/*
 * ngtcp2
 *
 * Copyright (c) 2017 ngtcp2 contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
#ifndef NGTCP2_PKT_H
#define NGTCP2_PKT_H

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif /* defined(HAVE_CONFIG_H) */

#include <ngtcp2/ngtcp2.h>

/* QUIC header macros */
#define NGTCP2_HEADER_FORM_BIT 0x80
#define NGTCP2_FIXED_BIT_MASK 0x40
#define NGTCP2_PKT_NUMLEN_MASK 0x03

/* Long header specific macros */
#define NGTCP2_LONG_TYPE_MASK 0x30
#define NGTCP2_LONG_RESERVED_BIT_MASK 0x0c

/* Short header specific macros */
#define NGTCP2_SHORT_RESERVED_BIT_MASK 0x18
#define NGTCP2_SHORT_KEY_PHASE_BIT 0x04

/* NGTCP2_SR_TYPE is a Type field of Stateless Reset. */
#define NGTCP2_SR_TYPE 0x1f

/* NGTCP2_MIN_LONG_HEADERLEN is the minimum length of long header.
   That is (1|1|TT|RR|PP)<1> + VERSION<4> + DCIL<1> + SCIL<1> +
   LENGTH<1> + PKN<1> */
#define NGTCP2_MIN_LONG_HEADERLEN (1 + 4 + 1 + 1 + 1 + 1)

/* STREAM frame specific macros */
#define NGTCP2_STREAM_FIN_BIT 0x01
#define NGTCP2_STREAM_LEN_BIT 0x02
#define NGTCP2_STREAM_OFF_BIT 0x04

/* NGTCP2_MIN_QUIC_PKTLEN is the minimum length of a valid QUIC
   packet. */
#define NGTCP2_MIN_QUIC_PKTLEN 21

/* NGTCP2_STREAM_OVERHEAD is the maximum number of bytes required
   other than payload for STREAM frame.  That is from type field to
   the beginning of the payload. */
#define NGTCP2_STREAM_OVERHEAD (1 + 8 + 8 + 8)

/* NGTCP2_CRYPTO_OVERHEAD is the maximum number of bytes required
   other than payload for CRYPTO frame.  That is from type field to
   the beginning of the payload. */
#define NGTCP2_CRYPTO_OVERHEAD (1 + 8 + 8)

/* NGTCP2_DATAGRAM_OVERHEAD is the maximum number of bytes required
   other than payload for DATAGRAM frame.  That is from type field to
   the beginning of the payload. */
#define NGTCP2_DATAGRAM_OVERHEAD (1 + 8)

/* NGTCP2_MAX_SERVER_STREAM_ID_BIDI is the maximum bidirectional
   server stream ID. */
#define NGTCP2_MAX_SERVER_STREAM_ID_BIDI ((int64_t)0x3ffffffffffffffdll)
/* NGTCP2_MAX_CLIENT_STREAM_ID_BIDI is the maximum bidirectional
   client stream ID. */
#define NGTCP2_MAX_CLIENT_STREAM_ID_BIDI ((int64_t)0x3ffffffffffffffcll)
/* NGTCP2_MAX_SERVER_STREAM_ID_UNI is the maximum unidirectional
   server stream ID. */
#define NGTCP2_MAX_SERVER_STREAM_ID_UNI ((int64_t)0x3fffffffffffffffll)
/* NGTCP2_MAX_CLIENT_STREAM_ID_UNI is the maximum unidirectional
   client stream ID. */
#define NGTCP2_MAX_CLIENT_STREAM_ID_UNI ((int64_t)0x3ffffffffffffffell)

/* NGTCP2_MAX_NUM_ACK_RANGES is the maximum number of Additional ACK
   ranges which this library can create, or decode. */
#define NGTCP2_MAX_ACK_RANGES 32

/* NGTCP2_MAX_PKT_NUM is the maximum packet number. */
#define NGTCP2_MAX_PKT_NUM ((int64_t)((1ll << 62) - 1))

/* NGTCP2_MIN_PKT_EXPANDLEN is the minimum packet size expansion to
   hide/trigger Stateless Reset. */
#define NGTCP2_MIN_PKT_EXPANDLEN 22

/* NGTCP2_RETRY_TAGLEN is the length of Retry packet integrity tag. */
#define NGTCP2_RETRY_TAGLEN 16

/* NGTCP2_PKT_LENGTHLEN is the number of bytes that is occupied by
   Length field in Long packet header. */
#define NGTCP2_PKT_LENGTHLEN 4

/* NGTCP2_PKT_TYPE_INITIAL_V1 is Initial long header packet type for
   QUIC v1. */
#define NGTCP2_PKT_TYPE_INITIAL_V1 0x0
/* NGTCP2_PKT_TYPE_0RTT_V1 is 0RTT long header packet type for QUIC
   v1. */
#define NGTCP2_PKT_TYPE_0RTT_V1 0x1
/* NGTCP2_PKT_TYPE_HANDSHAKE_V1 is Handshake long header packet type
   for QUIC v1. */
#define NGTCP2_PKT_TYPE_HANDSHAKE_V1 0x2
/* NGTCP2_PKT_TYPE_RETRY_V1 is Retry long header packet type for QUIC
   v1. */
#define NGTCP2_PKT_TYPE_RETRY_V1 0x3

