modtls_mbedtls.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Linaro Ltd.
 * Copyright (c) 2019 Paul Sokolovsky
 * Copyright (c) 2023 Damien P. George
 *
 * 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 "py/mpconfig.h"
#if MICROPY_PY_SSL && MICROPY_SSL_MBEDTLS

#include <stdio.h>
#include <string.h>
#include <errno.h> // needed because mp_is_nonblocking_error uses system error codes

#include "py/runtime.h"
#include "py/stream.h"
#include "py/objstr.h"
#include "py/reader.h"
#include "extmod/vfs.h"

// mbedtls_time_t
#include "mbedtls/platform.h"
#include "mbedtls/ssl.h"
#include "mbedtls/x509_crt.h"
#include "mbedtls/pk.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/debug.h"
#include "mbedtls/error.h"
#if MBEDTLS_VERSION_NUMBER >= 0x03000000
#include "mbedtls/build_info.h"
#else
#include "mbedtls/version.h"
#endif

#define MP_STREAM_POLL_RDWR (MP_STREAM_POLL_RD | MP_STREAM_POLL_WR)

// This corresponds to an SSLContext object.
typedef struct _mp_obj_ssl_context_t {
    mp_obj_base_t base;
    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;
    mbedtls_ssl_config conf;
    mbedtls_x509_crt cacert;
    mbedtls_x509_crt cert;
    mbedtls_pk_context pkey;
    int authmode;
    int *ciphersuites;
    mp_obj_t handler;
} mp_obj_ssl_context_t;

// This corresponds to an SSLSocket object.
typedef struct _mp_obj_ssl_socket_t {
    mp_obj_base_t base;
    mp_obj_ssl_context_t *ssl_context;
    mp_obj_t sock;
    mbedtls_ssl_context ssl;

    uintptr_t poll_mask; // Indicates which read or write operations the protocol needs next
    int last_error; // The last error code, if any
} mp_obj_ssl_socket_t;

static const mp_obj_type_t ssl_context_type;
static const mp_obj_type_t ssl_socket_type;

static const MP_DEFINE_STR_OBJ(mbedtls_version_obj, MBEDTLS_VERSION_STRING_FULL);

static mp_obj_t ssl_socket_make_new(mp_obj_ssl_context_t *ssl_context, mp_obj_t sock,
    bool server_side, bool do_handshake_on_connect, mp_obj_t server_hostname);

/******************************************************************************/
// Helper functions.

#ifdef MBEDTLS_DEBUG_C
static void mbedtls_debug(void *ctx, int level, const char *file, int line, const char *str) {
    (void)ctx;
    (void)level;
    mp_printf(&mp_plat_print, "DBG:%s:%04d: %s\n", file, line, str);
}
#endif

static NORETURN void mbedtls_raise_error(int err) {
    // Handle special cases.
    if (err == MBEDTLS_ERR_SSL_ALLOC_FAILED) {
        mp_raise_OSError(MP_ENOMEM);
    } else if (err == MBEDTLS_ERR_PK_BAD_INPUT_DATA) {
        mp_raise_ValueError(MP_ERROR_TEXT("invalid key"));
    } else if (err == MBEDTLS_ERR_X509_BAD_INPUT_DATA) {
        mp_raise_ValueError(MP_ERROR_TEXT("invalid cert"));
    }

    // _mbedtls_ssl_send and _mbedtls_ssl_recv (below) turn positive error codes from the
    // underlying socket into negative codes to pass them through mbedtls. Here we turn them
    // positive again so they get interpreted as the OSError they really are. The
    // cut-off of -256 is a bit hacky, sigh.
    if (err < 0 && err > -256) {
        mp_raise_OSError(-err);
    }

    #if defined(MBEDTLS_ERROR_C)
    // Including mbedtls_strerror takes about 1.5KB due to the error strings.
    // MBEDTLS_ERROR_C is the define used by mbedtls to conditionally include mbedtls_strerror.
    // It is set/unset in the MBEDTLS_CONFIG_FILE which is defined in the Makefile.

