🐛 Restored correct "allow free signup" setting from backup after buggy 4.3 upgrade (#12905)

refs https://github.com/TryGhost/Team/issues/634

- find earliest backup file created when a 4.3 migration was run, if found use the `members_allow_free_signup` value from there to change `members_signup_access` from `'all'` to `'invite'` if necessary

core/server/data/migrations/versions/4.4/01-restore-free-members-signup-setting-from-backup.js

@@ -0,0 +1,98 @@
+const logging = require('../../../../../shared/logging');
+const {createTransactionalMigration} = require('../../utils');
+const config = require('../../../../../shared/config');
+const fs = require('fs-extra');
+const path = require('path');
+const semver = require('semver');
+
+// 4.3.0 contained a buggy migration for members_allow_free_signup -> members_signup_access
+// meaning all sites switched to allowing free member signup.
+//
+// This migration attempts to fix that by finding the original value from the db backup file
+// created during migration and updating the new setting value to match
+
+// we only care about backups created since the bad release was published
+const MIN_DATE = new Date('2021-04-21T00:00:00.000Z');
+
+module.exports = createTransactionalMigration(
+    async function up(connection) {
+        const currentSetting = await connection('settings')
+            .where({key: 'members_signup_access'})
+            .select('value')
+            .first();
+
+        if (!currentSetting) {
+            logging.info('Skipping restore of "allow free signups", `members_signup_access` setting doesn\'t exist');
+            return;
+        }
+
+        if (currentSetting.value !== 'all') {
+            logging.info('Skipping restore of "allow free signups", setting changed since bad migration');
+            return;
+        }
+
+        // 1. find any backup files that have a date of 2021-04-21 or later
+        // 2. loop through backup files to find first one exported on 4.3.0 or later
+        // 3. load JSON and get correct value
+        // 4. update database if necessary
+        const contentPath = config.get('paths').contentPath;
+        const dataPath = path.join(contentPath, 'data');
+        const backupFileRegex = /ghost\.([\d]{4}-[\d]{2}-[\d]{2})-([\d]{2}-[\d]{2}-[\d]{2})\.json$/;
+
+        const backupFileDate = function (filename) {
+            const dateMatch = filename.match(backupFileRegex);
+            return new Date(`${dateMatch[1]}T${dateMatch[2].replace(/-/g, ':')}.000Z`);
+        };
+
+        logging.info('Restoring "allow free signups" value from backup files if needed');
+
+        let files;
+
+        try {
+            files = await fs.readdir(dataPath);
+        } catch (error) {
+            logging.info('Skipping restore, unable to read backup files');
+            return;
+        }
+
+        // filter to known backup files, later than min date, ordered earliest to latest
+        const backupFiles = files
+            .filter(filename => backupFileRegex.test(filename))
+            .filter(filename => backupFileDate(filename) > MIN_DATE)
+            .sort((a, b) => backupFileDate(a) - backupFileDate(b));
+
+        let hasRestored = false;
+
+        for (const backupFile of backupFiles) {
+            try {
+                const backup = require(path.join(dataPath, backupFile));
+
+                if (semver.satisfies(backup.meta.version, '4.3.x')) {
+                    const oldValue = backup.data.settings.find(s => s.key === 'members_allow_free_signup');
+
+                    if (oldValue && oldValue.value === 'false') {
+                        logging.info('Setting `members_signup_access` to \'invite\' to match previous `members_allow_free_signup` setting');
+
+                        await connection('settings')
+                            .where({key: 'members_signup_access'})
+                            .update({value: 'invite'});
+
+                        // found earliest backup we care about, don't check any more files
+                        hasRestored = true;
+                        break;
+                    }
+                }
+            } catch (error) {
+                // noop, move on to next file
+            }
+        }
+
+        if (!hasRestored) {
+            logging.info('Skipping restore, not necessary');
+        }
+    },
+
+    async function down() {
+        // noop
+    }
+);