path: root/contrib/restricted/aws/s2n/tls/s2n_connection.c

/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

#include "tls/s2n_connection.h"

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/param.h>
#include <time.h>
#include <unistd.h>

#include "api/s2n.h"
#include "crypto/s2n_certificate.h"
#include "crypto/s2n_cipher.h"
#include "crypto/s2n_crypto.h"
#include "crypto/s2n_fips.h"
#include "crypto/s2n_openssl_x509.h"
#include "error/s2n_errno.h"
#include "tls/extensions/s2n_client_server_name.h"
#include "tls/s2n_alerts.h"
#include "tls/s2n_cipher_suites.h"
#include "tls/s2n_handshake.h"
#include "tls/s2n_internal.h"
#include "tls/s2n_kem.h"
#include "tls/s2n_prf.h"
#include "tls/s2n_record.h"
#include "tls/s2n_resume.h"
#include "tls/s2n_security_policies.h"
#include "tls/s2n_tls.h"
#include "tls/s2n_tls_parameters.h"
#include "utils/s2n_atomic.h"
#include "utils/s2n_blob.h"
#include "utils/s2n_compiler.h"
#include "utils/s2n_io.h"
#include "utils/s2n_mem.h"
#include "utils/s2n_random.h"
#include "utils/s2n_safety.h"
#include "utils/s2n_socket.h"
#include "utils/s2n_timer.h"

#define S2N_SET_KEY_SHARE_LIST_EMPTY(keyshares) (keyshares |= 1)
#define S2N_SET_KEY_SHARE_REQUEST(keyshares, i) (keyshares |= (1 << (i + 1)))

/* Allocates and initializes memory for a new connection.
 *
 * Since customers can reuse a connection, ensure that values on the connection are
 * initialized in `s2n_connection_wipe` where possible. */
struct s2n_connection *s2n_connection_new(s2n_mode mode)
{
    struct s2n_blob blob = { 0 };
    PTR_GUARD_POSIX(s2n_alloc(&blob, sizeof(struct s2n_connection)));
    PTR_GUARD_POSIX(s2n_blob_zero(&blob));

    /* Cast 'through' void to acknowledge that we are changing alignment,
     * which is ok, as blob.data is always aligned.
     */
    struct s2n_connection *conn = (struct s2n_connection *) (void *) blob.data;

    PTR_GUARD_POSIX(s2n_connection_set_config(conn, s2n_fetch_default_config()));

    /* `mode` is initialized here since it's passed in as a parameter. */
    conn->mode = mode;

    /* Allocate the fixed-size stuffers */
    blob = (struct s2n_blob){ 0 };
    PTR_GUARD_POSIX(s2n_blob_init(&blob, conn->alert_in_data, S2N_ALERT_LENGTH));
    PTR_GUARD_POSIX(s2n_stuffer_init(&conn->alert_in, &blob));

    blob = (struct s2n_blob){ 0 };
    PTR_GUARD_POSIX(s2n_blob_init(&blob, conn->ticket_ext_data, S2N_TLS12_TICKET_SIZE_IN_BYTES));
    PTR_GUARD_POSIX(s2n_stuffer_init(&conn->client_ticket_to_decrypt, &blob));

    /* Allocate long term hash and HMAC memory */
    PTR_GUARD_RESULT(s2n_prf_new(conn));
    PTR_GUARD_RESULT(s2n_handshake_hashes_new(&conn->handshake.hashes));

    /* Initialize the growable stuffers. Zero length at first, but the resize
     * in _wipe will fix that
     */
    blob = (struct s2n_blob){ 0 };
    PTR_GUARD_POSIX(s2n_blob_init(&blob, conn->header_in_data, S2N_TLS_RECORD_HEADER_LENGTH));
    PTR_GUARD_POSIX(s2n_stuffer_init(&conn->header_in, &blob));
    PTR_GUARD_POSIX(s2n_stuffer_growable_alloc(&conn->out, 0));
    PTR_GUARD_POSIX(s2n_stuffer_growable_alloc(&conn->in, 0));
    PTR_GUARD_POSIX(s2n_stuffer_growable_alloc(&conn->handshake.io, 0));
    PTR_GUARD_RESULT(s2n_timer_start(conn->config, &conn->write_timer));

    /* NOTE: s2n_connection_wipe MUST be called last in this function.
     *
     * s2n_connection_wipe is used for initializing values but also used by customers to
     * reset/reuse the connection. Calling it last ensures that s2n_connection_wipe is
     * implemented correctly and safe.
     */
    PTR_GUARD_POSIX(s2n_connection_wipe(conn));
    return conn;
}

static int s2n_connection_zero(struct s2n_connection *conn, int mode, struct s2n_config *config)
{
    /* Zero the whole connection structure */
    POSIX_CHECKED_MEMSET(conn, 0, sizeof(struct s2n_connection));

    conn->mode = mode;
    conn->max_outgoing_fragment_length = S2N_DEFAULT_FRAGMENT_LENGTH;
    conn->handshake.end_of_messages = APPLICATION_DATA;
    s2n_connection_set_config(conn, config);

    return 0;
}

S2N_RESULT s2n_connection_wipe_all_keyshares(struct s2n_connection *conn)
{
    RESULT_ENSURE_REF(conn);

    RESULT_GUARD_POSIX(s2n_ecc_evp_params_free(&conn->kex_params.server_ecc_evp_params));
    RESULT_GUARD_POSIX(s2n_ecc_evp_params_free(&conn->kex_params.client_ecc_evp_params));

    RESULT_GUARD_POSIX(s2n_kem_group_free(&conn->kex_params.server_kem_group_params));
    RESULT_GUARD_POSIX(s2n_kem_group_free(&conn->kex_params.client_kem_group_params));

    return S2N_RESULT_OK;
}

static int s2n_connection_wipe_keys(struct s2n_connection *conn)
{
    /* Free any server key received (we may not have completed a
     * handshake, so this may not have been free'd yet) */
    POSIX_GUARD(s2n_pkey_free(&conn->handshake_params.server_public_key));
    POSIX_GUARD(s2n_pkey_zero_init(&conn->handshake_params.server_public_key));
    POSIX_GUARD(s2n_pkey_free(&conn->handshake_params.client_public_key));
    POSIX_GUARD(s2n_pkey_zero_init(&conn->handshake_params.client_public_key));
    s2n_x509_validator_wipe(&conn->x509_validator);
    POSIX_GUARD(s2n_dh_params_free(&conn->kex_params.server_dh_params));
    POSIX_GUARD_RESULT(s2n_connection_wipe_all_keyshares(conn));
    POSIX_GUARD(s2n_kem_free(&conn->kex_params.kem_params));
    POSIX_GUARD(s2n_free(&conn->handshake_params.client_cert_chain));
    POSIX_GUARD(s2n_free(&conn->ct_response));

    return 0;
}

static int s2n_connection_free_managed_recv_io(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    if (conn->managed_recv_io) {
        POSIX_GUARD(s2n_free_object((uint8_t **) &conn->recv_io_context, sizeof(struct s2n_socket_read_io_context)));
        conn->managed_recv_io = false;
        conn->recv = NULL;
    }
    return S2N_SUCCESS;
}

static int s2n_connection_free_managed_send_io(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    if (conn->managed_send_io) {
        POSIX_GUARD(s2n_free_object((uint8_t **) &conn->send_io_context, sizeof(struct s2n_socket_write_io_context)));
        conn->managed_send_io = false;
        conn->send = NULL;
    }
    return S2N_SUCCESS;
}

static int s2n_connection_free_managed_io(struct s2n_connection *conn)
{
    POSIX_GUARD(s2n_connection_free_managed_recv_io(conn));
    POSIX_GUARD(s2n_connection_free_managed_send_io(conn));
    return S2N_SUCCESS;
}

static int s2n_connection_wipe_io(struct s2n_connection *conn)
{
    if (s2n_connection_is_managed_corked(conn) && conn->recv) {
        POSIX_GUARD(s2n_socket_read_restore(conn));
    }
    if (s2n_connection_is_managed_corked(conn) && conn->send) {
        POSIX_GUARD(s2n_socket_write_restore(conn));
    }