    // Try to allocate memory for the message
    #define ERR_STR_MAX 80  // mbedtls_strerror truncates if it doesn't fit
    mp_obj_str_t *o_str = m_new_obj_maybe(mp_obj_str_t);
    byte *o_str_buf = m_new_maybe(byte, ERR_STR_MAX);
    if (o_str == NULL || o_str_buf == NULL) {
        mp_raise_OSError(err);
    }

    // print the error message into the allocated buffer
    mbedtls_strerror(err, (char *)o_str_buf, ERR_STR_MAX);
    size_t len = strlen((char *)o_str_buf);

    // Put the exception object together
    o_str->base.type = &mp_type_str;
    o_str->data = o_str_buf;
    o_str->len = len;
    o_str->hash = qstr_compute_hash(o_str->data, o_str->len);
    // raise
    mp_obj_t args[2] = { MP_OBJ_NEW_SMALL_INT(err), MP_OBJ_FROM_PTR(o_str)};
    nlr_raise(mp_obj_exception_make_new(&mp_type_OSError, 2, 0, args));
    #else
    // mbedtls is compiled without error strings so we simply return the err number
    mp_raise_OSError(err); // err is typically a large negative number
    #endif
}

static void ssl_check_async_handshake_failure(mp_obj_ssl_socket_t *sslsock, int *errcode) {
    if (
        #if MBEDTLS_VERSION_NUMBER >= 0x03000000
        (*errcode < 0) && (mbedtls_ssl_is_handshake_over(&sslsock->ssl) == 0) && (*errcode != MBEDTLS_ERR_SSL_CONN_EOF)
        #else
        (*errcode < 0) && (*errcode != MBEDTLS_ERR_SSL_CONN_EOF)
        #endif
        ) {
        // Asynchronous handshake is done by mbdetls_ssl_read/write.  If the return code is
        // MBEDTLS_ERR_XX (i.e < 0) and the handshake is not done due to a handshake failure,
        // then notify peer with proper error code and raise local error with mbedtls_raise_error.

        if (*errcode == MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE) {
            // Check if TLSv1.3 and use proper alert for this case (to be implemented)
            // uint8_t alert = MBEDTLS_SSL_ALERT_MSG_CERT_REQUIRED; tlsv1.3
            // uint8_t alert = MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE; tlsv1.2
            mbedtls_ssl_send_alert_message(&sslsock->ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        }

        if (*errcode == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED) {
            // The certificate may have been rejected for several reasons.
            char xcbuf[256];
            uint32_t flags = mbedtls_ssl_get_verify_result(&sslsock->ssl);
            int ret = mbedtls_x509_crt_verify_info(xcbuf, sizeof(xcbuf), "\n", flags);
            // The length of the string written (not including the terminated nul byte),
            // or a negative err code.
            if (ret > 0) {
                sslsock->sock = MP_OBJ_NULL;
                mbedtls_ssl_free(&sslsock->ssl);
                mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("%s"), xcbuf);
            }
        }

        sslsock->sock = MP_OBJ_NULL;
        mbedtls_ssl_free(&sslsock->ssl);
        mbedtls_raise_error(*errcode);
    }
}

static int ssl_sock_cert_verify(void *ptr, mbedtls_x509_crt *crt, int depth, uint32_t *flags) {
    mp_obj_ssl_context_t *o = ptr;
    if (o->handler == mp_const_none) {
        return 0;
    }
    mp_obj_array_t cert;
    mp_obj_memoryview_init(&cert, 'B', 0, crt->raw.len, crt->raw.p);
    return mp_obj_get_int(mp_call_function_2(o->handler, MP_OBJ_FROM_PTR(&cert), MP_OBJ_NEW_SMALL_INT(depth)));
}

/******************************************************************************/
// SSLContext type.

static mp_obj_t ssl_context_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
    mp_arg_check_num(n_args, n_kw, 1, 1, false);

    // This is the "protocol" argument.
    mp_int_t endpoint = mp_obj_get_int(args[0]);

    // Create SSLContext object.
    #if MICROPY_PY_SSL_FINALISER
    mp_obj_ssl_context_t *self = mp_obj_malloc_with_finaliser(mp_obj_ssl_context_t, type_in);
    #else
    mp_obj_ssl_context_t *self = mp_obj_malloc(mp_obj_ssl_context_t, type_in);
    #endif

    // Initialise mbedTLS state.
    mbedtls_ssl_config_init(&self->conf);
    mbedtls_entropy_init(&self->entropy);
    mbedtls_ctr_drbg_init(&self->ctr_drbg);
    mbedtls_x509_crt_init(&self->cacert);
    mbedtls_x509_crt_init(&self->cert);
    mbedtls_pk_init(&self->pkey);
    self->ciphersuites = NULL;
    self->handler = mp_const_none;

