/*
 * nghttp2 - HTTP/2.0 C Library
 *
 * Copyright (c) 2013 Tatsuhiro Tsujikawa
 *
 * 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.
 */
#include "nghttp2_hd.h"

#include <string.h>
#include <assert.h>
#include <stdio.h>

#include "nghttp2_frame.h"
#include "nghttp2_helper.h"

static const char *reqhd_table[] = {
  ":scheme", "http",
  ":scheme", "https",
  ":host", "",
  ":path", "/",
  ":method", "GET",
  "accept", "",
  "accept-charset", "",
  "accept-encoding", "",
  "accept-language", "",
  "cookie", "",
  "if-modified-since", "",
  "user-agent", "",
  "referer", "",
  "authorization", "",
  "allow", "",
  "cache-control", "",
  "connection", "",
  "content-length", "",
  "content-type", "",
  "date", "",
  "expect", "",
  "from", "",
  "if-match", "",
  "if-none-match", "",
  "if-range", "",
  "if-unmodified-since", "",
  "max-forwards", "",
  "proxy-authorization", "",
  "range", "",
  "via", "",
  NULL
};

static const char *reshd_table[] = {
  ":status", "200",
  "age", "",
  "cache-control", "",
  "content-length", "",
  "content-type", "",
  "date", "",
  "etag", "",
  "expires", "",
  "last-modified", "",
  "server", "",
  "set-cookie", "",
  "vary", "",
  "via", "",
  "access-control-allow-origin", "",
  "accept-ranges", "",
  "allow", "",
  "connection", "",
  "content-disposition", "",
  "content-encoding", "",
  "content-language", "",
  "content-location", "",
  "content-range", "",
  "link", "",
  "location", "",
  "proxy-authenticate", "",
  "refresh", "",
  "retry-after", "",
  "strict-transport-security", "",
  "transfer-encoding", "",
  "www-authenticate", "",
  NULL
};

typedef struct {
  nghttp2_nv *nva;
  size_t nvacap;
  size_t nvlen;
} nghttp2_nva_out;

int nghttp2_hd_entry_init(nghttp2_hd_entry *ent, uint8_t index, uint8_t flags,
                          uint8_t *name, uint16_t namelen,
                          uint8_t *value, uint16_t valuelen)
{
  int rv = 0;
  if(flags & NGHTTP2_HD_FLAG_NAME_ALLOC) {
    if(namelen == 0) {
      /* We should not allow empty header field name */
      ent->nv.name = NULL;
    } else {
      ent->nv.name = nghttp2_memdup(name, namelen);
      if(ent->nv.name == NULL) {
        rv = NGHTTP2_ERR_NOMEM;
        goto fail;
      }
    }
  } else {
    ent->nv.name = name;
  }
  if(flags & NGHTTP2_HD_FLAG_VALUE_ALLOC) {
    if(valuelen == 0) {
      ent->nv.value = NULL;
    } else {
      ent->nv.value = nghttp2_memdup(value, valuelen);
      if(ent->nv.value == NULL) {
        rv = NGHTTP2_ERR_NOMEM;
        goto fail2;
      }
    }
  } else {
    ent->nv.value = value;
  }
  ent->nv.namelen = namelen;
  ent->nv.valuelen = valuelen;
  ent->ref = 1;
  ent->index = index;
  ent->flags = flags;
  return 0;

 fail2:
  if(flags & NGHTTP2_HD_FLAG_NAME_ALLOC) {
    free(ent->nv.name);
  }
 fail:
  return rv;
}

void nghttp2_hd_entry_free(nghttp2_hd_entry *ent)
{
  assert(ent->ref == 0);
  if(ent->flags & NGHTTP2_HD_FLAG_NAME_ALLOC) {
    free(ent->nv.name);
  }
  if(ent->flags & NGHTTP2_HD_FLAG_VALUE_ALLOC) {
    free(ent->nv.value);
  }
}

static int nghttp2_hd_context_init(nghttp2_hd_context *context,
                                   nghttp2_hd_role role,
                                   nghttp2_hd_side side)
{
  int i;
  const char **ini_table;
  context->role = role;
  context->bad = 0;
  context->hd_table = malloc(sizeof(nghttp2_hd_entry*)*
                             NGHTTP2_INITIAL_HD_TABLE_SIZE);
  if(context->hd_table == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  memset(context->hd_table, 0, sizeof(nghttp2_hd_entry*)*
         NGHTTP2_INITIAL_HD_TABLE_SIZE);
  context->hd_table_capacity = NGHTTP2_INITIAL_HD_TABLE_SIZE;
  context->hd_tablelen = 0;