/* NGTCP2_PKT_TYPE_INITIAL_V2 is Initial long header packet type for
   QUIC v2. */
#define NGTCP2_PKT_TYPE_INITIAL_V2 0x1
/* NGTCP2_PKT_TYPE_0RTT_V2 is 0RTT long header packet type for QUIC
   v2. */
#define NGTCP2_PKT_TYPE_0RTT_V2 0x2
/* NGTCP2_PKT_TYPE_HANDSHAKE_V2 is Handshake long header packet type
   for QUIC v2. */
#define NGTCP2_PKT_TYPE_HANDSHAKE_V2 0x3
/* NGTCP2_PKT_TYPE_RETRY_V2 is Retry long header packet type for QUIC
   v2. */
#define NGTCP2_PKT_TYPE_RETRY_V2 0x0

/* NGTCP2_MIN_STREAM_DATALEN is the minimum length of STREAM frame to
   avoid too small frame.  It is not always enforced for various
   reasons.  For example, due to flow control, we might have fewer
   bytes available to send.  Therefore, it is only applied when the
   length of data to send is larger than this limit. */
#define NGTCP2_MIN_STREAM_DATALEN 256

/* NGTCP2_MAX_STREAM_DATACNT is the maximum number of ngtcp2_vec that
   a ngtcp2_stream can include. */
#define NGTCP2_MAX_STREAM_DATACNT 256

typedef struct ngtcp2_pcg32 ngtcp2_pcg32;

typedef struct ngtcp2_pkt_retry {
  ngtcp2_cid odcid;
  uint8_t *token;
  size_t tokenlen;
  uint8_t tag[NGTCP2_RETRY_TAGLEN];
} ngtcp2_pkt_retry;

#define NGTCP2_FRAME_PADDING 0x00
#define NGTCP2_FRAME_PING 0x01
#define NGTCP2_FRAME_ACK 0x02
#define NGTCP2_FRAME_ACK_ECN 0x03
#define NGTCP2_FRAME_RESET_STREAM 0x04
#define NGTCP2_FRAME_STOP_SENDING 0x05
#define NGTCP2_FRAME_CRYPTO 0x06
#define NGTCP2_FRAME_NEW_TOKEN 0x07
#define NGTCP2_FRAME_STREAM 0x08
#define NGTCP2_FRAME_MAX_DATA 0x10
#define NGTCP2_FRAME_MAX_STREAM_DATA 0x11
#define NGTCP2_FRAME_MAX_STREAMS_BIDI 0x12
#define NGTCP2_FRAME_MAX_STREAMS_UNI 0x13
#define NGTCP2_FRAME_DATA_BLOCKED 0x14
#define NGTCP2_FRAME_STREAM_DATA_BLOCKED 0x15
#define NGTCP2_FRAME_STREAMS_BLOCKED_BIDI 0x16
#define NGTCP2_FRAME_STREAMS_BLOCKED_UNI 0x17
#define NGTCP2_FRAME_NEW_CONNECTION_ID 0x18
#define NGTCP2_FRAME_RETIRE_CONNECTION_ID 0x19
#define NGTCP2_FRAME_PATH_CHALLENGE 0x1a
#define NGTCP2_FRAME_PATH_RESPONSE 0x1b
#define NGTCP2_FRAME_CONNECTION_CLOSE 0x1c
#define NGTCP2_FRAME_CONNECTION_CLOSE_APP 0x1d
#define NGTCP2_FRAME_HANDSHAKE_DONE 0x1e
#define NGTCP2_FRAME_DATAGRAM 0x30
#define NGTCP2_FRAME_DATAGRAM_LEN 0x31

typedef struct ngtcp2_frame_hd {
  uint64_t type;
} ngtcp2_frame_hd;

/* ngtcp2_stream represents STREAM and CRYPTO frames. */
typedef struct ngtcp2_stream {
  uint64_t type;
  /**
   * flags of decoded STREAM frame.  This gets ignored when encoding
   * STREAM frame.  CRYPTO frame does not include this field, and must
   * set it to 0.
   */
  uint8_t flags;
  /* CRYPTO frame does not include this field, and must set it to
     0. */
  int fin;
  /* CRYPTO frame does not include this field, and must set it to
     0. */
  int64_t stream_id;
  uint64_t offset;
  /* datacnt is the number of elements that data contains.  Although
     the length of data is 1 in this definition, the library may
     allocate extra bytes to hold more elements. */
  size_t datacnt;
  /* data points to ngtcp2_vec array which references data.  If
     datacnt == 0, this field may be NULL. */
  ngtcp2_vec *data;
} ngtcp2_stream;

typedef struct ngtcp2_ack_range {
  uint64_t gap;
  uint64_t len;
} ngtcp2_ack_range;

typedef struct ngtcp2_ack {
  uint64_t type;
  int64_t largest_ack;
  uint64_t ack_delay;
  /**
   * ack_delay_unscaled is an ack_delay multiplied by
   * 2**ack_delay_component * NGTCP2_MICROSECONDS.
   */
  ngtcp2_duration ack_delay_unscaled;
  struct {
    uint64_t ect0;
    uint64_t ect1;
    uint64_t ce;
  } ecn;
  uint64_t first_ack_range;
  size_t rangecnt;
  ngtcp2_ack_range *ranges;
} ngtcp2_ack;

typedef struct ngtcp2_padding {
  uint64_t type;
  /**
   * The length of contiguous PADDING frames.
   */
  size_t len;
} ngtcp2_padding;

typedef struct ngtcp2_reset_stream {
  uint64_t type;
  int64_t stream_id;
  uint64_t app_error_code;
  uint64_t final_size;
} ngtcp2_reset_stream;

typedef struct ngtcp2_connection_close {
  uint64_t type;
  uint64_t error_code;
  uint64_t frame_type;
  size_t reasonlen;
  uint8_t *reason;
} ngtcp2_connection_close;

typedef struct ngtcp2_max_data {
  uint64_t type;
  /**
   * max_data is Maximum Data.
   */
  uint64_t max_data;
} ngtcp2_max_data;

