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metamask-extension/app/scripts/lib/migrator/index.js

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import EventEmitter from 'events';
/**
* @typedef {Object} Migration
* @property {number} version - The migration version
* @property {Function} migrate - Returns a promise of the migrated data
*/
/**
* @typedef {Object} MigratorOptions
* @property {Array<Migration>} [migrations] - The list of migrations to apply
* @property {number} [defaultVersion] - The version to use in the initial state
*/
export default class Migrator extends EventEmitter {
/**
* @param {MigratorOptions} opts
*/
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constructor(opts = {}) {
super();
const migrations = opts.migrations || [];
// sort migrations by version
this.migrations = migrations.sort((a, b) => a.version - b.version);
// grab migration with highest version
const lastMigration = this.migrations.slice(-1)[0];
// use specified defaultVersion or highest migration version
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this.defaultVersion =
opts.defaultVersion || (lastMigration && lastMigration.version) || 0;
}
// run all pending migrations on meta in place
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async migrateData(versionedData = this.generateInitialState()) {
// get all migrations that have not yet been run
const pendingMigrations = this.migrations.filter(migrationIsPending);
// perform each migration
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for (const migration of pendingMigrations) {
try {
// attempt migration and validate
const migratedData = await migration.migrate(versionedData);
if (!migratedData.data) {
throw new Error('Migrator - migration returned empty data');
}
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if (
migratedData.version !== undefined &&
migratedData.meta.version !== migration.version
) {
throw new Error(
'Migrator - Migration did not update version number correctly',
);
}
// accept the migration as good
// eslint-disable-next-line no-param-reassign
versionedData = migratedData;
} catch (err) {
// rewrite error message to add context without clobbering stack
const originalErrorMessage = err.message;
err.message = `MetaMask Migration Error #${migration.version}: ${originalErrorMessage}`;
// emit error instead of throw so as to not break the run (gracefully fail)
this.emit('error', err);
// stop migrating and use state as is
return versionedData;
}
}
return versionedData;
/**
* Returns whether or not the migration is pending
*
* A migration is considered "pending" if it has a higher
* version number than the current version.
*
* @param {Migration} migration
* @returns {boolean}
*/
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function migrationIsPending(migration) {
return migration.version > versionedData.meta.version;
}
}
/**
* Returns the initial state for the migrator
*
* @param {Object} [data] - The data for the initial state
* @returns {{meta: {version: number}, data: any}}
*/
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generateInitialState(data) {
return {
meta: {
version: this.defaultVersion,
},
data,
};
}
}