add custom plugin to rewrite GU responses to fastly cache (#78)

Author: chuckadams

composer.lock

@@ -0,0 +1,57 @@
+<?php
+/**
+ * Plugin Name: FAIR Server - Git Updater Filter
+ * Description: Filter GU output to rewrite download urls
+ * Network: true
+ */
+
+namespace FAIRServer\GUFilter;
+
+add_filter('rest_pre_echo_response', __NAMESPACE__ . '\\rewrite_gu_response');
+
+function rewrite_gu_response($response)
+{
+    $download_link = $response['download_link'] ?? null;
+
+    if (!$download_link || !str_contains($download_link, 'fairpm/fair-plugin')) {
+        return $response;
+    }
+
+    $versions = $response['versions'] ?? null;
+    if (!$versions) {
+        error_log('WARNING: response contained download_link for fair-plugin but no versions: '
+            . print_r($response, true));
+        return $response;
+    }
+
+    $version = array_flip($versions)[$download_link] ?? null;
+    if (!$version) {
+        error_log('WARNING: download_link not contained in versions: ' . print_r($versions, true));
+        return $response;
+    }
+
+    // This is hairier than usual because 404 responses get cached longer than they ought to be
+
+    $mirror_url = "https://download.fair.pm/release/fair-connect-$version.zip";
+    $busted = null;
+    $key = "mirror_url:$mirror_url";
+
+    $status = get_transient($key);
+    if (!$status) {
+        $status = wp_remote_retrieve_response_code(wp_safe_remote_head($mirror_url));
+        if ((int)$status === 404) {
+            // 404 responses are cached for a while, so try again with a cachebuster
+            $busted = $mirror_url . '?' . time();
+            $status = wp_remote_retrieve_response_code(wp_safe_remote_head($busted));
+        }
+        set_transient($key, $status, 300); // cache for 5 minutes (which is way less time than 404s are being cached)
+    }
+
+    if ((int)$status !== 200) {
+        error_log(__FUNCTION__ . ": HEAD on $mirror_url returned status $status");
+        return $response;
+    }
+
+    $response['download_link'] = $busted ?? $mirror_url;
+    return $response;
+}