    #ifdef MBEDTLS_DEBUG_C
    // Debug level (0-4) 1=warning, 2=info, 3=debug, 4=verbose
    mbedtls_debug_set_threshold(3);
    #endif

    // Whenever the PSA interface is used (if MBEDTLS_PSA_CRYPTO), psa_crypto_init() needs to be called before any TLS related operations.
    // TLSv1.3 depends on the PSA interface, TLSv1.2 only uses the PSA stack if MBEDTLS_USE_PSA_CRYPTO is defined.
    #if defined(MBEDTLS_SSL_PROTO_TLS1_3) || defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_crypto_init();
    #endif

    const byte seed[] = "upy";
    int ret = mbedtls_ctr_drbg_seed(&self->ctr_drbg, mbedtls_entropy_func, &self->entropy, seed, sizeof(seed));
    if (ret != 0) {
        mbedtls_raise_error(ret);
    }

    ret = mbedtls_ssl_config_defaults(&self->conf, endpoint,
        MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT);
    if (ret != 0) {
        mbedtls_raise_error(ret);
    }

    if (endpoint == MBEDTLS_SSL_IS_CLIENT) {
        self->authmode = MBEDTLS_SSL_VERIFY_REQUIRED;
    } else {
        self->authmode = MBEDTLS_SSL_VERIFY_NONE;
    }
    mbedtls_ssl_conf_authmode(&self->conf, self->authmode);
    mbedtls_ssl_conf_verify(&self->conf, &ssl_sock_cert_verify, self);
    mbedtls_ssl_conf_rng(&self->conf, mbedtls_ctr_drbg_random, &self->ctr_drbg);
    #ifdef MBEDTLS_DEBUG_C
    mbedtls_ssl_conf_dbg(&self->conf, mbedtls_debug, NULL);
    #endif

    return MP_OBJ_FROM_PTR(self);
}

static void ssl_context_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
    mp_obj_ssl_context_t *self = MP_OBJ_TO_PTR(self_in);
    if (dest[0] == MP_OBJ_NULL) {
        // Load attribute.
        if (attr == MP_QSTR_verify_mode) {
            dest[0] = MP_OBJ_NEW_SMALL_INT(self->authmode);
        } else if (attr == MP_QSTR_verify_callback) {
            dest[0] = self->handler;
        } else {
            // Continue lookup in locals_dict.
            dest[1] = MP_OBJ_SENTINEL;
        }
    } else if (dest[1] != MP_OBJ_NULL) {
        // Store attribute.
        if (attr == MP_QSTR_verify_mode) {
            self->authmode = mp_obj_get_int(dest[1]);
            dest[0] = MP_OBJ_NULL;
            mbedtls_ssl_conf_authmode(&self->conf, self->authmode);
        } else if (attr == MP_QSTR_verify_callback) {
            dest[0] = MP_OBJ_NULL;
            self->handler = dest[1];
        }
    }
}

#if MICROPY_PY_SSL_FINALISER
static mp_obj_t ssl_context___del__(mp_obj_t self_in) {
    mp_obj_ssl_context_t *self = MP_OBJ_TO_PTR(self_in);
    mbedtls_pk_free(&self->pkey);
    mbedtls_x509_crt_free(&self->cert);
    mbedtls_x509_crt_free(&self->cacert);
    mbedtls_ctr_drbg_free(&self->ctr_drbg);
    mbedtls_entropy_free(&self->entropy);
    mbedtls_ssl_config_free(&self->conf);
    return mp_const_none;
}
static MP_DEFINE_CONST_FUN_OBJ_1(ssl_context___del___obj, ssl_context___del__);
#endif

// SSLContext.get_ciphers()
static mp_obj_t ssl_context_get_ciphers(mp_obj_t self_in) {
    mp_obj_t list = mp_obj_new_list(0, NULL);
    for (const int *cipher_list = mbedtls_ssl_list_ciphersuites(); *cipher_list; ++cipher_list) {
        const char *cipher_name = mbedtls_ssl_get_ciphersuite_name(*cipher_list);
        mp_obj_list_append(list, MP_OBJ_FROM_PTR(mp_obj_new_str_from_cstr(cipher_name)));
    }
    return list;
}
static MP_DEFINE_CONST_FUN_OBJ_1(ssl_context_get_ciphers_obj, ssl_context_get_ciphers);