  context->emit_set = malloc(sizeof(nghttp2_hd_entry*)*
                             NGHTTP2_INITIAL_EMIT_SET_SIZE);
  if(context->emit_set == NULL) {
    free(context->hd_table);
    return NGHTTP2_ERR_NOMEM;
  }
  memset(context->emit_set, 0, sizeof(nghttp2_hd_entry*)*
         NGHTTP2_INITIAL_EMIT_SET_SIZE);
  context->emit_set_capacity = NGHTTP2_INITIAL_EMIT_SET_SIZE;
  context->emit_setlen = 0;

  if(side == NGHTTP2_HD_SIDE_CLIENT) {
    ini_table = reqhd_table;
  } else {
    ini_table = reshd_table;
  }
  context->hd_table_bufsize = 0;
  for(i = 0; ini_table[i]; i += 2) {
    nghttp2_hd_entry *p = malloc(sizeof(nghttp2_hd_entry));
    if(p == NULL) {
      for(i = 0; i < context->hd_tablelen; ++i) {
        nghttp2_hd_entry_free(context->hd_table[i]);
        free(context->hd_table[i]);
      }
      free(context->emit_set);
      free(context->hd_table);
      return NGHTTP2_ERR_NOMEM;
    }
    nghttp2_hd_entry_init(p, i / 2, NGHTTP2_HD_FLAG_NONE,
                          (uint8_t*)ini_table[i], strlen(ini_table[i]),
                          (uint8_t*)ini_table[i + 1],
                          strlen(ini_table[i+1]));
    context->hd_table[context->hd_tablelen++] = p;
    context->hd_table_bufsize += NGHTTP2_HD_ENTRY_OVERHEAD +
      p->nv.namelen + p->nv.valuelen;
  }
  return 0;
}

int nghttp2_hd_deflate_init(nghttp2_hd_context *deflater, nghttp2_hd_side side)
{
  return nghttp2_hd_context_init(deflater, NGHTTP2_HD_ROLE_DEFLATE, side);
}

int nghttp2_hd_inflate_init(nghttp2_hd_context *inflater, nghttp2_hd_side side)
{
  return nghttp2_hd_context_init(inflater, NGHTTP2_HD_ROLE_INFLATE, side^1);
}

static void nghttp2_hd_context_free(nghttp2_hd_context *context)
{
  size_t i;
  for(i = 0; i < context->emit_setlen; ++i) {
    nghttp2_hd_entry *ent = context->emit_set[i];
    if(--ent->ref == 0) {
      nghttp2_hd_entry_free(ent);
      free(ent);
    }
  }
  for(i = 0; i < context->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = context->hd_table[i];
    --ent->ref;
    nghttp2_hd_entry_free(ent);
    free(ent);
  }
  free(context->emit_set);
  free(context->hd_table);
}

void nghttp2_hd_deflate_free(nghttp2_hd_context *deflater)
{
  nghttp2_hd_context_free(deflater);
}

void nghttp2_hd_inflate_free(nghttp2_hd_context *inflater)
{
  nghttp2_hd_context_free(inflater);
}

static size_t entry_room(size_t namelen, size_t valuelen)
{
  return NGHTTP2_HD_ENTRY_OVERHEAD + namelen + valuelen;
}

static int add_nva(nghttp2_nva_out *nva_out_ptr,
                   uint8_t *name, uint16_t namelen,
                   uint8_t *value, uint16_t valuelen)
{
  nghttp2_nv *nv;
  if(nva_out_ptr->nvacap == nva_out_ptr->nvlen) {
    size_t newcap = nva_out_ptr->nvacap == 0 ? 16 : nva_out_ptr->nvacap * 2;
    nghttp2_nv *new_nva = realloc(nva_out_ptr->nva, sizeof(nghttp2_nv)*newcap);
    if(new_nva == NULL) {
      return NGHTTP2_ERR_NOMEM;
    }
    nva_out_ptr->nva = new_nva;
    nva_out_ptr->nvacap = newcap;
  }
  nv = &nva_out_ptr->nva[nva_out_ptr->nvlen++];
  nv->name = name;
  nv->namelen = namelen;
  nv->value = value;
  nv->valuelen = valuelen;
  return 0;
}