    /* Remove all I/O-related members */
    POSIX_GUARD(s2n_connection_free_managed_io(conn));

    return 0;
}

static uint8_t s2n_default_verify_host(const char *host_name, size_t len, void *data)
{
    /* if present, match server_name of the connection using rules
     * outlined in RFC6125 6.4. */

    struct s2n_connection *conn = data;

    if (conn->server_name[0] == '\0') {
        return 0;
    }

    /* complete match */
    if (strlen(conn->server_name) == len && strncasecmp(conn->server_name, host_name, len) == 0) {
        return 1;
    }

    /* match 1 level of wildcard */
    if (len > 2 && host_name[0] == '*' && host_name[1] == '.') {
        const char *suffix = strchr(conn->server_name, '.');

        if (suffix == NULL) {
            return 0;
        }

        if (strlen(suffix) == len - 1 && strncasecmp(suffix, host_name + 1, len - 1) == 0) {
            return 1;
        }
    }

    return 0;
}

S2N_CLEANUP_RESULT s2n_connection_ptr_free(struct s2n_connection **conn)
{
    RESULT_ENSURE_REF(conn);
    RESULT_GUARD_POSIX(s2n_connection_free(*conn));
    *conn = NULL;
    return S2N_RESULT_OK;
}

int s2n_connection_free(struct s2n_connection *conn)
{
    POSIX_GUARD(s2n_connection_wipe_keys(conn));
    POSIX_GUARD_RESULT(s2n_psk_parameters_wipe(&conn->psk_params));

    POSIX_GUARD_RESULT(s2n_prf_free(conn));
    POSIX_GUARD_RESULT(s2n_handshake_hashes_free(&conn->handshake.hashes));

    POSIX_GUARD(s2n_connection_free_managed_io(conn));

    POSIX_GUARD(s2n_free(&conn->client_ticket));
    POSIX_GUARD(s2n_free(&conn->status_response));
    POSIX_GUARD(s2n_free(&conn->our_quic_transport_parameters));
    POSIX_GUARD(s2n_free(&conn->peer_quic_transport_parameters));
    POSIX_GUARD(s2n_free(&conn->server_early_data_context));
    POSIX_GUARD(s2n_free(&conn->tls13_ticket_fields.session_secret));
    POSIX_GUARD(s2n_stuffer_free(&conn->in));
    POSIX_GUARD(s2n_stuffer_free(&conn->out));
    POSIX_GUARD(s2n_stuffer_free(&conn->handshake.io));
    POSIX_GUARD(s2n_stuffer_free(&conn->post_handshake.in));
    s2n_x509_validator_wipe(&conn->x509_validator);
    POSIX_GUARD(s2n_client_hello_free_raw_message(&conn->client_hello));
    POSIX_GUARD(s2n_free(&conn->application_protocols_overridden));
    POSIX_GUARD(s2n_free(&conn->cookie));
    POSIX_GUARD_RESULT(s2n_crypto_parameters_free(&conn->initial));
    POSIX_GUARD_RESULT(s2n_crypto_parameters_free(&conn->secure));
    POSIX_GUARD(s2n_free_object((uint8_t **) &conn, sizeof(struct s2n_connection)));

    return 0;
}

int s2n_connection_set_config(struct s2n_connection *conn, struct s2n_config *config)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(config);

    if (conn->config == config) {
        return 0;
    }

    /* We only support one client certificate */
    if (s2n_config_get_num_default_certs(config) > 1 && conn->mode == S2N_CLIENT) {
        POSIX_BAIL(S2N_ERR_TOO_MANY_CERTIFICATES);
    }

    s2n_x509_validator_wipe(&conn->x509_validator);

    s2n_cert_auth_type auth_type = config->client_cert_auth_type;

    if (conn->client_cert_auth_type_overridden) {
        auth_type = conn->client_cert_auth_type;
    }

    int8_t dont_need_x509_validation = (conn->mode == S2N_SERVER) && (auth_type == S2N_CERT_AUTH_NONE);

    if (config->disable_x509_validation || dont_need_x509_validation) {
        POSIX_GUARD(s2n_x509_validator_init_no_x509_validation(&conn->x509_validator));
    } else {
        POSIX_GUARD(s2n_x509_validator_init(&conn->x509_validator, &config->trust_store, config->check_ocsp));
        if (!conn->verify_host_fn_overridden) {
            if (config->verify_host_fn != NULL) {
                conn->verify_host_fn = config->verify_host_fn;
                conn->data_for_verify_host = config->data_for_verify_host;
            } else {
                conn->verify_host_fn = s2n_default_verify_host;
                conn->data_for_verify_host = conn;
            }
        }

        if (config->max_verify_cert_chain_depth_set) {
            POSIX_GUARD(s2n_x509_validator_set_max_chain_depth(&conn->x509_validator, config->max_verify_cert_chain_depth));
        }
    }
    conn->tickets_to_send = config->initial_tickets_to_send;

    if (conn->psk_params.psk_list.len == 0 && !conn->psk_mode_overridden) {
        POSIX_GUARD(s2n_connection_set_psk_mode(conn, config->psk_mode));
        conn->psk_mode_overridden = false;
    }

    /* If at least one certificate does not have a private key configured,
     * the config must provide an async pkey callback.
     * The handshake could still fail if the callback doesn't offload the
     * signature, but this at least catches configuration mistakes.
     */
    if (config->no_signing_key) {
        POSIX_ENSURE(config->async_pkey_cb, S2N_ERR_NO_PRIVATE_KEY);
    }

    if (config->quic_enabled) {
        /* If QUIC is ever enabled for a connection via the config,
         * we should enforce that it can never be disabled by
         * changing the config.
         *
         * Enabling QUIC indicates that the connection is being used by
         * a QUIC implementation, which never changes. Disabling QUIC
         * partially through a connection could also potentially be
         * dangerous, as QUIC handles encryption.
         */
        POSIX_GUARD(s2n_connection_enable_quic(conn));
    }

    if (config->send_buffer_size_override) {
        conn->multirecord_send = true;
    }

    /* Historically, calling s2n_config_set_verification_ca_location enabled OCSP stapling
     * regardless of the value set by an application calling s2n_config_set_status_request_type.
     * We maintain this behavior for backwards compatibility.
     *
     * However, the s2n_config_set_verification_ca_location behavior predates client authentication
     * support for OCSP stapling, so could only affect whether clients requested OCSP stapling. We
     * therefore only have to maintain the legacy behavior for clients, not servers.
     * 
     * Note: The Rust bindings do not maintain the legacy behavior.
     */
    conn->request_ocsp_status = config->ocsp_status_requested_by_user;
    if (config->ocsp_status_requested_by_s2n && conn->mode == S2N_CLIENT) {
        conn->request_ocsp_status = true;
    }

    conn->config = config;
    return S2N_SUCCESS;
}

int s2n_connection_server_name_extension_used(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE(conn->mode == S2N_SERVER, S2N_ERR_INVALID_STATE);
    POSIX_ENSURE(!(conn->handshake.client_hello_received), S2N_ERR_INVALID_STATE);

    conn->server_name_used = 1;
    return S2N_SUCCESS;
}

int s2n_connection_set_ctx(struct s2n_connection *conn, void *ctx)
{
    POSIX_ENSURE_REF(conn);

    conn->context = ctx;
    return S2N_SUCCESS;
}

void *s2n_connection_get_ctx(struct s2n_connection *conn)
{
    return conn->context;
}

int s2n_connection_release_buffers(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);
    POSIX_PRECONDITION(s2n_stuffer_validate(&conn->out));
    POSIX_PRECONDITION(s2n_stuffer_validate(&conn->in));

