Limit rebuilds

Our build matrix will now only output images to be rebuild that had
actual changes. Either because the DokuWiki branch changed, the Docker
repo was updated or because the upstream PHP image changed.

Author: splitbrain

.github/matrix.php

@@ -0,0 +1,127 @@
+<?php
+/**
+ * This script generates the matrix for the Docker image build job
+ *
+ * It checks if changes in the DokuWiki branch, the upstream PHP image or the docker repo have been made
+ * since it ran last time (using the github action cache for persistence). This allows us to run this every
+ * day to catch any updates to the upstream images, while avoiding unnecessary rebuilds.
+ */
+
+
+/**
+ * Get the list of DokuWiki versions from the download server
+ *
+ * @return array
+ */
+function getVersions()
+{
+    $data = file_get_contents('https://download.dokuwiki.org/version');
+    return json_decode($data, true);
+}
+
+/**
+ * Get the last commit of a branch
+ *
+ * @param string $branch
+ * @return string
+ */
+function getLastCommit($branch)
+{
+    $opts = [
+        'http' => [
+            'method' => "GET",
+            'header' => join("\r\n", [
+                "Accept: application/vnd.github.v3+json",
+                "User-Agent: PHP"
+            ])
+        ]
+    ];
+    $context = stream_context_create($opts);
+
+    $data = file_get_contents('https://api.github.com/repos/dokuwiki/dokuwiki/commits/' . $branch, false, $context);
+    $json = json_decode($data, true);
+    return $json['sha'];
+}
+
+/**
+ * Get the image id of a given PHP image tag
+ *
+ * @param string $tag
+ * @return string
+ */
+function getImageId($tag)
+{
+    $repo = 'library/php';
+    $data = file_get_contents('https://auth.docker.io/token?service=registry.docker.io&scope=repository:' . $repo . ':pull');
+    $token = json_decode($data, true)['token'];
+
+
+    $opts = [
+        'http' => [
+            'method' => "GET",
+            'header' => join("\r\n", [
+                "Authorization: Bearer $token",
+                "Accept: application/vnd.docker.distribution.manifest.v2+json",
+            ])
+        ]
+    ];
+    $context = stream_context_create($opts);
+
+    $data = file_get_contents('https://index.docker.io/v2/' . $repo . '/manifests/' . $tag, false, $context);
+    $json = json_decode($data, true);
+    return $json['config']['digest'];
+}
+
+/**
+ * Get the image tag used in the current Dockerfile
+ *
+ * @return string
+ */
+function getImageTag()
+{
+    $df = file_get_contents('Dockerfile');
+    preg_match('/FROM php:(?<tag>\S*)/', $df, $matches);
+    return $matches['tag'];
+}
+
+
+$result = [];
+$self = $_ENV['GITHUB_SHA'] ?? 'unknown';
+$upstreamTag = getImageTag();
+$image = getImageId($upstreamTag);
+
+foreach (getVersions() as $release => $info) {
+    $branch = $release === 'oldstable' ? 'old-stable' : $release;
+    $commit = getLastCommit($branch);
+    $ident = join('-', [$release, $commit, $image, $self]);
+    $cache = '.github/matrix.cache/' . $release;
+
+    fwrite(STDERR, "Ident: $ident\n");
+    $last = @file_get_contents($cache);
+    if ($last === $ident) {
+        // this combination has been built before
+        fwrite(STDERR, "No change. Skipping $release\n");
+        continue;
+    }
+
+    // this branch needs to be built
+    $result[] = [
+        'version' => $info['version'],
+        'date' => $info['date'],
+        'name' => $info['name'],
+        'type' => $release,
+    ];
+    // update the cache
+    if (!is_dir('.github/matrix.cache')) {
+        mkdir('.github/matrix.cache');
+    }
+    file_put_contents($cache, $ident);
+}
+
+// output the result
+if ($result) {
+    echo "matrix=" . json_encode(['release' => $result]);
+} else {
+    echo "matrix=[]";
+}
+

.github/workflows/docker.yml

@@ -11,15 +11,28 @@ jobs:
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.2'
+      - name: Cache Setup
+        id: cache
+        uses: actions/cache@v4
+        with:
+          path: .github/matrix.cache/
+          key: ${{ runner.os }}-matrix-${{ hashFiles('.github/matrix.php') }}
       - name: Set up matrix
         id: set-matrix
         run: |
-          echo "matrix=$(curl https://download.dokuwiki.org/version | jq -c '{release: [.[]]}')" >> $GITHUB_OUTPUT
+          php .github/matrix.php >> $GITHUB_OUTPUT
 
   build:
     needs: buildmatrix
     name: Build Docker Image for ${{ matrix.release.type }}
     runs-on: ubuntu-latest
+    if: ${{ needs.buildmatrix.outputs.matrix != '[]' }}
     strategy:
       matrix: ${{fromJson(needs.buildmatrix.outputs.matrix)}}
     steps: