/*
 * ngtcp2
 *
 * Copyright (c) 2020 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.
 */
#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif /* defined(HAVE_CONFIG_H) */

#include <assert.h>

#include <ngtcp2/ngtcp2_crypto.h>
#include <ngtcp2/ngtcp2_crypto_gnutls.h>

#include <gnutls/gnutls.h>
#include <gnutls/crypto.h>
#include <string.h>

#include "ngtcp2_macro.h"
#include "shared.h"

ngtcp2_crypto_aead *ngtcp2_crypto_aead_aes_128_gcm(ngtcp2_crypto_aead *aead) {
  return ngtcp2_crypto_aead_init(aead, (void *)GNUTLS_CIPHER_AES_128_GCM);
}

ngtcp2_crypto_md *ngtcp2_crypto_md_sha256(ngtcp2_crypto_md *md) {
  md->native_handle = (void *)GNUTLS_DIG_SHA256;
  return md;
}

ngtcp2_crypto_ctx *ngtcp2_crypto_ctx_initial(ngtcp2_crypto_ctx *ctx) {
  ngtcp2_crypto_aead_init(&ctx->aead, (void *)GNUTLS_CIPHER_AES_128_GCM);
  ctx->md.native_handle = (void *)GNUTLS_DIG_SHA256;
  ctx->hp.native_handle = (void *)GNUTLS_CIPHER_AES_128_CBC;
  ctx->max_encryption = 0;
  ctx->max_decryption_failure = 0;
  return ctx;
}

ngtcp2_crypto_aead *ngtcp2_crypto_aead_init(ngtcp2_crypto_aead *aead,
                                            void *aead_native_handle) {
  aead->native_handle = aead_native_handle;
  aead->max_overhead = gnutls_cipher_get_tag_size(
    (gnutls_cipher_algorithm_t)(intptr_t)aead_native_handle);
  return aead;
}

ngtcp2_crypto_aead *ngtcp2_crypto_aead_retry(ngtcp2_crypto_aead *aead) {
  return ngtcp2_crypto_aead_init(aead, (void *)GNUTLS_CIPHER_AES_128_GCM);
}

static gnutls_cipher_algorithm_t
crypto_get_hp(gnutls_cipher_algorithm_t cipher) {
  switch (cipher) {
  case GNUTLS_CIPHER_AES_128_GCM:
  case GNUTLS_CIPHER_AES_128_CCM:
    return GNUTLS_CIPHER_AES_128_CBC;
  case GNUTLS_CIPHER_AES_256_GCM:
  case GNUTLS_CIPHER_AES_256_CCM:
    return GNUTLS_CIPHER_AES_256_CBC;
  case GNUTLS_CIPHER_CHACHA20_POLY1305:
    return GNUTLS_CIPHER_CHACHA20_32;
  default:
    return GNUTLS_CIPHER_UNKNOWN;
  }
}

static uint64_t
crypto_get_aead_max_encryption(gnutls_cipher_algorithm_t cipher) {
  switch (cipher) {
  case GNUTLS_CIPHER_AES_128_GCM:
  case GNUTLS_CIPHER_AES_256_GCM:
    return NGTCP2_CRYPTO_MAX_ENCRYPTION_AES_GCM;
  case GNUTLS_CIPHER_CHACHA20_POLY1305:
    return NGTCP2_CRYPTO_MAX_ENCRYPTION_CHACHA20_POLY1305;
  case GNUTLS_CIPHER_AES_128_CCM:
  case GNUTLS_CIPHER_AES_256_CCM:
    return NGTCP2_CRYPTO_MAX_ENCRYPTION_AES_CCM;
  default:
    return 0;
  }
}

static uint64_t
crypto_get_aead_max_decryption_failure(gnutls_cipher_algorithm_t cipher) {
  switch (cipher) {
  case GNUTLS_CIPHER_AES_128_GCM:
  case GNUTLS_CIPHER_AES_256_GCM:
    return NGTCP2_CRYPTO_MAX_DECRYPTION_FAILURE_AES_GCM;
  case GNUTLS_CIPHER_CHACHA20_POLY1305:
    return NGTCP2_CRYPTO_MAX_DECRYPTION_FAILURE_CHACHA20_POLY1305;
  case GNUTLS_CIPHER_AES_128_CCM:
  case GNUTLS_CIPHER_AES_256_CCM:
    return NGTCP2_CRYPTO_MAX_DECRYPTION_FAILURE_AES_CCM;
  default:
    return 0;
  }
}