    POSIX_ENSURE(s2n_stuffer_is_consumed(&conn->out), S2N_ERR_STUFFER_HAS_UNPROCESSED_DATA);
    POSIX_GUARD(s2n_stuffer_resize(&conn->out, 0));

    POSIX_ENSURE(s2n_stuffer_is_consumed(&conn->in), S2N_ERR_STUFFER_HAS_UNPROCESSED_DATA);
    POSIX_GUARD(s2n_stuffer_resize(&conn->in, 0));

    POSIX_ENSURE(s2n_stuffer_is_consumed(&conn->post_handshake.in), S2N_ERR_STUFFER_HAS_UNPROCESSED_DATA);
    POSIX_GUARD(s2n_stuffer_free(&conn->post_handshake.in));

    POSIX_POSTCONDITION(s2n_stuffer_validate(&conn->out));
    POSIX_POSTCONDITION(s2n_stuffer_validate(&conn->in));
    return S2N_SUCCESS;
}

int s2n_connection_free_handshake(struct s2n_connection *conn)
{
    /* We are done with the handshake */
    POSIX_GUARD_RESULT(s2n_handshake_hashes_free(&conn->handshake.hashes));
    POSIX_GUARD_RESULT(s2n_prf_free(conn));

    /* All IO should use conn->secure after the handshake.
     * However, if this method is called before the handshake completes,
     * the connection may still be using conn->initial.
     */
    if (conn->client != conn->initial && conn->server != conn->initial) {
        POSIX_GUARD_RESULT(s2n_crypto_parameters_free(&conn->initial));
    }

    /* Wipe the buffers we are going to free */
    POSIX_GUARD(s2n_stuffer_wipe(&conn->handshake.io));
    POSIX_GUARD(s2n_blob_zero(&conn->client_hello.raw_message));

    /* Truncate buffers to save memory, we are done with the handshake */
    POSIX_GUARD(s2n_stuffer_resize(&conn->handshake.io, 0));
    POSIX_GUARD(s2n_free(&conn->client_hello.raw_message));

    /* We can free extension data we no longer need */
    POSIX_GUARD(s2n_free(&conn->client_ticket));
    POSIX_GUARD(s2n_free(&conn->status_response));
    POSIX_GUARD(s2n_free(&conn->our_quic_transport_parameters));
    POSIX_GUARD(s2n_free(&conn->application_protocols_overridden));
    POSIX_GUARD(s2n_free(&conn->cookie));

    return 0;
}

/* An idempotent operation which initializes values on the connection.
 *
 * Called in order to reuse a connection structure for a new connection. Should wipe
 * any persistent memory, free any temporary memory, and set all fields back to their
 * defaults.
 */
int s2n_connection_wipe(struct s2n_connection *conn)
{
    /* First make a copy of everything we'd like to save, which isn't very much. */
    int mode = conn->mode;
    struct s2n_config *config = conn->config;
    struct s2n_stuffer alert_in = { 0 };
    struct s2n_stuffer client_ticket_to_decrypt = { 0 };
    struct s2n_stuffer handshake_io = { 0 };
    struct s2n_stuffer header_in = { 0 };
    struct s2n_stuffer in = { 0 };
    struct s2n_stuffer out = { 0 };

    /* Some required structures might have been freed to conserve memory between handshakes.
     * Restore them.
     */
    if (!conn->handshake.hashes) {
        POSIX_GUARD_RESULT(s2n_handshake_hashes_new(&conn->handshake.hashes));
    }
    POSIX_GUARD_RESULT(s2n_handshake_hashes_wipe(conn->handshake.hashes));
    struct s2n_handshake_hashes *handshake_hashes = conn->handshake.hashes;
    if (!conn->prf_space) {
        POSIX_GUARD_RESULT(s2n_prf_new(conn));
    }
    POSIX_GUARD_RESULT(s2n_prf_wipe(conn));
    struct s2n_prf_working_space *prf_workspace = conn->prf_space;
    if (!conn->initial) {
        POSIX_GUARD_RESULT(s2n_crypto_parameters_new(&conn->initial));
    } else {
        POSIX_GUARD_RESULT(s2n_crypto_parameters_wipe(conn->initial));
    }
    struct s2n_crypto_parameters *initial = conn->initial;
    if (!conn->secure) {
        POSIX_GUARD_RESULT(s2n_crypto_parameters_new(&conn->secure));
    } else {
        POSIX_GUARD_RESULT(s2n_crypto_parameters_wipe(conn->secure));
    }
    struct s2n_crypto_parameters *secure = conn->secure;

    /* Wipe all of the sensitive stuff */
    POSIX_GUARD(s2n_connection_wipe_keys(conn));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->alert_in));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->client_ticket_to_decrypt));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->handshake.io));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->post_handshake.in));
    POSIX_GUARD(s2n_blob_zero(&conn->client_hello.raw_message));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->header_in));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->in));
    POSIX_GUARD(s2n_stuffer_wipe(&conn->out));

    /* Free stuffers we plan to just recreate */
    POSIX_GUARD(s2n_stuffer_free(&conn->post_handshake.in));

    POSIX_GUARD_RESULT(s2n_psk_parameters_wipe(&conn->psk_params));

    /* Wipe the I/O-related info and restore the original socket if necessary */
    POSIX_GUARD(s2n_connection_wipe_io(conn));

    POSIX_GUARD(s2n_free(&conn->client_ticket));
    POSIX_GUARD(s2n_free(&conn->status_response));
    POSIX_GUARD(s2n_free(&conn->application_protocols_overridden));
    POSIX_GUARD(s2n_free(&conn->our_quic_transport_parameters));
    POSIX_GUARD(s2n_free(&conn->peer_quic_transport_parameters));
    POSIX_GUARD(s2n_free(&conn->server_early_data_context));
    POSIX_GUARD(s2n_free(&conn->tls13_ticket_fields.session_secret));
    POSIX_GUARD(s2n_free(&conn->cookie));

    /* Allocate memory for handling handshakes */
    POSIX_GUARD(s2n_stuffer_resize(&conn->handshake.io, S2N_LARGE_RECORD_LENGTH));

    /* Truncate the message buffers to save memory, we will dynamically resize it as needed */
    POSIX_GUARD(s2n_free(&conn->client_hello.raw_message));
    POSIX_GUARD(s2n_stuffer_resize(&conn->in, 0));
    POSIX_GUARD(s2n_stuffer_resize(&conn->out, 0));

    /* Remove context associated with connection */
    conn->context = NULL;
    conn->verify_host_fn_overridden = 0;
    conn->verify_host_fn = NULL;
    conn->data_for_verify_host = NULL;

    /* Clone the stuffers */
    /* ignore address warnings because dest is allocated on the stack */
#ifdef S2N_DIAGNOSTICS_PUSH_SUPPORTED
    #pragma GCC diagnostic push
    #pragma GCC diagnostic ignored "-Waddress"
#endif
    POSIX_CHECKED_MEMCPY(&alert_in, &conn->alert_in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&client_ticket_to_decrypt, &conn->client_ticket_to_decrypt, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&handshake_io, &conn->handshake.io, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&header_in, &conn->header_in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&in, &conn->in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&out, &conn->out, sizeof(struct s2n_stuffer));
#ifdef S2N_DIAGNOSTICS_POP_SUPPORTED
    #pragma GCC diagnostic pop
#endif

