;
  // Default maximum packet size used in the Linux TCP implementation.
  // Used in QUIC for congestion window computations in bytes.
  const QuicByteCount kDefaultTCPMSS = 1460;
  const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS;
  // The minimum size of a packet which can elicit a version negotiation packet,
  // as per section 8.1 of the QUIC spec.
  const QuicByteCount kMinPacketSizeForVersionNegotiation = 1200;
  
  // We match SPDY's use of 32 (since we'd compete with SPDY).
  const QuicPacketCount kInitialCongestionWindow = 32;
  
  // Do not allow initial congestion window to be greater than 200 packets.
  const QuicPacketCount kMaxInitialCongestionWindow = 200;
  
  // Do not allow initial congestion window to be smaller than 10 packets.
  const QuicPacketCount kMinInitialCongestionWindow = 10;
  
  // Minimum size of initial flow control window, for both stream and session.
  // This is only enforced when version.AllowsLowFlowControlLimits() is false.
  const QuicByteCount kMinimumFlowControlSendWindow = 16 * 1024;  // 16 KB
  // Default size of initial flow control window, for both stream and session.
  const QuicByteCount kDefaultFlowControlSendWindow = 16 * 1024;  // 16 KB
  
  // Maximum flow control receive window limits for connection and stream.
  const QuicByteCount kStreamReceiveWindowLimit = 16 * 1024 * 1024;   // 16 MB
  const QuicByteCount kSessionReceiveWindowLimit = 24 * 1024 * 1024;  // 24 MB
  
  // Minimum size of the CWND, in packets, when doing bandwidth resumption.
  const QuicPacketCount kMinCongestionWindowForBandwidthResumption = 10;
  
  // Default size of the socket receive buffer in bytes.
  const QuicByteCount kDefaultSocketReceiveBuffer = 1024 * 1024;
  
  // Don't allow a client to suggest an RTT shorter than 10ms.
  const uint32_t kMinInitialRoundTripTimeUs = 10 * kNumMicrosPerMilli;
  
  // Don't allow a client to suggest an RTT longer than 1 second.
  const uint32_t kMaxInitialRoundTripTimeUs = kNumMicrosPerSecond;
  
  // Maximum number of open streams per connection.
  const size_t kDefaultMaxStreamsPerConnection = 100;
  
  // Number of bytes reserved for public flags in the packet header.
  const size_t kPublicFlagsSize = 1;
  // Number of bytes reserved for version number in the packet header.
  const size_t kQuicVersionSize = 4;
  
  // Minimum number of active connection IDs that an end point can maintain.
  const uint32_t kMinNumOfActiveConnectionIds = 2;
  
  // Length of the retry integrity tag in bytes.
  // https://tools.ietf.org/html/draft-ietf-quic-transport-25#section-17.2.5
  const size_t kRetryIntegrityTagLength = 16;
  
  // By default, UnackedPacketsMap allocates buffer of 64 after the first packet
  // is added.
  const int kDefaultUnackedPacketsInitialCapacity = 64;
  
  // Signifies that the QuicPacket will contain version of the protocol.
  const bool kIncludeVersion = true;
  // Signifies that the QuicPacket will include a diversification nonce.
  const bool kIncludeDiversificationNonce = true;
  
  // Header key used to identify final offset on data stream when sending HTTP/2
  // trailing headers over QUIC.
  QUIC_EXPORT_PRIVATE extern const char* const kFinalOffsetHeaderKey;
  
  // Default maximum delayed ack time, in ms.
  // Uses a 25ms delayed ack timer. Helps with better signaling
  // in low-bandwidth (< ~384 kbps), where an ack is sent per packet.
  const int64_t kDefaultDelayedAckTimeMs = 25;
  
  // Default minimum delayed ack time, in ms (used only for sender control of ack
  // frequency).
  const uint32_t kDefaultMinAckDelayTimeMs = 5;
  
  // Default shift of the ACK delay in the IETF QUIC ACK frame.
  const uint32_t kDefaultAckDelayExponent = 3;
  
  // Minimum tail loss probe time in ms.
  static const int64_t kMinTailLossProbeTimeoutMs = 10;
  
  // The timeout before the handshake succeeds.
  const int64_t kInitialIdleTimeoutSecs = 5;
  // The maximum idle timeout that can be negotiated.
  const int64_t kMaximumIdleTimeoutSecs = 60 * 10;  // 10 minutes.
  // The default timeout for a connection until the crypto handshake succeeds.
  const int64_t kMaxTimeForCryptoHandshakeSecs = 10;  // 10 secs.
  