typedef struct ngtcp2_max_stream_data {
  uint64_t type;
  int64_t stream_id;
  uint64_t max_stream_data;
} ngtcp2_max_stream_data;

typedef struct ngtcp2_max_streams {
  uint64_t type;
  uint64_t max_streams;
} ngtcp2_max_streams;

typedef struct ngtcp2_ping {
  uint64_t type;
} ngtcp2_ping;

typedef struct ngtcp2_data_blocked {
  uint64_t type;
  uint64_t offset;
} ngtcp2_data_blocked;

typedef struct ngtcp2_stream_data_blocked {
  uint64_t type;
  int64_t stream_id;
  uint64_t offset;
} ngtcp2_stream_data_blocked;

typedef struct ngtcp2_streams_blocked {
  uint64_t type;
  uint64_t max_streams;
} ngtcp2_streams_blocked;

typedef struct ngtcp2_new_connection_id {
  uint64_t type;
  uint64_t seq;
  uint64_t retire_prior_to;
  ngtcp2_cid cid;
  uint8_t stateless_reset_token[NGTCP2_STATELESS_RESET_TOKENLEN];
} ngtcp2_new_connection_id;

typedef struct ngtcp2_stop_sending {
  uint64_t type;
  int64_t stream_id;
  uint64_t app_error_code;
} ngtcp2_stop_sending;

typedef struct ngtcp2_path_challenge {
  uint64_t type;
  uint8_t data[NGTCP2_PATH_CHALLENGE_DATALEN];
} ngtcp2_path_challenge;

typedef struct ngtcp2_path_response {
  uint64_t type;
  uint8_t data[NGTCP2_PATH_CHALLENGE_DATALEN];
} ngtcp2_path_response;

typedef struct ngtcp2_new_token {
  uint64_t type;
  uint8_t *token;
  size_t tokenlen;
} ngtcp2_new_token;

typedef struct ngtcp2_retire_connection_id {
  uint64_t type;
  uint64_t seq;
} ngtcp2_retire_connection_id;

typedef struct ngtcp2_handshake_done {
  uint64_t type;
} ngtcp2_handshake_done;

typedef struct ngtcp2_datagram {
  uint64_t type;
  /* dgram_id is an opaque identifier chosen by an application. */
  uint64_t dgram_id;
  /* datacnt is the number of elements that data contains. */
  size_t datacnt;
  /* data is a pointer to ngtcp2_vec array that stores data.  If
     datacnt == 0, this field may be NULL.*/
  ngtcp2_vec *data;
} ngtcp2_datagram;

typedef union ngtcp2_frame {
  ngtcp2_frame_hd hd;
  ngtcp2_stream stream;
  ngtcp2_ack ack;
  ngtcp2_padding padding;
  ngtcp2_reset_stream reset_stream;
  ngtcp2_connection_close connection_close;
  ngtcp2_max_data max_data;
  ngtcp2_max_stream_data max_stream_data;
  ngtcp2_max_streams max_streams;
  ngtcp2_ping ping;
  ngtcp2_data_blocked data_blocked;
  ngtcp2_stream_data_blocked stream_data_blocked;
  ngtcp2_streams_blocked streams_blocked;
  ngtcp2_new_connection_id new_connection_id;
  ngtcp2_stop_sending stop_sending;
  ngtcp2_path_challenge path_challenge;
  ngtcp2_path_response path_response;
  ngtcp2_new_token new_token;
  ngtcp2_retire_connection_id retire_connection_id;
  ngtcp2_handshake_done handshake_done;
  ngtcp2_datagram datagram;
} ngtcp2_frame;

typedef struct ngtcp2_pkt_chain ngtcp2_pkt_chain;

/*
 * ngtcp2_pkt_chain is the chain of incoming packets buffered.
 */
struct ngtcp2_pkt_chain {
  ngtcp2_path_storage path;
  ngtcp2_pkt_info pi;
  ngtcp2_pkt_chain *next;
  uint8_t *pkt;
  /* pktlen is length of a QUIC packet. */
  size_t pktlen;
  /* dgramlen is length of UDP datagram payload that a QUIC packet is
     included. */
  size_t dgramlen;
  ngtcp2_tstamp ts;
};

/*
 * ngtcp2_pkt_chain_new allocates ngtcp2_pkt_chain objects, and
 * assigns its pointer to |*ppc|.  The content of buffer pointed by
 * |pkt| of length |pktlen| is copied into |*ppc|.  The packet is
 * obtained via the network |path|.  The values of path->local and
 * path->remote are copied into |*ppc|.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_NOMEM
 *     Out of memory.
 */
int ngtcp2_pkt_chain_new(ngtcp2_pkt_chain **ppc, const ngtcp2_path *path,
                         const ngtcp2_pkt_info *pi, const uint8_t *pkt,
                         size_t pktlen, size_t dgramlen, ngtcp2_tstamp ts,
                         const ngtcp2_mem *mem);

/*
 * ngtcp2_pkt_chain_del deallocates |pc|.  It also frees the memory
 * pointed by |pc|.
 */
void ngtcp2_pkt_chain_del(ngtcp2_pkt_chain *pc, const ngtcp2_mem *mem);

/*
 * ngtcp2_pkt_hd_init initializes |hd| with the given values.  If
 * |dcid| and/or |scid| is NULL, Destination Connection ID and/or
 * Source Connection ID of |hd| is empty respectively.  |pkt_numlen|
 * is the number of bytes used to encode |pkt_num| and either 1, 2, or
 * 4.  |version| is QUIC version for long header.
 */
void ngtcp2_pkt_hd_init(ngtcp2_pkt_hd *hd, uint8_t flags, uint8_t type,
                        const ngtcp2_cid *dcid, const ngtcp2_cid *scid,
                        int64_t pkt_num, size_t pkt_numlen, uint32_t version);