    POSIX_GUARD(s2n_connection_zero(conn, mode, config));

    POSIX_CHECKED_MEMCPY(&conn->alert_in, &alert_in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&conn->client_ticket_to_decrypt, &client_ticket_to_decrypt, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&conn->handshake.io, &handshake_io, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&conn->header_in, &header_in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&conn->in, &in, sizeof(struct s2n_stuffer));
    POSIX_CHECKED_MEMCPY(&conn->out, &out, sizeof(struct s2n_stuffer));

    conn->handshake.hashes = handshake_hashes;
    conn->prf_space = prf_workspace;
    conn->initial = initial;
    conn->secure = secure;
    conn->client = conn->initial;
    conn->server = conn->initial;
    conn->handshake_params.client_cert_sig_scheme = &s2n_null_sig_scheme;
    conn->handshake_params.server_cert_sig_scheme = &s2n_null_sig_scheme;

    POSIX_GUARD_RESULT(s2n_psk_parameters_init(&conn->psk_params));
    conn->server_keying_material_lifetime = ONE_WEEK_IN_SEC;

    /* Require all handshakes hashes. This set can be reduced as the handshake progresses. */
    POSIX_GUARD(s2n_handshake_require_all_hashes(&conn->handshake));

    if (conn->mode == S2N_SERVER) {
        /* Start with the highest protocol version so that the highest common protocol version can be selected */
        /* during handshake. */
        conn->server_protocol_version = s2n_highest_protocol_version;
        conn->client_protocol_version = s2n_unknown_protocol_version;
        conn->actual_protocol_version = s2n_unknown_protocol_version;
    } else {
        /* For clients, also set actual_protocol_version.  Record generation uses that value for the initial */
        /* ClientHello record version. Not all servers ignore the record version in ClientHello. */
        conn->server_protocol_version = s2n_unknown_protocol_version;
        conn->client_protocol_version = s2n_highest_protocol_version;
        conn->actual_protocol_version = s2n_highest_protocol_version;
    }

    /* Initialize remaining values */
    conn->blinding = S2N_BUILT_IN_BLINDING;
    conn->session_ticket_status = S2N_NO_TICKET;

    return 0;
}

int s2n_connection_set_recv_ctx(struct s2n_connection *conn, void *ctx)
{
    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_connection_free_managed_recv_io(conn));
    conn->recv_io_context = ctx;
    return S2N_SUCCESS;
}

int s2n_connection_set_send_ctx(struct s2n_connection *conn, void *ctx)
{
    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_connection_free_managed_send_io(conn));
    conn->send_io_context = ctx;
    return S2N_SUCCESS;
}

int s2n_connection_set_recv_cb(struct s2n_connection *conn, s2n_recv_fn recv)
{
    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_connection_free_managed_recv_io(conn));
    conn->recv = recv;
    return S2N_SUCCESS;
}

int s2n_connection_set_send_cb(struct s2n_connection *conn, s2n_send_fn send)
{
    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_connection_free_managed_send_io(conn));
    conn->send = send;
    return S2N_SUCCESS;
}

int s2n_connection_get_client_cert_chain(struct s2n_connection *conn, uint8_t **der_cert_chain_out, uint32_t *cert_chain_len)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(der_cert_chain_out);
    POSIX_ENSURE_REF(cert_chain_len);
    POSIX_ENSURE_REF(conn->handshake_params.client_cert_chain.data);

    *der_cert_chain_out = conn->handshake_params.client_cert_chain.data;
    *cert_chain_len = conn->handshake_params.client_cert_chain.size;

    return 0;
}

int s2n_connection_get_cipher_preferences(struct s2n_connection *conn, const struct s2n_cipher_preferences **cipher_preferences)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->config);
    POSIX_ENSURE_REF(cipher_preferences);

    if (conn->security_policy_override != NULL) {
        *cipher_preferences = conn->security_policy_override->cipher_preferences;
    } else if (conn->config->security_policy != NULL) {
        *cipher_preferences = conn->config->security_policy->cipher_preferences;
    } else {
        POSIX_BAIL(S2N_ERR_INVALID_CIPHER_PREFERENCES);
    }

    POSIX_ENSURE_REF(*cipher_preferences);
    return 0;
}

int s2n_connection_get_security_policy(struct s2n_connection *conn, const struct s2n_security_policy **security_policy)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->config);
    POSIX_ENSURE_REF(security_policy);

    if (conn->security_policy_override != NULL) {
        *security_policy = conn->security_policy_override;
    } else if (conn->config->security_policy != NULL) {
        *security_policy = conn->config->security_policy;
    } else {
        POSIX_BAIL(S2N_ERR_INVALID_SECURITY_POLICY);
    }

    POSIX_ENSURE_REF(*security_policy);
    return 0;
}

int s2n_connection_get_kem_preferences(struct s2n_connection *conn, const struct s2n_kem_preferences **kem_preferences)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->config);
    POSIX_ENSURE_REF(kem_preferences);

    if (conn->security_policy_override != NULL) {
        *kem_preferences = conn->security_policy_override->kem_preferences;
    } else if (conn->config->security_policy != NULL) {
        *kem_preferences = conn->config->security_policy->kem_preferences;
    } else {
        POSIX_BAIL(S2N_ERR_INVALID_KEM_PREFERENCES);
    }

    POSIX_ENSURE_REF(*kem_preferences);
    return 0;
}

int s2n_connection_get_signature_preferences(struct s2n_connection *conn, const struct s2n_signature_preferences **signature_preferences)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->config);
    POSIX_ENSURE_REF(signature_preferences);

    if (conn->security_policy_override != NULL) {
        *signature_preferences = conn->security_policy_override->signature_preferences;
    } else if (conn->config->security_policy != NULL) {
        *signature_preferences = conn->config->security_policy->signature_preferences;
    } else {
        POSIX_BAIL(S2N_ERR_INVALID_SIGNATURE_ALGORITHMS_PREFERENCES);
    }

    POSIX_ENSURE_REF(*signature_preferences);
    return 0;
}

int s2n_connection_get_ecc_preferences(struct s2n_connection *conn, const struct s2n_ecc_preferences **ecc_preferences)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->config);
    POSIX_ENSURE_REF(ecc_preferences);

    if (conn->security_policy_override != NULL) {
        *ecc_preferences = conn->security_policy_override->ecc_preferences;
    } else if (conn->config->security_policy != NULL) {
        *ecc_preferences = conn->config->security_policy->ecc_preferences;
    } else {
        POSIX_BAIL(S2N_ERR_INVALID_ECC_PREFERENCES);
    }

    POSIX_ENSURE_REF(*ecc_preferences);
    return 0;
}

int s2n_connection_get_protocol_preferences(struct s2n_connection *conn, struct s2n_blob **protocol_preferences)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(protocol_preferences);

    *protocol_preferences = NULL;
    if (conn->application_protocols_overridden.size > 0) {
        *protocol_preferences = &conn->application_protocols_overridden;
    } else {
        POSIX_ENSURE_REF(conn->config);
        *protocol_preferences = &conn->config->application_protocols;
    }

