Hi Gurux Team,
I am facing an issue with FOTA Image Block Transfer in Gurux.DLMS Python.
The same meter and firmware FOTA work correctly using DLMS Director, but when I perform the same operation using the Python implementation, Image Transfer Initiate succeeds and Image Block Transfer fails with:
byte must be in range(0, 256)
The meter reports:
Image Block Size : 512 bytes
Image Transfer Enabled : True
Image Transfer Initiate (Method 1) is successful.
The failure occurs when sending Method 2 (Image Block Transfer), starting from Block 0.
The decrypted DLMS request shows:
Structure
UInt32 block number = 0
OctetString = 512 bytes
and the encoded OCTET STRING contains:
09 82 02 00
The complete communication log and current Python source code are attached.
Since the same FOTA works successfully with DLMS Director, could you please explain:
1. Why does the Python implementation generate the
"byte must be in range(0, 256)" error?
2. Is this related to the 512-byte OCTET STRING encoding,
GXByteBuffer, AXDR length encoding, or PDU/frame size?
3. What is the correct fix in the Gurux Python code so that
FOTA works the same way as DLMS Director?
Please point me to the exact code/function that needs to be changed.
Thank you
Kumaresh Dhara
Logs attached
======================================================================
FOTA CONFIGURATION
======================================================================
FOTA Mode : SEQUENTIAL
Firmware Path : D:\Script P_Shell\DLMS FOTA Tool\Testing_2024.bin
Firmware file found successfully.
Starting FOTA Update...
======================================================================
FOTA UPDATE STARTED
======================================================================
FOTA MODE : SEQUENTIAL
Firmware File : D:\Script P_Shell\DLMS FOTA Tool\Testing_2024.bin
Firmware Size : 261120 bytes
Image Transfer Object Found : 0.0.44.0.0.255
Reading Image Block Size from meter...
Decrypted PDU: C0 01 C1 00 12 00 00 2C 00 00 FF 02 00
<GetRequest>
<GetRequestNormal>
<InvokeIdAndPriority Value="C1" />
<AttributeDescriptor>
<ClassId Value="0012" />
<InstanceId Value="00002C0000FF" />
<AttributeId Value="02" />
</AttributeDescriptor>
</GetRequestNormal>
</GetRequest>
TX: 00:14:47 7E A0 2C 03 61 10 BC BE E6 E6 00 C8 1E 30 00 00 AC 95 59 95 7C 48 74 F9 A4 D2 3D F9 DB B7 C2 44 80 CF C5 67 18 A2 18 49 8C 45 BE 99 4C 7E
Encryption is applied.
Authentication is applied.
Decrypted PDU: C4 01 C1 00 06 00 00 02 00
<GetResponse>
<GetResponseNormal>
<InvokeIdAndPriority Value="C1" />
<Result>
<Data>
<UInt32 Value="00000200" />
</Data>
</Result>
</GetResponseNormal>
</GetResponse>
RX: 00:14:47 7E A0 28 61 03 30 42 0B E6 E7 00 CC 1A 30 00 00 AC 94 5A BE 51 E9 76 D6 62 7D 96 C0 7C D6 57 21 F5 C8 6E 47 F0 2D 99 89 27 7E
Meter Image Block Size : 512
Using Image Block Size : 512 bytes
Decrypted PDU: C0 01 C1 00 12 00 00 2C 00 00 FF 05 00
<GetRequest>
<GetRequestNormal>
<InvokeIdAndPriority Value="C1" />
<AttributeDescriptor>
<ClassId Value="0012" />
<InstanceId Value="00002C0000FF" />
<AttributeId Value="05" />
</AttributeDescriptor>
</GetRequestNormal>
</GetRequest>
TX: 00:14:47 7E A0 2C 03 61 32 AC BC E6 E6 00 C8 1E 30 00 00 AC 96 52 3C EC B5 64 6F 12 51 D0 20 EF 77 5A 06 3D F1 54 99 E5 B4 F0 A3 AF 33 6C F6 94 7E
Encryption is applied.
Authentication is applied.
Decrypted PDU: C4 01 C1 00 03 01
<GetResponse>
<GetResponseNormal>
<InvokeIdAndPriority Value="C1" />
<Result>
<Data>
<Boolean Value="True" />
</Data>
</Result>
</GetResponseNormal>
</GetResponse>
RX: 00:14:48 7E A0 25 61 03 52 D9 C0 E6 E7 00 CC 17 30 00 00 AC 95 B4 60 04 36 8A 4C 3C EB 7E 03 BF 6D DC B8 0A 77 31 2C A5 E5 7E
Image Transfer Enabled : True
Image Identifier : Testing_2024.bin
Reading firmware file...