// SSLContext.set_ciphers(ciphersuite)
static mp_obj_t ssl_context_set_ciphers(mp_obj_t self_in, mp_obj_t ciphersuite) {
    mp_obj_ssl_context_t *ssl_context = MP_OBJ_TO_PTR(self_in);

    // Check that ciphersuite is a list or tuple.
    size_t len = 0;
    mp_obj_t *ciphers;
    mp_obj_get_array(ciphersuite, &len, &ciphers);
    if (len == 0) {
        mbedtls_raise_error(MBEDTLS_ERR_SSL_BAD_CONFIG);
    }

    // Parse list of ciphers.
    ssl_context->ciphersuites = m_new(int, len + 1);
    for (size_t i = 0; i < len; ++i) {
        const char *ciphername = mp_obj_str_get_str(ciphers[i]);
        const int id = mbedtls_ssl_get_ciphersuite_id(ciphername);
        if (id == 0) {
            mbedtls_raise_error(MBEDTLS_ERR_SSL_BAD_CONFIG);
        }
        ssl_context->ciphersuites[i] = id;
    }
    ssl_context->ciphersuites[len] = 0;

    // Configure ciphersuite.
    mbedtls_ssl_conf_ciphersuites(&ssl_context->conf, (const int *)ssl_context->ciphersuites);

    return mp_const_none;
}
static MP_DEFINE_CONST_FUN_OBJ_2(ssl_context_set_ciphers_obj, ssl_context_set_ciphers);

static void ssl_context_load_key(mp_obj_ssl_context_t *self, mp_obj_t key_obj, mp_obj_t cert_obj) {
    size_t key_len;
    const byte *key = (const byte *)mp_obj_str_get_data(key_obj, &key_len);
    // len should include terminating null
    int ret;
    #if MBEDTLS_VERSION_NUMBER >= 0x03000000
    ret = mbedtls_pk_parse_key(&self->pkey, key, key_len + 1, NULL, 0, mbedtls_ctr_drbg_random, &self->ctr_drbg);
    #else
    ret = mbedtls_pk_parse_key(&self->pkey, key, key_len + 1, NULL, 0);
    #endif
    if (ret != 0) {
        mbedtls_raise_error(MBEDTLS_ERR_PK_BAD_INPUT_DATA); // use general error for all key errors
    }

    size_t cert_len;
    const byte *cert = (const byte *)mp_obj_str_get_data(cert_obj, &cert_len);
    // len should include terminating null
    ret = mbedtls_x509_crt_parse(&self->cert, cert, cert_len + 1);
    if (ret != 0) {
        mbedtls_raise_error(MBEDTLS_ERR_X509_BAD_INPUT_DATA); // use general error for all cert errors
    }

    ret = mbedtls_ssl_conf_own_cert(&self->conf, &self->cert, &self->pkey);
    if (ret != 0) {
        mbedtls_raise_error(ret);
    }
}

// SSLContext.load_cert_chain(certfile, keyfile)
static mp_obj_t ssl_context_load_cert_chain(mp_obj_t self_in, mp_obj_t cert, mp_obj_t pkey) {
    mp_obj_ssl_context_t *self = MP_OBJ_TO_PTR(self_in);
    ssl_context_load_key(self, pkey, cert);
    return mp_const_none;
}
static MP_DEFINE_CONST_FUN_OBJ_3(ssl_context_load_cert_chain_obj, ssl_context_load_cert_chain);

static void ssl_context_load_cadata(mp_obj_ssl_context_t *self, mp_obj_t cadata_obj) {
    size_t cacert_len;
    const byte *cacert = (const byte *)mp_obj_str_get_data(cadata_obj, &cacert_len);
    // len should include terminating null
    int ret = mbedtls_x509_crt_parse(&self->cacert, cacert, cacert_len + 1);
    if (ret != 0) {
        mbedtls_raise_error(MBEDTLS_ERR_X509_BAD_INPUT_DATA); // use general error for all cert errors
    }

    mbedtls_ssl_conf_ca_chain(&self->conf, &self->cacert, NULL);
}

// SSLContext.load_verify_locations(cadata)
static mp_obj_t ssl_context_load_verify_locations(mp_obj_t self_in, mp_obj_t cadata) {

    mp_obj_ssl_context_t *self = MP_OBJ_TO_PTR(self_in);
    ssl_context_load_cadata(self, cadata);
    return mp_const_none;
}
static MP_DEFINE_CONST_FUN_OBJ_2(ssl_context_load_verify_locations_obj, ssl_context_load_verify_locations);

static mp_obj_t ssl_context_wrap_socket(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    enum { ARG_server_side, ARG_do_handshake_on_connect, ARG_server_hostname };
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_server_side, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
        { MP_QSTR_do_handshake_on_connect, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = true} },
        { MP_QSTR_server_hostname, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
    };

    // Parse arguments.
    mp_obj_ssl_context_t *self = MP_OBJ_TO_PTR(pos_args[0]);
    mp_obj_t sock = pos_args[1];
    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
    mp_arg_parse_all(n_args - 2, pos_args + 2, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);

    // Create and return the new SSLSocket object.
    return ssl_socket_make_new(self, sock, args[ARG_server_side].u_bool,
        args[ARG_do_handshake_on_connect].u_bool, args[ARG_server_hostname].u_obj);
}
static MP_DEFINE_CONST_FUN_OBJ_KW(ssl_context_wrap_socket_obj, 2, ssl_context_wrap_socket);

static const mp_rom_map_elem_t ssl_context_locals_dict_table[] = {
    #if MICROPY_PY_SSL_FINALISER
    { MP_ROM_QSTR(MP_QSTR___del__), MP_ROM_PTR(&ssl_context___del___obj) },
    #endif
    { MP_ROM_QSTR(MP_QSTR_get_ciphers), MP_ROM_PTR(&ssl_context_get_ciphers_obj)},
    { MP_ROM_QSTR(MP_QSTR_set_ciphers), MP_ROM_PTR(&ssl_context_set_ciphers_obj)},
    { MP_ROM_QSTR(MP_QSTR_load_cert_chain), MP_ROM_PTR(&ssl_context_load_cert_chain_obj)},
    { MP_ROM_QSTR(MP_QSTR_load_verify_locations), MP_ROM_PTR(&ssl_context_load_verify_locations_obj)},
    { MP_ROM_QSTR(MP_QSTR_wrap_socket), MP_ROM_PTR(&ssl_context_wrap_socket_obj) },
};
static MP_DEFINE_CONST_DICT(ssl_context_locals_dict, ssl_context_locals_dict_table);

static MP_DEFINE_CONST_OBJ_TYPE(
    ssl_context_type,
    MP_QSTR_SSLContext,
    MP_TYPE_FLAG_NONE,
    make_new, ssl_context_make_new,
    attr, ssl_context_attr,
    locals_dict, &ssl_context_locals_dict
    );

/******************************************************************************/
// SSLSocket type.

static int _mbedtls_ssl_send(void *ctx, const byte *buf, size_t len) {
    mp_obj_t sock = *(mp_obj_t *)ctx;

    const mp_stream_p_t *sock_stream = mp_get_stream(sock);
    int err;

    mp_uint_t out_sz = sock_stream->write(sock, buf, len, &err);
    if (out_sz == MP_STREAM_ERROR) {
        if (mp_is_nonblocking_error(err)) {
            return MBEDTLS_ERR_SSL_WANT_WRITE;
        }
        return -err; // convert an MP_ERRNO to something mbedtls passes through as error
    } else {
        return out_sz;
    }
}

// _mbedtls_ssl_recv is called by mbedtls to receive bytes from the underlying socket
static int _mbedtls_ssl_recv(void *ctx, byte *buf, size_t len) {
    mp_obj_t sock = *(mp_obj_t *)ctx;

    const mp_stream_p_t *sock_stream = mp_get_stream(sock);
    int err;

    mp_uint_t out_sz = sock_stream->read(sock, buf, len, &err);
    if (out_sz == MP_STREAM_ERROR) {
        if (mp_is_nonblocking_error(err)) {
            return MBEDTLS_ERR_SSL_WANT_READ;
        }
        return -err;
    } else {
        return out_sz;
    }
}

static mp_obj_t ssl_socket_make_new(mp_obj_ssl_context_t *ssl_context, mp_obj_t sock,
    bool server_side, bool do_handshake_on_connect, mp_obj_t server_hostname) {

