fix: stuck on "Connecting..."

[Dzuchun]

I've encountered an issue with the same symptoms as #989, except in my case espflash would sometimes start working again after re-plugging the cable.

I reproduced the issue on the main branch, and traced to core reason -- when sending the Sync command, slip-codec's decoder appeared to be stuck reading bytes indefinitely here. Specifically -- byte 0x0a would be read indefinitely, never terminating the loop.

So I've added a byte count bounded variant of Connection::read (Connection::read_bounded), and used it to read the response (right now, the code expects responses of at most 44 bytes, so that was selected as an upper bound).

I also removed the claim that response is read with the timeout -- I am sure I've spent more than 100ms waiting for the Sync command to complete. My guess is that reading 0x0a from the port overrides the timeout, and thus the command itself never times out. This change is questionable, let me know if I should revert it, or...?

The tool works fine for me now -- ELF gets flashed every time.

As you could probably tell, I have little knowledge of what's actually going on. So I would appreciate extra attention to make sure this change doesn't actually break anything.

[Dzuchun]

My initial assumption that responses are up to 44 bytes long clearly was incorrect. However, I assume that response cannot be longer than the entire flash memory, so I bounded it by 5Mi now.

[Dzuchun]

Using 8MiB as a static upper bound still causes the tool to hang -- apparently, reading 8MiB one-by-one takes a while.

So I've added max response length guessing based of the CommandType:

• If Sync, expect at most 44 bytes
• By default, assume 8Mib

Apparently, this is enough to both pass the CI and solve the issue. Please let me know what you think.

[SergioGasquez]

Changes look good to me, but they introduce major breaking changes. There are two options:

• Restoring read_response, marking it as deprecated and adding two new functions
• Waiting for the espflash@v5 development to get this merged