adapters/tlsio_wolfssl.c

// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

#include <stdlib.h>
#define WOLFSSL_OPTIONS_IGNORE_SYS
#include "wolfssl/options.h"
#include "wolfssl/ssl.h"
#include "wolfssl/error-ssl.h"
#include "wolfssl/wolfcrypt/types.h"
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include "azure_c_shared_utility/gballoc.h"
#include "azure_c_shared_utility/tlsio.h"
#include "azure_c_shared_utility/tlsio_wolfssl.h"
#include "azure_c_shared_utility/socketio.h"
#include "azure_c_shared_utility/crt_abstractions.h"
#include "azure_c_shared_utility/optimize_size.h"
#include "azure_c_shared_utility/xlogging.h"
#include "azure_c_shared_utility/shared_util_options.h"
#include "azure_c_shared_utility/safe_math.h"

typedef enum TLSIO_STATE_ENUM_TAG
{
    TLSIO_STATE_NOT_OPEN,
    TLSIO_STATE_OPENING_UNDERLYING_IO,
    TLSIO_STATE_IN_HANDSHAKE,
    TLSIO_STATE_OPEN,
    TLSIO_STATE_CLOSING,
    TLSIO_STATE_ERROR
} TLSIO_STATE_ENUM;

typedef struct TLS_IO_INSTANCE_TAG
{
    XIO_HANDLE socket_io;
    ON_BYTES_RECEIVED on_bytes_received;
    ON_IO_OPEN_COMPLETE on_io_open_complete;
    ON_IO_CLOSE_COMPLETE on_io_close_complete;
    ON_IO_ERROR on_io_error;
    void* on_bytes_received_context;
    void* on_io_open_complete_context;
    void* on_io_close_complete_context;
    void* on_io_error_context;
    WOLFSSL* ssl;
    WOLFSSL_CTX* ssl_context;
    TLSIO_STATE_ENUM tlsio_state;
    unsigned char* socket_io_read_bytes;
    size_t socket_io_read_byte_count;
    ON_SEND_COMPLETE on_send_complete;
    void* on_send_complete_callback_context;
    char* certificate;
    char* x509certificate;
    char* x509privatekey;
    int wolfssl_device_id;
    char* hostname;
    bool ignore_host_name_check;
} TLS_IO_INSTANCE;

STATIC_VAR_UNUSED const char* const OPTION_WOLFSSL_SET_DEVICE_ID = "SetDeviceId";
static const size_t SOCKET_READ_LIMIT = 5;

/*this function will clone an option given by name and value*/
static void* tlsio_wolfssl_CloneOption(const char* name, const void* value)
{
    void* result;
    if ((name == NULL) || (value == NULL))
    {
        LogError("invalid parameter detected: const char* name=%p, const void* value=%p", name, value);
        result = NULL;
    }
    else
    {
        if (strcmp(name, OPTION_TRUSTED_CERT) == 0)
        {
            if (mallocAndStrcpy_s((char**)&result, value) != 0)
            {
                LogError("unable to mallocAndStrcpy_s TrustedCerts value");
                result = NULL;
            }
            else
            {
                /*return as is*/
            }
        }
        else if (strcmp(name, SU_OPTION_X509_CERT) == 0)
        {
            if (mallocAndStrcpy_s((char**)&result, value) != 0)
            {
                LogError("unable to mallocAndStrcpy_s x509certificate value");
                result = NULL;
            }
            else
            {
                /*return as is*/
            }
        }
        else if (strcmp(name, SU_OPTION_X509_PRIVATE_KEY) == 0)
        {
            if (mallocAndStrcpy_s((char**)&result, value) != 0)
            {
                LogError("unable to mallocAndStrcpy_s x509privatekey value");
                result = NULL;
            }
            else
            {
                /*return as is*/
            }
        }
        #ifdef INVALID_DEVID
        else if(strcmp(name, OPTION_WOLFSSL_SET_DEVICE_ID) == 0 )
        {
             int* value_clone;

             if ((value_clone = malloc(sizeof(int))) == NULL)
             {
                 LogError("unable to clone device id option");
             }
             else
             {
                 *value_clone = *(int*)value;
             }

             result = value_clone;
        }
        #endif
        else
        {
            LogError("not handled option : %s", name);
            result = NULL;
        }
    }
    return result;
}