  // Default limit on the number of undecryptable packets the connection buffers
  // before the CHLO/SHLO arrive.
  const size_t kDefaultMaxUndecryptablePackets = 10;
  
  // Default ping timeout.
  const int64_t kPingTimeoutSecs = 15;  // 15 secs.
  
  // Minimum number of RTTs between Server Config Updates (SCUP) sent to client.
  const int kMinIntervalBetweenServerConfigUpdatesRTTs = 10;
  
  // Minimum time between Server Config Updates (SCUP) sent to client.
  const int kMinIntervalBetweenServerConfigUpdatesMs = 1000;
  
  // Minimum number of packets between Server Config Updates (SCUP).
  const int kMinPacketsBetweenServerConfigUpdates = 100;
  
  // The number of open streams that a server will accept is set to be slightly
  // larger than the negotiated limit. Immediately closing the connection if the
  // client opens slightly too many streams is not ideal: the client may have sent
  // a FIN that was lost, and simultaneously opened a new stream. The number of
  // streams a server accepts is a fixed increment over the negotiated limit, or a
  // percentage increase, whichever is larger.
  const float kMaxStreamsMultiplier = 1.1f;
  const int kMaxStreamsMinimumIncrement = 10;
  
  // Available streams are ones with IDs less than the highest stream that has
  // been opened which have neither been opened or reset. The limit on the number
  // of available streams is 10 times the limit on the number of open streams.
  const int kMaxAvailableStreamsMultiplier = 10;
  
  // Track the number of promises that are not yet claimed by a
  // corresponding get.  This must be smaller than
  // kMaxAvailableStreamsMultiplier, because RST on a promised stream my
  // create available streams entries.
  const int kMaxPromisedStreamsMultiplier = kMaxAvailableStreamsMultiplier - 1;
  
  // TCP RFC calls for 1 second RTO however Linux differs from this default and
  // define the minimum RTO to 200ms, we will use the same until we have data to
  // support a higher or lower value.
  static const int64_t kMinRetransmissionTimeMs = 200;
  // The delayed ack time must not be greater than half the min RTO.
  static_assert(kDefaultDelayedAckTimeMs <= kMinRetransmissionTimeMs / 2,
                "Delayed ack time must be less than or equal half the MinRTO");
  
  // We define an unsigned 16-bit floating point value, inspired by IEEE floats
  // (http://en.wikipedia.org/wiki/Half_precision_floating-point_format),
  // with 5-bit exponent (bias 1), 11-bit mantissa (effective 12 with hidden
  // bit) and denormals, but without signs, transfinites or fractions. Wire format
  // 16 bits (little-endian byte order) are split into exponent (high 5) and
  // mantissa (low 11) and decoded as:
  //   uint64_t value;
  //   if (exponent == 0) value = mantissa;
  //   else value = (mantissa | 1 << 11) << (exponent - 1)
  const int kUFloat16ExponentBits = 5;
  const int kUFloat16MaxExponent = (1 << kUFloat16ExponentBits) - 2;     // 30
  const int kUFloat16MantissaBits = 16 - kUFloat16ExponentBits;          // 11
  const int kUFloat16MantissaEffectiveBits = kUFloat16MantissaBits + 1;  // 12
  const uint64_t kUFloat16MaxValue =  // 0x3FFC0000000
      ((UINT64_C(1) << kUFloat16MantissaEffectiveBits) - 1)
      << kUFloat16MaxExponent;
  
  // kDiversificationNonceSize is the size, in bytes, of the nonce that a server
  // may set in the packet header to ensure that its INITIAL keys are not
  // duplicated.
  const size_t kDiversificationNonceSize = 32;
  
  // The largest gap in packets we'll accept without closing the connection.
  // This will likely have to be tuned.
  const QuicPacketCount kMaxPacketGap = 5000;
  
  // The max number of sequence number intervals that
  // QuicPeerIssuedConnetionIdManager can maintain.
  const size_t kMaxNumConnectionIdSequenceNumberIntervals = 20;
  
