sdk/utils/pub/system_cache.dart

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library system_cache;

import 'dart:io';
import 'dart:async';

import 'git_source.dart';
import 'hosted_source.dart';
import 'io.dart';
import 'io.dart' as io show createTempDir;
import 'log.dart' as log;
import 'package.dart';
import 'pubspec.dart';
import 'sdk_source.dart';
import 'source.dart';
import 'source_registry.dart';
import 'utils.dart';
import 'version.dart';

/// The system-wide cache of installed packages.
///
/// This cache contains all packages that are downloaded from the internet.
/// Packages that are available locally (e.g. from the SDK) don't use this
/// cache.
class SystemCache {
  /// The root directory where this package cache is located.
  final String rootDir;

  String get tempDir => join(rootDir, '_temp');

  /// Packages which are currently being asynchronously installed to the cache.
  final Map<PackageId, Future<Package>> _pendingInstalls;

  /// The sources from which to install packages.
  final SourceRegistry sources;

  /// Creates a new package cache which is backed by the given directory on the
  /// user's file system.
  SystemCache(this.rootDir)
  : _pendingInstalls = new Map<PackageId, Future<Package>>(),
    sources = new SourceRegistry();

  /// Creates a system cache and registers the standard set of sources.
  factory SystemCache.withSources(String rootDir) {
    var cache = new SystemCache(rootDir);
    cache.register(new SdkSource());
    cache.register(new GitSource());
    cache.register(new HostedSource());
    cache.sources.setDefault('hosted');
    return cache;
  }

  /// Registers a new source. This source must not have the same name as a
  /// source that's already been registered.
  void register(Source source) {
    source.bind(this);
    sources.register(source);
  }

  /// Gets the package identified by [id]. If the package is already cached,
  /// reads it from the cache. Otherwise, requests it from the source.
  Future<Pubspec> describe(PackageId id) {
    if (id.isRoot) throw new ArgumentError("Cannot describe the root package.");

    // Try to get it from the system cache first.
    if (id.source.shouldCache) {
      return id.systemCacheDirectory.then((packageDir) {
        if (!dirExists(packageDir)) return id.describe();
        return new Pubspec.load(id.name, packageDir, sources);
      });
    }

    // Not cached, so get it from the source.
    return id.describe();
  }

  /// Ensures that the package identified by [id] is installed to the cache,
  /// loads it, and returns it.
  ///
  /// It is an error to try installing a package from a source with `shouldCache
  /// == false` to the system cache.
  Future<Package> install(PackageId id) {
    if (!id.source.shouldCache) {
      throw new ArgumentError("Package $id is not cacheable.");
    }

    var pending = _pendingInstalls[id];
    if (pending != null) return pending;

    var future = id.source.installToSystemCache(id)
        .whenComplete(() { _pendingInstalls.remove(id); });
    _pendingInstalls[id] = future;
    return future;
  }

  /// Create a new temporary directory within the system cache. The system
  /// cache maintains its own temporary directory that it uses to stage
  /// packages into while installing. It uses this instead of the OS's system
  /// temp directory to ensure that it's on the same volume as the pub system
  /// cache so that it can move the directory from it.
  Directory createTempDir() {
    var temp = ensureDir(tempDir);
    return io.createTempDir(join(temp, 'dir'));
  }

  /// Delete's the system cache's internal temp directory.
  Future deleteTempDir() {
    log.fine('Clean up system cache temp directory $tempDir.');
    return defer(() {
      if (!dirExists(tempDir)) return;
      return deleteDir(tempDir);
    });
  }
}