static int add_emit_set(nghttp2_hd_context *context, nghttp2_hd_entry *ent)
{
  if(context->emit_setlen == context->emit_set_capacity) {
    return NGHTTP2_ERR_HEADER_COMP;
  }
  context->emit_set[context->emit_setlen++] = ent;
  ++ent->ref;
  return 0;
}

static int emit_indexed_header(nghttp2_hd_context *context,
                               nghttp2_nva_out *nva_out_ptr,
                               nghttp2_hd_entry *ent)
{
  int rv;
  rv = add_emit_set(context, ent);
  if(rv != 0) {
    return rv;
  }
  ent->flags |= NGHTTP2_HD_FLAG_EMIT;
  return add_nva(nva_out_ptr,
                 ent->nv.name, ent->nv.namelen,
                 ent->nv.value, ent->nv.valuelen);
}

static int emit_newname_header(nghttp2_hd_context *context,
                               nghttp2_nva_out *nva_out_ptr,
                               nghttp2_nv *nv)
{
  return add_nva(nva_out_ptr,
                 nv->name, nv->namelen, nv->value, nv->valuelen);
}

static int emit_indname_header(nghttp2_hd_context *context,
                               nghttp2_nva_out *nva_out_ptr,
                               nghttp2_hd_entry *ent,
                               uint8_t *value, size_t valuelen)
{
  int rv;
  rv = add_emit_set(context, ent);
  if(rv != 0) {
    return rv;
  }
  return add_nva(nva_out_ptr, ent->nv.name, ent->nv.namelen, value, valuelen);
}

static nghttp2_hd_entry* add_hd_table_incremental(nghttp2_hd_context *context,
                                                  nghttp2_nv *nv)
{
  int rv;
  size_t i;
  nghttp2_hd_entry *new_ent;
  size_t room = entry_room(nv->namelen, nv->valuelen);
  if(context->hd_tablelen == context->hd_table_capacity ||
     room > NGHTTP2_HD_MAX_BUFFER_SIZE) {
    return NULL;
  }
  context->hd_table_bufsize += room;
  for(i = 0; i < context->hd_tablelen &&
        context->hd_table_bufsize > NGHTTP2_HD_MAX_BUFFER_SIZE; ++i) {
    nghttp2_hd_entry *ent = context->hd_table[i];
    context->hd_table_bufsize -= entry_room(ent->nv.namelen, ent->nv.valuelen);
    ent->index = NGHTTP2_HD_INVALID_INDEX;
    if(context->role == NGHTTP2_HD_ROLE_DEFLATE &&
       (ent->flags & NGHTTP2_HD_FLAG_IMPLICIT_EMIT)) {
      /* We will emit this entry later not to lose the header
         field. */
      rv = add_emit_set(context, ent);
      if(rv != 0) {
        return NULL;
      }
    }
    if(--ent->ref == 0) {
      nghttp2_hd_entry_free(ent);
      free(ent);
    }
  }
  if(i > 0) {
    size_t j;
    for(j = 0; i < context->hd_tablelen; ++i, ++j) {
      context->hd_table[j] = context->hd_table[i];
      context->hd_table[j]->index = j;
    }
    context->hd_tablelen = j;
  }
  new_ent = malloc(sizeof(nghttp2_hd_entry));
  if(new_ent == NULL) {
    return NULL;
  }
  rv = nghttp2_hd_entry_init(new_ent, context->hd_tablelen,
                             NGHTTP2_HD_FLAG_NAME_ALLOC |
                             NGHTTP2_HD_FLAG_VALUE_ALLOC,
                             nv->name, nv->namelen, nv->value, nv->valuelen);
  if(rv < 0) {
    return NULL;
  }
  context->hd_table[context->hd_tablelen++] = new_ent;
  new_ent->flags |= NGHTTP2_HD_FLAG_REFSET;
  return new_ent;
}

