Re: [lwip-users] lwIP with mbedTLS

[address@hidden]

Am 27.01.2019 um 10:44 schrieb Paweł:
> Hello,
> I'm trying to build an application using lwIP and mbedTLS. My goal is a 
> secure MQTT connection.
> I'm sure that MQTT without security layer works properly. lwIP works in 
> sys mode.
> I started of course with ALTCP layer and I can succesfully parse 
> certificate using code:
> mqttClientInfo.tls_config = altcp_tls_create_config_client(cert, 
> sizeof(cert));
>
> After mbedTLS tuning (choosing cipher method, etc.) I can see on 
> Wireshark proper Client Hello and Server Hello messages. Then Server 
> Hello Done, Certificate and Server Key Exchange message is coming (no 
> outgoing Client Key Exchange), but from observations I see that messages 
> from Server aren't properly handled by lwIP core.
> On console I can see that mbedTLS switched to parsing Server Hello 
> message but in fetch method input f_recv function (which is a pointer 
> to altcp_mbedtls_bio_recv) is returning MBEDTLS_ERR_SSL_WANT_READ which 
> means that there is nothing to read. What is interesting after this fail 
> lwIP signals receiving a TCP packet, with Server Hello message (I 
> cross-checked sequence numbers with Wireshark). So I digged deeper and 
> found out that everything in mbedTLS is called from lwIP thread context, 
> so secure layer can't wait for messages. I realized that when I was 
> trying to implement f_recv_timeout function.

I'm a bit confused: are you using the mqtt client provided with lwIP? If 
so, TLS should just work. No need to implement f_recv_timeout.

Regards,
Simon

> Questions:
> 1. Does anybody met similiar problems?
> 2. Can I check for incoming messages in mbedTLS, handle them normally in 
> lwIP core and come back to mbedTLS functions? Maybe there is a need for 
> separating threads for two of them?
>
> I encountered many problems during mbedTLS implementations but all of 
> them were affordable (missing defines, memory problems, etc.) but this 
> time I have no idea what to do next.
>
> Regards,
> Pawel
>
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