Issue #3399867: Provide metadata/changes.json endpoint to track updates

project_composer.changes.inc

+<?php
+
+/**
+ * Menu callback, list updates.
+ *
+ * Implementation of https://packagist.org/apidoc#track-package-updates.
+ */
+function project_composer_changes($release_category) {
+  if ($release_category !== 'current') {
+    return MENU_NOT_FOUND;
+  }
+
+  $time = (int) (microtime(TRUE) * 10000);
+
+  // Get since parameter.
+  if (isset($_REQUEST['since']) && ctype_digit($_REQUEST['since'])) {
+    $since = (int) $_REQUEST['since'];
+  }
+  else {
+    http_response_code(400);
+    drupal_json_output([
+      'error' => t('Invalid or missing "since" query parameter, make sure you store the timestamp at the initial point you started mirroring, then send that to begin receiving changes, e.g. !link for example.', [
+        '!link' => url(variable_get('project_composer_packages_url', 'https://packages.drupal.org') . '/8/metadata/changes.json', ['query' => ['since' => $time], 'absolute' => TRUE]),
+      ]),
+      'timestamp' => $time,
+    ]);
+    return;
+  }
+
+  // Make sure time is not too far in the past.
+  if ($time - $since > 24 * 60 * 60 * 10000) {
+    drupal_json_output([
+      'actions' => [[
+        'type' => 'resync',
+        'time' => floor($time / 10000),
+        'package' => '*',
+      ]],
+      'timestamp' => $time,
+    ]);
+    return;
+  }
+
+  // Generate output.
+  $actions = [];
+  $result = db_query('SELECT package, updated FROM {project_composer_update_log} WHERE category = :release_category AND updated > :since', [
+    ':release_category' => $release_category,
+    ':since' => floor($since / 10000),
+  ]);
+  foreach ($result as $row) {
+    $actions[] = [
+      'type' => 'update',
+      'package' => 'drupal/' . $row->package,
+      'time' => $row->updated
+    ];
+  }
+
+  drupal_json_output(['actions' => $actions, 'timestamp' => $time]);
+}

project_composer.module

@@ -41,6 +41,13 @@ function project_composer_menu() {
     'type' => MENU_CALLBACK,
     'file' => 'project_composer.sa.inc',
   ];
+  $items['packages/%project_composer_endpoint/changes.json'] = [
+    'page callback' => 'project_composer_changes',
+    'page arguments' => [1],
+    'access arguments' => ['access content'],
+    'type' => MENU_CALLBACK,
+    'file' => 'project_composer.changes.inc',
+  ];
 
   return $items;
 }