    // Verify the socket object has the full stream protocol
    mp_get_stream_raise(sock, MP_STREAM_OP_READ | MP_STREAM_OP_WRITE | MP_STREAM_OP_IOCTL);

    #if MICROPY_PY_SSL_FINALISER
    mp_obj_ssl_socket_t *o = mp_obj_malloc_with_finaliser(mp_obj_ssl_socket_t, &ssl_socket_type);
    #else
    mp_obj_ssl_socket_t *o = mp_obj_malloc(mp_obj_ssl_socket_t, &ssl_socket_type);
    #endif
    o->ssl_context = ssl_context;
    o->sock = sock;
    o->poll_mask = 0;
    o->last_error = 0;

    int ret;
    uint32_t flags = 0;

    mbedtls_ssl_init(&o->ssl);

    ret = mbedtls_ssl_setup(&o->ssl, &ssl_context->conf);
    if (ret != 0) {
        goto cleanup;
    }

    if (server_hostname != mp_const_none) {
        const char *sni = mp_obj_str_get_str(server_hostname);
        ret = mbedtls_ssl_set_hostname(&o->ssl, sni);
        if (ret != 0) {
            goto cleanup;
        }
    } else if (ssl_context->authmode == MBEDTLS_SSL_VERIFY_REQUIRED && server_side == false) {

        o->sock = MP_OBJ_NULL;
        mbedtls_ssl_free(&o->ssl);
        mp_raise_ValueError(MP_ERROR_TEXT("CERT_REQUIRED requires server_hostname"));
    }

    mbedtls_ssl_set_bio(&o->ssl, &o->sock, _mbedtls_ssl_send, _mbedtls_ssl_recv, NULL);

    if (do_handshake_on_connect) {
        while ((ret = mbedtls_ssl_handshake(&o->ssl)) != 0) {
            if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
                goto cleanup;
            }
            mp_event_wait_ms(1);
        }
    }

    return MP_OBJ_FROM_PTR(o);

cleanup:
    if (ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED) {
        flags = mbedtls_ssl_get_verify_result(&o->ssl);
    }

    o->sock = MP_OBJ_NULL;
    mbedtls_ssl_free(&o->ssl);

    if (ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED) {
        char xcbuf[256];
        int ret_info = mbedtls_x509_crt_verify_info(xcbuf, sizeof(xcbuf), "\n", flags);
        // The length of the string written (not including the terminated nul byte),
        // or a negative err code.
        if (ret_info > 0) {
            mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("%s"), xcbuf);
        }
    }

    mbedtls_raise_error(ret);
}

#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
static mp_obj_t mod_ssl_getpeercert(mp_obj_t o_in, mp_obj_t binary_form) {
    mp_obj_ssl_socket_t *o = MP_OBJ_TO_PTR(o_in);
    if (!mp_obj_is_true(binary_form)) {
        mp_raise_NotImplementedError(NULL);
    }
    const mbedtls_x509_crt *peer_cert = mbedtls_ssl_get_peer_cert(&o->ssl);
    if (peer_cert == NULL) {
        return mp_const_none;
    }
    return mp_obj_new_bytes(peer_cert->raw.p, peer_cert->raw.len);
}
static MP_DEFINE_CONST_FUN_OBJ_2(mod_ssl_getpeercert_obj, mod_ssl_getpeercert);
#endif

static mp_obj_t mod_ssl_cipher(mp_obj_t o_in) {
    mp_obj_ssl_socket_t *o = MP_OBJ_TO_PTR(o_in);
    const char *cipher_suite = mbedtls_ssl_get_ciphersuite(&o->ssl);
    const char *tls_version = mbedtls_ssl_get_version(&o->ssl);
    mp_obj_t tuple[2] = {mp_obj_new_str_from_cstr(cipher_suite),
                         mp_obj_new_str_from_cstr(tls_version)};

    return mp_obj_new_tuple(2, tuple);
}
static MP_DEFINE_CONST_FUN_OBJ_1(mod_ssl_cipher_obj, mod_ssl_cipher);

static mp_uint_t socket_read(mp_obj_t o_in, void *buf, mp_uint_t size, int *errcode) {
    mp_obj_ssl_socket_t *o = MP_OBJ_TO_PTR(o_in);
    o->poll_mask = 0;

    if (o->last_error) {
        *errcode = o->last_error;
        return MP_STREAM_ERROR;
    }