static int supported_cipher(gnutls_cipher_algorithm_t cipher) {
  switch (cipher) {
  case GNUTLS_CIPHER_AES_128_GCM:
  case GNUTLS_CIPHER_AES_256_GCM:
  case GNUTLS_CIPHER_CHACHA20_POLY1305:
  case GNUTLS_CIPHER_AES_128_CCM:
  case GNUTLS_CIPHER_AES_256_CCM:
    return 1;
  default:
    return 0;
  }
}

ngtcp2_crypto_ctx *ngtcp2_crypto_ctx_tls(ngtcp2_crypto_ctx *ctx,
                                         void *tls_native_handle) {
  gnutls_session_t session = tls_native_handle;
  gnutls_cipher_algorithm_t cipher;
  gnutls_digest_algorithm_t hash;
  gnutls_cipher_algorithm_t hp_cipher;

  cipher = gnutls_cipher_get(session);
  if (cipher == GNUTLS_CIPHER_UNKNOWN || cipher == GNUTLS_CIPHER_NULL) {
    return NULL;
  }

  if (!supported_cipher(cipher)) {
    return NULL;
  }

  hash = gnutls_prf_hash_get(session);
  if (hash == GNUTLS_DIG_UNKNOWN || hash == GNUTLS_DIG_NULL) {
    return NULL;
  }

  hp_cipher = crypto_get_hp(cipher);
  if (hp_cipher == GNUTLS_CIPHER_UNKNOWN || hp_cipher == GNUTLS_CIPHER_NULL) {
    return NULL;
  }

  ngtcp2_crypto_aead_init(&ctx->aead, (void *)cipher);
  ctx->md.native_handle = (void *)hash;
  ctx->hp.native_handle = (void *)hp_cipher;
  ctx->max_encryption = crypto_get_aead_max_encryption(cipher);
  ctx->max_decryption_failure = crypto_get_aead_max_decryption_failure(cipher);

  return ctx;
}

ngtcp2_crypto_ctx *ngtcp2_crypto_ctx_tls_early(ngtcp2_crypto_ctx *ctx,
                                               void *tls_native_handle) {
  gnutls_session_t session = tls_native_handle;
  gnutls_cipher_algorithm_t cipher;
  gnutls_digest_algorithm_t hash;
  gnutls_cipher_algorithm_t hp_cipher;

  cipher = gnutls_early_cipher_get(session);
  if (cipher == GNUTLS_CIPHER_UNKNOWN || cipher == GNUTLS_CIPHER_NULL) {
    return NULL;
  }

  if (!supported_cipher(cipher)) {
    return NULL;
  }

  hash = gnutls_early_prf_hash_get(session);
  if (hash == GNUTLS_DIG_UNKNOWN || hash == GNUTLS_DIG_NULL) {
    return NULL;
  }

  hp_cipher = crypto_get_hp(cipher);
  if (hp_cipher == GNUTLS_CIPHER_UNKNOWN || hp_cipher == GNUTLS_CIPHER_NULL) {
    return NULL;
  }

  ngtcp2_crypto_aead_init(&ctx->aead, (void *)cipher);
  ctx->md.native_handle = (void *)hash;
  ctx->hp.native_handle = (void *)hp_cipher;
  ctx->max_encryption = crypto_get_aead_max_encryption(cipher);
  ctx->max_decryption_failure = crypto_get_aead_max_decryption_failure(cipher);

  return ctx;
}

size_t ngtcp2_crypto_md_hashlen(const ngtcp2_crypto_md *md) {
  return gnutls_hash_get_len(
    (gnutls_digest_algorithm_t)(intptr_t)md->native_handle);
}

size_t ngtcp2_crypto_aead_keylen(const ngtcp2_crypto_aead *aead) {
  return gnutls_cipher_get_key_size(
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle);
}

size_t ngtcp2_crypto_aead_noncelen(const ngtcp2_crypto_aead *aead) {
  return gnutls_cipher_get_iv_size(
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle);
}

int ngtcp2_crypto_aead_ctx_encrypt_init(ngtcp2_crypto_aead_ctx *aead_ctx,
                                        const ngtcp2_crypto_aead *aead,
                                        const uint8_t *key, size_t noncelen) {
  gnutls_cipher_algorithm_t cipher =
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle;
  gnutls_aead_cipher_hd_t hd;

