Allow disabling of all network accesses

[ibbem]

Context

We use Nix to build our project reproducibly, including the github-pages documentation. This setup is also used in our CI to build the github-pages which are eventually deployed. Nix prohibits network connections (except if the output hash is specified, which is unpractical in this case) because the network is not reproducible. However, in some circumstances (e.g., the default installation on macOS) the Nix sandbox is disabled or weakened. Hence, github-metadata accesses the network which results in failing builds or differing outputs.

Feature Request

We would like to reliably disable network accesses without actually disabling the network.

Implemented solution

Network accesses are skipped if the environment variable PAGES_DISABLE_NETWORK is set.

Related issues

• Same feature request, although different motivation: Flag for disabling internet_connected #241
• Different use case, probably solved differently: Disable network requests #127

[ashmaroli]

Hello @ibbem, please revert the change to History.markdown. It gets updated automatically with the pull-request-title when the pull request is merged. Additionally, this requires a test to verify that setting the env var does what is intended.

P.S. You need not rebase your branch. All commits will be squashed automatically at merge.

[ibbem]

From my side, this PR is ready to be (squash) merged.
Is there anything else that I need to address?

[ashmaroli]

No @ibbem, this LGTM!
Thank you for your contribution.

@jekyllbot: merge +minor