    int ret = mbedtls_ssl_read(&o->ssl, buf, size);
    if (ret == MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY) {
        // end of stream
        return 0;
    }
    if (ret >= 0) {
        return ret;
    }
    if (ret == MBEDTLS_ERR_SSL_WANT_READ) {
        ret = MP_EWOULDBLOCK;
    } else if (ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
        // If handshake is not finished, read attempt may end up in protocol
        // wanting to write next handshake message. The same may happen with
        // renegotiation.
        ret = MP_EWOULDBLOCK;
        o->poll_mask = MP_STREAM_POLL_WR;
    #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
    } else if (ret == MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET) {
        // It appears a new session ticket being issued by the server right after
        // completed handshake is not uncommon and shouldn't be treated as fatal.
        // mbedtls itself states "This error code is experimental and may be
        // changed or removed without notice."
        ret = MP_EWOULDBLOCK;
    #endif
    } else {
        o->last_error = ret;
    }
    ssl_check_async_handshake_failure(o, &ret);
    *errcode = ret;
    return MP_STREAM_ERROR;
}

static mp_uint_t socket_write(mp_obj_t o_in, const void *buf, mp_uint_t size, int *errcode) {
    mp_obj_ssl_socket_t *o = MP_OBJ_TO_PTR(o_in);
    o->poll_mask = 0;

    if (o->last_error) {
        *errcode = o->last_error;
        return MP_STREAM_ERROR;
    }

    int ret = mbedtls_ssl_write(&o->ssl, buf, size);
    if (ret >= 0) {
        return ret;
    }
    if (ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
        ret = MP_EWOULDBLOCK;
    } else if (ret == MBEDTLS_ERR_SSL_WANT_READ) {
        // If handshake is not finished, write attempt may end up in protocol
        // wanting to read next handshake message. The same may happen with
        // renegotiation.
        ret = MP_EWOULDBLOCK;
        o->poll_mask = MP_STREAM_POLL_RD;
    } else {
        o->last_error = ret;
    }
    ssl_check_async_handshake_failure(o, &ret);
    *errcode = ret;
    return MP_STREAM_ERROR;
}

static mp_obj_t socket_setblocking(mp_obj_t self_in, mp_obj_t flag_in) {
    mp_obj_ssl_socket_t *o = MP_OBJ_TO_PTR(self_in);
    mp_obj_t sock = o->sock;
    mp_obj_t dest[3];
    mp_load_method(sock, MP_QSTR_setblocking, dest);
    dest[2] = flag_in;
    return mp_call_method_n_kw(1, 0, dest);
}
static MP_DEFINE_CONST_FUN_OBJ_2(socket_setblocking_obj, socket_setblocking);

static mp_uint_t socket_ioctl(mp_obj_t o_in, mp_uint_t request, uintptr_t arg, int *errcode) {
    mp_obj_ssl_socket_t *self = MP_OBJ_TO_PTR(o_in);
    mp_uint_t ret = 0;
    uintptr_t saved_arg = 0;
    mp_obj_t sock = self->sock;

    if (request == MP_STREAM_CLOSE) {
        if (sock == MP_OBJ_NULL) {
            // Already closed socket, do nothing.
            return 0;
        }
        self->sock = MP_OBJ_NULL;
        mbedtls_ssl_free(&self->ssl);
    } else if (request == MP_STREAM_POLL) {
        if (sock == MP_OBJ_NULL || self->last_error != 0) {
            // Closed or error socket, return NVAL flag.
            return MP_STREAM_POLL_NVAL;
        }

        // If the library signaled us that it needs reading or writing, only check that direction,
        // but save what the caller asked because we need to restore it later
        if (self->poll_mask && (arg & MP_STREAM_POLL_RDWR)) {
            saved_arg = arg & MP_STREAM_POLL_RDWR;
            arg = (arg & ~saved_arg) | self->poll_mask;
        }

        // Take into account that the library might have buffered data already
        int has_pending = 0;
        if (arg & MP_STREAM_POLL_RD) {
            has_pending = mbedtls_ssl_check_pending(&self->ssl);
            if (has_pending) {
                ret |= MP_STREAM_POLL_RD;
                if (arg == MP_STREAM_POLL_RD) {
                    // Shortcut if we only need to read and we have buffered data, no need to go to the underlying socket
                    return MP_STREAM_POLL_RD;
                }
            }
        }
    } else {
        // Unsupported ioctl.
        *errcode = MP_EINVAL;
        return MP_STREAM_ERROR;
    }