  // The maximum number of random padding bytes to add.
  const QuicByteCount kMaxNumRandomPaddingBytes = 256;
  
  // The size of stream send buffer data slice size in bytes. A data slice is
  // piece of stream data stored in contiguous memory, and a stream frame can
  // contain data from multiple data slices.
  const QuicByteCount kQuicStreamSendBufferSliceSize = 4 * 1024;
  
  // For When using Random Initial Packet Numbers, they can start
  // anyplace in the range 1...((2^31)-1) or 0x7fffffff
  QUIC_EXPORT_PRIVATE QuicPacketNumber MaxRandomInitialPacketNumber();
  
  // Used to represent an invalid or no control frame id.
  const QuicControlFrameId kInvalidControlFrameId = 0;
  
  // The max length a stream can have.
  const QuicByteCount kMaxStreamLength = (UINT64_C(1) << 62) - 1;
  
  // The max value that can be encoded using IETF Var Ints.
  const uint64_t kMaxIetfVarInt = UINT64_C(0x3fffffffffffffff);
  
  // The maximum stream id value that is supported - (2^32)-1
  const QuicStreamId kMaxQuicStreamId = 0xffffffff;
  
  // The maximum value that can be stored in a 32-bit QuicStreamCount.
  const QuicStreamCount kMaxQuicStreamCount = 0xffffffff;
  
  // Number of bytes reserved for packet header type.
  const size_t kPacketHeaderTypeSize = 1;
  
  // Number of bytes reserved for connection ID length.
  const size_t kConnectionIdLengthSize = 1;
  
  // Minimum length of random bytes in IETF stateless reset packet.
  const size_t kMinRandomBytesLengthInStatelessReset = 24;
  
  // Maximum length allowed for the token in a NEW_TOKEN frame.
  const size_t kMaxNewTokenTokenLength = 0xffff;
  
  // Default initial rtt used before any samples are received.
  const int kInitialRttMs = 100;
  
  // Default threshold of packet reordering before a packet is declared lost.
  static const QuicPacketCount kDefaultPacketReorderingThreshold = 3;
  
  // Default fraction (1/4) of an RTT the algorithm waits before determining a
  // packet is lost due to early retransmission by time based loss detection.
  static const int kDefaultLossDelayShift = 2;
  
  // Default fraction (1/8) of an RTT when doing IETF loss detection.
  static const int kDefaultIetfLossDelayShift = 3;
  
  // Maximum number of retransmittable packets received before sending an ack.
  const QuicPacketCount kDefaultRetransmittablePacketsBeforeAck = 2;
  // Wait for up to 10 retransmittable packets before sending an ack.
  const QuicPacketCount kMaxRetransmittablePacketsBeforeAck = 10;
  // Minimum number of packets received before ack decimation is enabled.
  // This intends to avoid the beginning of slow start, when CWNDs may be
  // rapidly increasing.
  const QuicPacketCount kMinReceivedBeforeAckDecimation = 100;
  // One quarter RTT delay when doing ack decimation.
  const float kAckDecimationDelay = 0.25;
  
  // The default alarm granularity assumed by QUIC code.
  const QuicTime::Delta kAlarmGranularity = QuicTime::Delta::FromMilliseconds(1);
  
  // Maximum number of unretired connection IDs a connection can have.
  const size_t kMaxNumConnectonIdsInUse = 10u;
  
  // Packet number of first sending packet of a connection. Please note, this
  // cannot be used as first received packet because peer can choose its starting
  // packet number.
  QUIC_EXPORT_PRIVATE QuicPacketNumber FirstSendingPacketNumber();
  
  // Used by clients to tell if a public reset is sent from a Google frontend.
  QUIC_EXPORT_PRIVATE extern const char* const kEPIDGoogleFrontEnd;
  QUIC_EXPORT_PRIVATE extern const char* const kEPIDGoogleFrontEnd0;
  
  // HTTP/3 Datagrams.
  enum : QuicDatagramFlowId {
    kFirstDatagramFlowIdClient = 0,
    kFirstDatagramFlowIdServer = 1,
    kDatagramFlowIdIncrement = 2,
  };
  
  }  // namespace quic
  
  #endif  // QUICHE_QUIC_CORE_QUIC_CONSTANTS_H_
  