/*
 * ngtcp2_pkt_encode_hd_long encodes |hd| as QUIC long header into
 * |out| which has length |outlen|.  It returns the number of bytes
 * written into |out| if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer is too short
 */
ngtcp2_ssize ngtcp2_pkt_encode_hd_long(uint8_t *out, size_t outlen,
                                       const ngtcp2_pkt_hd *hd);

/*
 * ngtcp2_pkt_encode_hd_short encodes |hd| as QUIC short header into
 * |out| which has length |outlen|.  It returns the number of bytes
 * written into |out| if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer is too short
 */
ngtcp2_ssize ngtcp2_pkt_encode_hd_short(uint8_t *out, size_t outlen,
                                        const ngtcp2_pkt_hd *hd);

/*
 * ngtcp2_frame_decoder is QUIC frame decoder.  For frames that
 * require the external buffers (e.g., ngtcp2_stream and ngtcp2_ack),
 * it provides those buffers on demand.
 */
typedef struct ngtcp2_frame_decoder {
  union {
    ngtcp2_vec data;
    ngtcp2_ack_range ack_ranges[NGTCP2_MAX_ACK_RANGES];
  } buf;
} ngtcp2_frame_decoder;

/**
 * @function
 *
 * `ngtcp2_frame_decoder_decode` decodes a QUIC frame from the buffer
 * pointed by |payload| whose length is |payloadlen|.
 *
 * This function returns the number of bytes read to decode a single
 * frame if it succeeds, or one of the following negative error codes:
 *
 * :enum:`NGTCP2_ERR_FRAME_ENCODING`
 *     Frame is badly formatted; or frame type is unknown; or
 *     |payloadlen| is 0.
 */
ngtcp2_ssize ngtcp2_frame_decoder_decode(ngtcp2_frame_decoder *frd,
                                         ngtcp2_frame *dest,
                                         const uint8_t *payload,
                                         size_t payloadlen);

/**
 * @function
 *
 * `ngtcp2_pkt_encode_frame` encodes a frame |fr| into the buffer
 * pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written to the buffer, or
 * one of the following negative error codes:
 *
 * :enum:`NGTCP2_ERR_NOBUF`
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_frame(uint8_t *out, size_t outlen,
                                     ngtcp2_frame *fr);

/*
 * ngtcp2_pkt_decode_version_negotiation decodes Version Negotiation
 * packet payload |payload| of length |payloadlen|, and stores the
 * result in |dest|.  |dest| must have enough capacity to store the
 * result.  |payloadlen| also must be a multiple of sizeof(uint32_t).
 *
 * This function returns the number of versions written in |dest|.
 */
size_t ngtcp2_pkt_decode_version_negotiation(uint32_t *dest,
                                             const uint8_t *payload,
                                             size_t payloadlen);

/*
 * ngtcp2_pkt_decode_stateless_reset decodes Stateless Reset payload
 * |payload| of length |payloadlen|.  The |payload| must start with
 * Stateless Reset Token.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_INVALID_ARGUMENT
 *     Payloadlen is too short.
 */
int ngtcp2_pkt_decode_stateless_reset(ngtcp2_pkt_stateless_reset *sr,
                                      const uint8_t *payload,
                                      size_t payloadlen);

/*
 * ngtcp2_pkt_decode_retry decodes Retry packet payload |payload| of
 * length |payloadlen|.  The |payload| must start with Retry token
 * field.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_INVALID_ARGUMENT
 *     Payloadlen is too short.
 */
int ngtcp2_pkt_decode_retry(ngtcp2_pkt_retry *dest, const uint8_t *payload,
                            size_t payloadlen);

/*
 * ngtcp2_pkt_decode_stream_frame decodes STREAM frame from |payload|
 * of length |payloadlen|.  The result is stored in the object pointed
 * by |dest|.  STREAM frame must start at payload[0].  This function
 * finishes when it decodes one STREAM frame, and returns the exact
 * number of bytes read to decode a frame if it succeeds, or one of
 * the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include STREAM frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_stream_frame(ngtcp2_stream *dest,
                                            const uint8_t *payload,
                                            size_t payloadlen);

/*
 * ngtcp2_pkt_decode_ack_frame decodes ACK frame from |payload| of
 * length |payloadlen|.  The result is stored in the object pointed by
 * |dest|.  ACK frame must start at payload[0].  This function
 * finishes when it decodes one ACK frame, and returns the exact
 * number of bytes read to decode a frame if it succeeds, or one of
 * the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include ACK frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_ack_frame(ngtcp2_ack *dest,
                                         const uint8_t *payload,
                                         size_t payloadlen);

/*
 * ngtcp2_pkt_decode_padding_frame decodes contiguous PADDING frames
 * from |payload| of length |payloadlen|.  It continues to parse
 * frames as long as the frame type is PADDING.  It finishes when it
 * encounters the frame type which is not PADDING, or all input data
 * is read.  The first byte (payload[0]) must be NGTCP2_FRAME_PADDING.
 * This function returns the exact number of bytes read to decode
 * PADDING frames.
 */
ngtcp2_ssize ngtcp2_pkt_decode_padding_frame(ngtcp2_padding *dest,
                                             const uint8_t *payload,
                                             size_t payloadlen);

/*
 * ngtcp2_pkt_decode_reset_stream_frame decodes RESET_STREAM frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  RESET_STREAM frame must start at
 * payload[0].  This function finishes when it decodes one
 * RESET_STREAM frame, and returns the exact number of bytes read to
 * decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include RESET_STREAM frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_reset_stream_frame(ngtcp2_reset_stream *dest,
                                                  const uint8_t *payload,
                                                  size_t payloadlen);

