ci/cd: fix IPv6 timeouts with force-ipv4 action

This commit introduces the `force-ipv4` GitHub action to address
connectivity issues caused by the lack of IPv6 support in GitHub
runners. Details:
- actions/runner#3138
- actions/runner-images#668

This change solves connection problems when Node's `fetch` API fails due
to `UND_ERR_CONNECT_TIMEOUT` errors. Details:
- actions/runner-images#9540
- actions/runner#3213

This action disables IPv6 at the system level, ensuring all outging
requests use IPv4. Resolving connectivity issues when running external
URL checks and Docker build checks.

This solution is a temporary workaround until GitHub runners support
IPv6 or Node `fetch` API has a working solution such as Happy Eyeball.
Detais:
- nodejs/node#41625
- nodejs/undici#1531

.github/actions/force-ipv4/README.md

@@ -0,0 +1,31 @@
+# force-ipv4
+
+## Overview
+
+This GitHub action enforces IPv4 for all outgoing network requests. It addresses connectivity issues encountered in GitHub runners, where IPv6 requests may lead to timeouts due to the lack of IPv6 support [1] [2].
+
+## Background
+
+Some applications attempt network connections over IPv6.
+Such as requests made by Node's `fetch` API causes `UND_ERR_CONNECT_TIMEOUT` errors [3] [4].
+This happens when the software cannot handle this such as by using Happy Eyeballs [5] [6].
+
+## Usage
+
+To use this action in your GitHub workflow, add the following step before any job that requires network access:
+
+```yaml
+- name: Enforce IPv4 Connectivity
+  uses: ./.github/actions/force-ipv4
+```
+
+## Note
+
+This action is a workaround addressing specific IPv6-related connectivity issues on GitHub runners and may not be necessary if GitHub's infrastructure evolves to fully support IPv6 in the future.
+
+[1]: https://archive.ph/2024.03.28-185829/https://github.com/actions/runner/issues/3138 "Actions Runner fails on IPv6 only host · Issue #3138 · actions/runner · GitHub | github.com"
+[2]: https://archive.ph/2024.03.28-185838/https://github.com/actions/runner-images/issues/668 "IPv6 on GitHub-hosted runners · Issue #668 · actions/runner-images · GitHub | github.com"
+[3]: https://archive.ph/2024.03.28-185847/https://github.com/actions/runner/issues/3213 "GitHub runner cannot send `fetch` with `node`, failing with IPv6 DNS error `UND_ERR_CONNECT_TIMEOUT` · Issue #3213 · actions/runner · GitHub | github.com"
+[4]: https://archive.ph/2024.03.28-185853/https://github.com/actions/runner-images/issues/9540 "Cannot send outbound requests using node fetch, failing with IPv6 DNS error UND_ERR_CONNECT_TIMEOUT · Issue #9540 · actions/runner-images · GitHub | github.com"
+[5]: https://archive.ph/2024.03.28-185900/https://github.com/nodejs/node/issues/41625 "Happy Eyeballs support (address IPv6 issues in Node 17) · Issue #41625 · nodejs/node · GitHub | github.com"
+[6]: https://archive.ph/2024.03.28-185910/https://github.com/nodejs/undici/issues/1531 "fetch times out in under 5 seconds · Issue #1531 · nodejs/undici · GitHub | github.com"

.github/actions/force-ipv4/action.yml

@@ -0,0 +1,12 @@
+inputs:
+  project-root:
+    required: false
+    default: '.'
+runs:
+  using: composite
+  steps:
+    -
+      name: Run prefer IPv4 script
+      shell: bash
+      run: ./.github/actions/force-ipv4/force-ipv4.sh
+      working-directory: ${{ inputs.project-root }}