Firmware loaded successfully : 261120 bytes
Total Blocks : 510
----------------------------------------------------------------------
SEQUENTIAL MODE SELECTED
Starting from Block 0
----------------------------------------------------------------------
----------------------------------------------------------------------
STEP 1 : IMAGE TRANSFER INITIATE
----------------------------------------------------------------------
Decrypted PDU: C3 01 C1 00 12 00 00 2C 00 00 FF 01 01 02 02 09 50 54 65 73 74 69 6E 67 5F 66 75 6C 6C 69 6D 61 67 65 5F 54 61 74 61 5F 31 50 5F 34 47 5F 43 53 50 44 43 4C 5F 4B 55 31 20 30 31 2E 32 34 2D 53 4B 30 33 30 30 2E 31 36 5F 54 41 43 48 30 2E 30 30 2E 34 32 5F 43 52 59 5F 32 30 32 34 2E 62 69 6E 06 00 03 FC 00
<ActionRequest>
<ActionRequestNormal>
<InvokeIdAndPriority Value="C1" />
<MethodDescriptor>
<ClassId Value="0012" />
<InstanceId Value="00002C0000FF" />
<MethodId Value="01" />
</MethodDescriptor>
<MethodInvocationParameters>
<Structure Qty="02" >
<OctetString Value="54657374696E675F66756C6C696D6167655F546174615F31505F34475F43535044434C5F4B55312030312E32342D534B303330302E31365F54414348302E30302E34325F4352595F323032342E62696E" />
<UInt32 Value="0003FC00" />
</Structure>
</MethodInvocationParameters>
</ActionRequestNormal>
</ActionRequest>
TX: 00:14:48 7E A0 85 03 61 54 C2 E1 E6 E6 00 CB 77 30 00 00 AC 97 76 22 CD B3 6C AC 73 FA F2 BC 39 86 D3 8B 57 99 51 CB 61 D5 77 79 97 A2 85 6F A1 BC 9C 48 11 49 CE 9B AE E5 7C E0 1B 5D 49 BE 3C DC B6 9B 75 A8 0B AB 2B F5 73 9E FF 42 17 98 87 FB 19 44 20 46 90 E4 63 0F 62 DE A8 B8 84 F5 EC ED 54 C6 6D 95 68 66 E3 53 F3 7F B2 DF 79 FC FE 5A B3 F3 E6 D9 FB 4C C9 75 8F 2B 0D DE 92 24 12 06 0D EF 91 D1 94 03 A1 6B 7E
Encryption is applied.
Authentication is applied.
Decrypted PDU: C7 01 C1 00 00
<ActionResponse>
<ActionResponseNormal>
<InvokeIdAndPriority Value="C1" />
<Result Value="Success" />
</ActionResponseNormal>
</ActionResponse>
RX: 00:14:48 7E A0 24 61 03 74 56 98 E6 E7 00 CF 16 30 00 00 AC 96 FB 09 C0 02 1E 55 0C B9 F8 52 D7 F1 2F 01 6C 44 86 7C D2 7E
Image Transfer Initiate : SUCCESS
----------------------------------------------------------------------
STEP 2 : IMAGE BLOCK TRANSFER
----------------------------------------------------------------------
Start Block : 0
End Block : 509
Block Size : 512
Sending Block 0/509 | 512 bytes
Decrypted PDU: C3 01 C1 00 12 00 00 2C 00 00 FF 02 01 02 02 06 00 00 00 00 09 82 02 00 86 15 FF FF 79 19 A6 16 00 00 6C 16 00 00 8D 16 00 00 00 00 CA 18 89 18 00 00 00 00 00 00 59 18 4B 16 14 18 00 00 2B 17 00 00 00 00 FD 18 F7 16 00 00 00 00 5C 19 00 00 E0 15 BF 16 00 00 11 17 00 00 00 00 E8 15 00 00 00 00 92 16 00 00 A1 16 9C 16 97 16 00 00 00 00 7B 19 00 00 00 00 BD 16 7D 19 00 00 00 00 00 00 00 00 00 00 A8 16 AE 16 B3 16 B8 16 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7E 3F E0 84 00 00 00 00 00 00 00 00 00 00 FF FF FF FF FF FF FF FF FF FF 32 00 85 D2 3F BF 1C 95 33 C0 74 5D 82 BF 0E BE 33 C0 00 00 80 41 D2 08 00 40 00 00 80 3F C6 3C 00 40 00 F0 73 45 04 C6 4B 45 48 BC 4D 47 3B 57 A2 47 70 C3 23 4D 70 C3 23 4D 70 C3 23 4D BE 38 81 4D BE 38 81 4D BE 38 81 4D DA 00 00 00 E2 00 00 00 EA 00 00 00 F2 00 00 00 01 00 40 42 0F 00 20 A1 07 00 01 00 40 42 0F 00 20 A1 07 00 0A D7 23 3C 66 66 E6 3F 00 00 20 41 00 00 20 42 00 00 8C 42 00 00 48 41 80 0C 00 00 00 00 F0 41 01 01 01 00 04 04 01 03 00 00 00 00 06 00 96 00 00 00 2A 43 00 80 84 43 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<ActionRequest>