/*
 * ngtcp2_pkt_decode_connection_close_frame decodes CONNECTION_CLOSE
 * frame from |payload| of length |payloadlen|.  The result is stored
 * in the object pointed by |dest|.  CONNECTION_CLOSE frame must start
 * at payload[0].  This function finishes when it decodes one
 * CONNECTION_CLOSE frame, and returns the exact number of bytes read
 * to decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include CONNECTION_CLOSE frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_connection_close_frame(
  ngtcp2_connection_close *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_max_data_frame decodes MAX_DATA frame from
 * |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  MAX_DATA frame must start at payload[0].
 * This function finishes when it decodes one MAX_DATA frame, and
 * returns the exact number of bytes read to decode a frame if it
 * succeeds, or one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include MAX_DATA frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_max_data_frame(ngtcp2_max_data *dest,
                                              const uint8_t *payload,
                                              size_t payloadlen);

/*
 * ngtcp2_pkt_decode_max_stream_data_frame decodes MAX_STREAM_DATA
 * frame from |payload| of length |payloadlen|.  The result is stored
 * in the object pointed by |dest|.  MAX_STREAM_DATA frame must start
 * at payload[0].  This function finishes when it decodes one
 * MAX_STREAM_DATA frame, and returns the exact number of bytes read
 * to decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include MAX_STREAM_DATA frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_max_stream_data_frame(
  ngtcp2_max_stream_data *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_max_streams_frame decodes MAX_STREAMS frame from
 * |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  MAX_STREAMS frame must start at
 * payload[0].  This function finishes when it decodes one MAX_STREAMS
 * frame, and returns the exact number of bytes read to decode a frame
 * if it succeeds, or one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include MAX_STREAMS frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_max_streams_frame(ngtcp2_max_streams *dest,
                                                 const uint8_t *payload,
                                                 size_t payloadlen);

/*
 * ngtcp2_pkt_decode_ping_frame decodes PING frame from |payload| of
 * length |payloadlen|.  The result is stored in the object pointed by
 * |dest|.  PING frame must start at payload[0].  This function
 * finishes when it decodes one PING frame, and returns the exact
 * number of bytes read to decode a frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_ping_frame(ngtcp2_ping *dest,
                                          const uint8_t *payload,
                                          size_t payloadlen);

/*
 * ngtcp2_pkt_decode_data_blocked_frame decodes DATA_BLOCKED frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  DATA_BLOCKED frame must start at
 * payload[0].  This function finishes when it decodes one
 * DATA_BLOCKED frame, and returns the exact number of bytes read to
 * decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include DATA_BLOCKED frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_data_blocked_frame(ngtcp2_data_blocked *dest,
                                                  const uint8_t *payload,
                                                  size_t payloadlen);

/*
 * ngtcp2_pkt_decode_stream_data_blocked_frame decodes
 * STREAM_DATA_BLOCKED frame from |payload| of length |payloadlen|.
 * The result is stored in the object pointed by |dest|.
 * STREAM_DATA_BLOCKED frame must start at payload[0].  This function
 * finishes when it decodes one STREAM_DATA_BLOCKED frame, and returns
 * the exact number of bytes read to decode a frame if it succeeds, or
 * one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include STREAM_DATA_BLOCKED frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_stream_data_blocked_frame(
  ngtcp2_stream_data_blocked *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_streams_blocked_frame decodes STREAMS_BLOCKED
 * frame from |payload| of length |payloadlen|.  The result is stored
 * in the object pointed by |dest|.  STREAMS_BLOCKED frame must start
 * at payload[0].  This function finishes when it decodes one
 * STREAMS_BLOCKED frame, and returns the exact number of bytes read
 * to decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include STREAMS_BLOCKED frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_streams_blocked_frame(
  ngtcp2_streams_blocked *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_new_connection_id_frame decodes NEW_CONNECTION_ID
 * frame from |payload| of length |payloadlen|.  The result is stored
 * in the object pointed by |dest|.  NEW_CONNECTION_ID frame must
 * start at payload[0].  This function finishes when it decodes one
 * NEW_CONNECTION_ID frame, and returns the exact number of bytes read
 * to decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include NEW_CONNECTION_ID frame; or the
 *     length of Connection ID is strictly less than NGTCP2_MIN_CIDLEN
 *     or greater than NGTCP2_MAX_CIDLEN.
 */
ngtcp2_ssize ngtcp2_pkt_decode_new_connection_id_frame(
  ngtcp2_new_connection_id *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_stop_sending_frame decodes STOP_SENDING frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  STOP_SENDING frame must start at
 * payload[0].  This function finishes when it decodes one
 * STOP_SENDING frame, and returns the exact number of bytes read to
 * decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include STOP_SENDING frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_stop_sending_frame(ngtcp2_stop_sending *dest,
                                                  const uint8_t *payload,
                                                  size_t payloadlen);

/*
 * ngtcp2_pkt_decode_path_challenge_frame decodes PATH_CHALLENGE frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  PATH_CHALLENGE frame must start at
 * payload[0].  This function finishes when it decodes one
 * PATH_CHALLENGE frame, and returns the exact number of bytes read to
 * decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include PATH_CHALLENGE frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_path_challenge_frame(ngtcp2_path_challenge *dest,
                                                    const uint8_t *payload,
                                                    size_t payloadlen);

