FMB_TCP_CONNECTION_TOUT_SEC causes an overflow (IDFGH-14951)

[femtotech]

Checklist

• Checked the issue tracker for similar issues to ensure this is not a duplicate
• Read the documentation to confirm the issue is not addressed there and your configuration is set correctly
• Tested with the latest version to ensure the issue hasn't been fixed

How often does this bug occurs?

always

Expected behavior

The SDK asks to input the number of seconds for the Modbus connection timeout (CONFIG_FMB_TCP_CONNECTION_TOUT_SEC). I didn't find the allowable range, but the internal #define (MB_TCP_DISCONNECT_TIMEOUT) is expressed in us and used by an int64 variable here.

Actual behavior (suspected bug)

The MB_TCP_DISCONNECT_TIMEOUT #define (here) states:

#define MB_TCP_DISCONNECT_TIMEOUT       ( CONFIG_FMB_TCP_CONNECTION_TOUT_SEC * 1000000 ) // disconnect timeout in uS

This would cause an overflow if, for example, one sets CONFIG_FMB_TCP_CONNECTION_TOUT_SEC = 3600.

Error logs or terminal output

This is the output when `CONFIG_FMB_TCP_CONNECTION_TOUT_SEC = 3600`

I (58248) MB_TCP_SLAVE_PORT: Socket (#55), accept client connection from address: 192.168.2.62
E (58250) MB_TCP_SLAVE_PORT: Client 0, Socket(#55) do not answer for 14 (us). Drop connection...
I (61228) MB_TCP_SLAVE_PORT: Socket (#55), accept client connection from address: 192.168.2.62
E (61232) MB_TCP_SLAVE_PORT: Client 0, Socket(#55) do not answer for 13 (us). Drop connection...
I (64299) MB_TCP_SLAVE_PORT: Socket (#55), accept client connection from address: 192.168.2.62
E (64301) MB_TCP_SLAVE_PORT: Client 0, Socket(#55) do not answer for 14 (us). Drop connection...

Steps to reproduce the behavior

1. set CONFIG_FMB_TCP_CONNECTION_TOUT_SEC = 3600
2. run a Modbus Client
3. try to connect

Project release version

1.0.17

System architecture

Intel/AMD 64-bit (modern PC, older Mac)

Operating system

Linux

Operating system version

Ubuntu 24.10

Shell

Bash

Additional context

I would propose the following patch:

#define MB_TCP_DISCONNECT_TIMEOUT       ( CONFIG_FMB_TCP_CONNECTION_TOUT_SEC * 1000000UL )

In this way, you can set CONFIG_FMB_TCP_CONNECTION_TOUT_SEC = 3600 and it will work fine.

[alisitsyn]

Hello, @femtotech,

Thank you for this report. The maximum time has never been checked and it was expected to have something like 5 seconds at maximum waiting for connections. The maximum value for (int64_t) = 9223372036854775807. I confirm the issue in the line where the constant is treated as an integer instead of (int64_t) and caused overflow as stated by the compilation warning:
esp-modbus/freemodbus/tcp_slave/port/port_tcp_slave.c:63:78: warning: integer overflow in expression of type 'int' results in '-694967296' [-Woverflow]
Your change solves the issue with incorrect comparison. However, I can not change this releasing the new component because the v1.0.17 is out of support because of v2 is in the focus. In spite of this I will try to fix this when possible in the master with low priority.

Could you try using v2 instead?