/*this function destroys an option previously created*/
static void tlsio_wolfssl_DestroyOption(const char* name, const void* value)
{
    /*since all options for this layer are actually string copies., disposing of one is just calling free*/
    if ((name == NULL) || (value == NULL))
    {
        LogError("invalid parameter detected: const char* name=%p, const void* value=%p", name, value);
    }
    else
    {
        if ((strcmp(name, OPTION_TRUSTED_CERT) == 0) ||
            (strcmp(name, SU_OPTION_X509_CERT) == 0) ||
            (strcmp(name, SU_OPTION_X509_PRIVATE_KEY) == 0) ||
            (strcmp(name, OPTION_WOLFSSL_SET_DEVICE_ID) == 0))
        {
            free((void*)value);
        }
        else
        {
            LogError("not handled option : %s", name);
        }
    }
}

static OPTIONHANDLER_HANDLE tlsio_wolfssl_retrieveoptions(CONCRETE_IO_HANDLE tls_io)
{
    OPTIONHANDLER_HANDLE result;
    if (tls_io == NULL)
    {
        LogError("NULL tls_io parameter");
        result = NULL;
    }
    else
    {
        result = OptionHandler_Create(tlsio_wolfssl_CloneOption, tlsio_wolfssl_DestroyOption, tlsio_wolfssl_setoption);
        if (result == NULL)
        {
            LogError("unable to OptionHandler_Create");
            /*return as is*/
        }
        else
        {
            /*this layer cares about the certificates and the x509 credentials*/
            TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;
            if (
                (tls_io_instance->x509certificate != NULL) &&
                (OptionHandler_AddOption(result, SU_OPTION_X509_CERT, tls_io_instance->x509certificate) != OPTIONHANDLER_OK)
                )
            {
                LogError("unable to save x509certificate option");
                OptionHandler_Destroy(result);
                result = NULL;
            }
            else if (
                (tls_io_instance->x509privatekey != NULL) &&
                (OptionHandler_AddOption(result, SU_OPTION_X509_PRIVATE_KEY, tls_io_instance->x509privatekey) != OPTIONHANDLER_OK)
                )
            {
                LogError("unable to save x509privatekey option");
                OptionHandler_Destroy(result);
                result = NULL;
            }
            else if (
                (tls_io_instance->certificate != NULL) &&
                (OptionHandler_AddOption(result, OPTION_TRUSTED_CERT, tls_io_instance->certificate) != OPTIONHANDLER_OK)
                )
            {
                LogError("unable to save TrustedCerts option");
                OptionHandler_Destroy(result);
                result = NULL;
            }
            #ifdef INVALID_DEVID
            else if (
                (tls_io_instance->wolfssl_device_id != INVALID_DEVID) &&
                (OptionHandler_AddOption(result, OPTION_WOLFSSL_SET_DEVICE_ID, &tls_io_instance->wolfssl_device_id) != OPTIONHANDLER_OK)
                )
            {
                LogError("unable to save deviceid option");
                OptionHandler_Destroy(result);
                result = NULL;
            }
            #endif
            else
            {
                /*all is fine, all interesting options have been saved*/
                /*return as is*/
            }
        }
    }

    return result;
}

static const IO_INTERFACE_DESCRIPTION tlsio_wolfssl_interface_description =
{
    tlsio_wolfssl_retrieveoptions,
    tlsio_wolfssl_create,
    tlsio_wolfssl_destroy,
    tlsio_wolfssl_open,
    tlsio_wolfssl_close,
    tlsio_wolfssl_send,
    tlsio_wolfssl_dowork,
    tlsio_wolfssl_setoption
};

static void indicate_error(TLS_IO_INSTANCE* tls_io_instance)
{
    if (tls_io_instance->on_io_error != NULL)
    {
        tls_io_instance->on_io_error(tls_io_instance->on_io_error_context);
    }
}

static void indicate_open_complete(TLS_IO_INSTANCE* tls_io_instance, IO_OPEN_RESULT open_result)
{
    if (tls_io_instance->on_io_open_complete != NULL)
    {
        tls_io_instance->on_io_open_complete(tls_io_instance->on_io_open_complete_context, open_result);
    }
}

static int decode_ssl_received_bytes(TLS_IO_INSTANCE* tls_io_instance)
{
    int result = 0;
    unsigned char buffer[64];

