Hi all,
I am trying to setup an app that will connect to a custom server via DTLS (no Particle Cloud connection).
It seems Particle uses the mbedtls library internally for its connection to the cloud. Ideally, I would like to leverage this library as well for my own purpose.
For now I have achieved getting a sample dtls_client to compile succesfully by copying the dtls_client.c code provided with mbedtls directly in my application file.
While the code compiles, I am getting undefined references for all mbedtls symbols. This suggest the app does not link against the mbedtls libraries by default. So the question is, how to I get my app to link against said library? Should I make a custom makefile for my app and link against the built libs prepared by compiling the system firmware?
The code looks like this:
#include "application.h"
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf Serial.printf
#define mbedtls_fprintf fprintf
#endif
#include <string.h>
#include "mbedtls/net.h"
#include "mbedtls/debug.h"
#include "mbedtls/ssl.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/error.h"
#include "mbedtls/certs.h"
#include "mbedtls/timing.h"
#define SERVER_PORT "4433"
#define SERVER_NAME "localhost"
#define SERVER_ADDR "127.0.0.1" /* forces IPv4 */
#define MESSAGE "Echo this"
#define READ_TIMEOUT_MS 1000
#define MAX_RETRY 5
#define DEBUG_LEVEL 0
SYSTEM_MODE(MANUAL);
void dtls_client();
void setup()
{
Serial.begin(9600);
Cellular.on();
Cellular.connect();
Serial.println("Waiting to be connected to the cellular network:");
}
bool cellularConnected = false;
void loop()
{
// Check connection to the nework.
if(!cellularConnected)
{
if(!Cellular.ready())
{
Serial.print(".");
return;
}
else
{
//Serial.println("Connected to cellular network with ip: %s", Cellular.localIP());
Serial.println("Connected to cellular network.");
cellularConnected = true;
}
}
// Do a connection test with the server every 30 sec.
delay(10000);
dtls_client();
delay(50000);
}
static void my_debug( void *ctx, int level,
const char *file, int line,
const char *str )
{
((void) level);
//mbedtls_fprintf( (FILE *) ctx, "%s:%04d: %s", file, line, str );
//fflush( (FILE *) ctx );
}
const char mbedtls_test_cas_pem[] = ""; //= TEST_CA_CRT_RSA TEST_CA_CRT_EC;
const size_t mbedtls_test_cas_pem_len = 0; //= sizeof( mbedtls_test_cas_pem );
void dtls_client()
{
int ret, len;
mbedtls_net_context server_fd;
uint32_t flags;
unsigned char buf[1024];
const char *pers = "dtls_client";
int retry_left = MAX_RETRY;
mbedtls_entropy_context entropy;
mbedtls_ctr_drbg_context ctr_drbg;
mbedtls_ssl_context ssl;
mbedtls_ssl_config conf;
mbedtls_x509_crt cacert;
mbedtls_timing_delay_context timer;
#if defined(MBEDTLS_DEBUG_C)
mbedtls_debug_set_threshold( DEBUG_LEVEL );
#endif
/*
* 0. Initialize the RNG and the session data
*/
mbedtls_net_init( &server_fd );
mbedtls_ssl_init( &ssl );
mbedtls_ssl_config_init( &conf );
mbedtls_x509_crt_init( &cacert );
mbedtls_ctr_drbg_init( &ctr_drbg );
mbedtls_printf( "\n . Seeding the random number generator..." );
mbedtls_entropy_init( &entropy );
if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
(const unsigned char *) pers,
strlen( pers ) ) ) != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ctr_drbg_seed returned %d\n", ret );
goto exit;
}
mbedtls_printf( " ok\n" );
/*
* 0. Load certificates
*/
mbedtls_printf( " . Loading the CA root certificate ..." );
//fflush( stdout );
ret = mbedtls_x509_crt_parse( &cacert, (const unsigned char *) mbedtls_test_cas_pem,
mbedtls_test_cas_pem_len );
if( ret < 0 )
{
mbedtls_printf( " failed\n ! mbedtls_x509_crt_parse returned -0x%x\n\n", -ret );
goto exit;
}
mbedtls_printf( " ok (%d skipped)\n", ret );
/*
* 1. Start the connection
*/
mbedtls_printf( " . Connecting to udp/%s/%s...", SERVER_NAME, SERVER_PORT );
if( ( ret = mbedtls_net_connect( &server_fd, SERVER_ADDR,
SERVER_PORT, MBEDTLS_NET_PROTO_UDP ) ) != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_net_connect returned %d\n\n", ret );
goto exit;
}
mbedtls_printf( " ok\n" );
/*
* 2. Setup stuff
*/
mbedtls_printf( " . Setting up the DTLS structure..." );
if( ( ret = mbedtls_ssl_config_defaults( &conf,
MBEDTLS_SSL_IS_CLIENT,
MBEDTLS_SSL_TRANSPORT_DATAGRAM,
MBEDTLS_SSL_PRESET_DEFAULT ) ) != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ssl_config_defaults returned %d\n\n", ret );
goto exit;
}
/* OPTIONAL is usually a bad choice for security, but makes interop easier
* in this simplified example, in which the ca chain is hardcoded.