    POSIX_ENSURE_REF(*protocol_preferences);
    return 0;
}

int s2n_connection_get_client_auth_type(struct s2n_connection *conn, s2n_cert_auth_type *client_cert_auth_type)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(client_cert_auth_type);

    if (conn->client_cert_auth_type_overridden) {
        *client_cert_auth_type = conn->client_cert_auth_type;
    } else {
        POSIX_ENSURE_REF(conn->config);
        *client_cert_auth_type = conn->config->client_cert_auth_type;
    }

    return 0;
}

int s2n_connection_set_client_auth_type(struct s2n_connection *conn, s2n_cert_auth_type client_cert_auth_type)
{
    conn->client_cert_auth_type_overridden = 1;
    conn->client_cert_auth_type = client_cert_auth_type;
    return 0;
}

int s2n_connection_set_read_fd(struct s2n_connection *conn, int rfd)
{
    struct s2n_blob ctx_mem = { 0 };
    struct s2n_socket_read_io_context *peer_socket_ctx;

    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_alloc(&ctx_mem, sizeof(struct s2n_socket_read_io_context)));
    POSIX_GUARD(s2n_blob_zero(&ctx_mem));

    peer_socket_ctx = (struct s2n_socket_read_io_context *) (void *) ctx_mem.data;
    peer_socket_ctx->fd = rfd;

    POSIX_GUARD(s2n_connection_set_recv_cb(conn, s2n_socket_read));
    POSIX_GUARD(s2n_connection_set_recv_ctx(conn, peer_socket_ctx));
    conn->managed_recv_io = true;

    /* This is only needed if the user is using corked io.
     * Take the snapshot in case optimized io is enabled after setting the fd.
     */
    POSIX_GUARD(s2n_socket_read_snapshot(conn));

    return 0;
}

int s2n_connection_get_read_fd(struct s2n_connection *conn, int *readfd)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(readfd);
    POSIX_ENSURE((conn->managed_recv_io && conn->recv_io_context), S2N_ERR_INVALID_STATE);

    const struct s2n_socket_read_io_context *peer_socket_ctx = conn->recv_io_context;
    *readfd = peer_socket_ctx->fd;
    return S2N_SUCCESS;
}

int s2n_connection_set_write_fd(struct s2n_connection *conn, int wfd)
{
    struct s2n_blob ctx_mem = { 0 };
    struct s2n_socket_write_io_context *peer_socket_ctx;

    POSIX_ENSURE_REF(conn);
    POSIX_GUARD(s2n_alloc(&ctx_mem, sizeof(struct s2n_socket_write_io_context)));

    peer_socket_ctx = (struct s2n_socket_write_io_context *) (void *) ctx_mem.data;
    peer_socket_ctx->fd = wfd;

    POSIX_GUARD(s2n_connection_set_send_cb(conn, s2n_socket_write));
    POSIX_GUARD(s2n_connection_set_send_ctx(conn, peer_socket_ctx));
    conn->managed_send_io = true;

    /* This is only needed if the user is using corked io.
     * Take the snapshot in case optimized io is enabled after setting the fd.
     */
    POSIX_GUARD(s2n_socket_write_snapshot(conn));

    uint8_t ipv6;
    if (0 == s2n_socket_is_ipv6(wfd, &ipv6)) {
        conn->ipv6 = (ipv6 ? 1 : 0);
    }

    conn->write_fd_broken = 0;

    return 0;
}

int s2n_connection_get_write_fd(struct s2n_connection *conn, int *writefd)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(writefd);
    POSIX_ENSURE((conn->managed_send_io && conn->send_io_context), S2N_ERR_INVALID_STATE);

    const struct s2n_socket_write_io_context *peer_socket_ctx = conn->send_io_context;
    *writefd = peer_socket_ctx->fd;
    return S2N_SUCCESS;
}
int s2n_connection_set_fd(struct s2n_connection *conn, int fd)
{
    POSIX_GUARD(s2n_connection_set_read_fd(conn, fd));
    POSIX_GUARD(s2n_connection_set_write_fd(conn, fd));
    return 0;
}

int s2n_connection_use_corked_io(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    /* Caller shouldn't be trying to set s2n IO corked on non-s2n-managed IO */
    POSIX_ENSURE(conn->managed_send_io, S2N_ERR_CORK_SET_ON_UNMANAGED);
    conn->corked_io = 1;

    return 0;
}

uint64_t s2n_connection_get_wire_bytes_in(struct s2n_connection *conn)
{
    if (conn->ktls_recv_enabled) {
        return 0;
    }
    return conn->wire_bytes_in;
}

uint64_t s2n_connection_get_wire_bytes_out(struct s2n_connection *conn)
{
    if (conn->ktls_send_enabled) {
        return 0;
    }
    return conn->wire_bytes_out;
}

const char *s2n_connection_get_cipher(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);
    PTR_ENSURE_REF(conn->secure);
    PTR_ENSURE_REF(conn->secure->cipher_suite);

    return conn->secure->cipher_suite->name;
}

int s2n_connection_get_cipher_iana_value(struct s2n_connection *conn, uint8_t *first, uint8_t *second)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->secure);
    POSIX_ENSURE_REF(conn->secure->cipher_suite);
    POSIX_ENSURE_MUT(first);
    POSIX_ENSURE_MUT(second);

    /* ensure we've negotiated a cipher suite */
    POSIX_ENSURE(memcmp(conn->secure->cipher_suite->iana_value,
                         s2n_null_cipher_suite.iana_value, sizeof(s2n_null_cipher_suite.iana_value))
                    != 0,
            S2N_ERR_INVALID_STATE);

    const uint8_t *iana_value = conn->secure->cipher_suite->iana_value;
    *first = iana_value[0];
    *second = iana_value[1];

    return S2N_SUCCESS;
}

const char *s2n_connection_get_curve(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);
    PTR_ENSURE_REF(conn->secure);
    PTR_ENSURE_REF(conn->secure->cipher_suite);

    if (conn->kex_params.server_ecc_evp_params.negotiated_curve) {
        /* TLS1.3 currently only uses ECC groups. */
        if (conn->actual_protocol_version >= S2N_TLS13 || s2n_kex_includes(conn->secure->cipher_suite->key_exchange_alg, &s2n_ecdhe)) {
            return conn->kex_params.server_ecc_evp_params.negotiated_curve->name;
        }
    }

    return "NONE";
}

const char *s2n_connection_get_kem_name(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);

    if (!conn->kex_params.kem_params.kem) {
        return "NONE";
    }

    return conn->kex_params.kem_params.kem->name;
}

const char *s2n_connection_get_kem_group_name(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);

    if (conn->actual_protocol_version < S2N_TLS13 || !conn->kex_params.client_kem_group_params.kem_group) {
        return "NONE";
    }

    return conn->kex_params.client_kem_group_params.kem_group->name;
}

int s2n_connection_get_client_protocol_version(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    return conn->client_protocol_version;
}

int s2n_connection_get_server_protocol_version(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    return conn->server_protocol_version;
}

int s2n_connection_get_actual_protocol_version(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    return conn->actual_protocol_version;
}

int s2n_connection_get_client_hello_version(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    return conn->client_hello_version;
}

int s2n_connection_client_cert_used(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    if (IS_CLIENT_AUTH_HANDSHAKE(conn) && is_handshake_complete(conn)) {
        if (IS_CLIENT_AUTH_NO_CERT(conn)) {
            return 0;
        }
        return 1;
    }
    return 0;
}

int s2n_connection_get_alert(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    S2N_ERROR_IF(s2n_stuffer_data_available(&conn->alert_in) != 2, S2N_ERR_NO_ALERT);

    uint8_t alert_code = 0;
    POSIX_GUARD(s2n_stuffer_read_uint8(&conn->alert_in, &alert_code));
    POSIX_GUARD(s2n_stuffer_read_uint8(&conn->alert_in, &alert_code));

    return alert_code;
}

int s2n_set_server_name(struct s2n_connection *conn, const char *server_name)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(server_name);