    // Pass all requests down to the underlying socket
    ret |= mp_get_stream(sock)->ioctl(sock, request, arg, errcode);

    if (request == MP_STREAM_POLL) {
        // The direction the library needed is available, return a fake result to the caller so that
        // it reenters a read or a write to allow the handshake to progress
        if (ret & self->poll_mask) {
            ret |= saved_arg;
        }
    }
    return ret;
}

static const mp_rom_map_elem_t ssl_socket_locals_dict_table[] = {
    { MP_ROM_QSTR(MP_QSTR_read), MP_ROM_PTR(&mp_stream_read_obj) },
    { MP_ROM_QSTR(MP_QSTR_readinto), MP_ROM_PTR(&mp_stream_readinto_obj) },
    { MP_ROM_QSTR(MP_QSTR_readline), MP_ROM_PTR(&mp_stream_unbuffered_readline_obj) },
    { MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mp_stream_write_obj) },
    { MP_ROM_QSTR(MP_QSTR_setblocking), MP_ROM_PTR(&socket_setblocking_obj) },
    { MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&mp_stream_close_obj) },
    #if MICROPY_PY_SSL_FINALISER
    { MP_ROM_QSTR(MP_QSTR___del__), MP_ROM_PTR(&mp_stream_close_obj) },
    #endif
    #if MICROPY_UNIX_COVERAGE
    { MP_ROM_QSTR(MP_QSTR_ioctl), MP_ROM_PTR(&mp_stream_ioctl_obj) },
    #endif
    #if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    { MP_ROM_QSTR(MP_QSTR_getpeercert), MP_ROM_PTR(&mod_ssl_getpeercert_obj) },
    #endif
    { MP_ROM_QSTR(MP_QSTR_cipher), MP_ROM_PTR(&mod_ssl_cipher_obj) },
};
static MP_DEFINE_CONST_DICT(ssl_socket_locals_dict, ssl_socket_locals_dict_table);

static const mp_stream_p_t ssl_socket_stream_p = {
    .read = socket_read,
    .write = socket_write,
    .ioctl = socket_ioctl,
};

static MP_DEFINE_CONST_OBJ_TYPE(
    ssl_socket_type,
    MP_QSTR_SSLSocket,
    MP_TYPE_FLAG_NONE,
    protocol, &ssl_socket_stream_p,
    locals_dict, &ssl_socket_locals_dict
    );

/******************************************************************************/
// ssl module.

static const mp_rom_map_elem_t mp_module_tls_globals_table[] = {
    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_tls) },

    // Classes.
    { MP_ROM_QSTR(MP_QSTR_SSLContext), MP_ROM_PTR(&ssl_context_type) },

    // Constants.
    { MP_ROM_QSTR(MP_QSTR_MBEDTLS_VERSION), MP_ROM_PTR(&mbedtls_version_obj)},
    { MP_ROM_QSTR(MP_QSTR_PROTOCOL_TLS_CLIENT), MP_ROM_INT(MBEDTLS_SSL_IS_CLIENT) },
    { MP_ROM_QSTR(MP_QSTR_PROTOCOL_TLS_SERVER), MP_ROM_INT(MBEDTLS_SSL_IS_SERVER) },
    { MP_ROM_QSTR(MP_QSTR_CERT_NONE), MP_ROM_INT(MBEDTLS_SSL_VERIFY_NONE) },
    { MP_ROM_QSTR(MP_QSTR_CERT_OPTIONAL), MP_ROM_INT(MBEDTLS_SSL_VERIFY_OPTIONAL) },
    { MP_ROM_QSTR(MP_QSTR_CERT_REQUIRED), MP_ROM_INT(MBEDTLS_SSL_VERIFY_REQUIRED) },
};
static MP_DEFINE_CONST_DICT(mp_module_tls_globals, mp_module_tls_globals_table);

const mp_obj_module_t mp_module_tls = {
    .base = { &mp_type_module },
    .globals = (mp_obj_dict_t *)&mp_module_tls_globals,
};

MP_REGISTER_MODULE(MP_QSTR_tls, mp_module_tls);

#endif // MICROPY_PY_SSL && MICROPY_SSL_MBEDTLS