static nghttp2_hd_entry* add_hd_table_subst(nghttp2_hd_context *context,
                                            nghttp2_nv *nv, size_t subindex)
{
  int rv;
  size_t i;
  int k;
  nghttp2_hd_entry *new_ent;
  size_t room = entry_room(nv->namelen, nv->valuelen);
  if(room > NGHTTP2_HD_MAX_BUFFER_SIZE ||
     context->hd_tablelen <= subindex) {
    return NULL;
  }
  context->hd_table_bufsize -=
    entry_room(context->hd_table[subindex]->nv.namelen,
               context->hd_table[subindex]->nv.valuelen);
  context->hd_table_bufsize += room;
  k = subindex;
  for(i = 0; i < context->hd_tablelen &&
        context->hd_table_bufsize > NGHTTP2_HD_MAX_BUFFER_SIZE; ++i, --k) {
    nghttp2_hd_entry *ent = context->hd_table[i];
    if(i != subindex) {
      context->hd_table_bufsize -= entry_room(ent->nv.namelen,
                                              ent->nv.valuelen);
    }
    ent->index = NGHTTP2_HD_INVALID_INDEX;
    if(context->role == NGHTTP2_HD_ROLE_DEFLATE &&
       (ent->flags & NGHTTP2_HD_FLAG_IMPLICIT_EMIT)) {
      /* We will emit this entry later not to lose the header
         field. */
      rv = add_emit_set(context, ent);
      if(rv != 0) {
        return NULL;
      }
    }
    if(--ent->ref == 0) {
      nghttp2_hd_entry_free(ent);
      free(ent);
    }
  }
  if(i > 0) {
    size_t j;
    if(k < 0) {
      j = 1;
    } else {
      j = 0;
    }
    for(; i < context->hd_tablelen; ++i, ++j) {
      context->hd_table[j] = context->hd_table[i];
      context->hd_table[j]->index = j;
    }
    context->hd_tablelen = j;
  }
  new_ent = malloc(sizeof(nghttp2_hd_entry));
  if(new_ent == NULL) {
    return NULL;
  }
  if(k >= 0) {
    nghttp2_hd_entry *ent = context->hd_table[k];
    ent->index = NGHTTP2_HD_INVALID_INDEX;
    if(context->role == NGHTTP2_HD_ROLE_DEFLATE &&
       (ent->flags & NGHTTP2_HD_FLAG_IMPLICIT_EMIT)) {
      /* We will emit this entry later not to lose the header
         field. */
      rv = add_emit_set(context, ent);
      if(rv != 0) {
        return NULL;
      }
    }
    if(--ent->ref == 0) {
      nghttp2_hd_entry_free(ent);
      free(ent);
    }
  } else {
    k = 0;
  }
  rv = nghttp2_hd_entry_init(new_ent, k,
                             NGHTTP2_HD_FLAG_NAME_ALLOC |
                             NGHTTP2_HD_FLAG_VALUE_ALLOC,
                             nv->name, nv->namelen, nv->value, nv->valuelen);
  if(rv < 0) {
    return NULL;
  }
  context->hd_table[new_ent->index] = new_ent;
  new_ent->flags |= NGHTTP2_HD_FLAG_REFSET;
  return new_ent;
}

static nghttp2_hd_entry* find_in_hd_table(nghttp2_hd_context *context,
                                          nghttp2_nv *nv)
{
  size_t i;
  for(i = 0; i < context->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = context->hd_table[i];
    if(nghttp2_nv_equal(&ent->nv, nv)) {
      return ent;
    }
  }
  return NULL;
}

static nghttp2_hd_entry* find_name_in_hd_table(nghttp2_hd_context *context,
                                               nghttp2_nv *nv)
{
  size_t i;
  for(i = 0; i < context->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = context->hd_table[i];
    if(ent->nv.namelen == nv->namelen &&
       memcmp(ent->nv.name, nv->name, nv->namelen) == 0) {
      return ent;
    }
  }
  return NULL;
}

static int ensure_write_buffer(uint8_t **buf_ptr, size_t *buflen_ptr,
                               size_t offset, size_t need)
{
  int rv;
  /* TODO Remove this limitation when header continuation is
     implemented. */
  if(need + offset > NGHTTP2_MAX_HTTP_FRAME_LENGTH) {
    return NGHTTP2_ERR_HEADER_COMP;
  }
  rv = nghttp2_reserve_buffer(buf_ptr, buflen_ptr, offset + need);
  if(rv != 0) {
    return NGHTTP2_ERR_NOMEM;
  }
  return 0;
}

static size_t count_encoded_length(size_t n, int prefix)
{
  size_t k = (1 << prefix) - 1;
  size_t len = 0;
  if(n >= k) {
    n -= k;
    ++len;
  } else {
    return 1;
  }
  do {
    ++len;
    if(n >= 128) {
      n >>= 7;
    } else {
      break;
    }
  } while(n);
  return len;
}

static size_t encode_length(uint8_t *buf, size_t n, int prefix)
{
  size_t k = (1 << prefix) - 1;
  size_t len = 0;
  if(n >= k) {
    *buf++ = k;
    n -= k;
    ++len;
  } else {
    *buf++ = n;
    return 1;
  }
  do {
    ++len;
    if(n >= 128) {
      *buf++ = (1 << 7) | (n & 0x7f);
      n >>= 7;
    } else {
      *buf++ = n;
      break;
    }
  } while(n);
  return len;
}