  (void)noncelen;

  if (gnutls_aead_cipher_init(
        &hd, cipher,
        &(gnutls_datum_t){
          .data = (uint8_t *)key,
          .size = (unsigned int)ngtcp2_crypto_aead_keylen(aead),
        }) != 0) {
    return -1;
  }

  aead_ctx->native_handle = hd;

  return 0;
}

int ngtcp2_crypto_aead_ctx_decrypt_init(ngtcp2_crypto_aead_ctx *aead_ctx,
                                        const ngtcp2_crypto_aead *aead,
                                        const uint8_t *key, size_t noncelen) {
  gnutls_cipher_algorithm_t cipher =
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle;
  gnutls_aead_cipher_hd_t hd;

  (void)noncelen;

  if (gnutls_aead_cipher_init(
        &hd, cipher,
        &(gnutls_datum_t){
          .data = (uint8_t *)key,
          .size = (unsigned int)ngtcp2_crypto_aead_keylen(aead),
        }) != 0) {
    return -1;
  }

  aead_ctx->native_handle = hd;

  return 0;
}

void ngtcp2_crypto_aead_ctx_free(ngtcp2_crypto_aead_ctx *aead_ctx) {
  if (aead_ctx->native_handle) {
    gnutls_aead_cipher_deinit(aead_ctx->native_handle);
  }
}

int ngtcp2_crypto_cipher_ctx_encrypt_init(ngtcp2_crypto_cipher_ctx *cipher_ctx,
                                          const ngtcp2_crypto_cipher *cipher,
                                          const uint8_t *key) {
  gnutls_cipher_algorithm_t cph =
    (gnutls_cipher_algorithm_t)(intptr_t)cipher->native_handle;
  gnutls_cipher_hd_t hd;

  if (gnutls_cipher_init(
        &hd, cph,
        &(gnutls_datum_t){
          .data = (uint8_t *)key,
          .size = (unsigned int)gnutls_cipher_get_key_size(cph),
        },
        NULL) != 0) {
    return -1;
  }

  cipher_ctx->native_handle = hd;

  return 0;
}

void ngtcp2_crypto_cipher_ctx_free(ngtcp2_crypto_cipher_ctx *cipher_ctx) {
  if (cipher_ctx->native_handle) {
    gnutls_cipher_deinit(cipher_ctx->native_handle);
  }
}

int ngtcp2_crypto_hkdf_extract(uint8_t *dest, const ngtcp2_crypto_md *md,
                               const uint8_t *secret, size_t secretlen,
                               const uint8_t *salt, size_t saltlen) {
  gnutls_mac_algorithm_t prf =
    (gnutls_mac_algorithm_t)(intptr_t)md->native_handle;

  if (gnutls_hkdf_extract(prf,
                          &(gnutls_datum_t){
                            .data = (uint8_t *)secret,
                            .size = (unsigned int)secretlen,
                          },
                          &(gnutls_datum_t){
                            .data = (uint8_t *)salt,
                            .size = (unsigned int)saltlen,
                          },
                          dest) != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_hkdf_expand(uint8_t *dest, size_t destlen,
                              const ngtcp2_crypto_md *md, const uint8_t *secret,
                              size_t secretlen, const uint8_t *info,
                              size_t infolen) {
  gnutls_mac_algorithm_t prf =
    (gnutls_mac_algorithm_t)(intptr_t)md->native_handle;

  if (gnutls_hkdf_expand(prf,
                         &(gnutls_datum_t){
                           .data = (uint8_t *)secret,
                           .size = (unsigned int)secretlen,
                         },
                         &(gnutls_datum_t){
                           .data = (uint8_t *)info,
                           .size = (unsigned int)infolen,
                         },
                         dest, destlen) != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_hkdf(uint8_t *dest, size_t destlen,
                       const ngtcp2_crypto_md *md, const uint8_t *secret,
                       size_t secretlen, const uint8_t *salt, size_t saltlen,
                       const uint8_t *info, size_t infolen) {
  gnutls_mac_algorithm_t prf =
    (gnutls_mac_algorithm_t)(intptr_t)md->native_handle;
  size_t keylen = ngtcp2_crypto_md_hashlen(md);
  uint8_t key[64];

