How to gain access to written bytes to calculate checksum?

[yanshay]

I have a struct that ends with a checksum of previous data.
I want to implement a custom writer for that field.
How can I gain in the writer access to the bytes that were already written?

In the past I did it and used deku::output but it seems the writer syntax has changed and now there is a deku::writer which doesn't seem to provide access to written bytes.

So how can I achieve something like that? It's pretty common in many binary protocols I've seen.

[wcampbell0x2a]

Take a glance at this example: https://github.com/sharksforarms/deku/blob/master/examples/deku_input.rs

[yanshay]

This example seems to be an example of reading.
Are you saying that it's also possible to do something similar when writing? I don't fully understand that example yet, and will look closer, just want to make sure I understand correctly what you mean.

[wcampbell0x2a]

Oh, yes. Maybe I shouldn't reply right after I get up 🤷‍♂️

I'll have to think about the writer.