* Production code should set a proper ca chain and use REQUIRED. */
mbedtls_ssl_conf_authmode( &conf, MBEDTLS_SSL_VERIFY_OPTIONAL );
mbedtls_ssl_conf_ca_chain( &conf, &cacert, NULL );
mbedtls_ssl_conf_rng( &conf, mbedtls_ctr_drbg_random, &ctr_drbg );
mbedtls_ssl_conf_dbg( &conf, my_debug, stdout );
if( ( ret = mbedtls_ssl_setup( &ssl, &conf ) ) != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ssl_setup returned %d\n\n", ret );
goto exit;
}
if( ( ret = mbedtls_ssl_set_hostname( &ssl, SERVER_NAME ) ) != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ssl_set_hostname returned %d\n\n", ret );
goto exit;
}
mbedtls_ssl_set_bio( &ssl, &server_fd,
mbedtls_net_send, mbedtls_net_recv, mbedtls_net_recv_timeout );
mbedtls_ssl_set_timer_cb( &ssl, &timer, mbedtls_timing_set_delay,
mbedtls_timing_get_delay );
mbedtls_printf( " ok\n" );
/*
* 4. Handshake
*/
mbedtls_printf( " . Performing the SSL/TLS handshake..." );
do ret = mbedtls_ssl_handshake( &ssl );
while( ret == MBEDTLS_ERR_SSL_WANT_READ ||
ret == MBEDTLS_ERR_SSL_WANT_WRITE );
if( ret != 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ssl_handshake returned -0x%x\n\n", -ret );
goto exit;
}
mbedtls_printf( " ok\n" );
/*
* 5. Verify the server certificate
*/
mbedtls_printf( " . Verifying peer X.509 certificate..." );
/* In real life, we would have used MBEDTLS_SSL_VERIFY_REQUIRED so that the
* handshake would not succeed if the peer's cert is bad. Even if we used
* MBEDTLS_SSL_VERIFY_OPTIONAL, we would bail out here if ret != 0 */
if( ( flags = mbedtls_ssl_get_verify_result( &ssl ) ) != 0 )
{
char vrfy_buf[512];
mbedtls_printf( " failed\n" );
mbedtls_x509_crt_verify_info( vrfy_buf, sizeof( vrfy_buf ), " ! ", flags );
mbedtls_printf( "%s\n", vrfy_buf );
}
else
mbedtls_printf( " ok\n" );
/*
* 6. Write the echo request
*/
send_request:
mbedtls_printf( " > Write to server:" );
len = sizeof( MESSAGE ) - 1;
do ret = mbedtls_ssl_write( &ssl, (unsigned char *) MESSAGE, len );
while( ret == MBEDTLS_ERR_SSL_WANT_READ ||
ret == MBEDTLS_ERR_SSL_WANT_WRITE );
if( ret < 0 )
{
mbedtls_printf( " failed\n ! mbedtls_ssl_write returned %d\n\n", ret );
goto exit;
}
len = ret;
mbedtls_printf( " %d bytes written\n\n%s\n\n", len, MESSAGE );
/*
* 7. Read the echo response
*/
mbedtls_printf( " < Read from server:" );
len = sizeof( buf ) - 1;
memset( buf, 0, sizeof( buf ) );
do ret = mbedtls_ssl_read( &ssl, buf, len );
while( ret == MBEDTLS_ERR_SSL_WANT_READ ||
ret == MBEDTLS_ERR_SSL_WANT_WRITE );
if( ret <= 0 )
{
switch( ret )
{
case MBEDTLS_ERR_SSL_TIMEOUT:
mbedtls_printf( " timeout\n\n" );
if( retry_left-- > 0 )
goto send_request;
goto exit;
case MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY:
mbedtls_printf( " connection was closed gracefully\n" );
ret = 0;
goto close_notify;
default:
mbedtls_printf( " mbedtls_ssl_read returned -0x%x\n\n", -ret );
goto exit;
}
}
len = ret;
mbedtls_printf( " %d bytes read\n\n%s\n\n", len, buf );
/*
* 8. Done, cleanly close the connection
*/
close_notify:
mbedtls_printf( " . Closing the connection..." );
/* No error checking, the connection might be closed already */
do ret = mbedtls_ssl_close_notify( &ssl );
while( ret == MBEDTLS_ERR_SSL_WANT_WRITE );
ret = 0;
mbedtls_printf( " done\n" );
/*
* 9. Final clean-ups and exit
*/
exit:
#ifdef MBEDTLS_ERROR_C
if( ret != 0 )
{
char error_buf[100];
mbedtls_strerror( ret, error_buf, 100 );
mbedtls_printf( "Last error was: %d - %s\n\n", ret, error_buf );
}
#endif
mbedtls_net_free( &server_fd );
mbedtls_x509_crt_free( &cacert );
mbedtls_ssl_free( &ssl );
mbedtls_ssl_config_free( &conf );
mbedtls_ctr_drbg_free( &ctr_drbg );
mbedtls_entropy_free( &entropy );
#if defined(_WIN32)
mbedtls_printf( " + Press Enter to exit this program.\n" );
#endif
/* Shell can not handle large exit numbers -> 1 for errors */
if( ret < 0 )
ret = 1;
}