    int rcv_bytes = 0;
    do
    {
        rcv_bytes = wolfSSL_read(tls_io_instance->ssl, buffer, sizeof(buffer));
        if (rcv_bytes > 0)
        {
            if (tls_io_instance->on_bytes_received != NULL)
            {
                tls_io_instance->on_bytes_received(tls_io_instance->on_bytes_received_context, buffer, rcv_bytes);
            }
        }
    } while (rcv_bytes > 0);
    return result;
}

static void on_underlying_io_open_complete(void* context, IO_OPEN_RESULT open_result)
{
    TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;

    if (open_result != IO_OPEN_OK)
    {
        LogError("Underlying IO open failed");
        tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
        indicate_open_complete(tls_io_instance, IO_OPEN_ERROR);
    }
    else
    {
        int res;
        tls_io_instance->tlsio_state = TLSIO_STATE_IN_HANDSHAKE;

        res = wolfSSL_connect(tls_io_instance->ssl);
        if (res != SSL_SUCCESS)
        {
            // Error codes explained in https://www.wolfssl.com/docs/wolfssl-manual/appendix-c/
            LogError("WolfSSL connect failed (%d)", wolfSSL_get_error(tls_io_instance->ssl, res));
            indicate_open_complete(tls_io_instance, IO_OPEN_ERROR);
            tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
        }
    }
}

static void on_underlying_io_bytes_received(void* context, const unsigned char* buffer, size_t size)
{
    if (context != NULL)
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;
        unsigned char* new_socket_io_read_bytes;

        size_t realloc_size = safe_add_size_t(tls_io_instance->socket_io_read_byte_count, size);
        if (realloc_size == SIZE_MAX ||
            (new_socket_io_read_bytes = (unsigned char*)realloc(tls_io_instance->socket_io_read_bytes, realloc_size)) == NULL)
        {
            LogError("Failed allocating memory for received bytes, size:%zu", realloc_size);
            tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
            indicate_error(tls_io_instance);
        }
        else
        {
            tls_io_instance->socket_io_read_bytes = new_socket_io_read_bytes;
            (void)memcpy(tls_io_instance->socket_io_read_bytes + tls_io_instance->socket_io_read_byte_count, buffer, size);
            tls_io_instance->socket_io_read_byte_count += size;
        }
    }
    else
    {
        LogInfo("Supplied context is NULL on bytes_received");
    }
}

static void on_underlying_io_error(void* context)
{
    if (context != NULL)
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;

        switch (tls_io_instance->tlsio_state)
        {
        default:
            LogError("Unknown TLS IO WolfSSL state: %d", (int)tls_io_instance->tlsio_state);
            break;

        case TLSIO_STATE_NOT_OPEN:
        case TLSIO_STATE_ERROR:
            break;

        case TLSIO_STATE_OPENING_UNDERLYING_IO:
        case TLSIO_STATE_IN_HANDSHAKE:
            tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
            indicate_open_complete(tls_io_instance, IO_OPEN_ERROR);
            break;

        case TLSIO_STATE_OPEN:
            tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
            indicate_error(tls_io_instance);
            break;
        }
    }
    else
    {
        LogInfo("Supplied context is NULL on io_error");
    }
}

static void on_underlying_io_close_complete(void* context)
{
    TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;

    if (tls_io_instance->tlsio_state != TLSIO_STATE_CLOSING)
    {
        LogError("on_underlying_io_close_complete called when not in CLOSING state");
    }
    else
    {
        if (tls_io_instance->on_io_close_complete != NULL)
        {
            tls_io_instance->on_io_close_complete(tls_io_instance->on_io_close_complete_context);
        }
        tls_io_instance->tlsio_state = TLSIO_STATE_NOT_OPEN;
    }
}

static int on_io_recv(WOLFSSL *ssl, char *buf, int sz, void *context)
{
    int result;
    if (context != NULL)
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;
        unsigned char* new_socket_io_read_bytes;
        size_t socket_reads = 0;