  assert(keylen <= sizeof(key));

  if (gnutls_hkdf_extract(prf,
                          &(gnutls_datum_t){
                            .data = (uint8_t *)secret,
                            .size = (unsigned int)secretlen,
                          },
                          &(gnutls_datum_t){
                            .data = (uint8_t *)salt,
                            .size = (unsigned int)saltlen,
                          },
                          key) != 0) {
    return -1;
  }

  if (gnutls_hkdf_expand(prf,
                         &(gnutls_datum_t){
                           .data = (uint8_t *)key,
                           .size = (unsigned int)keylen,
                         },
                         &(gnutls_datum_t){
                           .data = (uint8_t *)info,
                           .size = (unsigned int)infolen,
                         },
                         dest, destlen) != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_encrypt(uint8_t *dest, const ngtcp2_crypto_aead *aead,
                          const ngtcp2_crypto_aead_ctx *aead_ctx,
                          const uint8_t *plaintext, size_t plaintextlen,
                          const uint8_t *nonce, size_t noncelen,
                          const uint8_t *aad, size_t aadlen) {
  gnutls_cipher_algorithm_t cipher =
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle;
  gnutls_aead_cipher_hd_t hd = aead_ctx->native_handle;
  size_t taglen = gnutls_cipher_get_tag_size(cipher);
  size_t ciphertextlen = plaintextlen + taglen;

  if (gnutls_aead_cipher_encrypt(hd, nonce, noncelen, aad, aadlen, taglen,
                                 plaintext, plaintextlen, dest,
                                 &ciphertextlen) != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_decrypt(uint8_t *dest, const ngtcp2_crypto_aead *aead,
                          const ngtcp2_crypto_aead_ctx *aead_ctx,
                          const uint8_t *ciphertext, size_t ciphertextlen,
                          const uint8_t *nonce, size_t noncelen,
                          const uint8_t *aad, size_t aadlen) {
  gnutls_cipher_algorithm_t cipher =
    (gnutls_cipher_algorithm_t)(intptr_t)aead->native_handle;
  gnutls_aead_cipher_hd_t hd = aead_ctx->native_handle;
  size_t taglen = gnutls_cipher_get_tag_size(cipher);
  size_t plaintextlen;

  if (taglen > ciphertextlen) {
    return -1;
  }

  plaintextlen = ciphertextlen - taglen;

  if (gnutls_aead_cipher_decrypt(hd, nonce, noncelen, aad, aadlen, taglen,
                                 ciphertext, ciphertextlen, dest,
                                 &plaintextlen) != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_hp_mask(uint8_t *dest, const ngtcp2_crypto_cipher *hp,
                          const ngtcp2_crypto_cipher_ctx *hp_ctx,
                          const uint8_t *sample) {
  gnutls_cipher_algorithm_t cipher =
    (gnutls_cipher_algorithm_t)(intptr_t)hp->native_handle;
  gnutls_cipher_hd_t hd = hp_ctx->native_handle;

  switch (cipher) {
  case GNUTLS_CIPHER_AES_128_CBC:
  case GNUTLS_CIPHER_AES_256_CBC: {
    /* Emulate one block AES-ECB by invalidating the effect of IV */
    static const uint8_t iv[16] = {0};
    uint8_t buf[16];

    gnutls_cipher_set_iv(hd, (uint8_t *)iv, sizeof(iv));

    if (gnutls_cipher_encrypt2(hd, sample, 16, buf, sizeof(buf)) != 0) {
      return -1;
    }

    memcpy(dest, buf, 5);
  } break;

  case GNUTLS_CIPHER_CHACHA20_32: {
    static const uint8_t PLAINTEXT[16] = {0};
    uint8_t buf[5 + 16];
    size_t buflen = sizeof(buf);

    gnutls_cipher_set_iv(hd, (void *)sample, 16);

    if (gnutls_cipher_encrypt2(hd, PLAINTEXT, sizeof(PLAINTEXT), buf, buflen) !=
        0) {
      return -1;
    }