/*
 * ngtcp2_pkt_decode_path_response_frame decodes PATH_RESPONSE frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  PATH_RESPONSE frame must start at
 * payload[0].  This function finishes when it decodes one
 * PATH_RESPONSE frame, and returns the exact number of bytes read to
 * decode a frame if it succeeds, or one of the following negative
 * error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include PATH_RESPONSE frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_path_response_frame(ngtcp2_path_response *dest,
                                                   const uint8_t *payload,
                                                   size_t payloadlen);

/*
 * ngtcp2_pkt_decode_crypto_frame decodes CRYPTO frame from |payload|
 * of length |payloadlen|.  The result is stored in the object pointed
 * by |dest|.  CRYPTO frame must start at payload[0].  This function
 * finishes when it decodes one CRYPTO frame, and returns the exact
 * number of bytes read to decode a frame if it succeeds, or one of
 * the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include CRYPTO frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_crypto_frame(ngtcp2_stream *dest,
                                            const uint8_t *payload,
                                            size_t payloadlen);

/*
 * ngtcp2_pkt_decode_new_token_frame decodes NEW_TOKEN frame from
 * |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  NEW_TOKEN frame must start at
 * payload[0].  This function finishes when it decodes one NEW_TOKEN
 * frame, and returns the exact number of bytes read to decode a frame
 * if it succeeds, or one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include NEW_TOKEN frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_new_token_frame(ngtcp2_new_token *dest,
                                               const uint8_t *payload,
                                               size_t payloadlen);

/*
 * ngtcp2_pkt_decode_retire_connection_id_frame decodes
 * RETIRE_CONNECTION_ID frame from |payload| of length |payloadlen|.
 * The result is stored in the object pointed by |dest|.
 * RETIRE_CONNECTION_ID frame must start at payload[0].  This function
 * finishes when it decodes one RETIRE_CONNECTION_ID frame, and
 * returns the exact number of bytes read to decode a frame if it
 * succeeds, or one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include RETIRE_CONNECTION_ID frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_retire_connection_id_frame(
  ngtcp2_retire_connection_id *dest, const uint8_t *payload, size_t payloadlen);

/*
 * ngtcp2_pkt_decode_handshake_done_frame decodes HANDSHAKE_DONE frame
 * from |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  HANDSHAKE_DONE frame must start at
 * payload[0].  This function finishes when it decodes one
 * HANDSHAKE_DONE frame, and returns the exact number of bytes read to
 * decode a frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_handshake_done_frame(ngtcp2_handshake_done *dest,
                                                    const uint8_t *payload,
                                                    size_t payloadlen);

/*
 * ngtcp2_pkt_decode_datagram_frame decodes DATAGRAM frame from
 * |payload| of length |payloadlen|.  The result is stored in the
 * object pointed by |dest|.  DATAGRAM frame must start at payload[0].
 * This function finishes when it decodes one DATAGRAM frame, and
 * returns the exact number of bytes read to decode a frame if it
 * succeeds, or one of the following negative error codes:
 *
 * NGTCP2_ERR_FRAME_ENCODING
 *     Payload is too short to include DATAGRAM frame.
 */
ngtcp2_ssize ngtcp2_pkt_decode_datagram_frame(ngtcp2_datagram *dest,
                                              const uint8_t *payload,
                                              size_t payloadlen);

/*
 * ngtcp2_pkt_encode_stream_frame encodes STREAM frame |fr| into the
 * buffer pointed by |out| of length |outlen|.
 *
 * This function assigns <the serialized frame type> &
 * ~NGTCP2_FRAME_STREAM to fr->flags.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_stream_frame(uint8_t *out, size_t outlen,
                                            ngtcp2_stream *fr);

/*
 * ngtcp2_pkt_encode_ack_frame encodes ACK frame |fr| into the buffer
 * pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_ack_frame(uint8_t *out, size_t outlen,
                                         const ngtcp2_ack *fr);

/*
 * ngtcp2_pkt_encode_padding_frame encodes PADDING frame |fr| into the
 * buffer pointed by |out| of length |outlen|.
 *
 * This function encodes consecutive fr->len PADDING frames.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write frame(s).
 */
ngtcp2_ssize ngtcp2_pkt_encode_padding_frame(uint8_t *out, size_t outlen,
                                             const ngtcp2_padding *fr);

/*
 * ngtcp2_pkt_encode_reset_stream_frame encodes RESET_STREAM frame
 * |fr| into the buffer pointed by |out| of length |buflen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_reset_stream_frame(uint8_t *out, size_t outlen,
                                     const ngtcp2_reset_stream *fr);

/*
 * ngtcp2_pkt_encode_connection_close_frame encodes CONNECTION_CLOSE
 * frame |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_connection_close_frame(uint8_t *out, size_t outlen,
                                         const ngtcp2_connection_close *fr);

/*
 * ngtcp2_pkt_encode_max_data_frame encodes MAX_DATA frame |fr| into
 * the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_max_data_frame(uint8_t *out, size_t outlen,
                                              const ngtcp2_max_data *fr);

/*
 * ngtcp2_pkt_encode_max_stream_data_frame encodes MAX_STREAM_DATA
 * frame |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_max_stream_data_frame(uint8_t *out, size_t outlen,
                                        const ngtcp2_max_stream_data *fr);

/*
 * ngtcp2_pkt_encode_max_streams_frame encodes MAX_STREAMS
 * frame |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_max_streams_frame(uint8_t *out, size_t outlen,
                                                 const ngtcp2_max_streams *fr);

/*
 * ngtcp2_pkt_encode_ping_frame encodes PING frame |fr| into the
 * buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_ping_frame(uint8_t *out, size_t outlen,
                                          const ngtcp2_ping *fr);