        AZURE_UNREFERENCED_PARAMETER(ssl);
        while (tls_io_instance->socket_io_read_byte_count == 0 && socket_reads < SOCKET_READ_LIMIT)
        {
            xio_dowork(tls_io_instance->socket_io);
            if (tls_io_instance->tlsio_state != TLSIO_STATE_IN_HANDSHAKE)
            {
                break;
            }
            socket_reads++;
        }

        result = tls_io_instance->socket_io_read_byte_count;
        if (result > sz)
        {
            result = sz;
        }

        if (result > 0)
        {
            size_t read_byte_count = safe_subtract_size_t(tls_io_instance->socket_io_read_byte_count, (size_t)result);
            (void)memcpy(buf, tls_io_instance->socket_io_read_bytes, result);
            (void)memmove(tls_io_instance->socket_io_read_bytes, tls_io_instance->socket_io_read_bytes + result, read_byte_count);

            tls_io_instance->socket_io_read_byte_count = read_byte_count;
            if (tls_io_instance->socket_io_read_byte_count > 0)
            {
                new_socket_io_read_bytes = (unsigned char*)realloc(tls_io_instance->socket_io_read_bytes, tls_io_instance->socket_io_read_byte_count);
                if (new_socket_io_read_bytes != NULL)
                {
                    tls_io_instance->socket_io_read_bytes = new_socket_io_read_bytes;
                }
            }
            else
            {
                free(tls_io_instance->socket_io_read_bytes);
                tls_io_instance->socket_io_read_bytes = NULL;
            }
        }

        if (tls_io_instance->tlsio_state == TLSIO_STATE_ERROR)
        {
            result = WOLFSSL_CBIO_ERR_GENERAL;
        }
        else if ( (result == 0) && (tls_io_instance->tlsio_state == TLSIO_STATE_OPEN))
        {
#ifdef HAVE_SECURE_RENEGOTIATION
            if (wolfSSL_SSL_renegotiate_pending(tls_io_instance->ssl) == 0) // SERVER_HELLODONE_COMPLETE
            {
                result = WOLFSSL_CBIO_ERR_WANT_READ;
            }
            // If Server Hello not complete during renegotiation, do not return error.
#else
            result = WOLFSSL_CBIO_ERR_WANT_READ;
#endif
        }
        else if ((result == 0) && (tls_io_instance->tlsio_state == TLSIO_STATE_CLOSING || tls_io_instance->tlsio_state == TLSIO_STATE_NOT_OPEN))
        {
            result = WOLFSSL_CBIO_ERR_CONN_CLOSE;
        }
    }
    else
    {
        result = WOLFSSL_CBIO_ERR_GENERAL;
    }
    return result;
}

static int on_io_send(WOLFSSL *ssl, char *buf, int sz, void *context)
{
    int result;
    AZURE_UNREFERENCED_PARAMETER(ssl);

    TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;

    if (xio_send(tls_io_instance->socket_io, buf, sz, tls_io_instance->on_send_complete, tls_io_instance->on_send_complete_callback_context) != 0)
    {
        LogError("Failed sending bytes through underlying IO");
        tls_io_instance->tlsio_state = TLSIO_STATE_ERROR;
        indicate_error(tls_io_instance);
        result = WOLFSSL_CBIO_ERR_GENERAL;
    }
    else
    {
        result = sz;
    }

    return result;
}

static int on_handshake_done(WOLFSSL* ssl, void* context)
{
    AZURE_UNREFERENCED_PARAMETER(ssl);
    TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)context;
    if (tls_io_instance->tlsio_state != TLSIO_STATE_IN_HANDSHAKE)
    {
        LogInfo("on_handshake_done called when not in IN_HANDSHAKE state");
    }
    else
    {
        tls_io_instance->tlsio_state = TLSIO_STATE_OPEN;
        indicate_open_complete(tls_io_instance, IO_OPEN_OK);
    }

    return 0;
}

static int add_certificate_to_store(TLS_IO_INSTANCE* tls_io_instance)
{
    int result;
    if (tls_io_instance->certificate != NULL)
    {
        int res = wolfSSL_CTX_load_verify_buffer(tls_io_instance->ssl_context, (const unsigned char*)tls_io_instance->certificate, strlen(tls_io_instance->certificate), SSL_FILETYPE_PEM);
        if (res != SSL_SUCCESS)
        {
            LogError("wolfSSL_CTX_load_verify_buffer failed");
            result = MU_FAILURE;
        }
        else
        {
            result = 0;
        }
    }
    else
    {
        result = 0;
    }
    return result;
}

static int x509_wolfssl_add_credentials(WOLFSSL* ssl, char* x509certificate, char* x509privatekey) {

    int result;

