Memory Leak in _modbus_tcp_flush.

[preetamj84]

libmodbus version

all

Operating system

Windows x64

Description of the Modbus network (server, client, links, etc)

client

Expected behavior

Memory Leak should not Happen

Actual behavior

When we use _modbus_tcp_flush function, memory leak is observed. Bytes do not get freed as expected.Output that appears is "" Invalid TID received.. 0 bytes freed. ""

Steps to reproduce the behavior (commands or source code)

Scenario1 : connected a target modbus device with modbus tcp/ip gateway.Gateway device goes out of network while field device is ON. Scenario2: target device goes off, while gateway is ON. Scenario3: continuous timeout due to say wrong slave id or correct slave id but target device is off.

libmodbus output with debug mode enabled

Invalid TID received.. 0 bytes freed. **

[stephane]

In your report, you have indicated all modbus versions but this message (Invalid TID received) doesn't exist in master branch. Which version do you use?

BTW a message with '0 bytes freed' doesn't mean there is a leak in the program.

[preetamj84]

Lib Modbus Version is 3.0.6

And the statement appears in the following code in modbus_tcp.c int _modbus_tcp_pre_check_confirmation(modbus_t _ctx, const uint8_t req, const uint8_t rsp, int rsplength) { / Check TID */ if (req[0] != rsp[0] || req[1] != rsp[1]) { if (ctx->debug) { fprintf(stderr, "Invalid TID received 0x%X (not 0x%X)\n", (rsp[0] << 8) + rsp[1], (req[0] << 8) + req[1]); } errno = INVALID_DATA; return -1; } else { return 0; } }

This routine is called from the function check_confirmation in modbus.c

To explain correctly when it says Invalid TID received followed by statement, 0 bytes freed,at that point of time, In Task manager, the memory shows as increased after this point. Secondly, when the statement gets printed as Invalid TID Received, say 9 bytes freed, at that time, memory does not increase.

[stephane]

Before further investigation, do you have the same behaviour with libmodbus v3.1.4 (or master) ?

[studioraga]

I am seeing the same error while using ./unit-test-client tcp

Output that appears is "" Invalid TID received.

This is seen with stable version 3.0.6 and master v3.1.4) ...