.github/actions/force-ipv4/force-ipv4.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+
+main() {
+  if is_linux; then
+    echo 'Configuring Linux...'
+
+    configure_warp_with_doh_and_ipv6_exclusion_on_linux # [WORKS] Resolves the issue when run independently on GitHub runners lacking IPv6 support.
+    prefer_ipv4_on_linux # [DOES NOT WORK] It does not resolve the issue when run independently on GitHub runners without IPv6 support.
+
+    # Considered alternatives:
+    # - `sysctl` commands, and direct changes to `/proc/sys/net/` and `/etc/sysctl.conf` led to silent
+    #   Node 18 exits (code: 13) when using `fetch`.
+  elif is_macos; then
+    echo 'Configuring macOS...'
+
+    configure_warp_with_doh_and_ipv6_exclusion_on_macos # [WORKS] Resolves the issue when run independently on GitHub runners lacking IPv6 support.
+    disable_ipv6_on_macos # [WORKS INCONSISTENTLY] Resolves the issue inconsistently when run independently on GitHub runners without IPv6 support.
+  fi
+  echo "IPv4: $(curl --ipv4 --silent --max-time 15 --retry 3 --user-agent Mozilla https://api.ip.sb/geoip)"
+  echo "IPv6: $(curl --ipv6 --silent --max-time 15 --retry 3 --user-agent Mozilla https://api.ip.sb/geoip)"
+}
+
+is_linux() {
+  [[ "$(uname -s)" == "Linux" ]]
+}
+
+is_macos() {
+  [[ "$(uname -s)" == "Darwin" ]]
+}
+
+configure_warp_with_doh_and_ipv6_exclusion_on_linux() {
+  install_warp_on_debian
+  configure_warp_doh_and_exclude_ipv6
+}
+
+configure_warp_with_doh_and_ipv6_exclusion_on_macos() {
+  brew install cloudflare-warp
+  configure_warp_doh_and_exclude_ipv6
+}
+
+configure_warp_doh_and_exclude_ipv6() {
+  echo 'Beginning configuration of the Cloudflare WARP client with DNS-over-HTTPS and IPv6 exclusion...'
+  echo 'Initiating client registration with Cloudflare...'
+  warp-cli --accept-tos registration new
+  echo 'Configuring WARP to operate in DNS-over-HTTPS mode (warp+doh)...'
+  warp-cli --accept-tos mode warp+doh
+  echo 'Excluding IPv6 traffic from WARP by configuring it as a split tunnel...'
+  warp-cli --accept-tos add-excluded-route '::/0' # Exclude IPv6, forcing IPv4 resolution
+  # `tunnel ip add` does not work with IP ranges, see https://community.cloudflare.com/t/cant-cidr-for-split-tunnling/630834
+  echo 'Establishing WARP connection...'
+  warp-cli --accept-tos connect
+}
+
+install_warp_on_debian() {
+  curl -fsSL https://pkg.cloudflareclient.com/pubkey.gpg | sudo gpg --yes --dearmor --output /usr/share/keyrings/cloudflare-warp-archive-keyring.gpg
+  echo "deb [arch=amd64 signed-by=/usr/share/keyrings/cloudflare-warp-archive-keyring.gpg] https://pkg.cloudflareclient.com/ $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/cloudflare-client.list
+  sudo apt-get update
+  sudo apt-get install -y cloudflare-warp
+}
+
+disable_ipv6_on_macos() {
+  networksetup -listallnetworkservices \
+    | tail -n +2 \
+    | while IFS= read -r interface; do
+        echo "Disabling IPv6 on: $interface..."
+        networksetup -setv6off "$interface"
+      done
+}
+
+prefer_ipv4_on_linux() {
+  local -r gai_config_file_path='/etc/gai.conf'
+  if [ ! -f "$gai_config_file_path" ]; then
+      echo "Creating $gai_config_file_path since it doesn't exist..."
+      touch "$gai_config_file_path"
+  fi
+  echo "precedence ::ffff:0:0/96  100" | sudo tee -a "$gai_config_file_path" > /dev/null
+  echo "Configuration complete."
+}
+
+main

.github/workflows/checks.build.yaml

@@ -95,6 +95,9 @@ jobs:
       -
         name: Run Docker image on port 8080
         run: docker run -d -p 8080:80 --rm --name privacy.sexy undergroundwires/privacy.sexy:latest
+      -
+        name: Enforce IPv4 Connectivity # Used due to GitHub runners' lack of IPv6 support, preventing request timeouts.
+        uses: ./.github/actions/force-ipv4
       -
         name: Check server is up and returns HTTP 200
         run: >-

.github/workflows/checks.external-urls.yaml

@@ -17,6 +17,9 @@ jobs:
       -
         name: Install dependencies
         uses: ./.github/actions/npm-install-dependencies
+      -
+        name: Enforce IPv4 Connectivity # Used due to GitHub runners' lack of IPv6 support, preventing request timeouts.
+        uses: ./.github/actions/force-ipv4
       -
         name: Test
         run: npm run check:external-urls