    if (wolfSSL_use_certificate_chain_buffer(ssl, (unsigned char*)x509certificate, strlen(x509certificate)) != SSL_SUCCESS)
    {
        LogError("unable to load x509 client certificate");
        result = MU_FAILURE;
    }
    else if (wolfSSL_use_PrivateKey_buffer(ssl, (unsigned char*)x509privatekey, strlen(x509privatekey), SSL_FILETYPE_PEM) != SSL_SUCCESS)
    {
        LogError("unable to load x509 client private key");
        result = MU_FAILURE;
    }
    else
    {
        result = 0;
    }
    return result;
}

static void destroy_wolfssl_instance(TLS_IO_INSTANCE* tls_io_instance)
{
    wolfSSL_free(tls_io_instance->ssl);
    tls_io_instance->ssl = NULL;
}

static int create_wolfssl_instance(TLS_IO_INSTANCE* tls_io_instance)
{
    int result;
    tls_io_instance->ssl = wolfSSL_new(tls_io_instance->ssl_context);
    if (tls_io_instance->ssl == NULL)
    {
        LogError("Failed to add certificates to store");
        result = MU_FAILURE;
    }
    else
    {
        tls_io_instance->socket_io_read_bytes = NULL;
        tls_io_instance->socket_io_read_byte_count = 0;
        tls_io_instance->on_send_complete = NULL;
        tls_io_instance->on_send_complete_callback_context = NULL;
#ifdef INVALID_DEVID
        tls_io_instance->wolfssl_device_id = INVALID_DEVID;
#endif

        wolfSSL_set_using_nonblock(tls_io_instance->ssl, 1);
        wolfSSL_SetHsDoneCb(tls_io_instance->ssl, on_handshake_done, tls_io_instance);
        wolfSSL_SetIOWriteCtx(tls_io_instance->ssl, tls_io_instance);
        wolfSSL_SetIOReadCtx(tls_io_instance->ssl, tls_io_instance);

        tls_io_instance->tlsio_state = TLSIO_STATE_NOT_OPEN;
        result = 0;

#ifdef HAVE_SECURE_RENEGOTIATION
        if (wolfSSL_UseSecureRenegotiation(tls_io_instance->ssl) != SSL_SUCCESS)
        {
            LogError("unable to enable secure renegotiation");
            result = MU_FAILURE;
        }
#endif
    }
    return result;
}

static int enable_domain_check(TLS_IO_INSTANCE* tls_io_instance)
{
    int result = 0;

    if (!tls_io_instance->ignore_host_name_check)
    {
        if (wolfSSL_check_domain_name(tls_io_instance->ssl, tls_io_instance->hostname) != WOLFSSL_SUCCESS)
        {
            result = MU_FAILURE;
        }
    }

    return result;
}

static int prepare_wolfssl_open(TLS_IO_INSTANCE* tls_io_instance)
{
    int result;

    if (enable_domain_check(tls_io_instance))
    {
        LogError("Failed to configure domain name verification");
        result = MU_FAILURE;
    }
    else if (add_certificate_to_store(tls_io_instance) != 0)
    {
        LogError("Failed to add certificates to store");
        result = MU_FAILURE;
    }
    /*x509 authentication can only be build before underlying connection is realized*/
    else if ((tls_io_instance->x509certificate != NULL) &&
        (tls_io_instance->x509privatekey != NULL) &&
        (x509_wolfssl_add_credentials(tls_io_instance->ssl, tls_io_instance->x509certificate, tls_io_instance->x509privatekey) != 0))
    {
        destroy_wolfssl_instance(tls_io_instance);
        LogError("unable to use x509 authentication");
        result = MU_FAILURE;
    }
    else
    {
        result = 0;
    }
    return result;
}

int tlsio_wolfssl_init(void)
{
    (void)wolfSSL_library_init();
    wolfSSL_load_error_strings();
    return 0;
}

void tlsio_wolfssl_deinit(void)
{
}

CONCRETE_IO_HANDLE tlsio_wolfssl_create(void* io_create_parameters)
{
    TLS_IO_INSTANCE* result;

    if (io_create_parameters == NULL)
    {
        LogError("NULL io_create_parameters");
        result = NULL;
    }
    else
    {
        TLSIO_CONFIG* tls_io_config = io_create_parameters;

        result = (TLS_IO_INSTANCE*)malloc(sizeof(TLS_IO_INSTANCE));
        if (result == NULL)
        {
            LogError("Failed allocating memory for the TLS IO instance.");
        }
        else
        {
            (void)memset(result, 0, sizeof(TLS_IO_INSTANCE));
            result->tlsio_state = TLSIO_STATE_NOT_OPEN;

            result->ssl_context = wolfSSL_CTX_new(wolfTLSv1_2_client_method());
            if (result->ssl_context == NULL)
            {
                LogError("Cannot create the wolfSSL context");
                free(result);
                result = NULL;
            }
            else if (mallocAndStrcpy_s(&result->hostname, tls_io_config->hostname) != 0)
            {
                LogError("Failed copying the target hostname.");
                free(result);
                result = NULL;
            }
            else
            {
                // Set the recv and send function on the wolfssl context object
                wolfSSL_SetIOSend(result->ssl_context, on_io_send);
                wolfSSL_SetIORecv(result->ssl_context, on_io_recv);

                SOCKETIO_CONFIG socketio_config;
                const IO_INTERFACE_DESCRIPTION* underlying_io_interface;
                void* io_interface_parameters;

                if (tls_io_config->underlying_io_interface != NULL)
                {
                    underlying_io_interface = tls_io_config->underlying_io_interface;
                    io_interface_parameters = tls_io_config->underlying_io_parameters;
                }
                else
                {
                    socketio_config.hostname = tls_io_config->hostname;
                    socketio_config.port = tls_io_config->port;
                    socketio_config.accepted_socket = NULL;

                    underlying_io_interface = socketio_get_interface_description();
                    io_interface_parameters = &socketio_config;
                }

                if (underlying_io_interface == NULL)
                {
                    LogError("Failed getting socket IO interface description.");
                    wolfSSL_CTX_free(result->ssl_context);
                    free(result->hostname);
                    free(result);
                    result = NULL;
                }
                else
                {
                    result->socket_io = xio_create(underlying_io_interface, io_interface_parameters);
                    if (result->socket_io == NULL)
                    {
                        LogError("Failure connecting to underlying socket_io");
                        wolfSSL_CTX_free(result->ssl_context);
                        free(result->hostname);
                        free(result);
                        result = NULL;
                    }
                    else if (create_wolfssl_instance(result) != 0)
                    {
                        LogError("Failure connecting to underlying socket_io");
                        wolfSSL_CTX_free(result->ssl_context);
                        free(result->hostname);
                        free(result);
                        result = NULL;
                    }
                }
            }
        }
    }

    return result;
}

void tlsio_wolfssl_destroy(CONCRETE_IO_HANDLE tls_io)
{
    if (tls_io != NULL)
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;
        if (tls_io_instance->socket_io_read_bytes != NULL)
        {
            free(tls_io_instance->socket_io_read_bytes);
            tls_io_instance->socket_io_read_bytes = NULL;
        }
        if (tls_io_instance->certificate != NULL)
        {
            free(tls_io_instance->certificate);
            tls_io_instance->certificate = NULL;
        }
        if (tls_io_instance->x509certificate != NULL)
        {
            free(tls_io_instance->x509certificate);
            tls_io_instance->x509certificate = NULL;
        }
        if (tls_io_instance->x509privatekey != NULL)
        {
            free(tls_io_instance->x509privatekey);
            tls_io_instance->x509privatekey = NULL;
        }
        destroy_wolfssl_instance(tls_io_instance);

        wolfSSL_CTX_free(tls_io_instance->ssl_context);
        tls_io_instance->ssl_context = NULL;

        xio_destroy(tls_io_instance->socket_io);
        free(tls_io_instance->hostname);
        free(tls_io);
    }
}

int tlsio_wolfssl_open(CONCRETE_IO_HANDLE tls_io, ON_IO_OPEN_COMPLETE on_io_open_complete, void* on_io_open_complete_context, ON_BYTES_RECEIVED on_bytes_received, void* on_bytes_received_context, ON_IO_ERROR on_io_error, void* on_io_error_context)
{
    int result;

    if (tls_io == NULL)
    {
        LogError("NULL tls_io instance");
        result = MU_FAILURE;
    }
    else
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;

        if (tls_io_instance->tlsio_state != TLSIO_STATE_NOT_OPEN)
        {
            LogError("Invalid state encountered.");
            result = MU_FAILURE;
        }
        else
        {
            tls_io_instance->on_bytes_received = on_bytes_received;
            tls_io_instance->on_bytes_received_context = on_bytes_received_context;

