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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