examples/contrib/message-parser.py broken after v1.1.0

[jordan-heemskerk]

Tested 1.2.0 and bleeding edge.

v1.1.0:

$:~/dev/modbus/pymodbus/examples/contrib$ ./message-parser.py -b -m 000112340006ff076d
================================================================================
Decoding Message 000112340006ff076d
================================================================================
ServerDecoder
--------------------------------------------------------------------------------
name            = ReadExceptionStatusRequest
check           = 0x0
skip_encode     = 0x0
unit_id         = 0xff
transaction_id  = 0x1
protocol_id     = 0x1234
documentation   =
    This function code is used to read the contents of eight Exception Status
    outputs in a remote device.  The function provides a simple method for
    accessing this information, because the Exception Output references are
    known (no output reference is needed in the function).

ClientDecoder
--------------------------------------------------------------------------------
name            = ReadExceptionStatusResponse
status          = 0x6d
protocol_id     = 0x1234
unit_id         = 0xff
skip_encode     = 0x0
check           = 0x0
transaction_id  = 0x1
documentation   =
    The normal response contains the status of the eight Exception Status
    outputs. The outputs are packed into one data byte, with one bit
    per output. The status of the lowest output reference is contained
    in the least significant bit of the byte.  The contents of the eight
    Exception Status outputs are device specific.

v1.2.0 and current master:

$:~/dev/modbus/pymodbus/examples/contrib$ ./message-parser.py -b -m 000112340006ff076d
================================================================================
Decoding Message 000112340006ff076d
================================================================================
ServerDecoder
--------------------------------------------------------------------------------
ClientDecoder
--------------------------------------------------------------------------------

I dug around a bit to see what was changed between versions but I'm very new to this codebase. Any help would be appreciated.

[jordan-heemskerk]

I've managed to track it down to this commit

edc1a18 Fix bogus calculation in ModbusSocketFramer.checkFrame (one of the tests also seemed wrong, I had to fix it)

Specifically, this part of the commit.

diff --git a/pymodbus/transaction.py b/pymodbus/transaction.py
index 57d0e33..cc4f56d 100644
--- a/pymodbus/transaction.py
+++ b/pymodbus/transaction.py
@@ -182,7 +182,7 @@ class ModbusSocketFramer(IModbusFramer):
             if self.__header['len'] < 2:
                 self.advanceFrame()
             # we have at least a complete message, continue
-            elif len(self.__buffer) >= self.__header['len']:
+            elif len(self.__buffer) - self.__hsize + 1 >= self.__header['len']:
                 return True
         # we don't have enough of a message yet, wait
         return False

If I checkout master and change that line back to

elif len(self.__buffer) >= self.__header['len']:

then the message-parser.py example works again.

I'll leave it to someone more knowledgeable which calculation is actually correct.