            tls_io_instance->on_io_open_complete = on_io_open_complete;
            tls_io_instance->on_io_open_complete_context = on_io_open_complete_context;

            tls_io_instance->on_io_error = on_io_error;
            tls_io_instance->on_io_error_context = on_io_error_context;

            tls_io_instance->tlsio_state = TLSIO_STATE_OPENING_UNDERLYING_IO;

            if (prepare_wolfssl_open(tls_io_instance) != 0)
            {
                LogError("Cannot create wolfssl instance.");
                tls_io_instance->tlsio_state = TLSIO_STATE_NOT_OPEN;
                result = MU_FAILURE;
            }
            else if (xio_open(tls_io_instance->socket_io, on_underlying_io_open_complete, tls_io_instance, on_underlying_io_bytes_received, tls_io_instance, on_underlying_io_error, tls_io_instance) != 0)
            {
                LogError("Cannot open the underlying IO.");
                tls_io_instance->tlsio_state = TLSIO_STATE_NOT_OPEN;
                result = MU_FAILURE;
            }
            else
            {
                result = 0;
            }
        }
    }

    return result;
}

int tlsio_wolfssl_close(CONCRETE_IO_HANDLE tls_io, ON_IO_CLOSE_COMPLETE on_io_close_complete, void* callback_context)
{
    int result = 0;

    if (tls_io == NULL)
    {
        LogError("NULL tls_io handle.");
        result = MU_FAILURE;
    }
    else
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;

        if ((tls_io_instance->tlsio_state == TLSIO_STATE_NOT_OPEN) ||
            (tls_io_instance->tlsio_state == TLSIO_STATE_CLOSING))
        {
            LogError("Close called while not open.");
            result = MU_FAILURE;
        }
        else
        {
            tls_io_instance->tlsio_state = TLSIO_STATE_CLOSING;
            tls_io_instance->on_io_close_complete = on_io_close_complete;
            tls_io_instance->on_io_close_complete_context = callback_context;

            if (xio_close(tls_io_instance->socket_io, on_underlying_io_close_complete, tls_io_instance) != 0)
            {
                LogError("xio_close failed.");
                result = MU_FAILURE;
            }
            else
            {
                result = 0;
            }
        }
    }

    return result;
}

int tlsio_wolfssl_send(CONCRETE_IO_HANDLE tls_io, const void* buffer, size_t size, ON_SEND_COMPLETE on_send_complete, void* callback_context)
{
    int result;

    if (tls_io == NULL || buffer == NULL || size == 0)
    {
        LogError("Invalid parameter specified tls_io: %p, buffer: %p, size: %ul", tls_io, buffer, (unsigned int)size);
        result = MU_FAILURE;
    }
    else
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;

        if (tls_io_instance->tlsio_state != TLSIO_STATE_OPEN)
        {
            LogError("send called while not open");
            result = MU_FAILURE;
        }
        else
        {
            tls_io_instance->on_send_complete = on_send_complete;
            tls_io_instance->on_send_complete_callback_context = callback_context;

            int res = wolfSSL_write(tls_io_instance->ssl, buffer, size);
            if ((res < 0) || ((size_t)res != size)) // Best way I can think of to safely compare an int to a size_t
            {
                LogError("Error writing data through WolfSSL");
                result = MU_FAILURE;
            }
            else
            {
                result = 0;
            }

            // remove on send complete and callback context
            tls_io_instance->on_send_complete = NULL;
            tls_io_instance->on_send_complete_callback_context = NULL;
        }
    }

    return result;
}

void tlsio_wolfssl_dowork(CONCRETE_IO_HANDLE tls_io)
{
    if (tls_io == NULL)
    {
        LogError("NULL tls_io");
    }
    else
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;
        if (tls_io_instance->tlsio_state == TLSIO_STATE_IN_HANDSHAKE ||
            tls_io_instance->tlsio_state == TLSIO_STATE_OPEN ||
            tls_io_instance->tlsio_state == TLSIO_STATE_CLOSING)
        {
            decode_ssl_received_bytes(tls_io_instance);
        }

        xio_dowork(tls_io_instance->socket_io);
    }
}


static int process_option(char** destination, const char* name, const char* value)
{

