FIT Runtime Error at byte: 72 Invalid field definition base type

4900661 11 days ago

Hi all

I was trying to parse a fitfile created from a SRM power sensor using the python sdk.

The Decoder returns the error: FIT Runtime Error at byte: 72 Invalid field definition base type'.

Which makes that i can`t find any records in the message. The site https://www.fitfileviewer.com/ also complains about some incorrect format but can still extract the records. Any suggestions?

I put the file in attachment.

srm.fit

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0 Ben FIT 11 days ago

There is a second error at byte 121 too. Both strings in the file have an unexpected, but not completely wrong, data type in the message definition.

Is this happening in every file from this device or just this file?

I manually edited this file in a hex editor and it should decode in the Python SDK for you.

fixed_srm.fit

0 4900661 10 days ago in reply to Ben FIT

Thanks Ben for the rapid response, I really appriciate it!

It`s happening for every file and there are sadly still many to come. Is it possible to share what you have done so i can implement it.

Thanks in advance

0 Ben FIT 8 days ago in reply to 4900661

The issue is that the data type used in the example file for string fields is 0x87. The Python and JavaScript SDKs expect 0x07. 0x87 is technically correct since the protocol says to use bits 0-4 for the base type. Bits 5-6 are reserved. Bit 7 is the endianness flag (not the endianness itself, that is elsewhere). So the Python SDK needs to mask that value (plus a few other things to make it work)

If you want to try and hack something together for just these files, change the 0x07 on these two lines to 0x87. I am mostly sure that would work for these files, and completely sure that will break other files.
https://github.com/garmin/fit-python-sdk/blob/main/garmin_fit_sdk/fit.py#L23

https://github.com/garmin/fit-python-sdk/blob/main/garmin_fit_sdk/fit.py#L62

The real fix will involve art by adding "& 0x1F" to this line, changing the definitions on the lines above, and making another changes to support develop[er data.
https://github.com/garmin/fit-python-sdk/blob/main/garmin_fit_sdk/decoder.py#L220

We can get a fix out in the next few weeks.

0 4900661 7 days ago in reply to Ben FIT

super!

Thanks a lot for the rapid and detailed response!