/*
 * ngtcp2_pkt_encode_data_blocked_frame encodes DATA_BLOCKED frame
 * |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_data_blocked_frame(uint8_t *out, size_t outlen,
                                     const ngtcp2_data_blocked *fr);

/*
 * ngtcp2_pkt_encode_stream_data_blocked_frame encodes
 * STREAM_DATA_BLOCKED frame |fr| into the buffer pointed by |out| of
 * length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_stream_data_blocked_frame(
  uint8_t *out, size_t outlen, const ngtcp2_stream_data_blocked *fr);

/*
 * ngtcp2_pkt_encode_streams_blocked_frame encodes STREAMS_BLOCKED
 * frame |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_streams_blocked_frame(uint8_t *out, size_t outlen,
                                        const ngtcp2_streams_blocked *fr);

/*
 * ngtcp2_pkt_encode_new_connection_id_frame encodes NEW_CONNECTION_ID
 * frame |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_new_connection_id_frame(uint8_t *out, size_t outlen,
                                          const ngtcp2_new_connection_id *fr);

/*
 * ngtcp2_pkt_encode_stop_sending_frame encodes STOP_SENDING frame
 * |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_stop_sending_frame(uint8_t *out, size_t outlen,
                                     const ngtcp2_stop_sending *fr);

/*
 * ngtcp2_pkt_encode_path_challenge_frame encodes PATH_CHALLENGE frame
 * |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_path_challenge_frame(uint8_t *out, size_t outlen,
                                       const ngtcp2_path_challenge *fr);

/*
 * ngtcp2_pkt_encode_path_response_frame encodes PATH_RESPONSE frame
 * |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_path_response_frame(uint8_t *out, size_t outlen,
                                      const ngtcp2_path_response *fr);

/*
 * ngtcp2_pkt_encode_crypto_frame encodes CRYPTO frame |fr| into the
 * buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_crypto_frame(uint8_t *out, size_t outlen,
                                            const ngtcp2_stream *fr);

/*
 * ngtcp2_pkt_encode_new_token_frame encodes NEW_TOKEN frame |fr| into
 * the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_new_token_frame(uint8_t *out, size_t outlen,
                                               const ngtcp2_new_token *fr);

/*
 * ngtcp2_pkt_encode_retire_connection_id_frame encodes
 * RETIRE_CONNECTION_ID frame |fr| into the buffer pointed by |out| of
 * length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_retire_connection_id_frame(
  uint8_t *out, size_t outlen, const ngtcp2_retire_connection_id *fr);

/*
 * ngtcp2_pkt_encode_handshake_done_frame encodes HANDSHAKE_DONE frame
 * |fr| into the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize
ngtcp2_pkt_encode_handshake_done_frame(uint8_t *out, size_t outlen,
                                       const ngtcp2_handshake_done *fr);

/*
 * ngtcp2_pkt_encode_datagram_frame encodes DATAGRAM frame |fr| into
 * the buffer pointed by |out| of length |outlen|.
 *
 * This function returns the number of bytes written if it succeeds,
 * or one of the following negative error codes:
 *
 * NGTCP2_ERR_NOBUF
 *     Buffer does not have enough capacity to write a frame.
 */
ngtcp2_ssize ngtcp2_pkt_encode_datagram_frame(uint8_t *out, size_t outlen,
                                              const ngtcp2_datagram *fr);

/*
 * ngtcp2_pkt_adjust_pkt_num finds the full 62 bits packet number for
 * |pkt_num|, which is encoded in |pkt_numlen| bytes.  The
 * |max_pkt_num| is the highest successfully authenticated packet
 * number.
 */
int64_t ngtcp2_pkt_adjust_pkt_num(int64_t max_pkt_num, int64_t pkt_num,
                                  size_t pkt_numlen);

/*
 * ngtcp2_pkt_validate_ack verifies whether |fr| is malformed or not.
 * |min_pkt_num| is the minimum packet number that a local endpoint
 * sends.  It is an error to receive acknowledgements for a packet
 * less than |min_pkt_num|.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_ACK_FRAME
 *     ACK frame is malformed
 * NGTCP2_ERR_PROTO
 *     |fr| contains a packet number less than |min_pkt_num|.
 */
int ngtcp2_pkt_validate_ack(const ngtcp2_ack *fr, int64_t min_pkt_num);

/*
 * ngtcp2_pkt_stream_max_datalen returns the maximum number of bytes
 * which can be sent for stream denoted by |stream_id|.  |offset| is
 * an offset within the stream.  |len| is the estimated number of
 * bytes to send.  |left| is the size of buffer.  If |left| is too
 * small to write STREAM frame, this function returns (size_t)-1.
 */
size_t ngtcp2_pkt_stream_max_datalen(int64_t stream_id, uint64_t offset,
                                     uint64_t len, size_t left);

/*
 * ngtcp2_pkt_crypto_max_datalen returns the maximum number of bytes
 * which can be sent for crypto stream.  |offset| is an offset within
 * the crypto stream.  |len| is the estimated number of bytes to send.
 * |left| is the size of buffer.  If |left| is too small to write
 * CRYPTO frame, this function returns (size_t)-1.
 */
size_t ngtcp2_pkt_crypto_max_datalen(uint64_t offset, size_t len, size_t left);

/*
 * ngtcp2_pkt_datagram_framelen returns the length of DATAGRAM frame
 * to encode |len| bytes of data.
 */
size_t ngtcp2_pkt_datagram_framelen(size_t len);

/*
 * ngtcp2_pkt_verify_reserved_bits verifies that the first byte |c| of
 * the packet header has the correct reserved bits.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_PROTO
 *     Reserved bits has wrong value.
 */
int ngtcp2_pkt_verify_reserved_bits(uint8_t c);

