`wg create`: infinite loop when file exists

[abitrolly]

Describe the bug

When specifying config for wireguard tunnel, if the file exists, the command enters an endless loop that can not be interrupted or killed.

touch wgvpn.conf
fly wg create personal ams wgvpn wgvpn.conf

• fly version

flyctl v0.3.217 linux/amd64 Commit: a6da01f BuildDate: 2025-11-14T20:30:19Z

** Command output: **

$ fly wg create personal ams wgvpn /tmp
Creating WireGuard peer "wgvpn" in region "ams" for organization personal

!!!! WARNING: Output includes private key. Private keys cannot be recovered !!!!
!!!! after creating the peer; if you lose the key, you'll need to remove    !!!!
!!!! and re-add the peering connection.                                     !!!!
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists
Can't create '/tmp': open /tmp: file exists

There is a one liner fix to return the error here.

https://github.com/superfly/flyctl/blob/a6da01fd0840f18fb5c57c66e6335aba85dd08f9/internal/command/wireguard/others.go#L75C7-L75C14

But the code looks a bit messy, so I decided to make it more readable first #4664

[abitrolly]

There is also interactive mode, which works when filename is not set.

$ fly wg create personal ams wgvpn
Creating WireGuard peer "wgvpn" in region "ams" for organization personal

!!!! WARNING: Output includes private key. Private keys cannot be recovered !!!!
!!!! after creating the peer; if you lose the key, you'll need to remove    !!!!
!!!! and re-add the peering connection.                                     !!!!
? Filename to store WireGuard configuration in, or 'stdout':
Provide a filename (or 'stdout')
? Filename to store WireGuard configuration in, or 'stdout':  /tmp
Can't create '/tmp': open /tmp: file exists
? Filename to store WireGuard configuration in, or 'stdout':  wgvpn.conf
Can't create 'wgvpn.conf': open wgvpn.conf: file exists
? Filename to store WireGuard configuration in, or 'stdout':  stdout

[Interface]
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