    memcpy(dest, buf, 5);
  } break;
  default:
    assert(0);
  }

  return 0;
}

ngtcp2_encryption_level
ngtcp2_crypto_gnutls_from_gnutls_record_encryption_level(
  gnutls_record_encryption_level_t gtls_level) {
  switch (gtls_level) {
  case GNUTLS_ENCRYPTION_LEVEL_INITIAL:
    return NGTCP2_ENCRYPTION_LEVEL_INITIAL;
  case GNUTLS_ENCRYPTION_LEVEL_HANDSHAKE:
    return NGTCP2_ENCRYPTION_LEVEL_HANDSHAKE;
  case GNUTLS_ENCRYPTION_LEVEL_APPLICATION:
    return NGTCP2_ENCRYPTION_LEVEL_1RTT;
  case GNUTLS_ENCRYPTION_LEVEL_EARLY:
    return NGTCP2_ENCRYPTION_LEVEL_0RTT;
  default:
    assert(0);
    abort();
  }
}

gnutls_record_encryption_level_t
ngtcp2_crypto_gnutls_from_ngtcp2_encryption_level(
  ngtcp2_encryption_level encryption_level) {
  switch (encryption_level) {
  case NGTCP2_ENCRYPTION_LEVEL_INITIAL:
    return GNUTLS_ENCRYPTION_LEVEL_INITIAL;
  case NGTCP2_ENCRYPTION_LEVEL_HANDSHAKE:
    return GNUTLS_ENCRYPTION_LEVEL_HANDSHAKE;
  case NGTCP2_ENCRYPTION_LEVEL_1RTT:
    return GNUTLS_ENCRYPTION_LEVEL_APPLICATION;
  case NGTCP2_ENCRYPTION_LEVEL_0RTT:
    return GNUTLS_ENCRYPTION_LEVEL_EARLY;
  default:
    assert(0);
    abort();
  }
}

int ngtcp2_crypto_read_write_crypto_data(
  ngtcp2_conn *conn, ngtcp2_encryption_level encryption_level,
  const uint8_t *data, size_t datalen) {
  gnutls_session_t session = ngtcp2_conn_get_tls_native_handle(conn);
  int rv;

  if (datalen > 0) {
    rv = gnutls_handshake_write(
      session,
      ngtcp2_crypto_gnutls_from_ngtcp2_encryption_level(encryption_level), data,
      datalen);
    if (rv != 0) {
      if (!gnutls_error_is_fatal(rv)) {
        return 0;
      }
      gnutls_alert_send_appropriate(session, rv);
      return -1;
    }
  }

  if (!ngtcp2_conn_get_handshake_completed(conn)) {
    rv = gnutls_handshake(session);
    if (rv < 0) {
      if (!gnutls_error_is_fatal(rv)) {
        return 0;
      }
      gnutls_alert_send_appropriate(session, rv);
      return -1;
    }

    ngtcp2_conn_tls_handshake_completed(conn);
  }

  return 0;
}

int ngtcp2_crypto_set_remote_transport_params(ngtcp2_conn *conn, void *tls) {
  (void)conn;
  (void)tls;
  /* Nothing to do; GnuTLS applications are supposed to register the
     quic_transport_parameters extension with
     gnutls_session_ext_register. */
  return 0;
}

int ngtcp2_crypto_set_local_transport_params(void *tls, const uint8_t *buf,
                                             size_t len) {
  (void)tls;
  (void)buf;
  (void)len;
  /* Nothing to do; GnuTLS applications are supposed to register the
     quic_transport_parameters extension with
     gnutls_session_ext_register. */
  return 0;
}

int ngtcp2_crypto_get_path_challenge_data_cb(ngtcp2_conn *conn, uint8_t *data,
                                             void *user_data) {
  (void)conn;
  (void)user_data;

  if (gnutls_rnd(GNUTLS_RND_RANDOM, data, NGTCP2_PATH_CHALLENGE_DATALEN) != 0) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

int ngtcp2_crypto_get_path_challenge_data2_cb(ngtcp2_conn *conn,
                                              ngtcp2_path_challenge_data *data,
                                              void *user_data) {
  (void)conn;
  (void)user_data;

  if (gnutls_rnd(GNUTLS_RND_RANDOM, data->data,
                 NGTCP2_PATH_CHALLENGE_DATALEN) != 0) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

int ngtcp2_crypto_random(uint8_t *data, size_t datalen) {
  if (gnutls_rnd(GNUTLS_RND_RANDOM, data, datalen) != 0) {
    return -1;
  }

