libfetch: Further improve connection polling

[des]

Summary

• Reorganize the connection loop to make it a little more readable

• Start the timeout clock earlier

• Correctly calculate the poll timeout before calling poll()

• Don't leak the socket on failure

Fixes: 848f360c8f9a ("libfetch: Apply timeout to connection attempts")
Fixes: b02e02958dad ("libfetch: Fix handling of connection failures")
MFC after: 3 days

[markj]

lib/libfetch/common.c

652

Probably we need to preserve errno around this too?

686–695

Do you need to test err == 0 first?

731

The socket is cleaned up here, how is it leaked?

[des]

lib/libfetch/common.c

652

No, fetch_verbose() is a wrapper around fetch_info() which saves and restores errno.

686–695

yes

[des]

rf

[des]

lib/libfetch/common.c

731

If there were multiple addresses we'd leak all but the last socket.