installer: make sure we can always test the installer in ci and locally

Just now there is a dependency on cachix, which means we cannot test
the installer in CI if forks do not have the necessary secrets set up.
We replace this with a simple http server that serves the installer and
can be both used in CI and locally.

scripts/prepare-installer-for-github-actions

@@ -1,10 +1,11 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-script=$(nix-build -A outputs.hydraJobs.installerScriptForGHA --no-out-link)
-installerHash=$(echo "$script" | cut -b12-43 -)
+nix build -L ".#installerScriptForGHA" ".#binaryTarball"
 
-installerURL=https://$CACHIX_NAME.cachix.org/serve/$installerHash/install
-
-echo "::set-output name=installerURL::$installerURL"
+mkdir -p out
+cp ./result/install "out/install"
+name="$(basename "$(realpath ./result-1)")"
+# everything before the first dash
+cp -r ./result-1 "out/${name%%-*}"

scripts/serve-installer-for-github-actions

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+if [[ ! -d out ]]; then
+  echo "run prepare-installer-for-github-actions first"
+  exit 1
+fi
+cd out
+PORT=${PORT:-8126}
+nohup python -m http.server "$PORT" >/dev/null 2>&1 &
+pid=$!
+
+while ! curl -s "http://localhost:$PORT"; do
+  sleep 1
+  if ! kill -0 $pid; then
+    echo "Failed to start http server"
+    exit 1
+  fi
+done
+
+echo 'To install nix, run the following command:'
+echo "sh <(curl http://localhost:$PORT/install) --tarball-url-prefix http://localhost:$PORT"