device monitor: more graceful exit on disconnect

[belm0]

Fixes #3939

$ pio device monitor
--- Available filters and text transformations: colorize, debug, default, direct, nocontrol, printable
--- More details at https://bit.ly/pio-monitor-filters
--- Miniterm on /dev/cu.wchusbserial51850172701  115200,8,N,1 ---
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
fps:  64.4,  render:  1.0 ms
fps:  64.4,  render:  1.0 ms
fps:  64.4,  render:  1.0 ms
fps:  64.4,  render:  1.0 ms
--- receive exception ---

--- exit ---

[belm0]

I'll make a small change to honor --quiet

[ivankravets]

Sorry, I don't think we will be able to merge it. We support multiple versions of PySerial. We don't plan to maintain this part of 3rd party code in future PlatformIO releases.

If we can import the original miniterm code and "mock" some parts, it could make sense.

[belm0]

This PR doesn't constrain the version of pyserial used by platformio. As long as the API used by the miniterm module is available, it's fine.

miniterm is a stand-alone application or example. It's not tightly coupled to the pyserial implementation, and it only uses the public pyserial API.

[ivankravets]

How about importing the existing miniterm module and mocking only specific functions? Python allows this.

from serial  import Miniterm

Miniterm.dump_port_settings = mocked_func

[belm0]

How about importing the existing miniterm module and mocking only specific functions?

That would be contrary to the goal you stated. By monkey-patching the library's miniterm, the result will be tightly bound to a specific version range of pyserial, and likely to break in the future. It's better to copy the code that is using the public API. (I don't expect the API to be broken trivially, given the number of pyserial users.)

Imagine if the pyserial author had never put miniterm into the library, and just left it in the examples directory. Wouldn't platformio have just used that as a reference point to get the job done?

[ivankravets]

Thanks again for the PR! I've finally found time and refactored the device monitor module. See 7f351bc

Please re-test with pio upgrade --dev.