    S2N_ERROR_IF(conn->mode != S2N_CLIENT, S2N_ERR_CLIENT_MODE);

    int len = strlen(server_name);
    S2N_ERROR_IF(len > S2N_MAX_SERVER_NAME, S2N_ERR_SERVER_NAME_TOO_LONG);

    POSIX_CHECKED_MEMCPY(conn->server_name, server_name, len);

    return 0;
}

const char *s2n_get_server_name(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);

    if (conn->server_name[0]) {
        return conn->server_name;
    }

    PTR_GUARD_POSIX(s2n_extension_process(&s2n_client_server_name_extension, conn, &conn->client_hello.extensions));

    if (!conn->server_name[0]) {
        return NULL;
    }

    return conn->server_name;
}

const char *s2n_get_application_protocol(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);

    if (strlen(conn->application_protocol) == 0) {
        return NULL;
    }

    return conn->application_protocol;
}

int s2n_connection_get_session_id_length(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);
    /* Stateful session resumption in TLS1.3 using session id is not yet supported. */
    if (conn->actual_protocol_version >= S2N_TLS13) {
        return 0;
    }
    return conn->session_id_len;
}

int s2n_connection_get_session_id(struct s2n_connection *conn, uint8_t *session_id, size_t max_length)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(session_id);

    const int session_id_len = s2n_connection_get_session_id_length(conn);
    POSIX_GUARD(session_id_len);

    POSIX_ENSURE((size_t) session_id_len <= max_length, S2N_ERR_SESSION_ID_TOO_LONG);

    POSIX_CHECKED_MEMCPY(session_id, conn->session_id, session_id_len);

    return session_id_len;
}

int s2n_connection_set_blinding(struct s2n_connection *conn, s2n_blinding blinding)
{
    POSIX_ENSURE_REF(conn);
    conn->blinding = blinding;

    return 0;
}

#define ONE_S INT64_C(1000000000)
#define TEN_S INT64_C(10000000000)

static S2N_RESULT s2n_connection_get_delay_impl(struct s2n_connection *conn, uint64_t *delay)
{
    RESULT_ENSURE_REF(conn);
    RESULT_ENSURE_REF(delay);

    if (!conn->delay) {
        *delay = 0;
        return S2N_RESULT_OK;
    }

    uint64_t elapsed = 0;
    RESULT_GUARD(s2n_timer_elapsed(conn->config, &conn->write_timer, &elapsed));

    if (elapsed > conn->delay) {
        *delay = 0;
        return S2N_RESULT_OK;
    }

    *delay = conn->delay - elapsed;

    return S2N_RESULT_OK;
}

uint64_t s2n_connection_get_delay(struct s2n_connection *conn)
{
    uint64_t delay = 0;
    if (s2n_result_is_ok(s2n_connection_get_delay_impl(conn, &delay))) {
        return delay;
    } else {
        return UINT64_MAX;
    }
}

static S2N_RESULT s2n_connection_kill(struct s2n_connection *conn)
{
    RESULT_ENSURE_REF(conn);
    RESULT_GUARD(s2n_connection_set_closed(conn));

    /* Delay between 10 and 30 seconds in nanoseconds */
    int64_t min = TEN_S, max = 3 * TEN_S;

    /* Keep track of the delay so that it can be enforced */
    uint64_t rand_delay = 0;
    RESULT_GUARD(s2n_public_random(max - min, &rand_delay));

    conn->delay = min + rand_delay;

    /* Restart the write timer */
    RESULT_GUARD(s2n_timer_start(conn->config, &conn->write_timer));

    if (conn->blinding == S2N_BUILT_IN_BLINDING) {
        struct timespec sleep_time = { .tv_sec = conn->delay / ONE_S, .tv_nsec = conn->delay % ONE_S };

        int r = 0;
        do {
            r = nanosleep(&sleep_time, &sleep_time);
        } while (r != 0);
    }

    return S2N_RESULT_OK;
}

S2N_CLEANUP_RESULT s2n_connection_apply_error_blinding(struct s2n_connection **conn)
{
    RESULT_ENSURE_REF(conn);
    if (*conn == NULL) {
        return S2N_RESULT_OK;
    }

    int error_code = s2n_errno;
    int error_type = s2n_error_get_type(error_code);

    switch (error_type) {
        case S2N_ERR_T_OK:
            /* Ignore no error */
            return S2N_RESULT_OK;
        case S2N_ERR_T_BLOCKED:
            /* All blocking errors are retriable and should trigger no further action. */
            return S2N_RESULT_OK;
        default:
            break;
    }

    switch (error_code) {
        /* Don't invoke blinding on some of the common errors.
         *
         * Be careful adding new errors here. Disabling blinding for an
         * error that can be triggered by secret / encrypted values can
         * potentially lead to a side channel attack.
         *
         * We may want to someday add an explicit error type for these errors.
         */
        case S2N_ERR_CLOSED:
        case S2N_ERR_CANCELLED:
        case S2N_ERR_CIPHER_NOT_SUPPORTED:
        case S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED:
            RESULT_GUARD(s2n_connection_set_closed(*conn));
            break;
        default:
            /* Apply blinding to all other errors */
            RESULT_GUARD(s2n_connection_kill(*conn));
            break;
    }

    return S2N_RESULT_OK;
}

S2N_RESULT s2n_connection_set_closed(struct s2n_connection *conn)
{
    RESULT_ENSURE_REF(conn);
    s2n_atomic_flag_set(&conn->read_closed);
    s2n_atomic_flag_set(&conn->write_closed);
    return S2N_RESULT_OK;
}

const uint8_t *s2n_connection_get_ocsp_response(struct s2n_connection *conn, uint32_t *length)
{
    PTR_ENSURE_REF(conn);
    PTR_ENSURE_REF(length);

    *length = conn->status_response.size;
    return conn->status_response.data;
}

S2N_RESULT s2n_connection_set_max_fragment_length(struct s2n_connection *conn, uint16_t max_frag_length)
{
    RESULT_ENSURE_REF(conn);

    if (conn->negotiated_mfl_code) {
        /* Respect the upper limit agreed on with the peer */
        RESULT_ENSURE_LT(conn->negotiated_mfl_code, s2n_array_len(mfl_code_to_length));
        conn->max_outgoing_fragment_length = MIN(mfl_code_to_length[conn->negotiated_mfl_code], max_frag_length);
    } else {
        conn->max_outgoing_fragment_length = max_frag_length;
    }

    /* If no buffer has been initialized yet, no need to resize.
     * The standard I/O logic will handle initializing the buffer.
     */
    if (s2n_stuffer_is_freed(&conn->out)) {
        return S2N_RESULT_OK;
    }

    uint16_t max_wire_record_size = 0;
    RESULT_GUARD(s2n_record_max_write_size(conn, conn->max_outgoing_fragment_length, &max_wire_record_size));
    if ((conn->out.blob.size < max_wire_record_size)) {
        RESULT_GUARD_POSIX(s2n_realloc(&conn->out.blob, max_wire_record_size));
    }

    return S2N_RESULT_OK;
}

int s2n_connection_prefer_throughput(struct s2n_connection *conn)
{
    POSIX_GUARD_RESULT(s2n_connection_set_max_fragment_length(conn, S2N_LARGE_FRAGMENT_LENGTH));
    return S2N_SUCCESS;
}

int s2n_connection_prefer_low_latency(struct s2n_connection *conn)
{
    POSIX_GUARD_RESULT(s2n_connection_set_max_fragment_length(conn, S2N_SMALL_FRAGMENT_LENGTH));
    return S2N_SUCCESS;
}

int s2n_connection_set_dynamic_buffers(struct s2n_connection *conn, bool enabled)
{
    POSIX_ENSURE_REF(conn);
    conn->dynamic_buffers = enabled;
    return S2N_SUCCESS;
}

int s2n_connection_set_dynamic_record_threshold(struct s2n_connection *conn, uint32_t resize_threshold, uint16_t timeout_threshold)
{
    POSIX_ENSURE_REF(conn);
    S2N_ERROR_IF(resize_threshold > S2N_TLS_MAX_RESIZE_THRESHOLD, S2N_ERR_INVALID_DYNAMIC_THRESHOLD);

    conn->dynamic_record_resize_threshold = resize_threshold;
    conn->dynamic_record_timeout_threshold = timeout_threshold;
    return 0;
}

int s2n_connection_set_verify_host_callback(struct s2n_connection *conn, s2n_verify_host_fn verify_host_fn, void *data)
{
    POSIX_ENSURE_REF(conn);

    conn->verify_host_fn = verify_host_fn;
    conn->data_for_verify_host = data;
    conn->verify_host_fn_overridden = 1;

    return 0;
}

int s2n_connection_recv_stuffer(struct s2n_stuffer *stuffer, struct s2n_connection *conn, uint32_t len)
{
    POSIX_ENSURE_REF(conn->recv);
    /* Make sure we have enough space to write */
    POSIX_GUARD(s2n_stuffer_reserve_space(stuffer, len));

    int r = 0;
    S2N_IO_RETRY_EINTR(r,
            conn->recv(conn->recv_io_context, stuffer->blob.data + stuffer->write_cursor, len));
    POSIX_ENSURE(r >= 0, S2N_ERR_RECV_STUFFER_FROM_CONN);

    /* Record just how many bytes we have written */
    POSIX_GUARD(s2n_stuffer_skip_write(stuffer, r));
    return r;
}

int s2n_connection_send_stuffer(struct s2n_stuffer *stuffer, struct s2n_connection *conn, uint32_t len)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(conn->send);
    if (conn->write_fd_broken) {
        POSIX_BAIL(S2N_ERR_SEND_STUFFER_TO_CONN);
    }
    /* Make sure we even have the data */
    S2N_ERROR_IF(s2n_stuffer_data_available(stuffer) < len, S2N_ERR_STUFFER_OUT_OF_DATA);

    int w = 0;
    S2N_IO_RETRY_EINTR(w,
            conn->send(conn->send_io_context, stuffer->blob.data + stuffer->read_cursor, len));
    if (w < 0 && errno == EPIPE) {
        conn->write_fd_broken = 1;
    }
    POSIX_ENSURE(w >= 0, S2N_ERR_SEND_STUFFER_TO_CONN);

    POSIX_GUARD(s2n_stuffer_skip_read(stuffer, w));
    return w;
}

int s2n_connection_is_managed_corked(const struct s2n_connection *s2n_connection)
{
    POSIX_ENSURE_REF(s2n_connection);

    return (s2n_connection->managed_send_io && s2n_connection->corked_io);
}

const uint8_t *s2n_connection_get_sct_list(struct s2n_connection *conn, uint32_t *length)
{
    if (!length) {
        return NULL;
    }

    *length = conn->ct_response.size;
    return conn->ct_response.data;
}

int s2n_connection_is_client_auth_enabled(struct s2n_connection *s2n_connection)
{
    s2n_cert_auth_type auth_type;
    POSIX_GUARD(s2n_connection_get_client_auth_type(s2n_connection, &auth_type));

    return (auth_type != S2N_CERT_AUTH_NONE);
}

struct s2n_cert_chain_and_key *s2n_connection_get_selected_cert(struct s2n_connection *conn)
{
    PTR_ENSURE_REF(conn);
    return conn->handshake_params.our_chain_and_key;
}

uint8_t s2n_connection_get_protocol_version(const struct s2n_connection *conn)
{
    if (conn == NULL) {
        return S2N_UNKNOWN_PROTOCOL_VERSION;
    }

    if (conn->actual_protocol_version != S2N_UNKNOWN_PROTOCOL_VERSION) {
        return conn->actual_protocol_version;
    }

    if (conn->mode == S2N_CLIENT) {
        return conn->client_protocol_version;
    }
    return conn->server_protocol_version;
}

DEFINE_POINTER_CLEANUP_FUNC(struct s2n_cert_chain *, s2n_cert_chain_free);

int s2n_connection_get_peer_cert_chain(const struct s2n_connection *conn, struct s2n_cert_chain_and_key *cert_chain_and_key)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(cert_chain_and_key);
    POSIX_ENSURE_REF(cert_chain_and_key->cert_chain);

    /* Ensure that cert_chain_and_key is empty BEFORE we modify it in any way.
     * That includes before tying its cert_chain to DEFER_CLEANUP.
     */
    POSIX_ENSURE(cert_chain_and_key->cert_chain->head == NULL, S2N_ERR_INVALID_ARGUMENT);

    DEFER_CLEANUP(struct s2n_cert_chain *cert_chain = cert_chain_and_key->cert_chain, s2n_cert_chain_free_pointer);
    struct s2n_cert **insert = &cert_chain->head;

    const struct s2n_x509_validator *validator = &conn->x509_validator;
    POSIX_ENSURE_REF(validator);
    POSIX_ENSURE(s2n_x509_validator_is_cert_chain_validated(validator), S2N_ERR_CERT_NOT_VALIDATED);

    /* X509_STORE_CTX_get1_chain() returns a validated cert chain if a previous call to X509_verify_cert() was successful.
     * X509_STORE_CTX_get0_chain() is a better API because it doesn't return a copy. But it's not available for Openssl 1.0.2.
     * See the comments here:
     * https://www.openssl.org/docs/man1.0.2/man3/X509_STORE_CTX_get1_chain.html
     */
    DEFER_CLEANUP(STACK_OF(X509) *cert_chain_validated = X509_STORE_CTX_get1_chain(validator->store_ctx),
            s2n_openssl_x509_stack_pop_free);
    POSIX_ENSURE_REF(cert_chain_validated);

    int cert_count = sk_X509_num(cert_chain_validated);
    POSIX_ENSURE_GTE(cert_count, 0);

    for (size_t cert_idx = 0; cert_idx < (size_t) cert_count; cert_idx++) {
        X509 *cert = sk_X509_value(cert_chain_validated, cert_idx);
        POSIX_ENSURE_REF(cert);
        DEFER_CLEANUP(uint8_t *cert_data = NULL, s2n_crypto_free);
        int cert_size = i2d_X509(cert, &cert_data);
        POSIX_ENSURE_GT(cert_size, 0);

        struct s2n_blob mem = { 0 };
        POSIX_GUARD(s2n_alloc(&mem, sizeof(struct s2n_cert)));

        struct s2n_cert *new_node = (struct s2n_cert *) (void *) mem.data;
        POSIX_ENSURE_REF(new_node);

        new_node->next = NULL;
        *insert = new_node;
        insert = &new_node->next;

        POSIX_GUARD(s2n_alloc(&new_node->raw, cert_size));
        POSIX_CHECKED_MEMCPY(new_node->raw.data, cert_data, cert_size);
    }