<ActionRequestNormal>
<InvokeIdAndPriority Value="C1" />
<MethodDescriptor>
<ClassId Value="0012" />
<InstanceId Value="00002C0000FF" />
<MethodId Value="02" />
</MethodDescriptor>
<MethodInvocationParameters>
<Structure Qty="02" >
<UInt32 Value="00000000" />
<OctetString Value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
</Structure>
</MethodInvocationParameters>
</ActionRequestNormal>
</ActionRequest>
byte must be in range(0, 256)
DisconnectRequest
TX: 00:14:48 7E A0 11 03 61 76 F1 7F E6 E6 00 62 03 80 01 00 BD 9B 7E
RX: 00:14:48 7E A0 36 61 03 96 9D A6 E6 E7 00 63 28 80 01 00 BE 23 04 21 28 1F 30 00 00 AC 96 34 08 07 5D 01 C2 CD C8 12 1B D5 6E 0F E7 51 E4 A3 E7 8B B7 DF 4F 87 6A A5 9F 49 BB 7E
TX: 00:14:48 7E A0 07 03 61 53 65 81 7E
RX: 00:14:49 7E A0 20 61 03 73 05 9E 81 80 14 05 02 03 40 06 02 03 40 07 04 00 00 00 01 08 04 00 00 00 01 B7 29 7E
Ended. Press any key to continue.
Hi, The firmware is updated…
Hi,
The firmware is updated regularly, so there should be no reason for this issue.
Can you get the traceback from this so I can see where this error occurs?
Can you also get the hex trace from the meter reply?
Add a plain hex trace.
Regards,
Mikko
Hi Mikko, Thank you for the…
Hi Mikko,
Thank you for the response.
I checked this further and the issue is specifically related to the **Image Block Size returned by the meter**.
The same Python FOTA code is working correctly when the meter reports a smaller block size, for example **128 bytes**. In that case, the Python code reads the block size from the meter, creates the corresponding block, and the Image Block Transfer works successfully.
The issue occurs when the meter reports:
```text
Image Block Size : 512 bytes
Image Transfer Enabled : True
```
The Python code automatically uses the 512-byte block size and creates a 512-byte OCTET STRING for Method 2.
Image Transfer Initiate (Method 1) succeeds. The failure occurs when sending the first Image Block Transfer (Block 0).
The error is:
```text
byte must be in range(0, 256)
```
This error is generated locally by the Python code. There is no meter error response associated with this exception.
The decrypted request for Block 0 is:
```text
Structure
UInt32 = 00000000
OctetString = 512 bytes
```
The beginning of the encoded OCTET STRING is:
```text
09 82 02 00
```
where `02 00` represents the length of 512 bytes.
Therefore, it appears that the issue may be occurring while encoding the OCTET STRING length or adding the encoded data to the byte buffer when the length is greater than 255 bytes.
I have attached the traceback as requested, along with the plain hexadecimal communication trace.
The behavior can be summarized as:
```text
Block Size = 128 bytes
-> Image Block Transfer works
Block Size = 512 bytes
-> Image Transfer Initiate works
-> Image Block Transfer fails locally
-> "byte must be in range(0, 256)"
```
Could you please check the traceback and advise which Gurux Python function is responsible for this encoding?
If possible, please point me to the exact function/file that needs to be corrected for OCTET STRING lengths greater than 255 bytes.
Regards,
Kumaresh Dhara
Hi Kumaresh Dhara, This is…
Hi Kumaresh Dhara,
This is tested with an image block size of 512 bytes, and it worked without problems.
Can you run
python --version
Let me know the output and the Python version that you are using.
Regards,
Mikko