Web Workflow serial terminal occasionally disconnects

[RetiredWizard]

CircuitPython version

Adafruit CircuitPython 8.0.0-alpha.1-89-gb38109c48-dirty on 2022-08-02; ESP32-S3-DevKitC-1-N8R2 with ESP32S3
Adafruit CircuitPython 8.0.0-alpha.1-89-gb38109c48-dirty on 2022-08-02; Adafruit Feather ESP32S3 4MB Flash 2MB PSRAM with ESP32S3
Adafruit CircuitPython 8.0.0-alpha.1-89-gb38109c48-dirty on 2022-08-02; Adafruit Feather ESP32S2 with ESP32S2

Code/REPL

from supervisor import runtime
print("Press any key to stop output")
while runtime.serial_bytes_available == 0:
    print("0123456789"*5+"abcdefghijklmnopqrstuvwxyz")

Behavior

Usually Within a 10 or 20 seconds or so of starting this python script the Web Workflow serial terminal will become disconnected (stop showing output from the serial port and the ctrl-c,d and send buttons go grey). Refreshing the screen will reconnect the terminal and output will continue unless it has been stopped from the usb serial terminal.

Description

In most cases the following message is displayed in the browser developer console:

But occasionally this message is displayed:

Additional information

No response

[RetiredWizard]

I wouldn't be surprised if a network error was triggering this in a similar way the file manager is being disrupted in issue #6654

[tannewt]

I'm going to unblock 8 on this. It'd be good for others to chime in if they see this.

[RetiredWizard]

I'm not sure about the frame header error, but I can still disconnect the web workflow serial terminal with the utf-8 decode error even after applying #6742 :(

[RetiredWizard]

While playing with the serial terminal I stumbled on a reliable way to reproduce the disconnect. I don't really understand what's going on with the STR variables here, but if you read a single character from the attached file it reads a string of length 4 into that single character. If you then print that character the serial terminal disconnects and you get the following message in the developer console:

 WebSocket connection to 'ws://10.0.0.206/cp/serial/' failed: Could not decode a text frame as UTF-8

Once this file has been moved to the microcontroller flash, typing these commands into the repl will cause the error:

 f = open('disconnect.txt')
 a = f.read(1)
 print(a)

I'm thinking that when there is a communications error it's possible to mangle the character data being sent via the web socket and if you end up with a malformed character similar to the one in the attached file, attempting to display it over the serial terminal causes the disconnect. I created the attached disconnect file when attempting to type data into a file using the serial terminal.

disconnect.txt