    ZERO_TO_DISABLE_DEFER_CLEANUP(cert_chain);

    return S2N_SUCCESS;
}

static S2N_RESULT s2n_signature_scheme_to_tls_iana(const struct s2n_signature_scheme *sig_scheme,
        s2n_tls_hash_algorithm *converted_scheme)
{
    RESULT_ENSURE_REF(sig_scheme);
    RESULT_ENSURE_REF(converted_scheme);

    switch (sig_scheme->hash_alg) {
        case S2N_HASH_MD5:
            *converted_scheme = S2N_TLS_HASH_MD5;
            break;
        case S2N_HASH_SHA1:
            *converted_scheme = S2N_TLS_HASH_SHA1;
            break;
        case S2N_HASH_SHA224:
            *converted_scheme = S2N_TLS_HASH_SHA224;
            break;
        case S2N_HASH_SHA256:
            *converted_scheme = S2N_TLS_HASH_SHA256;
            break;
        case S2N_HASH_SHA384:
            *converted_scheme = S2N_TLS_HASH_SHA384;
            break;
        case S2N_HASH_SHA512:
            *converted_scheme = S2N_TLS_HASH_SHA512;
            break;
        case S2N_HASH_MD5_SHA1:
            *converted_scheme = S2N_TLS_HASH_MD5_SHA1;
            break;
        default:
            *converted_scheme = S2N_TLS_HASH_NONE;
            break;
    }

    return S2N_RESULT_OK;
}

int s2n_connection_get_selected_digest_algorithm(struct s2n_connection *conn,
        s2n_tls_hash_algorithm *converted_scheme)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(converted_scheme);

    POSIX_GUARD_RESULT(s2n_signature_scheme_to_tls_iana(
            conn->handshake_params.server_cert_sig_scheme, converted_scheme));

    return S2N_SUCCESS;
}

int s2n_connection_get_selected_client_cert_digest_algorithm(struct s2n_connection *conn,
        s2n_tls_hash_algorithm *converted_scheme)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(converted_scheme);

    POSIX_GUARD_RESULT(s2n_signature_scheme_to_tls_iana(
            conn->handshake_params.client_cert_sig_scheme, converted_scheme));
    return S2N_SUCCESS;
}

static S2N_RESULT s2n_signature_scheme_to_signature_algorithm(const struct s2n_signature_scheme *sig_scheme,
        s2n_tls_signature_algorithm *converted_scheme)
{
    RESULT_ENSURE_REF(sig_scheme);
    RESULT_ENSURE_REF(converted_scheme);

    switch (sig_scheme->sig_alg) {
        case S2N_SIGNATURE_RSA:
            *converted_scheme = S2N_TLS_SIGNATURE_RSA;
            break;
        case S2N_SIGNATURE_ECDSA:
            *converted_scheme = S2N_TLS_SIGNATURE_ECDSA;
            break;
        case S2N_SIGNATURE_RSA_PSS_RSAE:
            *converted_scheme = S2N_TLS_SIGNATURE_RSA_PSS_RSAE;
            break;
        case S2N_SIGNATURE_RSA_PSS_PSS:
            *converted_scheme = S2N_TLS_SIGNATURE_RSA_PSS_PSS;
            break;
        default:
            *converted_scheme = S2N_TLS_SIGNATURE_ANONYMOUS;
            break;
    }

    return S2N_RESULT_OK;
}

int s2n_connection_get_selected_signature_algorithm(struct s2n_connection *conn,
        s2n_tls_signature_algorithm *converted_scheme)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(converted_scheme);

    POSIX_GUARD_RESULT(s2n_signature_scheme_to_signature_algorithm(
            conn->handshake_params.server_cert_sig_scheme, converted_scheme));

    return S2N_SUCCESS;
}

int s2n_connection_get_selected_client_cert_signature_algorithm(struct s2n_connection *conn,
        s2n_tls_signature_algorithm *converted_scheme)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(converted_scheme);

    POSIX_GUARD_RESULT(s2n_signature_scheme_to_signature_algorithm(
            conn->handshake_params.client_cert_sig_scheme, converted_scheme));

    return S2N_SUCCESS;
}

/*
 * Gets the config set on the connection.
 */
int s2n_connection_get_config(struct s2n_connection *conn, struct s2n_config **config)
{
    POSIX_ENSURE_REF(conn);
    POSIX_ENSURE_REF(config);

    if (s2n_fetch_default_config() == conn->config) {
        POSIX_BAIL(S2N_ERR_NULL);
    }

    *config = conn->config;

    return S2N_SUCCESS;
}

S2N_RESULT s2n_connection_dynamic_free_out_buffer(struct s2n_connection *conn)
{
    RESULT_ENSURE_REF(conn);

    /* free the out buffer if we're in dynamic mode and it's completely flushed */
    if (conn->dynamic_buffers && s2n_stuffer_is_consumed(&conn->out)) {
        /* since outgoing buffers are already encrypted, the buffers don't need to be zeroed, which saves some overhead */
        RESULT_GUARD_POSIX(s2n_stuffer_free_without_wipe(&conn->out));

        /* reset the stuffer to its initial state */
        RESULT_GUARD_POSIX(s2n_stuffer_growable_alloc(&conn->out, 0));
    }

    return S2N_RESULT_OK;
}

S2N_RESULT s2n_connection_dynamic_free_in_buffer(struct s2n_connection *conn)
{
    RESULT_ENSURE_REF(conn);

    /* free the `in` buffer if we're in dynamic mode and it's completely flushed */
    if (conn->dynamic_buffers && s2n_stuffer_is_consumed(&conn->in)) {
        /* when copying the buffer into the application, we use `s2n_stuffer_erase_and_read`, which already zeroes the memory */
        RESULT_GUARD_POSIX(s2n_stuffer_free_without_wipe(&conn->in));

        /* reset the stuffer to its initial state */
        RESULT_GUARD_POSIX(s2n_stuffer_growable_alloc(&conn->in, 0));
    }

    return S2N_RESULT_OK;
}

bool s2n_connection_check_io_status(struct s2n_connection *conn, s2n_io_status status)
{
    if (!conn) {
        return false;
    }

    bool read_closed = s2n_atomic_flag_test(&conn->read_closed);
    bool write_closed = s2n_atomic_flag_test(&conn->write_closed);
    bool full_duplex = !read_closed && !write_closed;

    /*
     *= https://tools.ietf.org/rfc/rfc8446#section-6.1
     *# Note that this is a change from versions of TLS prior to TLS 1.3 in
     *# which implementations were required to react to a "close_notify" by
     *# discarding pending writes and sending an immediate "close_notify"
     *# alert of their own.
     */
    if (s2n_connection_get_protocol_version(conn) < S2N_TLS13) {
        switch (status) {
            case S2N_IO_WRITABLE:
            case S2N_IO_READABLE:
            case S2N_IO_FULL_DUPLEX:
                return full_duplex;
            case S2N_IO_CLOSED:
                return !full_duplex;
        }
    }

    switch (status) {
        case S2N_IO_WRITABLE:
            return !write_closed;
        case S2N_IO_READABLE:
            return !read_closed;
        case S2N_IO_FULL_DUPLEX:
            return full_duplex;
        case S2N_IO_CLOSED:
            return read_closed && write_closed;
    }

    return false;
}

S2N_RESULT s2n_connection_get_secure_cipher(struct s2n_connection *conn, const struct s2n_cipher **cipher)
{
    RESULT_ENSURE_REF(conn);
    RESULT_ENSURE_REF(cipher);
    RESULT_ENSURE_REF(conn->secure);
    RESULT_ENSURE_REF(conn->secure->cipher_suite);
    RESULT_ENSURE_REF(conn->secure->cipher_suite->record_alg);
    *cipher = conn->secure->cipher_suite->record_alg->cipher;
    return S2N_RESULT_OK;
}