Misleading comment about bubbleHeaderLength about xdripswift

[JohanDegraeve]

Hi, ok. Is it possible to make a pull request ? This code is actually from Bubble Dev team. I reshuffled some code but this comment is original. thanks, Johan

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Op 22 november 2019 om 12:06 schreef Guido Soranzio ***@***.***>: The following comment is misleading: // length of header added by Bubble in front of data dat is received from Libre sensor private let bubbleHeaderLength = 8 (https://github.com/JohanDegraeve/xdripswift/blob/f2d7bc5303094ba238d7dc8c9a0daeb70f682421/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L37-L38) Bubble adds a footer of 8 bytes at the end of the FRAM when sending the data packet. xdripswift itself is accumulating the patchUid and the first 344 FRAM bytes from the data packet reaching the same length of 352 bytes. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub #35?email_source=notifications&email_token=ADJTATPG5PDIXB5IAFPT4WDQU64LFA5CNFSM4JQPFDKKYY3PNVWWK3TUL52HS4DFUVEXG43VMWVGG33NNVSW45C7NFSM4H3LM72A , or unsubscribe https://github.com/notifications/unsubscribe-auth/ADJTATMFJPXO52NUNXJTWRDQU64LFANCNFSM4JQPFDKA .

[JohanDegraeve]

I think this comment is correct. The header is in front, which is the sensor serial number https://github.com/JohanDegraeve/xdripswift/blob/master/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L170

the data is after the header : https://github.com/JohanDegraeve/xdripswift/blob/master/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L193
ibreData: (rxBuffer.subdata(in: bubbleHeaderLength..<(344 + bubbleHeaderLength)))

[gui-dos]

The patchUID, the serial number is computed from, comes with the packet whose response type is 0xC0.
The patchInfo comes with the new packet whose response type is 0xC1.
Then comes the data packet, whose response type is 0x82 and whose length is 352 byte: 344 FRAM bytes plus 8 null footer bytes.

In the xDrip sources the constant 8 is called indeed BUBBLE_FOOTER:
https://github.com/NightscoutFoundation/xDrip/blob/b7bc355cea2128f72a4e09c82ce1d937e14c81e0/app/src/main/java/com/eveningoutpost/dexdrip/Models/Bubble.java#L52s

I tested all this thoroughly with https://gist.github.com/gui-dos/83fbd9b6f3a7dfe17b2dd77a59c8ddde

The comment says "added by Bubble in front of data that is received from Libre" but Bubble instead appends a trail at the end of the data that is received from Libre. The serial is sent separately in a packet 10 bytes long, the patchInfo is extracted from its 14 byte packet.

[JohanDegraeve]

The packet which starts with 0xC0 is added to the rxBuffer, at that moment the rxBuffer is still empty

https://github.com/JohanDegraeve/xdripswift/blob/master/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L160

Then come several packets 0x82, these are being appended to the rxBuffer, which means after the first packet
https://github.com/JohanDegraeve/xdripswift/blob/master/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L164

Once all packets are received, the full data is processed, starting by reading the serialnumber
https://github.com/JohanDegraeve/xdripswift/blob/master/xdrip/Transmitter/CGMBluetoothTransmitter/Libre/Bubble/CGMBubbleTransmitter.swift#L170 which is the first 8 bytes.

So i think the name and comment are correct

[gui-dos]

The newer firmwares are sending the 0xC0 patchUid packet, the 0xC1 patchInfo packet and the 0x82 data packets, in this sequence.

If you are going to accumulate also the patchInfo in the unified rxBuffer, you will have to change the bubbleHeaderLength constant. But are the patchUid and the PatchInfo really a "header"?

[JohanDegraeve]

I haven't started yet with support of new firmware versions.

It's just the way it's coded. I could have processed packet 0xC0 immediately when receiving (ie decoding the sensor serial number). In that case the header length definition wouldn't be needed at all.

After all it's not a header indeed, as it's a seperate packet.
But I don't believe right now this comment or property name needs to be changed.

[gui-dos]

Unfortunately https://github.com/jizhongwen/xdripswift hasn't been updated since August even if on TestFlight there have been published more updated betas (https://testflight.apple.com/join/5DrayRKU). Curious to have a look to their implementation :).