/*
 * Decodes |prefx| prefixed integer stored from |in|. The |last|
 * represents the 1 beyond the last of the valid contiguous memory
 * region from |in|. The decoded integer must be strictly less than 1
 * << 16.
 *
 * This function returns the next byte of read byte. This function
 * stores the decoded integer in |*res| if it succeeds, or stores -1
 * in |*res|, indicating decoding error.
 */
static  uint8_t* decode_length(ssize_t *res, uint8_t *in, uint8_t *last,
                               int prefix)
{
  int k = (1 << prefix) - 1, r;
  if(in == last) {
    *res = -1;
    return in;
  }
  if((*in & k) == k) {
    *res = k;
  } else {
    *res = (*in) & k;
    return in + 1;
  }
  ++in;
  for(r = 0; in != last; ++in, r += 7) {
    *res += (*in & 0x7f) << r;
    if(*res >= (1 << 16)) {
      *res = -1;
      return in + 1;
    }
    if((*in & (1 << 7)) == 0) {
      break;
    }
  }
  if(*in & (1 << 7)) {
    *res = -1;
    return NULL;
  } else {
    return in + 1;
  }
}

static int emit_indexed_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                              size_t *offset_ptr, size_t index)
{
  int rv;
  uint8_t *bufp;
  size_t blocklen = count_encoded_length(index, 7);
  rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
  if(rv != 0) {
    return rv;
  }
  bufp = *buf_ptr + *offset_ptr;
  encode_length(bufp, index, 7);
  (*buf_ptr)[*offset_ptr] |= 0x80u;
  *offset_ptr += blocklen;
  return 0;
}

static int emit_indname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                              size_t *offset_ptr, size_t index,
                              const uint8_t *value, size_t valuelen,
                              int inc_indexing)
{
  int rv;
  uint8_t *bufp;
  size_t blocklen = count_encoded_length(index + 1, 5) +
    count_encoded_length(valuelen, 8) + valuelen;
  rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
  if(rv != 0) {
    return rv;
  }
  bufp = *buf_ptr + *offset_ptr;
  bufp += encode_length(bufp, index + 1, 5);
  bufp += encode_length(bufp, valuelen, 8);
  memcpy(bufp, value, valuelen);
  (*buf_ptr)[*offset_ptr] |= inc_indexing ? 0x40u : 0x60u;
  assert(bufp+valuelen - (*buf_ptr + *offset_ptr) == (ssize_t)blocklen);
  *offset_ptr += blocklen;
  return 0;
}

static int emit_newname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                              size_t *offset_ptr, nghttp2_nv *nv,
                              int inc_indexing)
{
  int rv;
  uint8_t *bufp;
  size_t blocklen = 1 + count_encoded_length(nv->namelen, 8) + nv->namelen +
    count_encoded_length(nv->valuelen, 8) + nv->valuelen;
  rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
  if(rv != 0) {
    return rv;
  }
  bufp = *buf_ptr + *offset_ptr;
  *bufp++ = inc_indexing ? 0x40u : 0x60u;
  bufp += encode_length(bufp, nv->namelen, 8);
  memcpy(bufp, nv->name, nv->namelen);
  bufp += nv->namelen;
  bufp += encode_length(bufp, nv->valuelen, 8);
  memcpy(bufp, nv->value, nv->valuelen);
  *offset_ptr += blocklen;
  return 0;
}

static int emit_subst_indname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                    size_t *offset_ptr, size_t index,
                                    const uint8_t *value, size_t valuelen,
                                    size_t subindex)
{
  int rv;
  uint8_t *bufp;
  size_t blocklen = count_encoded_length(index + 1, 6) +
    count_encoded_length(subindex, 8) +
    count_encoded_length(valuelen, 8) + valuelen;
  rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
  if(rv != 0) {
    return rv;
  }
  bufp = *buf_ptr + *offset_ptr;
  bufp += encode_length(bufp, index + 1, 6);
  bufp += encode_length(bufp, subindex, 8);
  bufp += encode_length(bufp, valuelen, 8);
  memcpy(bufp, value, valuelen);
  *offset_ptr += blocklen;
  return 0;
}

