Socket send function hangs

[Nikil Rao]

Hi,

I have a custom board with nrf9160 and I'm using it to send messages to the AWS server via mqtt. I managed to reproduce a bug where the TLS socket send function hangs (similar to -https://devzone.nordicsemi.com/f/nordic-q-a/62249/hang-in-sendmsg-on-the-nrf9160). I was using v1.3 of ncs.

Steps to reproduce - 

• Connect to LTE netwrok. 
• Connect to AWS via MQTT
• When a successful connection is established, send a disconnect message
• When successfully disconnected, reconnect and keep repeating this loop
• On the 21st connection/disconnection cycle the function gets stuck in the mqtt_client_tls_write function while calling the 
  send(client->transport.tls.sock, data + offset, datalen - offset, 0);
  function

I switched to the latest master branch of ncs and changed the send function to send(client->transport.tls.sock, data + offset, datalen - offset, MSG_DONTWAIT) Now the send function doesn't hang but returns a value of -1 and the errno is -EAGAIN when I follow the steps to reproduce this bug.

How do I handle the socket timeout gracefully? After this timeout, if I try to reconnect to AWS I get 

aws_iot: getaddrinfo, error -10
aws_iot: client_broker_init, error: -10

and I have to restart the device to get it working again

I also noticed an error case which doesn't seem to be handled in aws_iot.c. When the socket send function returns -1, then in file mqtt.c, the function client_connect calls client_disconnect which in turn calls disconnect_event_notify function. This notifies the aws_iot client with 

evt.type = MQTT_EVT_CONNACK;

evt.result = -ECONNREFUSED;

which is not handled properly in aws_iot.c. Handling this properly still causes the same error I mentioned before though.

Any help will be appreciated. Thanks in advance!

Nikil

[Nikil Rao]

Hi Håkon,

I have CONFIG_MQTT_KEEPALIVE=1200 in my code. Moreover this is what I get when I enable MQTT logs - 

[00:00:21.134,094]<dbg> net_mqtt_sock_tls.mqtt_client_tls_connect: (0x20020ff8): Created socket 1
[00:00:31.134,979]<dbg> net_mqtt_sock_tls.mqtt_client_tls_connect: (0x20020ff8): Connect completed
[00:00:31.135,101]<dbg> net_mqtt_enc.connect_request_encode: (0x20020ff8): Encoding Protocol Description. Str:MQTT Size:00000004.
[00:00:31.135,101]<dbg> net_mqtt_enc.pack_utf8_str: (0x20020ff8): >> str_size:00000006 cur:0x2002919a, end:0x2002957d
[00:00:31.135,131]<dbg> net_mqtt_enc.pack_uint16: (0x20020ff8): >> val:0004 cur:0x2002919a, end:0x2002957d
[00:00:31.135,131]<dbg> net_mqtt_enc.connect_request_encode: (0x20020ff8): Encoding Protocol Version 04.
[00:00:31.135,131]<dbg> net_mqtt_enc.pack_uint8: (0x20020ff8): >> val:04 cur:0x200291a0, end:0x2002957d
[00:00:31.135,162]<dbg> net_mqtt_enc.pack_uint8: (0x20020ff8): >> val:00 cur:0x200291a1, end:0x2002957d
[00:00:31.135,162]<dbg> net_mqtt_enc.connect_request_encode: (0x20020ff8): Encoding Keep Alive Time 04b0.
[00:00:31.135,162]<dbg> net_mqtt_enc.pack_uint16: (0x20020ff8): >> val:04b0 cur:0x200291a2, end:0x2002957d
[00:00:31.135,162]<dbg> net_mqtt_enc.connect_request_encode: (0x20020ff8): Encoding Client Id. Str:nrf-352656100388050 Size:00000013.
[00:00:31.135,192]<dbg> net_mqtt_enc.pack_utf8_str: (0x20020ff8): >> str_size:00000015 cur:0x200291a4, end:0x2002957d
[00:00:31.135,192]<dbg> net_mqtt_enc.pack_uint16: (0x20020ff8): >> val:0013 cur:0x200291a4, end:0x2002957d
[00:00:31.135,223]<dbg> net_mqtt_enc.mqtt_encode_fixed_header: (0x20020ff8): << msg type:0x10 length:0x0000001f
[00:00:31.135,223]<dbg> net_mqtt_enc.packet_length_encode: (0x20020ff8): >> length:0x0000001f cur:0x00000000, end:0x00000000
[00:00:31.135,223]<dbg> net_mqtt_enc.mqtt_encode_fixed_header: (0x20020ff8): Fixed header length = 02
[00:00:31.135,223]<dbg> net_mqtt_enc.pack_uint8: (0x20020ff8): >> val:10 cur:0x20029198, end:0x2002957d
[00:00:31.135,253]<dbg> net_mqtt_enc.packet_length_encode: (0x20020ff8): >> length:0x0000001f cur:0x20029199, end:0x2002957d
[00:00:31.135,986]<dbg> net_mqtt.client_connect: (0x20020ff8): Connect completed

Encoding Keep Alive Time 04b0. shows that it is indeed 1200 seconds