What is the best way to check if the host is listening

[laenzlinger]

Is there a good way to check, if the host will accept data.

Is the only way to do this with some error handling? E.g. to send a message and wait for a certain time if the WouldBlock error would go away?

Thanks for any hints

[sourcebox]

I ran into a similar issue years ago with Windows, where the data was not read until some application opened the port. But apparently there is no other solution than checking if the data was sent after a timeout, which is what you suggested.

[laenzlinger]

I forgt to mention that I am testing with a linux host.

In case the host is not connected, the device state is not UsbDeviceState::Configured
But as soon as a USB host is connected, it looks like I can not use the device state anymore.

@sourcebox then I would need to check try re-sending and after a timeout, detect that there is no host application listening.

Since I am sending also to MIDI out on UART, I would probably check in a background task if an application is listening on usb. Is there a good midi message to send, just for that purpose?

[sourcebox]

Since I am sending also to MIDI out on UART, I would probably check in a background task if an application is listening on usb. Is there a good midi message to send, just for that purpose?

There's an "Active Sensing" message [0xFE] that shouldn't cause any harm. It's possible (but unlikely) that a host expects it periodically when it has been received once.

You could also send an empty SysEx message with no payload like [0xF0, 0xF7]. That should be ignored completely.