static int emit_subst_newname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                    size_t *offset_ptr, nghttp2_nv *nv,
                                    size_t subindex)
{
  int rv;
  uint8_t *bufp;
  size_t blocklen = 1 + count_encoded_length(nv->namelen, 8) + nv->namelen +
    count_encoded_length(subindex, 8) +
    count_encoded_length(nv->valuelen, 8) + nv->valuelen;
  rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
  if(rv != 0) {
    return rv;
  }
  bufp = *buf_ptr + *offset_ptr;
  *bufp++ = 0;
  bufp += encode_length(bufp, nv->namelen, 8);
  memcpy(bufp, nv->name, nv->namelen);
  bufp += nv->namelen;
  bufp += encode_length(bufp, subindex, 8);
  bufp += encode_length(bufp, nv->valuelen, 8);
  memcpy(bufp, nv->value, nv->valuelen);
  *offset_ptr += blocklen;
  return 0;
}

static int intcompar(const void *lhs, const void *rhs)
{
  return *(int*)lhs - *(int*)rhs;
}

static int deflate_nv(nghttp2_hd_context *deflater,
                      uint8_t **buf_ptr, size_t *buflen_ptr,
                      size_t *offset_ptr,
                      nghttp2_nv *nv)
{
  int rv;
  nghttp2_hd_entry *ent;
  ent = find_in_hd_table(deflater, nv);
  if(ent) {
    if((ent->flags & NGHTTP2_HD_FLAG_REFSET) == 0) {
      ent->flags |= NGHTTP2_HD_FLAG_REFSET | NGHTTP2_HD_FLAG_EMIT;
      rv = emit_indexed_block(buf_ptr, buflen_ptr, offset_ptr, ent->index);
      if(rv != 0) {
        return rv;
      }
    } else {
      int num_emits = 0;
      if(ent->flags & NGHTTP2_HD_FLAG_EMIT) {
        /* occurrences of the same indexed representation. Emit index
           twice. */
        num_emits = 2;
      } else if(ent->flags & NGHTTP2_HD_FLAG_IMPLICIT_EMIT) {
        /* ent was implicitly emitted because it is the common
           header field. To support occurrences of the same indexed
           representation, we have to emit 4 times. This is because
           "implicitly emitted" means actually not emitted at
           all. So first 2 emits performs 1st header appears in the
           reference set. And another 2 emits are done for 2nd
           (current) header. */
        ent->flags ^= NGHTTP2_HD_FLAG_IMPLICIT_EMIT;
        ent->flags |= NGHTTP2_HD_FLAG_EMIT;
        num_emits = 4;
      }
      for(; num_emits > 0; --num_emits) {
        rv = emit_indexed_block(buf_ptr, buflen_ptr, offset_ptr, ent->index);
        if(rv != 0) {
          break;
        }
      }
    }
  } else {
    uint8_t index = NGHTTP2_HD_INVALID_INDEX;
    int incidx = 0;
    ent = find_name_in_hd_table(deflater, nv);
    if(ent) {
      index = ent->index;
    }
    if(entry_room(nv->namelen, nv->valuelen)
       < NGHTTP2_HD_MAX_ENTRY_SIZE) {
      nghttp2_hd_entry *new_ent;
      new_ent = add_hd_table_incremental(deflater, nv);
      if(!new_ent) {
        return NGHTTP2_ERR_HEADER_COMP;
      }
      new_ent->flags |= NGHTTP2_HD_FLAG_EMIT;
      incidx = 1;
    }
    if(index == NGHTTP2_HD_INVALID_INDEX) {
      rv = emit_newname_block(buf_ptr, buflen_ptr, offset_ptr, nv, incidx);
    } else {
      rv = emit_indname_block(buf_ptr, buflen_ptr, offset_ptr, index,
                              nv->value, nv->valuelen, incidx);
    }
    if(rv != 0) {
      return rv;
    }
  }
  return 0;
}

