diff --git a/quic/core/quic_constants.h b/quic/core/quic_constants.h
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+// 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 "base/macros.h"
+#include "net/third_party/quiche/src/quic/core/quic_types.h"
+#include "net/third_party/quiche/src/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 kNumMicrosPerMilli = 1000;
+const uint64_t kNumMicrosPerSecond = 1000 * 1000;
+
+// 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, 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 kMaxPacketSize = 1452;
+// The maximum packet size of any QUIC packet over IPv4.
+// 1500(Ethernet) - 20(IPv4 header) - 8(UDP header) = 1472.
+const QuicByteCount kMaxV4PacketSize = 1472;
+// ETH_MAX_MTU - MAX(sizeof(iphdr), sizeof(ip6_hdr)) - sizeof(udphdr).
+const QuicByteCount kMaxGsoPacketSize = 65535 - 40 - 8;
+// 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;
+
+// Minimum size of initial flow control window, for both stream and session.
+const uint32_t kMinimumFlowControlSendWindow = 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
+
+// Default limit on the size of uncompressed headers.
+const QuicByteCount kDefaultMaxUncompressedHeaderSize = 16 * 1024;  // 16 KB
+
+// Minimum size of the CWND, in packets, when doing bandwidth resumption.
+const QuicPacketCount kMinCongestionWindowForBandwidthResumption = 10;
+
+// Maximum number of tracked packets.
+const QuicPacketCount kMaxTrackedPackets = 10000;
+
+// 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 15 seconds.
+const uint32_t kMaxInitialRoundTripTimeUs = 15 * 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;
+
+// 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;
+
+// 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 default idle timeout.
+const int64_t kDefaultIdleTimeoutSecs = 30;
+// 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 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
+// TODO(fkastenholz): Should update this to 64 bits for IETF Quic.
+const QuicStreamId kMaxQuicStreamId = 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;
+
+// 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;
+
+}  // namespace quic
+
+#endif  // QUICHE_QUIC_CORE_QUIC_CONSTANTS_H_