Fixing cannot unmarshal into big.int large network_ip_availabilities_total metric

[fnzv]

Hi there!

We encountered an issue releated to the openstack-exporter where a large number of IPv6 private and public networks can generate the following error:

ts=2025-05-19T11:59:33.865Z caller=exporter.go:112 level=info msg="Collecting metrics for exporter" exporter=openstack_neutron metrics=network_ip_availabilities_total
ts=2025-05-19T11:59:34.010Z caller=exporter.go:138 level=error err="Failed to collect metric for exporter" exporter=neutron error="failed to collect metric: network_ip_availabilities_total, error: math/big: cannot unmarshal \"xxxxxxxxxxxe+24\" into a *big.Int" 

In order to fix that we used a float64 thus being able to contain the large number provided by Openstack APIs
Hoping this could help also other people having the same issue

[Sharpz7]

Hey @fnzv

@mnaser and I are new maintainers of the repository and will aim to get reviews on all outstanding PR's ASAP.

Can you ensure that you are using GPG verified signatures and force new commits?

Thanks!

[fnzv]

Hey @Sharpz7 and @mnaser 👋

I just rebased and force pushed the verified commit

[Sharpz7]

@fnzv I would appreciate reviews on the other priority-labelled tickets if you have the time so I can get them merged too :). I am personally still working on integration tests to increase confidence in merges. I have asked others to do the same on this PR.

[Copilot]

Pull request overview

This PR fixes a critical unmarshaling error in the Neutron exporter that occurs when handling large IPv6 network IP availability counts. The issue arose because gophercloud's default unmarshaling attempted to parse large numbers (e.g., 1.8446744073709552e+19) into big.Int, which cannot handle scientific notation. The fix introduces custom JSON unmarshaling using json.Number to preserve the numeric string representation and then converts to float64 for Prometheus metrics.

Key changes:

• Implements custom struct definitions with json.Number fields to handle large IP counts
• Bypasses gophercloud's built-in unmarshaling to avoid the big.Int error
• Adds proper JSON round-trip processing to decode network IP availability data
• Includes minor formatting fixes for consistency with Go style guidelines

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