ssize_t nghttp2_hd_deflate_hd(nghttp2_hd_context *deflater,
                              uint8_t **buf_ptr, size_t *buflen_ptr,
                              size_t nv_offset,
                              nghttp2_nv *nv, size_t nvlen)
{
  size_t i, j, k, offset;
  int rv = 0;
  int common_hd[NGHTTP2_INITIAL_HD_TABLE_SIZE];
  size_t common_hdlen = 0;
  if(deflater->bad) {
    return NGHTTP2_ERR_HEADER_COMP;
  }
  offset = nv_offset;
  /* First emit indexed repr to remove deleted header fields */
  for(i = 0; i < deflater->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = deflater->hd_table[i];
    if((ent->flags & NGHTTP2_HD_FLAG_REFSET) == 0) {
      continue;
    }
    for(j = 0; j < nvlen; ++j) {
      if(nghttp2_nv_equal(&ent->nv, &nv[j])) {
        break;
      }
    }
    if(j < nvlen) {
      /* Assuming the encoder does not put duplicated entry in the
         header table, this entry is common header field between
         previous header set. So it is "implicitly emitted". */
      ent->flags |= NGHTTP2_HD_FLAG_IMPLICIT_EMIT;
      common_hd[common_hdlen++] = j;
      continue;
    }
    ent->flags ^= NGHTTP2_HD_FLAG_REFSET;
    rv = emit_indexed_block(buf_ptr, buflen_ptr, &offset, ent->index);
    if(rv < 0) {
      goto fail;
    }
  }
  qsort(common_hd, common_hdlen, sizeof(int), intcompar);
  for(i = 0, k = 0; i < nvlen; ++i) {
    if(k < common_hdlen) {
      /* Skip implicitly emitted name/value pair */
      if((uint8_t)common_hd[k] == i) {
        ++k;
        continue;
      }
    }
    rv = deflate_nv(deflater, buf_ptr, buflen_ptr, &offset, &nv[i]);
    if(rv != 0) {
      goto fail;
    }
  }
  /* Encode the lost common headers. Keep in mind that
     deflater->emit_setlen may be increased by deflate_nv(). */
  for(i = 0; i < deflater->emit_setlen; ++i) {
    nghttp2_hd_entry *ent = deflater->emit_set[i];
    rv = deflate_nv(deflater, buf_ptr, buflen_ptr, &offset, &ent->nv);
    if(rv != 0) {
      goto fail;
    }
  }
  for(i = 0; i < deflater->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = deflater->hd_table[i];
    ent->flags &= ~(NGHTTP2_HD_FLAG_EMIT | NGHTTP2_HD_FLAG_IMPLICIT_EMIT);
  }
  return offset - nv_offset;
 fail:
  deflater->bad = 1;
  return rv;
}

ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
                              nghttp2_nv **nva_ptr,
                              uint8_t *in, size_t inlen)
{
  size_t i;
  int rv = 0;
  uint8_t *last = in + inlen;
  nghttp2_nva_out nva_out;
  memset(&nva_out, 0, sizeof(nva_out));
  if(inflater->bad) {
    return NGHTTP2_ERR_HEADER_COMP;
  }
  *nva_ptr = NULL;
  for(; in != last;) {
    uint8_t c = *in;
    if(c & 0x80u) {
      /* Indexed Header Repr */
      ssize_t index;
      nghttp2_hd_entry *ent;
      in = decode_length(&index, in, last, 7);
      if(index < 0) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      if(inflater->hd_tablelen <= index) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      ent = inflater->hd_table[index];
      ent->flags ^= NGHTTP2_HD_FLAG_REFSET;
      if(ent->flags & NGHTTP2_HD_FLAG_REFSET) {
        rv = emit_indexed_header(inflater, &nva_out, ent);
        if(rv < 0) {
          goto fail;
        }
      }
    } else if(c == 0x40u || c == 0x60u || c == 0) {
      /* Literal Header Repr - New Name */
      nghttp2_nv nv;
      ssize_t namelen, valuelen, subindex;
      if(++in == last) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      in = decode_length(&namelen, in, last, 8);
      if(namelen < 0 || in + namelen > last) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      if(!nghttp2_check_header_name(in, namelen)) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      nv.name = in;
      in += namelen;
      if(c == 0) {
        in = decode_length(&subindex, in, last, 8);
        if(subindex < 0) {
          rv = NGHTTP2_ERR_HEADER_COMP;
          goto fail;
        }
      }
      in = decode_length(&valuelen, in, last, 8);
      if(valuelen < 0 || in + valuelen > last) {
        rv =  NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      nv.namelen = namelen;
      nv.value = in;
      nv.valuelen = valuelen;
      in += valuelen;
      nghttp2_downcase(nv.name, nv.namelen);
      if(c == 0x60u) {
        rv = emit_newname_header(inflater, &nva_out, &nv);
      } else {
        nghttp2_hd_entry *new_ent;
        if(c == 0) {
          new_ent = add_hd_table_subst(inflater, &nv, subindex);
        } else {
          new_ent = add_hd_table_incremental(inflater, &nv);
        }
        if(new_ent) {
          rv = emit_indexed_header(inflater, &nva_out, new_ent);
        } else {
          rv = NGHTTP2_ERR_HEADER_COMP;
        }
      }
      if(rv != 0) {
        goto fail;
      }
    } else {
      /* Literal Header Repr - Indexed Name */
      nghttp2_hd_entry *ent;
      uint8_t *value;
      ssize_t valuelen, index, subindex;
      in = decode_length(&index, in, last, (c & 0x40u) ? 5 : 6);
      if(index < 0) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      --index;
      if(inflater->hd_tablelen <= index) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      ent = inflater->hd_table[index];
      if((c & 0x40u) == 0) {
        in = decode_length(&subindex, in, last, 8);
        if(subindex < 0) {
          rv = NGHTTP2_ERR_HEADER_COMP;
          goto fail;
        }
      }
      in = decode_length(&valuelen, in , last, 8);
      if(valuelen < 0 || in + valuelen > last) {
        rv = NGHTTP2_ERR_HEADER_COMP;
        goto fail;
      }
      value = in;
      in += valuelen;
      if((c & 0x60u) == 0x60u) {
        rv = emit_indname_header(inflater, &nva_out, ent, value, valuelen);
      } else {
        nghttp2_nv nv;
        nghttp2_hd_entry *new_ent;
        ++ent->ref;
        nv.name = ent->nv.name;
        nv.namelen = ent->nv.namelen;
        nv.value = value;
        nv.valuelen = valuelen;
        if((c & 0x40u) == 0) {
          new_ent = add_hd_table_subst(inflater, &nv, subindex);
        } else {
          new_ent = add_hd_table_incremental(inflater, &nv);
        }
        if(--ent->ref == 0) {
          nghttp2_hd_entry_free(ent);
          free(ent);
        }
        if(new_ent) {
          rv = emit_indexed_header(inflater, &nva_out, new_ent);
        } else {
          rv = NGHTTP2_ERR_HEADER_COMP;
        }
      }
      if(rv != 0) {
        goto fail;
      }
    }
  }
  for(i = 0; i < inflater->hd_tablelen; ++i) {
    nghttp2_hd_entry *ent = inflater->hd_table[i];
    if((ent->flags & NGHTTP2_HD_FLAG_REFSET) &&
       (ent->flags & NGHTTP2_HD_FLAG_EMIT) == 0) {
      rv = emit_indexed_header(inflater, &nva_out, ent);
      if(rv < 0) {
        goto fail;
      }
    }
    ent->flags &= ~NGHTTP2_HD_FLAG_EMIT;
  }
  nghttp2_nv_array_sort(nva_out.nva, nva_out.nvlen);
  *nva_ptr = nva_out.nva;
  return nva_out.nvlen;
 fail:
  inflater->bad = 1;
  free(nva_out.nva);
  return rv;
}

int nghttp2_hd_end_headers(nghttp2_hd_context *context)
{
  size_t i;
  for(i = 0; i < context->emit_setlen; ++i) {
    nghttp2_hd_entry *ent = context->emit_set[i];
    if(--ent->ref == 0) {
      nghttp2_hd_entry_free(ent);
      free(ent);
    }
  }
  context->emit_setlen = 0;
  return 0;
}

int nghttp2_hd_emit_indname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                  size_t *offset_ptr, size_t index,
                                  const uint8_t *value, size_t valuelen,
                                  int inc_indexing)
{
  return emit_indname_block(buf_ptr, buflen_ptr, offset_ptr,
                            index, value, valuelen, inc_indexing);
}

int nghttp2_hd_emit_newname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                  size_t *offset_ptr, nghttp2_nv *nv,
                                  int inc_indexing)
{
  return emit_newname_block(buf_ptr, buflen_ptr, offset_ptr, nv, inc_indexing);
}

int nghttp2_hd_emit_subst_indname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                        size_t *offset_ptr, size_t index,
                                        const uint8_t *value, size_t valuelen,
                                        size_t subindex)
{
  return emit_subst_indname_block(buf_ptr, buflen_ptr, offset_ptr, index,
                                  value, valuelen, subindex);
}

int nghttp2_hd_emit_subst_newname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
                                        size_t *offset_ptr, nghttp2_nv *nv,
                                        size_t subindex)
{
  return emit_subst_newname_block(buf_ptr, buflen_ptr, offset_ptr, nv,
                                  subindex);
}