KeyboardInterrupt Exception when Cancelling Receiving

[peterstory]

A stack trace containing a KeyboardInterrupt exception is displayed when cancelling receiving.

Not observed on macOS, testing with either the main or user-study branches. The error does occur when running from the .app!

Observed on Linux when using the .deb installer. Not observed when installed from either the main or user-study branches. So this issue is specific to PyInstaller: https://github.com/pyinstaller/pyinstaller/issues/3646

This code suggests that pyinstaller always exits with -1 or a successful return code: https://github.com/pyinstaller/pyinstaller/pull/3515/files#diff-6f619220d264acecf4826ad08ebc2ef4881ecd22b92f4561a7b1ae2be399b8c4R886

[peterstory]

Tests:

• Send a large file
  • Expected: no error
• Cancel receiving
  • Expected: no error
• Send a large transfer, cancel it midway, then send it again
  • Expected: error

Completed:

• [x] On macOS, from CLI for issue-19 branch
• [x] On macOS, from .app for issue-19 branch
• [ ] On Linux, from CLI for issue-19 branch
• [ ] On Linux, from .deb for issue-19 branch
• [x] On Linux, from .deb for user-study branch (rebased on issue-19)

Finally:

• [x] Update the unit tests so they pass

[peterstory]

Known error states:

• Cancel sending a large file. tar gets stuck (in a system call?), requiring TERM to exit. Ideally, we shouldn't show an error in this case.
• Start sending a large file, cancel it, then send it again. The receiver's tar will exit. The receiver's pydiode will hang, since its stdout isn't being read. Thus, pydiode will be automatically quit using TERM (since it's stuck). We should show an error, since this means that files were written, and they might be corrupt (since the EOF packet couldn't be checked).

In both cases, we have non-zero exit codes. But we only want to show an error in the second case.

[peterstory]

I tested with the rebased code on Linux, and I'm not getting an error when I click "Cancel Receiving." Everything seems to work properly!