/*
 * ngtcp2_pkt_encode_pseudo_retry encodes Retry pseudo-packet in the
 * buffer pointed by |dest| of length |destlen|.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_BUF
 *     Buffer is too short.
 */
ngtcp2_ssize ngtcp2_pkt_encode_pseudo_retry(
  uint8_t *dest, size_t destlen, const ngtcp2_pkt_hd *hd, uint8_t unused,
  const ngtcp2_cid *odcid, const uint8_t *token, size_t tokenlen);

/*
 * ngtcp2_pkt_verify_retry_tag verifies Retry packet.  The buffer
 * pointed by |pkt| of length |pktlen| must contain Retry packet
 * including packet header.  The odcid and tag fields of |retry| must
 * be specified.  |aead| must be AEAD_AES_128_GCM.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGTCP2_ERR_PROTO
 *     Verification failed.
 */
int ngtcp2_pkt_verify_retry_tag(uint32_t version, const ngtcp2_pkt_retry *retry,
                                const uint8_t *pkt, size_t pktlen,
                                ngtcp2_encrypt encrypt,
                                const ngtcp2_crypto_aead *aead,
                                const ngtcp2_crypto_aead_ctx *aead_ctx);

/*
 * ngtcp2_pkt_versioned_type returns versioned packet type for a
 * version |version| that corresponds to the version-independent
 * |pkt_type|.
 */
uint8_t ngtcp2_pkt_versioned_type(uint32_t version, uint32_t pkt_type);

/**
 * @function
 *
 * `ngtcp2_pkt_get_type_long` returns the version-independent long
 * packet type.  |version| is the QUIC version.  |c| is the first byte
 * of Long packet header.  If |version| is not supported by the
 * library, it returns 0.
 */
uint8_t ngtcp2_pkt_get_type_long(uint32_t version, uint8_t c);

/*
 * ngtcp2_pkt_split_vec_rand appends ngtcp2_vec at most |max_add|
 * times to the array pointed by |data| of length |datacnt| by
 * splitting the existing ngtcp2_vec into two.  Which ngtcp2_vec to
 * split is chosen randomly.  |offsets| contains the offset of each
 * ngtcp2_vec pointed by |data|.  |offsets| is also updated.  The
 * arrays must have the capacity at least |datacnt| + |max_add|.
 * |pcg| is a random number generator.
 *
 * This function returns |datacnt| plus the number of ngtcp2_vec that
 * are appended.
 */
size_t ngtcp2_pkt_split_vec_rand(ngtcp2_vec *data, size_t datacnt,
                                 uint64_t *offsets, ngtcp2_pcg32 *pcg,
                                 size_t max_add);

/*
 * ngtcp2_pkt_split_vec_at splits data[0] at offset |at|, and the
 * right side of ngtcp2_vec is assigned to data[datacnt].  Similarly,
 * offsets[0] + |at| is assigned to offsets[datacnt].  |data| must
 * point to the array of ngtcp2_vec of length |datacnt|, and |datacnt|
 * must be greater than 0.  |at| must be strictly less than data->len.
 *
 * This function returns |datacnt| + 1.
 */
size_t ngtcp2_pkt_split_vec_at(ngtcp2_vec *data, size_t datacnt,
                               uint64_t *offsets, size_t at);

/*
 * ngtcp2_pkt_find_server_name searches TLS Server Name Indication
 * extension in |v|.  If it is found, assign the portion of server
 * name to the object pointed by |server_name|, and returns nonzero.
 * Otherwise, it returns 0.  If |v| contains the extension partially,
 * the function returns 0.  |v| must not be empty.
 */
int ngtcp2_pkt_find_server_name(ngtcp2_vec *server_name, const ngtcp2_vec *v);

/*
 * ngtcp2_pkt_append_ping_and_padding appends PING and PADDING frames
 * to the array pointed by |data| of length |datacnt|.  The capacity
 * of array must be at least NGTCP2_MAX_STREAM_DATACNT.  |n| is the
 * number of bytes available for serialized PING and PADDING frames.
 * |pcg| is a random number generator.  Which frames to add is
 * determined randomly.
 *
 * The special encoding of PING and PADDING frames into ngtcp2_vec:
 *
 * - .base is NULL.
 * - If .len is 0, it represents PING.  Otherwise, PADDING of .len
 *   length.
 *
 * This function returns |datacnt| plus the number of frames added.
 */
size_t ngtcp2_pkt_append_ping_and_padding(ngtcp2_vec *data, size_t datacnt,
                                          ngtcp2_pcg32 *pcg, size_t n);

/*
 * ngtcp2_pkt_permutate_vec permutates |data| and |offsets|, both have
 * the |datacnt| elements.  |pcg| is a random number generator.
 */
void ngtcp2_pkt_permutate_vec(ngtcp2_vec *data, size_t datacnt,
                              uint64_t *offsets, ngtcp2_pcg32 *pcg);

/*
 * ngtcp2_pkt_remove_vec_partial removes the portion of data that
 * contains part of |part| from data[0].  This function does not
 * remove whole range of |part|.  The length of removed data is chosen
 * randomly.  The removed portion of data is assigned to the object
 * pointed by |removed_data|.  If there is data located after the
 * removed data, it will be assigned to data[datacnt].
 * offsets[datacnt] is also updated, and the function returns
 * |datacnt| + 1.  Otherwise, this function returns |datacnt|.
 */
size_t ngtcp2_pkt_remove_vec_partial(ngtcp2_vec *removed_data, ngtcp2_vec *data,
                                     size_t datacnt, uint64_t *offsets,
                                     ngtcp2_pcg32 *pcg, const ngtcp2_vec *part);

#endif /* !defined(NGTCP2_PKT_H) */