  return 0;
}

static int secret_func(gnutls_session_t session,
                       gnutls_record_encryption_level_t gtls_level,
                       const void *rx_secret, const void *tx_secret,
                       size_t secretlen) {
  ngtcp2_crypto_conn_ref *conn_ref = gnutls_session_get_ptr(session);
  ngtcp2_conn *conn = conn_ref->get_conn(conn_ref);
  ngtcp2_encryption_level level =
    ngtcp2_crypto_gnutls_from_gnutls_record_encryption_level(gtls_level);

  if (rx_secret &&
      ngtcp2_crypto_derive_and_install_rx_key(conn, NULL, NULL, NULL, level,
                                              rx_secret, secretlen) != 0) {
    return -1;
  }

  if (tx_secret &&
      ngtcp2_crypto_derive_and_install_tx_key(conn, NULL, NULL, NULL, level,
                                              tx_secret, secretlen) != 0) {
    return -1;
  }

  return 0;
}

static int read_func(gnutls_session_t session,
                     gnutls_record_encryption_level_t gtls_level,
                     gnutls_handshake_description_t htype, const void *data,
                     size_t datalen) {
  ngtcp2_crypto_conn_ref *conn_ref = gnutls_session_get_ptr(session);
  ngtcp2_conn *conn = conn_ref->get_conn(conn_ref);
  ngtcp2_encryption_level level =
    ngtcp2_crypto_gnutls_from_gnutls_record_encryption_level(gtls_level);
  int rv;

  if (htype == GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC) {
    return 0;
  }

  rv = ngtcp2_conn_submit_crypto_data(conn, level, data, datalen);
  if (rv != 0) {
    ngtcp2_conn_set_tls_error(conn, rv);
    return -1;
  }

  return 0;
}

static int alert_read_func(gnutls_session_t session,
                           gnutls_record_encryption_level_t gtls_level,
                           gnutls_alert_level_t alert_level,
                           gnutls_alert_description_t alert_desc) {
  ngtcp2_crypto_conn_ref *conn_ref = gnutls_session_get_ptr(session);
  ngtcp2_conn *conn = conn_ref->get_conn(conn_ref);
  (void)gtls_level;
  (void)alert_level;

  ngtcp2_conn_set_tls_alert(conn, (uint8_t)alert_desc);

  return 0;
}

static int tp_recv_func(gnutls_session_t session, const uint8_t *data,
                        size_t datalen) {
  ngtcp2_crypto_conn_ref *conn_ref = gnutls_session_get_ptr(session);
  ngtcp2_conn *conn = conn_ref->get_conn(conn_ref);
  int rv;

  rv = ngtcp2_conn_decode_and_set_remote_transport_params(conn, data, datalen);
  if (rv != 0) {
    ngtcp2_conn_set_tls_error(conn, rv);
    return -1;
  }

  return 0;
}

static int tp_send_func(gnutls_session_t session, gnutls_buffer_t extdata) {
  ngtcp2_crypto_conn_ref *conn_ref = gnutls_session_get_ptr(session);
  ngtcp2_conn *conn = conn_ref->get_conn(conn_ref);
  uint8_t buf[256];
  ngtcp2_ssize nwrite;
  int rv;

  nwrite = ngtcp2_conn_encode_local_transport_params(conn, buf, sizeof(buf));
  if (nwrite < 0) {
    return -1;
  }

  rv = gnutls_buffer_append_data(extdata, buf, (size_t)nwrite);
  if (rv != 0) {
    return -1;
  }

  return 0;
}

static int crypto_gnutls_configure_session(gnutls_session_t session) {
  int rv;

  gnutls_handshake_set_secret_function(session, secret_func);
  gnutls_handshake_set_read_function(session, read_func);
  gnutls_alert_set_read_function(session, alert_read_func);

  rv = gnutls_session_ext_register(
    session, "QUIC Transport Parameters",
    NGTCP2_TLSEXT_QUIC_TRANSPORT_PARAMETERS_V1, GNUTLS_EXT_TLS, tp_recv_func,
    tp_send_func, NULL, NULL, NULL,
    GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_CLIENT_HELLO | GNUTLS_EXT_FLAG_EE);
  if (rv != 0) {
    return -1;
  }

  return 0;
}

int ngtcp2_crypto_gnutls_configure_server_session(gnutls_session_t session) {
  return crypto_gnutls_configure_session(session);
}

int ngtcp2_crypto_gnutls_configure_client_session(gnutls_session_t session) {
  return crypto_gnutls_configure_session(session);
}