    (void) name;

    int result;
    if (*destination != NULL)
    {
        free(*destination);
        *destination = NULL;
    }
    if (mallocAndStrcpy_s(destination, value) != 0)
    {
        LogError("unable to process option %s",name);
        result = MU_FAILURE;
    }
    else
    {
        result = 0;
    }
    return result;
}

#if defined(LIBWOLFSSL_VERSION_HEX) && LIBWOLFSSL_VERSION_HEX >= 0x04000000
static void logging_callback(const int logLevel, const char *const logMessage)
{
    if (logLevel == ERROR_LOG)
    {
        LogError("tlsio_wolfssl: %s", logMessage);
    }
    else
    {
        LogInfo("tlsio_wolfssl: %s", logMessage);
    }
}
#endif // LIBWOLFSSL_VERSION_HEX >= 0x04000000

int tlsio_wolfssl_setoption(CONCRETE_IO_HANDLE tls_io, const char* optionName, const void* value)
{
    int result;

    if (tls_io == NULL || optionName == NULL)
    {
        LogError("Bad arguments, tls_io = %p, optionName = %p", tls_io, optionName);
        result = MU_FAILURE;
    }
    else
    {
        TLS_IO_INSTANCE* tls_io_instance = (TLS_IO_INSTANCE*)tls_io;

        if (strcmp(OPTION_TRUSTED_CERT, optionName) == 0)
        {
            result  = process_option(&tls_io_instance->certificate, optionName, value);
        }
        else if (strcmp(SU_OPTION_X509_CERT, optionName) == 0 || strcmp(OPTION_X509_ECC_CERT, optionName) == 0)
        {
            result = process_option(&tls_io_instance->x509certificate, optionName, value);
        }
        else if (strcmp(SU_OPTION_X509_PRIVATE_KEY, optionName) == 0 || strcmp(OPTION_X509_ECC_KEY, optionName) == 0)
        {
            result = process_option(&tls_io_instance->x509privatekey, optionName, value);
        }
        else if (strcmp(optionName, OPTION_SET_TLS_RENEGOTIATION) == 0)
        {
            // No need to do anything for WolfSSL
            result = 0;
        }
#ifdef INVALID_DEVID
        else if (strcmp(OPTION_WOLFSSL_SET_DEVICE_ID, optionName) == 0)
        {
            int device_id = *((int *)value);
            if (tls_io_instance->ssl != NULL && wolfSSL_SetDevId(tls_io_instance->ssl, device_id) != WOLFSSL_SUCCESS)
            {
                LogError("Failure setting device id on ssl");
                result = MU_FAILURE;
            }
            else
            {
                // Save the device Id even if ssl object not yet created.
                tls_io_instance->wolfssl_device_id = device_id;
                result = 0;
            }
        }
#endif
        else if (strcmp("ignore_host_name_check", optionName) == 0)
        {
            bool* server_name_check = (bool*)value;
            tls_io_instance->ignore_host_name_check = *server_name_check;
            result = 0;
        }
#if defined(LIBWOLFSSL_VERSION_HEX) && LIBWOLFSSL_VERSION_HEX >= 0x04000000
        else if (strcmp("debug_log", optionName) == 0)
        {
            bool* enable_debug_logging = (bool*)value;
            if (enable_debug_logging)
            {
                if (!wolfSSL_Debugging_ON())
                {
                    LogError("wolfSSL_Debugging_ON failed.");
                    result = MU_FAILURE;
                }
                else if (!wolfSSL_SetLoggingCb(&logging_callback))
                {
                    LogError("wolfSSL_SetLoggingCb failed.");
                    result = MU_FAILURE;
                }
                else
                {
                    result = 0;
                }
            }
            else
            {
                LogError("tlsio WolfSSL layer does not support disabling debug_logs after they have been enabled.");
                result = MU_FAILURE;
            }
        }
#endif // LIBWOLFSSL_VERSION_HEX >= 0x04000000
        else
        {
            if (tls_io_instance->socket_io == NULL)
            {
                LogError("NULL underlying IO handle");
                result = MU_FAILURE;
            }
            else
            {
                result = xio_setoption(tls_io_instance->socket_io, optionName, value);
            }
        }
    }

    return result;
}
const IO_INTERFACE_DESCRIPTION* tlsio_wolfssl_get_interface_description(void)
{
    return &tlsio_wolfssl_interface_description;
}