The current webrepl-code seems to be a bit outdated lack behind the feature progress of mpremote. Additionally, the current file-transfer logic that aims to work while the REPL is blocked, however this can lead to filesystem corruption if the blocking code accesses the filesystem at the same time.

I propose the following:

• move the password-checking logic from _webrepl to webrepl.py
• remove the current file-transfer protocol, and with it the _webrepl module.
• move the repl interaction from websocket "text" packages to "binary" packages, as the output from the repl is not required to be valid UTF-8, but just a byte sequence.
• implement the same logic that mpremote uses for file transfers in the webrepl client.

Removing _webrepl and moving the password logic to webrepl.py even seems to make the firmware smaller:

   text    data     bss     dec     hex filename                                                                       
 606100       0  381308  987408   f1110 /home/jenkins/tmp/micropython/ports/rp2/build-RPI_PICO_W/firmware.elf
 605668       0  381292  986960   f0f50 /home/jenkins/tmp/micropython/ports/rp2/build-RPI_PICO_W/firmware.elf

I've implemented a proof-of-concept here: https://github.com/felixdoerre/webreplv2 together with a new webrepl client.

The benefits over the current webrepl are:

• Allow binary data transfers over the websocket (this also helps other usages of the webrepl, like Thonny, or using the websocket as backend for mpremote instead of a serial device)
• Implement a File-Browser in the webrepl-client, with file up- and download using the same primitives as mpremote
• Implement mip to install packages directly from the webrepl-client
• Implement the filesystem-mounting feature
• Implement direct mounting of a local directory through the browser (without uploading). Due to webapi limitations this is only a readonly mount.
• Allow browser-saving of the webrepl password
• Auto-connect the webrepl, if the target (and password) is known.

Do you want to include this into micropython, replacing the current webrepl module?