Hledger: [hledger-web] Lacking IPv6 support

[evilham]

Hello, I'm trying out hledger (considering migrating from GnuCash) and found lack of IPv6 support in hledger-web's server to be an issue.

It's possible that the changes are minima, but I understand that everything is work :-). Just opening to document it.

Cheers and thank you.

Further information:

> uname -oprb
FreeBSD 13.0-CURRENT amd64 5b8f656016fa216bb99a3853141b8d4d9eb9b6de
> hledger-web --version
hledger-web 1.16.1
> hledger-web --serve --host '::1' --port 8080
hledger-web: --host requires an IP address, not "::1" (use -h to see usage)

[simonmichael]

Thanks for the report.

[CRTified]

I'll try to solve this issue.

The error itself comes from the function checkWebOpts, where the value of the host option is checked against ".0123456789".
This is basically a whitelist for allowed characters, but it does not prevent hosts like 999.999.999.999, which will crash when Network.Socket.getAddrInfo uses it.

Adding : to the whitelist allows ::1 as host, but browser access won't work, as IPv6 addresses need to be surrounded by brackets like http://[::1]/.

Calling hledger-web with the modified whitelist like this:

hledger-web --host ::1 --base-url=http://[::1]:5000

gives a simple workaround, but still launches the wrong URL in the browser.

Basically, to solve this issue, I'd try the following steps:

1. Generally allow IPv6 addresses (e.g. by adding : or checking the address with other means)
2. Depending on the IP version, switch to a default base-url that uses brackets

As a first step, I'll just add : to the whitelist and check for that to change the base-url, but it might be sane to use something that completely validates the IP address.

I'll open a PR as soon as I've made progress.